Unit 4: Cell Theory Discovery of cells Cells are far too small to see with the naked eye Invention of the microscope 1590 Zacharias and Hans Janssen made one of the first compound microscopes 1660 Robert Hooke made a compound microscope Hooke looked at cork and noticed room like structures he called cells He calculated that a square inch of cork contained about 1 200 000 000 cells Drawing by Rita Greer - The original is a pencil drawing by Rita Greer, history painter, 2006. This was digitized by Rita and sent via email to the Department of Engineering Science, Oxford University, where it was subsequently uploaded to Wikimedia., FAL, https://commons.wikimedia.org/w/index.php?curid=7667256 1660 Anton van Leeuwenhoek made a simple microscope (only one lens) that could magnify a specimen 266 times He viewed many samples of water from lakes, gums and gutters finding many small organisms that moved in different ways and named these organisms animalcules (little animals) Microscope picture: see page for author [CC BY 4.0 (http://creativecommons.org/licenses/by/4.0)], via Wikimedia Commons Development of cell theory 1838 Matthias Schleiden Concluded all plants are made of cells based on his own research 1839 Theodor Schwann Concluded all animals are made of cells, therefore all living things are made up of cells 1855 Rudolf Virchow Proposed that new cells are formed only from already existing cells Cell theory All living things are composed of cells Cells are the basic units of structure and functions in living things All cells are produced from other cells Cells are usually very small It is very tricky to count the number of cells in the human body Not all of us are the same size We contain microbes The number changes as we recycle cells Best current estimate is 37.2 trillion cells in the human body
Why are the cells so small? Very small cells are easier to replace without disruption to the organism Very small cells can specialize which also makes replacement much easier Mathematics Surface to volume ratio Compare two cubic cells Cell 1 10 μm (micrometers) on a side Surface area = 10 μm x 10 μm x 6 = 600 μm 2 Volume= 10 μm x 10 μm x 10 μm = 1000 μm 3 Surface area / Volume = 600 / 1000 = 0.6 Cell 2 20 μm on a side Surface area = 20 μm x 20 μm x 6 = 2400 μm 2 Volume = 20 μm x 20 μm x 20 μm = 8000 μm 3 Surface area / Volume = 2400 / 8000 = 0.3 By BallenaBlanca - https://commons.wikimedia.org/wiki/file:esquema_del_epitelio _del_intestino_delgado.png, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=48093230 Notice that Cell 1 has twice the surface area to volume ratio and therefor can transport needed materials in the cell and wastes out of the cell twice as fast Speed of diffusion this limits cell size because large cells cannot transport things from one part of the cell to another part fast enough to survive Limiting surface area / volume ratios Some cells that specialize in exchanging materials have many, tiny, finger-like extensions called microvilli Microvilli (see picture inset of small intestine villi) greatly increase surface area without adding much to the volume of a cell Comparing eubacteria and archaebacteria Not too long ago, archaea were classified as bacteria (hence the name archaebacterial) but now we know that they have a distinct evolutionary history and a much different biochemistry than bacteria Similarities Both are prokaryotes (mostly single celled but never with a nucleus or membraned organelles) Both have cell walls Both have ribosomes Both have similar shapes rods, cocci (spherical), and spirals Both have flagella to move Both reproduce asexually through binary fission, budding, and fragmentation Differences Eubacteria Cell membrane is ester linked lipid (peptidoglycan) Flagella are like a hollow stalk subunits move up the central pore and add on at the tip Can form spores that are dormant for years Are found almost everywhere in normal environments Archaebacteria Cell membrane is ether linked lipid (no peptidoglycan) Flagella add on at the base Do not form spores Are found in harsh conditions like hot vents, salty areas, and very acidic environments
Comparing prokaryotes and eukaryotes Prokaryotes Eukaryotes By This vector image is completely made by Ali Zifan - Own work; used information from Biology 10e Textbook (chapter 4, Pg: 63) by: Peter Raven, Kenneth Mason, Jonathan Losos, Susan Singer McGraw-Hill Education., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=44194140 Similarities Cells Cell membrane Ribosomes (smaller) Differences No true nucleus (have a nucleoid) No membrane bound organelles Circular DNA multiple proteins act together to fold and condense DNA Chlorophyll scattered in the cytoplasm Cell wall is usually chemically complexed (peptidoglycan) Cell size usually 1-10 μm By Zaldua I., Equisoain J.J., Zabalza A., Gonzalez E.M., Marzo A., Public University of Navarre - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=46386894 Cells Cell membrane Ribosomes (larger) True membrane bound nucleus present Membrane bound organelles present Endoplasmic reticulum Golgi apparatus Lysosomes Peroxisomes Mitochondria Linear DNA DNA wraps around proteins called histones Chlorophyll contained in chloroplasts (only plants have chlorophyll) Cell wall is chemically simpler (only in plants and fungi most eukaryotes have no cell wall) Cell size usually 10-100 μm
Parts of a eukaryotic cell Ribosomes make proteins Endoplasmic reticulum Rough associated with ribosomes Smooth makes lipids Nucleus Nucleolus condensed region where ribosomes are formed Chromatin DNA plus associated proteins Nuclear envelope membrane around the nucleus that has pores that allow materials to move in and out Golgi body (or apparatus) modifies proteins Centriole important part of centrosomes which are involved in organizing microtubules in the cytoplasm Lysosomes digest food Peroxisomes metabolize wastes (not shown) Mitochondria produce energy By Mediran (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons Comparing plant and animal cells Animal cells Plant cells Animal cells have centrioles, centrosomes, and lysosomes that plant cells do not have Plant cells have cell walls, chloroplasts, plasmodesmata, plastids, and a large central vacuole that animal cells do not have Source: Boundless. Characteristics of Eukaryotic Cells. Boundless Biology. Boundless, 26 May. 2016. Retrieved 26 Nov. 2016 from https://www.boundless.com/biology/textbooks/boundless-biology-textbook/cell-structure-4/eukaryotic-cells-60/characteristics-of-eukaryotic-cells-313-11446/
Multicellular organisms Advantages of multicellular organisms Longer lifespan An overall larger body size (usually fewer predators and better ability to maintain homeostasis) Cell differentiation (allows more structures, functions, and complexity) Levels of organization in multicellular organisms Organelles little organs typically, membrane bound structures or compartments in cells that perform a specific function Examples: nucleus carries instructions for cells, peroxisomes metabolize wastes, and mitochondria provide energy Cell the basic structural, functional, and biological unit of living organisms Often called the building blocks of life Examples: neurons (nerve cells), erythrocytes (red blood cells), epidermal cells (skin cells) Tissue groups of cells with a similar structure that work together for a specific function The four types of human tissues are: epithelial, connective, muscular, and nervous Organ collection of tissues joined in a structural unit to server a common function Examples: skeleton, muscles, teeth, stomach, intestines, liver, kidneys, lungs, brain, veins, arteries, spleen, pancreas, spinal nerves, eye, ear, and skin System groups of structures that perform the broadest functions in an animal The eleven main types of human systems are: cardiovascular / circulatory, digestive / excretory, endocrine, integumentary / exocrine, lymphatic / immune, muscular / skeletal, nervous, reproductive, renal / urinary, respiratory, and vestibular Structure vs Function Structure describes what something looks like or its makeup Function describes what a structure does or the job it performs Example: mitochondrion Structure: a roughly ovoid organelle encased by an outer membrane and having an inner membrane with many folds called cristae that contains its own DNA Function: energy production Transport in cells Diffusion Osmosis By JrPol - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=4586487 Diffusion the random mixing of substances due to the natural movement of particles This process will always carry substances from areas of higher concentration to areas of lower concentration By OpenStax - https://cnx.org/contents/fptk1zmh@8.25:fei3c8ot@10/preface, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=30131189 Osmosis the process by which solvent molecules tend to pass through a semipermeable membrane from a less concentrated solution to a more concentrated solution In cells, this process will always carry solvent (water) from areas of higher concentration to areas of lower concentration across the plasma (or cell) membrane
Conditions for osmosis Osmosis is, basically, diffusion across a semipermeable membrane and requires: A semipermeable membrane A concentration gradient Cell walls are phospholipid bilayers that form a liposome Water (and any charged particles that dissolve in water) cannot pass through the plasma membrane except through pores (or holes in the membrane Passive transport The movement of substances across cell membranes by osmosis Passive transport always moves ions from higher concentrations to lower concentrations (with or down the concentration gradient) Requires no energy input from the cell Typically, passive transport occurs through ion channels which are composed of four proteins that form a pore (or hole) through the plasma (or cell) membrane Ion channels are usually very fast (often a million ions per second or more) Schematic diagram of an ion channel. 1 - channel domains (typically four per channel), 2 - outer vestibule, 3 - selectivity filter, 4 - diameter of selectivity filter, 5 - phosphorylation site, 6 - cell membrane. Active transport Forcing the movement of substances across cell membranes against osmosis Active transport always moves ions from lower concentrations to higher concentrations or up the concentration gradient Typically, active transport occurs through ion transporters (or ion pumps like the Na + /K + pump) Ion pumps require cellular energy from some source (often ATP) Example: the Na + /K + pump Moves 3 Na + ions out of the cell and 2 K + ions into the cell In a typical cell, 1/5 the metabolic energy is required for ion pumps In a neuron, up to 2/3 the metabolic energy is required for ion pumps By BruceBlaus. Blausen.com staff. "Blausen gallery 2014". Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762. Derivative by Mikael Häggström - File:Blausen_0211_CellMembra
Similarities and Differences between Active and Passive Transport Similarities Both involve movement of ions across a plasma (or cell) membrane Both require a pore to move ions through the plasma membrane Both are required to maintain proper cell functioning Differences Passive Moves from high to low concentration Requires no metabolic energy Makes use of osmosis through ion channels Active Moves from low to high concentration Requires metabolic energy from ATP Uses Na + /K + pumps (or some ion pump) Moving large particles in and out of cells Endocytosis a form of active transport in which cells transport large molecules into the cell by engulfing them The cell walls expand outward (or inward) and engulf the large particles The substances that enter the cell will be surrounded by membranes (vesicles or vacuoles) There are three types of endocytosis Phagocytosis transports solid particles Pinocytosis transports particles in liquids Receptor-mediated endocytosis transports particles with specific sites that can bind to a receptor in the cell membrane The vacuoles that form in this manner will be protein coated vacuoles Exocytosis a form of active transport in which cells transport large molecules out of the cell Proteins that are to be transported out of the cell are surrounded by membranes and are called secretory vesicles The membrane of the secretory vesicle fuses with the cell membrane then opens to the outside of the cell to push the protein out
Basal Metabolic Rate (BMR) the minimal amount of energy the body requires to function at rest BMR is expressed in food calories (kcal) Some resting body processes include breathing, blood circulation, maintaining body temperature, brain function, nerve function, and muscle contraction (especially the heart), and cell metabolism Cell metabolism refers to all the processes a cell requires for functioning Catabolism processes which break larger molecules into smaller ones generally for body use to release energy Anabolism processes which assemble smaller molecules into larger ones whereby energy is stored in chemical bonds for later use The BMR is most accurately determined by experimental measurement for an individual Usually, BMR is estimated by use of a mathematical formula The Mifflin St Jeor Equation: BMR = ( 10.0 m + 6.25 h 1 kg 1 cm 5.0 a kcal + s) 1 yr day Where m = mass in kg = wt lbs x 2.2 h = height in cm = h in x 2.54 a = age in years s = +5 for males and 161 for females Photosynthesis Photo means light and synthesis means putting together During photosynthesis, carbon dioxide (CO 2 ) and water (H 2 O) are put together by plants using light energy from the sun to form sugars The chemical that allows plants to do this is called chlorophyll In plant cells, chlorophyll is found in the chloroplasts Plants break down some of the sugars they make into smaller molecules in order to release the energy they need for their cells to function Some of the sugars are used to build cellulose Some of the sugars are stored for later use Organisms that eat plants are using these stored sugars as food Nearly all living things obtain energy either directly or indirectly from the energy of sunlight captured during photosynthesis Chemical equations Scientists use chemical symbols and chemical equations as a kind of a shortcut to represent processes such as photosynthesis Substances that are used in the reaction are called the reactants Reactants are listed on the left of the equation Substances that are produced by the reaction are called the products Products are listed on the right side of the equation The photosynthesis equation: Reactants Products 6 (CO2) + 6 (H2O) + sunlight C6H12O6 + 6 O2 carbon dioxide + water + sunlight glucose + oxygen where the reactants are carbon dioxide and water and the products are glucose (a sugar) and oxygen as a waste product for the plant The arrow in the equation is a yields sign and can be read as yields or as reacts to produce The entire equation would be read as: Carbon dioxide plus water react to produce glucose plus oxygen.
Steps of photosynthesis 1. Stage 1 Capturing the sun's energy Chlorophyll in the chloroplasts captures sunlight in two systems Photosystem I (PSI) Sunlight causes chlorophyll to lose an electron (e ) The electron moves down the chloroplast electron transport chain This happens twice producing 2 e Photosystem II (PSII) Sunlight causes the splitting of water producing 2 e, 2 H + ions, and ½ O 2 molecule These 2 e replace the e lost by chlorophyll in PSI 2. Stage 2 Using energy to make food Calvin cycle CO 2 enters the stoma on the underside of leaves and H 2 O enters from the roots A complex set of reactions uses energy and the electrons from Stage 1, the H 2 O, and the CO 2 to produce the sugar glucose (C 6 H 12 O 6 ) Plants throw out waste O 2 formed in PSII through the stoma and use the glucose as food Cellular respiration Although cellular respiration is often referred to as respiration it should not be confused with breathing (which is also called respiration) Respiration is the process by which cells obtain energy from glucose During respiration cells break down simple food molecules such as sugars to release the energy they contain Respiration occurs in two stages Stage 1 occurs in the cytoplasm of the cells Glucose is broken down into smaller molecules No oxygen is involved Only a small amount of energy is released Stage 2 occurs in the mitochondria The small molecules from Stage 1 are broken down into even smaller molecules The chemical reactions in the mitochondria require oxygen A large amount of energy is released (explaining why mitochondria are called powerhouses) Carbon dioxide (CO 2 ) and water (H 2 O) are also released in respiration When humans breathe out they release CO 2 and H 2 O The respiration equation: C6H12O6 + 6 O2 6 (CO2) + 6 (H2O) + energy glucose + oxygen carbon dioxide + water + energy
Note that the respiration equation is the reverse of the photosynthesis reaction Because these two reactions are opposite, they form a cycle that helps keep the CO 2 and O 2 levels nearly constant on Earth Fermentation Some single-celled organisms live deep in the ocean, in mud, or in other places where there is no oxygen Such organisms use fermentation to obtain energy instead of respiration Fermentation a process that produces energy for cells without using oxygen The amount of energy released during fermentation is much less than during respiration Alcoholic fermentation Yeast is an example of an organism that uses alcoholic fermentation Bakers and brewers use alcoholic fermentation because this method also produces CO 2 The CO 2 bubbles cause bread to rise and form the bubbles in beer Lactic acid fermentation When cells in the human body use oxygen faster than it can be replaced, the cells can generate some energy by a fermentation process that also produces lactic acid Lactic acid causes the painful sensation that results in muscles that feel sore and weak Similarities and Differences between Respiration and Fermentation Stages of Respiration and Fermentation Respiration Fermentation Stage 1: in the cytoplasm Stage 1: in the cytoplasm Glycolysis produces 2 ATP molecules and Glycolysis produces 2 ATP molecules and 2 pyruvate molecules 2 pyruvate molecules Stage 2: in the mitochondria Stage 2: no oxygen, can t use mitochondria Krebs cycle makes CO 2 and 2 ATP Pyruvate converted to lactic acid Electron transport chain about 34 ATP Repeat from Stage 1 Total: 38 ATP Total: 2 ATP Similarities Both methods produce energy for cells Both produce energy by creating adenosine triphosphate (ATP) Both use glycolysis in the cytoplasm Differences Respiration Starts in cytoplasm moves to mitochondria Requires oxygen Produces much more energy (38 ATP) Fermentation Process never moves out of cytoplasm Proceeds without use of oxygen Produces much less energy (2 ATP) Life cycle of a cell Why cells reproduce For single celled organisms, reproduction carries on the species For multicellular organisms: Growth increase the number of cells (growth of the organism) Maintenance replace cells that grow old and die Repair replace damaged cells Stage 1: Interphase the period before cell division Growth cell reaches full size and copies of chloroplasts (plants) and mitochondria are made Replication DNA is copied so that the cell has two identical sets of DNA Preparation for cell division structures are made that are used for division
Stage 2: Mitosis the period when the cell nucleus divides into two new nuclei Prophase The threadlike chromatin in the nucleus condenses to form chromosomes Chromosomes are double-rod structures Chromatid one single rod in a chromosome The two chromatids are identical because the cell DNA has replicated The chromatids are held together by a structure called a centromere The pairs of centrioles move to opposite ends of the cell Spindle fibers form a bridge between the opposite ends of the cell The nuclear envelope breaks down Metaphase Chromosomes line up across the center of the cell This prepares the chromosomes so they can split with one daughter chromatid to each end Each chromosome attaches to a spindle fiber at its centromere Anaphase The centromeres split One chromatid is drawn by its spindle fiber to one end of the cell and the other chromatid moves to the opposite end of the cell drawn by its spindle fiber The cell stretches out as the opposite ends are pushed apart Telophase The chromosomes unwind, stretch out, and lose their rod-like appearance A new nuclear envelope forms around each region of chromosomes Stage 3: Cytokinesis the period when the cell completes the process of division Cytokinesis starts at about the same time as the telophase
Cytokinesis specifically for animal and plant cells: Animal cells The cell membrane pinches in around the middle of the cell The cell splits in two Each daughter cell ends up with an identical set of chromosomes and about half the organelles Plant cells The cell wall cannot pinch together in the middle of the cell Instead, the cell makes a structure called a cell plate which eventually forms into new cell membranes that separate the two daughter cells A new cell wall forms around the two cell membranes Time required for the cell cycle to occur in human liver cells (time measured in hours) Length of the Cell Cycle 0.83 0.17 10 2 9 Interphase Growth Interphase DNA Replication Interphase Division Prep Mitosis Cytokinesis Binary fission in prokaryotic cells 1. The DNA replicates 2. Each copy of the DNA attaches to the cell membrane at opposite ends of the cell 3. The cell splits and each end pulls its copy of the DNA into its part of the new cell Similarities in mitosis and binary fission: Both are asexual forms of cell reproduction Both replicate DNA into two exact copies Both split cells into two exact copy daughter cells
Differences in mitosis and binary fission Mitosis Occurs in eukaryotic cells Many chromosomes are involved Proceeds in five complex steps Binary Fission Occurs in prokaryotic cells Only one single strand of DNA is involved Proceeds in three simple steps This is the last page.