3 Cellular Level of Organization Lecture Presentation by Lori Garrett
Section 1: Introduction to Cells Learning Outcomes 3.1 Describe the cell theory and the process of cellular differentiation. 3.2 Describe a body cell and its organelles, including the structure and function of each. 3.3 Describe the structural and functional features of the plasma membrane. 3.4 Differentiate among the structures and functions of the cytoskeleton.
Section 1: Introduction to Cells Learning Outcomes (continued) 3.5 Describe the ribosome and smooth and rough endoplasmic reticula, and indicate their specific functions. 3.6 Describe the Golgi apparatus, and indicate its specific functions. 3.7 Describe the structure of a mitochondrion, and explain the significance of mitochondria to cellular function.
Module 3.1: Cellular differentiation produces specialized cells Typical cell Smallest living unit in the body ~0.1 mm in diameter Could not be examined until invention of microscope in 17th century
Module 3.1: Introduction to Cells Cell theory 1. Cells are building blocks of all plants and animals 2. All new cells come from division of preexisting cells 3. Cells are smallest living units that perform all vital physiological functions
Module 3.1: Introduction to Cells Cell cooperation Each cell maintains homeostasis at cellular level Coordinated activities of cells allow homeostasis at higher organizational levels All cells are descendants from a single cell: the fertilized ovum At fertilization, zygote forms Fertilized ovum contains genetic potential to become any cell First cell divisions create smaller parcels of cytoplasm
Module 3.1: Introduction to Cells Cellular differentiation Regional differences in original ovum cytoplasm means now different composition of cytoplasm in resulting daughter cells Cytoplasmic differences affect DNA in daughter cells and cause specific genes to turn on or off Result is specialization of cells Process of gradual specialization is called cellular differentiation Specialized cells form tissues of the body
Cell differentiation
Module 3.1: Review A. Describe the cell theory. B. Identify the cell from which all the cells of your body are descendants. C. Define cellular differentiation. Learning Outcome: Describe the cell theory and the process of cellular differentiation.
Module 3.2: Cells are the smallest living units of life Body fluid distribution Cells surrounded by watery medium called extracellular fluid Called interstitial fluid (interstitium, something standing between) in most tissues Fluid inside cell is intracellular fluid or cytosol Cell plasma membrane separates cell contents (cytoplasm) from extracellular fluid
Module 3.2: The cell and its organelles Basic cell structure Surrounded by a plasma membrane Contains cytoplasm Material of varying consistency found between cell membrane and nuclear membrane Subdivided into: Cytosol (intracellular fluid) the fluid part of cytoplasm Organelles ( little organs ) intracellular structures with specific functions
Module 3.2: The cell and its organelles Organelles Divided into membranous and nonmembranous Nonmembranous Not completely enclosed by membranes In direct contact with cytosol Membranous Enclosed in a phospholipid membrane Isolated from cytosol
Module 3.2: The cell and its organelles Peroxisome STRUCTURE: Vesicles containing degradative enzymes FUNCTION: Break down organic compounds Neutralize toxic compounds
Module 3.2: The cell and its organelles Lysosome STRUCTURE: Vesicles containing digestive enzymes FUNCTION: Break down organic compounds and damaged organelles or pathogens
Module 3.2: The cell and its organelles Microvilli STRUCTURE: Membrane extensions containing microfilaments FUNCTION: Increase surface area for absorption
Module 3.2: The cell and its organelles Golgi apparatus STRUCTURE: Stacks of flattened membranes (cisternae) containing chambers FUNCTION: Store, alter, and package synthesized products
Module 3.2: The cell and its organelles Nucleus STRUCTURE: Fluid nucleoplasm containing enzymes, proteins, DNA, and nucleotides Surrounded by double membrane called nuclear envelope FUNCTION: Controls metabolism Stores and processes genetic information Controls protein synthesis
Module 3.2: The cell and its organelles Endoplasmic reticulum (ER) STRUCTURE: Network of membranous sheets and channels FUNCTION: Synthesizes secretory products; stores and transports within cell; detoxifies drugs and toxins
Module 3.2: The cell and its organelles Endoplasmic reticulum (ER) (continued) Smooth ER No attached ribosomes Synthesizes lipids and carbohydrates Rough ER Attached ribosomes Modifies/packages newly synthesized proteins
Module 3.2: The cell and its organelles Ribosomes STRUCTURE: RNA and proteins Fixed: attached to endoplasmic reticulum Free: scattered in cytoplasm FUNCTION: Synthesize proteins
Module 3.2: The cell and its organelles Mitochondrion STRUCTURE: Double membrane Inner membrane contains metabolic enzymes FUNCTION: Produces 95 percent of cellular ATP
Module 3.2: The cell and its organelles Cytoskeleton STRUCTURE: Proteins organized into fine filaments or slender tubes Centrosome Organizing center containing pair of centrioles FUNCTION: Strengthens and supports cell Moves cellular structures and materials within the cell
Module 3.2: Review A. Distinguish between the cytoplasm and cytosol. B. Identify the membranous organelles, and describe their functions. C. Describe the functions of the cytoskeleton. D. Describe the external environment of most of the body s cells. Learning Outcome: Describe a body cell and its organelles, including the structure and function of each.
Module 3.3: The plasma membrane isolates the cell from its environment and performs varied functions Plasma membrane selectively permeable barrier separating inside of cell from extracellular fluid Controls: Entry of ions and nutrients Elimination of wastes Release of secretions
Module 3.3: Plasma membrane Composed of: Phospholipid bilayer Proteins 1. Integral 2. Transmembrane 3. Peripheral 4. Glycocalyx layer formed by superficial membrane carbohydrates
Plasma membrane
Module 3.3: Plasma membrane Phospholipid bilayer Measures 6 10 nm Two layers of phospholipids Hydrophilic heads at membrane surface Hydrophobic tails facing each other on the inside Phospholipids interspersed with cholesterol molecules Cholesterol has hydrophilic and hydrophobic portions (amphipathic) Functions to stiffen the plasma membrane
Module 3.3: Plasma membrane Proteins Integral proteins Part of cell membrane and cannot be removed without damaging cell Often span entire cell membrane (these are called transmembrane proteins) Can transport water or solutes Peripheral proteins Attached to cell membrane inner or outer surface Easily removable Fewer than integral proteins May have regulatory or enzymatic functions
Module 3.3: Plasma membrane Plasma membrane components Glycocalyx Components of complex molecules Proteoglycans (carbohydrates with protein attached) Glycoproteins (protein with carbohydrates attached) Glycolipids (lipids with carbohydrates attached) Functions Cell recognition Binding to extracellular structures Lubrication of cell surface
Module 3.3: Plasma membrane Plasma membrane functions Physical isolation Regulation of exchange with external environment Sensitivity to environment Structural support Lipid bilayer provides isolation Proteins perform most other functions
Module 3.3: Review A. Which structural component of the plasma membrane is mostly responsible for isolating a cell from its external environment? B. List the general functions of the plasma membrane. C. Which type of integral protein allows water and small ions to pass through the plasma membrane? D. What characteristics of phospholipids accounts for their packing into a double layer? Learning Outcome: Describe the structural and functional features of the plasma membrane.
Module 3.4: The cytoskeleton plays both a structural and a functional role Cytoskeleton Functions as cell s skeleton Provides internal protein framework Gives cytoplasm strength and flexibility Components include: 1. Microfilaments 2. Intermediate filaments 3. Microtubules
Module 3.4: The cytoskeleton Microfilaments 6 nm in diameter (smallest cytoskeletal element) Typically composed of actin Commonly at periphery of cell
Module 3.4: The cytoskeleton Microfilaments (continued) Microvilli Finger-shaped extensions of cell membrane Have core of microfilaments to stiffen and anchor Enhance surface area of cell for absorption Terminal web (microfilaments inside plasma membrane in cells forming a layer or lining)
Module 3.4: The cytoskeleton Intermediate filaments 7 11 nm in diameter Strongest and most durable cytoskeletal elements
Module 3.4: The cytoskeleton Microtubules ~25 nm in diameter Hollow tubes built from globular protein tubulin Largest components of cytoskeleton Extend outward from centrosome (near nucleus)
Module 3.4: The cytoskeleton Centrioles Composed of microtubules (9 groups of triplets) Two in each centrosome Control movement of DNA strands during cell division Cells without centrioles cannot divide Red blood cells Skeletal muscle cells
Module 3.4: The cytoskeleton Cilia Long, slender plasma membrane extensions Motile cilia common in respiratory and reproductive tracts Microtubules surrounding a central pair Anchored to cell surface with basal body
Motile cilia beat rhythmically
Module 3.4: The cytoskeleton Cilia (continued) Primary cilium functions as sensor Flagella are longer than cilia and beat in a wavelike fashion
Module 3.4: Review A. List the three basic components of the cytoskeleton. B. Which cytoskeletal component is common to both centrioles and cilia? C. What is the function of motile cilia? D. Which cytoskeletal structure is found only in males? Learning Outcome: Differentiate among the structures and functions of the cytoskeleton.
Module 3.5: Ribosomes and endoplasmic reticulum Ribosomes Responsible for protein synthesis Two subunits (1 large, 1 small) containing special proteins and ribosomal RNA (rrna) Must join together before synthesis begins
Module 3.5: Ribosomes and endoplasmic reticulum Ribosomes (continued) Free ribosomes Throughout cytoplasm Manufactured proteins enter cytosol Bound or fixed ribosomes Attached to rough endoplasmic reticulum Synthesize proteins for export out of cell
Module 3.5: Ribosomes and endoplasmic reticulum Endoplasmic reticulum (ER) Network of intracellular membranes continuous with nuclear envelope, which surrounds nucleus Forms hollow tubes, sheets, and chambers (cisternae, singular, cisterna, reservoir for water) Synthesizes and stores proteins, lipids, and carbohydrates
Module 3.5: Ribosomes and endoplasmic reticulum Two types of endoplasmic reticulum (ER) 1. Smooth (SER) Lacks ribosomes Cisternae are often tubular
Module 3.5: Ribosomes and endoplasmic reticulum Two types of endoplasmic reticulum (ER) (continued) 2. Rough (RER) Has attached (fixed) ribosomes Modifies newly synthesized proteins Exports those proteins to Golgi apparatus Proportion of SER to RER depends on the cell and its functions
Module 3.5: Ribosomes and endoplasmic reticulum Polypeptide formation in RER Polypeptide synthesized on attached ribosome Growing chain enters cisterna of RER Polypeptide assumes secondary/tertiary structures Completed protein may become enzyme or glycoprotein Products not destined for RER are packaged into transport vesicles Deliver products to Golgi apparatus
Module 3.5: Review A. Describe the immediate cellular destinations of newly synthesized proteins from free ribosomes and fixed ribosomes. B. Compare and contrast the structure of SER and RER. C. Why do certain cells in the ovaries and testes contain large amounts of SER? D. The ER is connected to and continuous with what other organelle in the cell? Learning Outcome: Describe the ribosome and smooth and rough endoplasmic reticula, and indicate their specific functions.
Module 3.6: The Golgi apparatus is a packaging center Golgi apparatus (Golgi complex) Functions 1. Renews or modifies plasma membrane 2. Modifies or packages secretions into secretory vesicles for release from cell (exocytosis) 3. Packages special enzymes within vesicles for use in cytosol (lysosomes) Typically consists of 5 6 flattened discs (cisternae) May be more than one apparatus in a cell Situated near nucleus
Module 3.6: Golgi apparatus Golgi apparatus process 1. Transport vesicles filled with proteins and/or glycoproteins from rough ER arrive at cis face ( receiving side ) of Golgi apparatus. 2. Transport vesicles fuse, forming new cisternae. Enzymes in Golgi apparatus modify arriving products. 3. Products modified and re-packaged as they move toward trans face ( shipping side ). 4. Finalized products packaged in secretory vesicles and released from trans face.
Golgi apparatus process
Module 3.6: Golgi apparatus Golgi apparatus products 1. Membrane renewal vesicles Add to plasma membrane Allow alteration of plasma membrane properties, changing sensitivity and functions of cells 2. Secretory vesicles Contain hormones or enzymes for extracellular release 3. Lysosomes Contain digestive enzymes for intracellular use
Module 3.6: Golgi apparatus Lysosomes Vesicles that isolate digestive processes from the rest of the cytoplasm Three basic functions 1. Fusion with another organelle and digestion of contents 2. Fusion with another vesicle containing fluid or solid extracellular materials and digestion of contents 3. Release of digestive enzymes within the cytoplasm when cell is injured or dying, resulting in autolysis (enzymes destroy cytoplasm) Leads to suicide packets name for lysosomes
Lysosomes
Module 3.6: Golgi apparatus Membrane flow Continuous movement and exchange of materials between organelles using vesicles Can replace parts of cell membrane to allow cell to grow, mature, or respond to changing environment In an actively secreting cell, the entire membrane surface can be replaced in 1 hour.
Module 3.6: Review A. List the three major functions of the Golgi apparatus. B. What do lysosomes contain? C. Describe three functions of lysosomes. Learning Outcome: Describe the Golgi apparatus, and indicate its specific functions.
Module 3.7: Mitochondria are the powerhouses of the cell Mitochondria (mitos, thread + chondrion, granule) Produce energy (ATP) for cells Vary in number per cell depending on cell s energy requirements (more energy needs = more mitochondria) Mitochondria account for 30 percent of the heart cardiac muscle cells Red blood cells have no mitochondria Contain their own DNA (mtdna) and ribosomes
Module 3.7: Mitochondria Mitochondrial double membrane Outer membrane surrounds organelle Inner membrane contains folds called cristae Inner membrane encloses liquid called matrix Cristae increase surface area exposed to matrix Metabolic enzymes in matrix catalyze reactions providing energy for cellular function
Cut-away view of mitochondrion organelle
Mitochondrion organelle
Module 3.7: Mitochondria Steps of ATP production 1. Glycolysis (glycos, sugar -lysis, a loosening) Occurs in cytosol 1 glucose 2 pyruvate Pyruvate absorbed into mitochondria 2. In mitochondrial matrix: CO 2 removed from pyruvate Enters citric acid (or TCA, tricarboxylic acid) cycle Systematically removes CO 2 and hydrogen atoms
Module 3.7: Mitochondria Steps of ATP production (continued) 3. Enzymes and coenzymes use hydrogen atoms to catalyze ATP from ADP Also forms H 2 O 4. ATP leaves mitochondrion
ATP Production
Module 3.7: Mitochondria Aerobic metabolism or cellular respiration ATP production that requires oxygen Occurs in the mitochondria Much more efficient than ATP production without oxygen (e.g., glycolysis) Produces about 95 percent of ATP needed by cell Remaining 5 percent produced by enzymatic reactions in the cytoplasm
Module 3.7: Review A. Describe the structure of a mitochondrion. B. Most of a cell s ATP is produced within its mitochondria. What gas do mitochondria require to produce ATP, and what gas results? C. What does the presence of many mitochondria imply about a cell s energy requirements? Learning Outcome: Describe the structure of a mitochondrion, and explain the significance of mitochondria to cellular function.
Section 2: Structure and Function of the Nucleus Learning Outcomes 3.8 Describe the role of the nucleus in maintaining homeostasis at the cellular level. 3.9 Describe the functions of the cell nucleus, and distinguish between chromatin and a chromosome. 3.10 Discuss the nature of the genetic code, and summarize the process of protein synthesis. 3.11 Summarize the process of transcription. 3.12 Summarize the process of translation.
Module 3.8: The nucleus is the control center for cellular homeostasis Nucleus Usually largest cellular structure Control center for cellular operations Can direct synthesis of >100,000 different proteins Genetic information coded in sequence of nucleotides Determines cell structure and function Usually only one per cell Exceptions Skeletal muscle cells have many Mature red blood cells have none o Because of no nucleus, they disintegrate within 3 4 months
Module 3.8: Role of the nucleus The nucleus directs cellular responses to environmental (ECF) changes Short-term adjustments Enzyme activity changes Long-term adjustments Changes in enzymes produced Changes in cell structure from changes in structural proteins Often occur as part of growth, development, and aging
Module 3.8: Review A. How is genetic information coded in the cell? B. How many nuclei do most body cells contain? C. Describe why the nucleus is said to be the control center for the cell. Learning Outcome: Describe the role of the nucleus in maintaining homeostasis at the cellular level.
Module 3.9: The nucleus contains DNA, RNA, organizing proteins, and enzymes Nuclear structures and functions Nuclear envelope Separates nucleus from cytoplasm Double membrane Perinuclear space (peri-, around) o Space between layers Nuclear pores Passageways that allow chemical communication between nucleus and cytoplasm Movement of ions and small molecules regulated by proteins at the pores Account for about 10% of the surface of the nucleus
Module 3.9: Contents of the cell nucleus Nucleoplasm Fluid contents of nucleus Contains network of fine filaments for structural support Also contains ions, enzymes, nucleotides, and small amounts of RNA and DNA
Module 3.9: Contents of the cell nucleus Nucleoli (singular, nucleolus) Transient nuclear organelles Composed of RNA, enzymes, and proteins (histones) Assemble RNA subunits Most prominent in cells manufacturing large amounts of proteins Examples: liver, nerve, muscle cells
Module 3.9: Contents of the cell nucleus DNA in the nucleus Stores instructions for protein synthesis Strands in nucleus coiled, allowing much to be packed in small space Wrap around histone molecules forming nucleosomes Loosely coiled (chromatin) in nondividing cells Tightly coiled (chromosomes) in dividing cells
Module 3.9: Contents of the cell nucleus DNA during cell division Starts by becoming tighter and more complex, forming chromosomes Two copies of each chromosome held together at centromere 23 paired chromosomes in somatic (general body) cells One each from mother/father Carry instructions for proteins and RNA Also some regulatory and unknown functions
Module 3.9: Review A. Describe the contents and the structure of the nucleus. B. What molecule in the nucleus contains instructions for making proteins? C. How many chromosomes are contained within a typical somatic cell? D. The total length of the DNA within a human cell nucleus is approximately 2 meters. How does the DNA fit into the relatively small space of a human nucleus, which ranges some 6 10 µm in diameter? Learning Outcome: Describe the functions of the cell nucleus, and distinguish between chromatin and a chromosome.
Module 3.10: Protein synthesis involves DNA, enzymes, and three types of RNA DNA Long parallel chains of nucleotides Chains held by hydrogen bonds between nitrogenous bases Four nitrogenous bases 1. Adenine (A) 2. Thymine (T) 3. Cytosine (C) 4. Guanine (G)
Module 3.10: The genetic code and protein synthesis DNA (continued) Genetic information stored in sequence of base pairs Known as the genetic code Triplet code Gene Sequence of three nitrogenous bases (triplet) Specifies single amino acid Functional unit of heredity Contains all the DNA nucleotides to produce a specific protein Size varies (~300 3000 nucleotides)
Module 3.10: The genetic code and protein synthesis
Module 3.10: The genetic code and protein synthesis Steps in protein synthesis 1. Gene activation Removal of histones and DNA uncoiling 2. DNA strands separate
Module 3.10: The genetic code and protein synthesis 3. Enzymes assemble nucleotides into a single strand of messenger RNA (mrna) Complementary base pairing matches DNA nucleotide sequence with new mrna sequence (A-U; G-C) Series of three RNA nucleotides called a codon Each codon codes for specific amino acid 4. mrna leaves nucleus through nuclear pores
Module 3.10: The genetic code and protein synthesis 5. At a ribosome in the cytoplasm, codons of mrna bind to anticodons (triplets of corresponding nucleotides) on transfer RNA (trna) 6. trna carries a specific amino acid (associated with specific anticodon)
Module 3.10: The genetic code and protein synthesis 7. Ribosomal RNA (rrna) of the ribosome strings amino acids together
Protein synthesis
Module 3.10: The genetic code and protein synthesis
Module 3.10: Review A. What is a gene? B. Why is the genetic code described as a triplet code? C. List the three types of RNA involved in protein synthesis. D. Which type of RNA links the genetic information in the nucleus with the cytoplasmic sites of protein synthesis? Learning Outcome: Discuss the nature of the genetic code, and summarize the process of protein synthesis.
Module 3.11: Transcription encodes genetic instructions on a strand of RNA Transcription ( to copy or rewrite ) Takes place in the nucleus Production of RNA from DNA template All three types of RNA are formed
Module 3.11: Transcription Steps of transcription 1. Gene activation Occurs at control segment or promoter (1st segment of gene) Only template strand of DNA used to synthesize RNA
Module 3.11: Transcription Steps of transcription 2. Beginning of assembly RNA polymerase (enzyme) binds to promoter Begins assembly of mrna strand
Module 3.11: Transcription Steps of transcription (continued) 3. Continuation of mrna strand RNA polymerase promotes hydrogen bonding between nucleotides on DNA template strand and complementary RNA nucleotides in nucleoplasm Example: (DNA triplet TAC = mrna AUG) Nucleotides connected by covalent bonding
Module 3.11: Transcription Steps of transcription (continued) 4. Transcription ends Stop codon reached mrna detaches Complementary DNA strands reassociate (with hydrogen bonding between complementary base pairs)
Steps of transcription
Module 3.11: Transcription Final processing of mrna Initial strand of mrna called immature mrna or pre-mrna Before leaving nucleus, mrna requires additional processing Introns (noncoding sequences) removed Remaining coding segments (exons) spliced together Changing the editing can produce mrna for different proteins
Module 3.11: Review A. What is transcription? B. Define DNA template strand. C. Name the substrates and product in the enzymatic reaction catalyzed by RNA polymerase. D. What process would be affected if a cell could not synthesize the enzyme RNA polymerase? Learning Outcome: Summarize the process of transcription.
Module 3.12: Translation builds polypeptides as directed by an mrna strand Translation Formation of a linear chain of amino acids from an mrna strand Translates genetic information from nucleic acids to proteins Occurs in cytoplasm on ribosomes Three phases 1. Initiation 2. Elongation 3. Termination
Module 3.12: Translation Steps of translation 1. Initiation phase mrna binds to small ribosomal subunit near the P site trna binds to P site and to start codon on mrna strand Binding occurs between mrna codons and trna complementary anticodons Small and large ribosomal subunits interlock around mrna strand forming initiation complex Additional trna binds to A site More than 20 kinds of trna Each carries an amino acid
Initiation phase
Module 3.12: Translation Steps of translation (continued) 2. Elongation Ribosomal enzymes remove amino acid from trna at P site and attach it to trna in A site Ribosome links amino acids forming dipeptide Ribosome moves to next codon on mrna strand trna from P site moves to E site and is released This trna can go bind to another amino acid More trnas arrive, match codon to anticodon, and continue forming polypeptide
Elongation
Module 3.12: Translation Steps of translation (continued) 3. Termination Stop codon on mrna Recognized by protein releasing factor Ribosomal enzyme breaks bond between polypeptide and trna in P site Ribosomal subunits detach Leaves intact mrna and new polypeptide
Module 3.12: Translation
Module 3.12: Translation Translation Produces a typical protein in ~20 seconds mrna can interact with other ribosomes and produce more proteins Multiple ribosomes can attach to a single mrna strand to quickly produce many proteins
BioFlix: Protein Synthesis
Module 3.12: Review A. What is translation? B. The nucleotide sequence of three mrna codons is AUU-GCA-CUA. What is the complementary anticodon sequence for the second codon? C. During the process of transcription, a nucleotide was deleted from an mrna sequence that coded for a protein. What effect will this deletion have on the amino acid sequence of the protein? Learning Outcome: Summarize the process of translation.
Section 3: How Substances Enter and Leave the Cell Learning Outcomes 3.13 Contrast permeable, selectively permeable, and impermeable membranes. 3.14 Explain the process of diffusion, and identify its significance in the body. 3.15 Explain the process of osmosis, and identify its significance in the body.
Section 3: How Substances Enter and Leave the Cell Learning Outcomes (continued) 3.16 Describe carrier-mediated transport and its role in the absorption and removal of specific substances. 3.17 Describe vesicular transport as a mechanism for facilitating the absorption or removal of specific substances from cells.
Module 3.13: The plasma membrane is a selectively permeable membrane Permeability Property determining which substances can enter or leave cytoplasm Freely permeable Any substance can pass (not found in living cells) Selectively permeable Some substances cross Impermeable No substances can pass (not found in living cells) Plasma membrane must allow some movement in and out of cells to enable intercellular communication and coordination
Module 3.13: Permeability of membranes
Module 3.13: Permeability of membranes Selectively permeable membranes Permit free passage of some materials and restrict others 1. Characteristics of material to pass Size Molecular shape Lipid solubility Electrical charge Other factors 2. Characteristics of cell membrane What lipids and proteins present How components are arranged
Module 3.13: Permeability of membranes Types of membrane transport 1. Passive (do not require ATP) Diffusion Carrier-mediated transport 2. Active (require ATP) Vesicular transport Carrier-mediated transport
Module 3.13: Review A. Define permeability. B. Identify three different types of membranes based on permeability. C. Distinguish between passive and active processes of membrane passage. D. What kinds of molecules are involved in both active and passive processes of membrane passage. Learning Outcome: Contrast permeable, selectively permeable, and impermeable membranes.
Module 3.14: Diffusion is passive movement driven by concentration differences Diffusion Net movement of a substance from higher concentration to lower concentration. Concentration gradient Concentration difference when molecules are not evenly distributed At an even distribution, molecular motion continues but no net movement
Module 3.14: Diffusion Diffusion (continued) Slow in air and water but important over small distances
Module 3.14: Diffusion Movement of water and solutes across plasma membrane: Selectively restricted diffusion Movement across lipid portion of membrane Examples: lipids, lipid-soluble molecules, soluble gases Movement through membrane channel Examples: water, small water-soluble molecules, ions Movement using carrier molecules Example: large molecules
Diffusion across a plasma membrane EXTRACELLULAR FLUID
Module 3.14: Diffusion Factors that influence diffusion rates Distance Shorter distance = faster diffusion Molecule or ion size Smaller size = faster diffusion Temperature Higher temperature = faster diffusion Concentration gradient Steeper gradient = faster diffusion Electrical forces Attraction of opposite charges (+, ) Repulsion of like charges (+,+ or, )
Module 3.14: Review A. Define diffusion. B. Describe the colliding molecules in the figure below (with the sugar cube in water). C. Identify factors that influence diffusion rates. D. How would a decrease in the oxygen concentration in the lungs affect oxygen diffusion into the blood? Learning Outcome: Explain the process of diffusion, and identify its significance in the body.
Module 3.15: Osmosis is the diffusion of water molecules across a selectively permeable membrane Osmosis (osmos, a push) Net diffusion of water across a membrane Maintains similar overall solute concentrations between the cytosol and extracellular fluid Osmotic flow Movement of water driven by osmosis
Module 3.15: Osmosis Osmosis (continued) Osmotic pressure Indication of force of pure water moving into a solution with higher solute concentration Hydrostatic pressure Fluid force Can be estimate of osmotic pressure when applied to stop osmotic flow
Water movement through a selectively permeable membrane
Module 3.15: Osmosis Osmolarity and tonicity Osmolarity (osmotic concentration) Total solute concentration in an aqueous solution Tonicity Effect of osmotic solutions on cell volume How a solution affects a cell
Module 3.15: Osmosis Three effects of tonicity 1. Isotonic (iso-, same tonos, tension) Solution that does not cause osmotic flow across membrane
Module 3.15: Osmosis Three effects of tonicity (continued) 2. Hypotonic Causes osmotic flow into cell Example: swelling and hemolysis (hemo-, blood + lysis, loosening) of red blood cell
Module 3.15: Osmosis Three effects of tonicity (continued) 3. Hypertonic Causes osmotic flow out of cell Example: shriveling and crenation of RBCs
Effects of tonicity
Module 3.15: Osmosis Importance of tonicity vs. osmolarity Administering large fluid volumes to patients with blood loss or dehydration If administered solution has same osmolarity as ICF but higher concentrations of individual ions/molecules Diffusion of solutes may occur across cell membrane Water will follow through osmosis Cell volume increases Normal saline often administered in emergency 0.9 percent or 0.9 g/dl of NaCl Isotonic with blood
Module 3.15: Review A. Describe osmosis. B. Describe osmotic pressure, and state in which solution below it is greater. C. Contrast the effects of a hypotonic solution and a hypertonic solution on a red blood cell. D. Some pediatricians recommend using a 10 percent salt solution to relieve nasal congestion in infants. Explain the effects this treatment would have on the cells lining the nasal cavity. Would it be effective? Learning Outcome: Explain the process of osmosis, and identify its significance in the body.
Module 3.16: In carrier-mediated transport, integral proteins facilitate membrane passage Carrier proteins Transport hydrophilic or large molecules across cell membrane Many move specific molecules through the plasma membrane in only one direction Some move more than one substance in the same direction (cotransport) Some move more than one substance in opposite directions Process called countertransport Carrier called an exchange pump
Module 3.16: Carrier-mediated transport 1. Facilitated diffusion Requires no ATP Passive transport (moves from high concentration to low concentration) Carrier binds to molecule, then changes shape to move molecule across membrane Rate of transport limited by number of available carrier proteins Once all carrier proteins saturated, no increase in rate of transport
Module 3.16: Carrier-mediated transport 2. Active transport Active process requiring energy molecule or ATP Independent of concentration gradient Examples: Ion pumps (Na +, K +, Ca 2+, and Mg 2+ ) Sodium potassium ATPase Exchanges 3 intracellular sodium ions for 2 extracellular potassium ions
Module 3.16: Carrier-mediated transport 3. Secondary active transport Transport mechanism itself does not require ATP Cell often needs ATP to maintain homeostasis associated with transport Movement for one of two substances follows concentration gradient Example: Sodium and glucose cotransporter
A&P Flix: Membrane Transport
Module 3.16: Review A. Describe the process of carrier-mediated transport. B. What two factors limit the rate of facilitated diffusion across a plasma membrane? C. What do the transport processes of facilitated diffusion and active transport have in common? D. During digestion, the concentration of hydrogen ions (H + ) in the stomach contents increases to many times that in cells lining the stomach. Which transport process could be responsible? Learning Outcome: Describe carrier-mediated transport and its role in the absorption and removal of specific substances.
Module 3.17: In vesicular transport, vesicles selectively carry materials into or out of cell Vesicular transport Materials move across cell membrane in small membranous sacs called vesicles Sacs form at or fuse with plasma membrane Two major types (both require ATP) 1. Endocytosis Importing extracellular substances into vesicles called endosomes 2. Exocytosis Movement of wastes or secretory products from intracellular vesicle to outside the cell
Module 3.17: Vesicular transport Receptor-mediated endocytosis Brings specific molecules into cell using receptor molecules on membrane surface a. Target molecule (ligand) binds to receptor
Module 3.17: Vesicular transport Receptor-mediated endocytosis (continued) b. Plasma membrane folds around receptors bound to ligands, forming pocket that pinches off c. Endosome called clathrin-coated vesicle forms
Module 3.17: Vesicular transport Receptor-mediated endocytosis (continued) d. Vesicle fuses with lysosomes
Module 3.17: Vesicular transport Receptor-mediated endocytosis (continued) e. Ligands freed from receptors and enter cytoplasm
Module 3.17: Vesicular transport Receptor-mediated endocytosis (continued) f. Lysosome detaches from vesicle
Module 3.17: Vesicular transport Receptor-mediated endocytosis (continued) g. Vesicle fuses with plasma membrane again
Receptor-mediated endocytosis
Module 3.17: Vesicular transport Pinocytosis ( cell drinking ) Formation of endosomes with ECF No receptor proteins involved Brings fluid and small molecules into cell
Module 3.17: Vesicular transport Phagocytosis ( cell eating ) Produces phagosomes containing solids No receptors involved Cytoplasmic extensions (pseudopodia) surround object and bring it into cell Only specialized cells (phagocytes or macrophages) perform phagocytosis
Module 3.17: Vesicular transport Exocytosis functional opposite of endocytosis Vesicle contents are released to extracellular environment
Module 3.17: Review A. Describe endocytosis. B. Describe the three types of endocytosis. C. Describe exocytosis. D. Some white blood cells engulf bacteria and bring them into the cell. What is this process called? Learning Outcome: Describe vesicular transport as a mechanism for facilitating the absorption or removal of specific substances from cells.
Section 4: Cell Life Cycle Learning Outcomes 3.18 Distinguish between interphase and cell division in the cell cycle. 3.19 Describe interphase, and explain its significance. 3.20 Describe the process of mitosis and its role in the cell life cycle. 3.21 Clinical Module: Discuss the relationship between cell division and cancer.
Module 3.18: Interphase and cell division make up the life cycle of a cell Life starts as a single cell At maturity, roughly 75 trillion cells in the body Cell division form of cellular reproduction Responsible for initial increase in cell number Essential to continued development and survival Cells have varying life spans and abilities to divide Often genetically controlled death occurs (apoptosis) Cell life cycle ends when cell dies
Module 3.18: Cell life cycle Two types of cell division 1. Mitosis 2 daughter cells produced Each with 46 chromosomes 2. Meiosis Produces sex cells Each with only 23 chromosomes
Module 3.18: Cell life cycle Mitosis Form of cellular reproduction Division of single cell produces pair of daughter cells Half the size of parent cell Grow to size of original cell before dividing
Module 3.18: Cell life cycle Divisions of cell life cycle 1. Interphase (nondividing period) Cell performs normal activities
Module 3.18: Cell life cycle Divisions of cell life cycle (continued) 2. Cell division Begins with mitosis Distribution of identical copies of chromosomes to each daughter cell Ends with cytokinesis (division of the cytoplasm)
Module 3.18: Review A. Explain why cell division is important. B. Define apoptosis. C. When does cell division begin and end? Learning Outcome: Distinguish between interphase and cell division in the cell cycle.
Module 3.19: During interphase, the cell prepares for cell division Division of interphase Somatic (body) cells spend most of their lives in interphase For cells not preparing to divide, they stay in: G 0 phase Performing normal cell functions Examples: o Skeletal muscle cells and most neurons Stay in this phase forever o Stem cells Never enter G 0 Divide repeatedly
Module 3.19: Interphase For cells preparing to divide, interphase divided into: G 1 phase Normal cell functions, cell growth, duplication of organelles, protein synthesis S phase DNA replication, synthesis of histones and other proteins to allow duplication of chromosomes G 2 phase Last minute protein synthesis and centriole replication
Module 3.19: Interphase DNA replication process DNA helicase Unwinds DNA strands Disrupts hydrogen bonds between bases DNA polymerase Binds to exposed bases Promotes bonding between current DNA strand and complementary nucleotides in nucleoplasm Covalently links nucleotides together
Module 3.19: Interphase DNA replication process (continued) DNA polymerase (continued) Works only in one direction One polymerase works continuously along one strand toward zipper forming the leading strand
Module 3.19: Interphase DNA replication process (continued) DNA polymerase (continued) Works only in one direction One polymerase works away from zipper forming the lagging strand o As unzipping occurs, another polymerase binds closer point of unzipping o Two new DNA segments spliced together with DNA ligases Two identical DNA strands formed
DNA replication
A&P Flix: DNA Replication
Module 3.19: Review A. Describe interphase, and identify its stages. B. A cell is actively manufacturing enough organelles to serve two functional cells. This cell is probably in what phase of interphase? C. What enzymes must be present for DNA replication to proceed normally? D. DNA replication occurs during what two cellular processes? Learning Outcome: Describe interphase, and explain its significance.
Module 3.20: Mitosis distributes chromosomes before cytokinesis separates the daughter cells M phase of cell cycle Includes mitosis and cytokinesis Mitosis Division and duplication of the cell s nucleus Divided into four stages: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase Cytokinesis Division of cytoplasm
Module 3.20: Mitosis Interphase DNA replicated, DNA is loosely coiled and no visible chromosomes
Module 3.20: Mitosis Phases of mitosis 1. Prophase (pro-, before) Nuclear envelope disintegrates Chromosomes coil and become visible under light microscope Replicated centrioles move to poles Astral rays (extend from centrioles) Spindle fibers (interconnect centriole pairs)
Module 3.20: Mitosis Phases of mitosis (continued) 1. Prophase (continued) Each copy of chromosome called chromatid Pair connected at centromere Raised region (kinetochore) at centromere attaches to spindle fibers
Module 3.20: Mitosis Phases of mitosis (continued) 2. Metaphase (meta, after) Chromosomes align at metaphase plate
Module 3.20: Mitosis Phases of mitosis (continued) 3. Anaphase (ana-, apart) Centromere splits Chromatids separate Chromatids drawn toward opposite sides along spindle apparatus
Module 3.20: Mitosis Phases of mitosis (continued) 4. Telophase (telo-, end) Cells prepare to enter interphase Cytoplasm constricts along metaphase plate (cleavage furrow) Nuclear membranes re-form Nuclei enlarge Chromosomes uncoil to chromatin
Module 3.20: Mitosis Cytokinesis (cyto-, cell + kinesis, motion) Begins with formation of cleavage furrow Continues through telophase Completion marks end of cell division
Module 3.20: Mitosis
A&P Flix: Mitosis
Module 3.20: Review A. Define mitosis, and list its four stages. B. What is a chromatid, and how many are present during normal mitosis in a human cell? C. What would happen if spindle fibers failed to form in a cell during mitosis? Learning Outcome: Describe the process of mitosis and its role in the cell life cycle.
Module 3.21: CLINICAL MODULE: Tumors and cancer are characterized by abnormal cell growth and division Cancer Illness that disrupts normal rates of cell division Characterized by permanent DNA sequence changes (mutations) Most common in tissues with actively dividing cells Examples: skin, intestinal lining Cancerous cells compete with normal cells for resources Usually begins with single abnormal cell
Module 3.21: CLINICAL MODULE: Tumors and cancer Tumor (neoplasm) Mass or swelling produced by abnormal cell growth and division 1. Benign tumor Cells remain within original tissue Seldom a threat Can be removed surgically if necessary
Module 3.21: CLINICAL MODULE: Tumors and cancer Malignant tumor Cells divide rapidly Released chemicals stimulate blood vessel growth (angiogenesis) to tumor area
Module 3.21: CLINICAL MODULE: Tumors and cancer Malignant tumor (continued) Accelerated growth due to blood vessel growth and supply to the area Tumor spreads to surrounding tissue by invasion Cells migrate to other areas and establish new tumors (called metastasis)
Module 3.21: CLINICAL MODULE: Tumors and cancer Malignant cells disrupt function No longer perform original functions or: Perform functions in an abnormal way Example: Malignant tumor of thyroid gland produces abnormal amounts of thyroid hormone Cancer cells compete with normal cells for space and nutrients
Module 3.21: Review A. Define cancer. B. What is a benign tumor? C. Define metastasis. D. How does angiogenesis aid tumor growth? Learning Outcome: Discuss the relationship between cell division and cancer.