Chapter 3: Cells Lectures by Mark Manteuffel, St. Louis Community College
Learning Objectives Be able to describe: what a cell is & two main classes of cells. structure & functions of cell membranes. how molecules move across membranes. how cells are connected & communicate with each other. 9 important landmarks in eukaryotic cells.
Cell Theory 1. All living organisms are made up of one or more cells. 2. All cells arise from other pre-existing cells.
Cells most basic units of organism can function independently perform all necessary life functions reproduce themselves.
All cells are either A. Prokaryotic cells = prokaryotes NO nucleus (DNA free in cell) first cells on earth B. Eukaryotic cells = eukaryotes - Have a nucleus (contains cell s DNA) - & other organelles
The 2 main classes of cells 1. Prokaryotic cells a) bacteria b) archaebacteria 2. Eukaryotic cells a) protists b) plants c) fungi d) animals
Eukaryotic cells have organelles.
Endosymbiosis Theory Explains presence of 2 organelles in eukaryotes mitochondria in plants & animals. chloroplasts in plants & algae
endosymbiosis
invagination
What determines whether a protein resides on the surface or extends through the bilayer?
4 primary types of membrane proteins each performs a different function.
The Plasma Membrane Fluid Mosaic In addition to proteins and phospholipids, two other molecules are found in the plasma membrane: 1. Short, branched carbohydrate chains 2. Cholesterol All can move laterally in membrane
3.7 Membrane surfaces have a fingerprint that identifies the cell. Cells with an improper fingerprint are recognized as foreign and are attacked by your body s defenses.
Why is it extremely unlikely that a person will catch HIV from casual contact such as shaking hands with an infected individual?
Membrane proteins act as receptors or channels help molecules into & out of cell send signals into cell & nucleus communicate with other cells act as enzymes catalyze reactions on inner & outer cell surfaces
Why are plasma membranes such complex structures? They perform several critical functions. Take in food & nutrients Dispose of waste products Build & export molecules Regulate heat exchange Regulate flow of materials in & out of cell
3-6. Faulty membranes can cause disease.
3.8 Passive transport is the spontaneous diffusion of molecules across a membrane. There are two types of passive transport: 1. Diffusion 2. Osmosis
Diffusion and Concentration Gradients Solutes Solvents
Simple Diffusion
Facilitated Diffusion Most molecules can t get through plasma membranes on their own. Channels Carrier molecules Transport proteins
Defects in Transport Proteins Can reduce or even bring facilitated diffusion to a complete stop Serious health consequences Many genetic diseases Cystinuria and kidney stones
3.9 Osmosis is the passive diffusion of water across a membrane.
Cells in Solution Tonicity The relative concentration of solutes outside of the cell relative to inside the cell Hypertonic Hypotonic Isotonic
The Direction of Osmosis Determined only by a difference in total concentration of all the molecules dissolved in the water It does not matter what solutes they are.
Two distinct types of active transport: 1. Primary 2. Secondary (Differ only in the source of the fuel)
Primary Active Transport: Uses Energy Directly from ATP
Secondary Active Transport An indirect method many transporter proteins use for fueling their activities The transport protein simultaneously moves one molecule against its concentration gradient while letting another flow down its concentration gradient.
Secondary Active Transport No ATP is used directly. 1. energy from ATP was used to pump one of the molecules involved against their concentration gradient. 2. then that molecule crosses with its gradient 3. and helps the other across against its gradient
3.11 Endocytosis and exocytosis are used for bulk transport of particles. Many molecules are just too big to get into a cell by passive or active transport.
Three types of endocytosis: 1. Phagocytosis 2. Pinocytosis 3. Receptor-mediated endocytosis
3.12 Connections between cells hold them in place and enable them to communicate with each other. Involves numerous types of protein and glycoprotein adhesion molecules
Tight Junctions form continuous, water-tight seals around cells and also anchor cells in place particularly important in the small intestine where digestion occurs
Desmosomes are like spot welds or rivets that fasten cells together into strong sheets function like Velcro : they hold cells together but are not water-tight found in much of the tissue-lining cavities of animal bodies
Gap Junctions pores surrounded by special proteins that form open channels between two cells Gap junctions are an important mechanism for cell-to-cell communication.
Plasmodesmata Tube-like channels connecting the cells to each other and enabling communication and transport between them Consider a plant as one big cell?
The nucleus the largest and most prominent organelle in most eukaryotic cells. has two primary functions: genetic control center storehouse for hereditary information
Chromatin a mass of long, thin fibers consisting of DNA wound around proteins (histones) packs DNA into nucleus tightly when a gene is expressed DNA unwinds open to nuclear machinery RNA RNA gets shipped out to cytoplasm
Nucleolus an area near the center of the nucleus where subunits of the ribosomes are assembled Ribosomes are little protein factories.
3.14 Cytoplasm and cytoskeleton: the cell s internal environment, physical support, and movement
Take-home message 3.14 The inner scaffolding of the cell, which is made from proteins, is the cytoskeleton. It consists of three types of protein fibers microtubules, intermediate filaments, and microfilaments.
Cytoskeleton: Three Chief Purposes
Cilia and Flagellum
3.15 Mitochondria: the cell s energy converters
Bag-within-a-Bag Structure: the intermembrane space and the matrix
Which cell type contains the most mitochondria per cell? 1. Liver 2. Muscle 3. White blood cell 4. Dermal cell 5. White adipose cell 6. Red blood cell Please insert Figure 3-31
Take-home message 3.15 In mitochondria, the energy contained within the chemical bonds of carbohydrate, fat, and protein molecules is converted into carbon dioxide, water, and ATP the energy source for all cellular functions and activities. Mitochondria may have their evolutionary origins as symbiotic bacteria living within other cells.
3.16 Lysosomes are the cell s garbage disposals.
Lysosomes round, membrane-enclosed, acid-filled vesicles that function as garbage disposals
The Endomembrane System
3.17 Endoplasmic reticulum: where cells build proteins and disarm toxins
Rough Endoplasmic Reticulum
The Smooth Endoplasmic Reticulum
3.18 Golgi apparatus: Where the cell processes products for delivery throughout the body
3.19 The cell wall provides additional protection & support for plant cells.
3.20 Vacuoles: multipurpose storage sacs for plant cells
The central vacuole can play an important role in five different areas of plant life: 1. Nutrient storage 2. Waste management 3. Predator deterrence 4. Sexual reproduction 5. Physical support
3.21 Chloroplasts: the plant cell s power plant
The stroma and interconnected little flattened sacs called thylakoids
Endosymbiosis Theory Revisited Chloroplasts resemble photosynthetic bacteria Circular DNA Dual outer membrane
3.3 Eukaryotic cells have compartments with specialized functions.