Unit 3 Cell Structure and Function Cells Cell theory The cell is the basic unit of life The cells of all living things exhibit the seven characteristics of life All living things are made of cells Cells make up all tissues in a multicellular organism All cells in a multicellular organism have certain parts in common, but they are specialized in structure and function New cells only come from pre-existing cells There is no such thing as spontaneous generation Example maggots will not grow on meat that is sealed flies are needed to give rise to the maggots Cells Plasma Membrane Most human cells are about 100 μm in diameter (about the width of a human hair) Prokaryotes bacteria and single-celled organisms Eukaryotes animals, plants, fungi Both types of cells have a plasma membrane made up of a phospholipid bilayer Selectively permeable allows certain molecules to enter the cell; proteins on the surface aid in this process
Cells Eukaryotic Cell All types of cells contain cytoplasm a semifluid (gel-like) medium that contains water, proteins and other molecules suspended or dissolved into it Organelles the structures contained within the cell Most organelles are surrounded by a membrane Prokaryotes lack membrane-bound organelles Organelles Nucleus membrane-bound structure in which DNA is found Prokaryotic cells lack a defined nucleus the DNA is located centrally within the cell, but not in a nucleus Nuclear membrane (envelope) selectively permeable membrane that surrounds the nucleus; contains pores Nucleolus within the nucleus; produces ribosomes Organelles Chromatin coiled strands of DNA; how DNA exists before replication begins Ribosomes site of protein synthesis Rough endoplasmic reticulum (ER) transport system; aids in protein production; contains ribosomes Smooth endoplasmic reticulum (ER) transport system; aids in lipid production; does not contain ribosomes
Organelles Mitochondria carries out cellular respiration; produces ATP Microfilaments protein fibers that add support and strength to the cell Microtubules cylinders of protein that aid in muscle movement Lysosome digests macromolecules and cell parts Organelles Peroxisomes involved in the breakdown of lipids Centrioles specialized microtubules involved in cell division Golgi apparatus packaging center for proteins Cilia used for movement or sensory purposes History of the Eukaryotic Cell First cells to arise were prokaryotes Bacteria Archaea The eukaryotic cell is believed to have evolved from the archaea Nucleus was formed by a pocket forming in the plasma membrane enclosing the DNA Organelles evolved by engulfing other prokaryotic cells, which were not digested Plasma Membrane Phospholipid bilayer with attached or embedded proteins Polar head attracted to water Nonpolar tail not attracted to water At body temperature, the phospholipid bilayer is a liquid it has the consistency of olive oil The embedded proteins can change their positions
Plasma Membrane Plasma Membrane Cholesterol lends support to the membrane Glycoproteins and glycolipids short chains of sugars of proteins and lipids Blood types Receptors for hormones Form channels through which substances can enter the cell Carrier proteins enzymes Plasma Membrane Functions Keeps a cell intact Allows only certain molecules to enter and exit the cell selectively permeable Small molecules O 2 and CO 2 can pass through easily Water passes through using protein channels called aquaporins Ions and large molecules cannot cross without more assistance Diffusion Diffusion the movement of molecules from an area of high concentration to an area of low concentration until they are evenly distributed (equilibrium is achieved) No cellular energy is needed
Osmosis Osmosis movement of water from an area of high concentration to an area of low concentration (diffusion of water) Tonicity the water concentration of a solution on either side of a membrane Isotonic same concentration of water on both sides of a membrane no net movement of water Osmosis Hypotonic solution has a higher concentration of water than the cells placed into it water enters the cell causing it to swell and maybe burst Lysis bursting of a cell Hemolysis bursting of a red blood cell Hypertonic - solution has lower concentration of water than the cells placed into it water leaves the cell causing it to shrink or shrivel Crenation the shrinking of red blood cells Osmotic pressure controls water movement Small and large intestines kidneys Facilitated Transport Facilitated transport a molecule is moved across a membrane from an area of high concentration to an area of low concentration by the use of protein carrier in the membrane Does not need energy (passive transport) Each protein carrier (called a transporter) will only bind to a particular molecule (because of its shape) Active Transport Active transport movement from an area of low concentration to an area of high concentration Requires both a protein carrier and energy obtained through the breakdown of glucose (ATP energy storage molecule) When ATP is broken down, energy is released The proteins involved are called pumps One such pump moves Na+ ions outside the cell and K+ inside the cell associated with nerve and muscle cells
Endocytosis and Exocytosis Endocytosis - the plasma membrane pinches in, forming a pouch Phagocytosis white blood cells engulf pathogens Pinocytosis molecules and fluid Exocytosis when a vesicle within the cell fuses with the plasma membrane and is then secreted from the cell Neurotransmitters how they exit one nerve cell and enter another Receptor-mediated endocytosis use of receptor proteins to aid in the process of endocytosis The Nucleus Every cell in our body contains the same genes Genes segments of DNA that code for the production of proteins Each type of cell has certain genes turned on and certain genes turned off Nucleoplasm the medium in which the chromatin is immersed It has a different ph than cytoplasm, therefore it is a different substance Ribosomes Composed of RNA May be attached to the rough ER or may be free within the cytoplasm They may be single or in groups called polyribosomes Endomembrane System Endoplasmic reticulum Rough ribosomes produces proteins Smooth no ribosomes produces lipids Makes testosterone in the testes Forms vesicles (tiny sacs enclosed by a membrane) used for transport Golgi Apparatus modifies proteins and lipids so that they can move to other parts of the cell Adds sugars to make glycoproteins and glycolipids
Endomembrane System Lysosomes Produced by the Golgi apparatus Contain hydrolytic enzymes Numerous in white blood cells to engulf microbes Autodigestion cell parts are broken down by the lysosomes Tay-Sachs disease caused by lack of a particular enzyme in the lysosomes causing an undigested substance to collect in nerve cells causing developmental problems and early death Cytoskeleton Cytoskeleton all of the protein fibers that exist in the cytoplasm Maintains a cell s shape Anchors the organelles in the cytoplasm Assists in their movement Microtubules assembled in a organelle called the centrosome Maintains a cell s shape Act as tracks along which the organelles move Form spindle fibers during cell division to assist with the movement of chromosomes Actin filiaments larger than microtubules and aid in movement Cytoskeleton Intermediate filaments intermediate in size between microtubules and actin filaments Structure and function differ according to the type of cell Cilia and flagellum aid in movement Cilia Respiratory tract trap debris Fallopian tubes aid in egg movement Flagellum Sperm cells Cell Junctions Adhesion junctions cytoskeletons of adjacent cells are interconnected Skin cells Tight junctions connects plasma membrane proteins of neighboring cells Digestive system and kidneys Gap junctions channel proteins of adjacent cells fuse Communication
Mitochondria Convert the chemical energy of glucose into the chemical energy of ATP through cellular respiration Use up O 2 and give off CO 2 Cristae folds of the inner membrane ATP production occurs here Matrix inner space filled with a gel-like fluid Contains enzymes used to break down glucose Metabolism Metabolism all of the chemical reactions that occur in a cell Metabolism often requires pathways and each reaction requires a specific enzyme 1 2 3 4 5 6 A B C D E F G Feedback inhibition one of the end products interacts with an enzyme early in the pathway (slows it down or speeds it up) Enzymes Substrates the reactant(s) involved in a reaction with an enzyme Enzymes are often named for their substrate Lipase breaks down lipids Active site the part of the enzyme where it is brought together with the substrate An enzyme s specificity is caused by the shape of the active site the enzyme and substrate form a perfect fit like puzzle pieces
Enzymes After a reaction is complete, the enzyme is ready to be used again E + S ES E + P E = enzyme, S = substrate, ES = enzymesubstrate complex, P = product Coenzymes non-protein molecules that assist enzymes vitamins Cellular Respiration Blood bring oxygen and glucose to cells Breaks down glucose to CO 2 and water Three pathways Glycolysis The Citric Acid Cycle The Electron Transport Chain Allows for the gradual breakdown of a glucose molecule to release its energy If glucose was broken down all at once, too much energy would be lost as heat Cellular Respiration Glycolysis Glucose (6 carbons) is split into 2 pyruvate (3 carbons) molecules Cytoplasm Occurs in every type of cell Anaerobic does not require oxygen Removes hydrogen atoms and electrons from glucose resulting in NAOH Needs 2 ATP to start, and produces 4 ATP net yield of 2 ATP molecules If oxygen is available, the pyruvate then enters the mitochondria Cellular Respiration Citric Acid Cycle Also called the Kreb s cycle Occurs in the matrix of mitochondria NADH carries away hydrogen atoms and electrons Produces 2 ATP per glucose So far - 4 ATP have been produced from each glucose molecule
Cellular Respiration Electron Transport Chain NADH from glycolysis and the citric acid cycle deliver hydrogen atoms and electrons to carrier proteins in the cristae of the mitochondria Each carrier accepts 2 electrons and passes them to the next carrier as they are passed they lose energy Oxygen is the final carrier accepting 2 electrons and combining with hydrogen to become water Aerobic oxygen is present Produces 32 ATP per glucose Total 36 ATP The energy in ATP is released when it is broken down into ADP (ATP ADP + P = energy) Cellular Respiration Fermentation Anaerobic does not involve oxygen When there is no oxygen, the electron transport chain will not function Glycolysis will still occur and causes pyruvate to be changed into lactate Provides a burst of energy for a short amount of time Produces 2 ATP molecules and lactate, which causes muscles to cramp and fatigue Prolonged fermentation will lead to death Yeast also perform fermentation produces alcohol and CO 2 CO 2 causes bread to rise Alcohol beer and wine production