The Working Cell: G: Membrane Transport & H: Enzymes. Chapter 5

Transcription

1 The Working Cell: G: Membrane Transport & H: Enzymes Chapter 5

2 Standards Unit G: Membrane Transport I can recognize the fluid mosaic model and accurately identify and describe the function of the components. I can compare and contrast the various ways substances cross the cell membrane. I can recognize the various ways substances cross the membrane and provide examples from the human body for each. I can predict changes to a cell mass and size placed in solutions of differing concentrations I can use data to create a graph to show the relationship between concentration and mass. I can use a graph to extrapolate the concentration that is isotonic to a cell.

3 TEM 200,000 MEMBRANE STRUCTURE AND FUNCTION Crash Course: Membranes and Transport 5.10 Membranes organize the chemical activities of cells Membranes provide structural order for metabolism The plasma membrane of the cell is selectively permeable controlling the flow of substances into or out of the cell Outside of cell Cytoplasm

4 5.11 Membrane phospholipids form a bilayer Phospholipids Hydrophilic head Have a hydrophilic head and two hydrophobic tails and are the main structural components of membranes Phospholipids form a two-layer sheet called a phospholipid bilayer, with the heads facing outward and the tails facing inward Phosphate group O CH O C O C O O O P O O Figure 5.11A + N CH 3 CH 3 CH 3 Hydrophilic heads Hydrophobic tails Water CH CH Symbol Figure 5.11B Water CH 3 CH 3 Hydrophobic tails

5 5.12 The membrane is a fluid mosaic of phospholipids and proteins A membrane is a fluid mosaic with proteins and other molecules embedded in a phospholipid bilayer where the phospholipids are constantly moving and shifting (FLUID) Membrane proteins are located studded within the membrane giving it a mosaic appearance (MOSAIC) Figure 5.12 Fibers of the extracellular matrix Carbohydrate (of glycoprotein) Glycoprotein Glycolipid Plasma membrane Phospholipid Microfilaments of cytoskeleton Cholesterol Proteins Cytoplasm

6 5.13 Proteins make the membrane a mosaic of functions Many membrane proteins function as enzymes Other membrane proteins function as receptors for chemical messages from other cells Membrane proteins also function in transport moving substances across the membrane Messenger molecule Receptor Activated molecule ATP Figure 5.13A Figure 5.13B Figure 5.13C

7 5.14 Passive transport is diffusion across a membrane In passive transport, substances diffuse through membranes without work (energy) by the cell spreading from areas of high concentration to areas of low concentration Small nonpolar molecules such as O 2 and CO 2 diffuse easily across the phospholipid bilayer of a membrane Molecules of dye Membrane Equilibrium Figure 5.14A Equilibrium Figure 5.14B

8 5.15 Transport proteins may facilitate diffusion across membranes Many kinds of molecules do not diffuse freely across membranes For these molecules, transport proteins provide passage across membranes through a process called facilitated diffusion Solute molecule Figure 5.15 Transport protein

9 5.16 Osmosis is the diffusion of water across a membrane In osmosis water travels from a solution of lower solute concentration to one of higher solute concentration Why would water move in this direction? Lower concentration of solute Higher concentration of solute Equal concentration of solute Solute molecule H 2 O Selectively permeable membrane Water molecule Figure 5.16 Net flow of water Solute molecule with cluster of water molecules

10 5.17 Water balance between cells and their surroundings is crucial to organisms The control of water balance is called osmoregulation Osmosis causes cells to shrink in hypertonic solutions and swell in hypotonic solutions In hypertonic solutions animals cells are shriveled and plants cells are plasmolyzed why does this happen? In hypotonic solutions animal cells burst/lysis and plant cells are in turgid (their ideal state) why does this happen? In isotonic solutions animal cells are normal, but plant cells are limp why?? Isotonic solution Hypotonic solution Hypertonic solution H 2 O H 2 O H 2 O H 2 O Animal cell (1) Normal (2) Lysed (3) Shriveled H 2 O H 2 O H 2 O Plasma membrane H 2 O Plant cell Figure 5.17 (4) Flaccid (5) Turgid (6) Shriveled (plasmolyzed)

11 5.18 Cells expend energy for active transport Transport proteins can move solutes against a concentration gradient through active transport, which requires ATP Transport protein Solute ATP P ADP Protein changes shape P Phosphate detaches P 1 Solute binding 2 Phosphorylation 3 Transport 4 Protein reversion Figure 5.18

12 5.19 Exocytosis and endocytosis transport large molecules To move large molecules or particles through a membrane A vesicle may fuse with the membrane and expel its contents (exocytosis) Fluid outside cell Vesicle Protein Cytoplasm Figure 5.19A

13 Membranes may fold inward enclosing material from the outside (endocytosis) Vesicle forming Figure 5.19B

14 LM 230 TEM 54,000 Endocytosis can occur in three ways Phagocytosis Pinocytosis Receptor-mediated endocytosis Pseudopodium of amoeba Food being ingested Plasma membrane Material bound to receptor proteins PIT Cytoplasm Phagocytosis Pinocytosis Receptor-mediated endocytosis TEM 96,500 Figure 5.19C

15 CONNECTION 5.20 Faulty membranes can overload the blood with cholesterol LDL Low-density lipoproteins receptor mediated endocytosis Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors hypercholesterolemia Figure 5.20 LDL particle Cholesterol Protein Plasma membrane Phospholipid outer layer Receptor protein Vesicle Cytoplasm

16 Standards Unit H: Enzymes I can relate the function of thyroxin to metabolism. I can use words and models to show the lock and key function of enzymes. I can describe how co-enzymes and co-factors assist enzymes. I can explain how enzymes help our metabolic reactions to occur I can model/show how thyroxin production is regulated. I can relate protein structure to the denaturation of enzymes and provide examples of conditions that cause denaturation. I can represent the rate of enzyme activity graphically.

17 Cool Fires Attract Mates and Meals Fireflies use light to send signals to potential mates instead of using chemical signals like most other insects The light comes from a set of chemical reactions that occur in light-producing organs at the rear of the insect Females of some species produce a light pattern that attracts males of other species, which are then eaten by the female

18 ENERGY AND THE CELL 5.1 Energy is the capacity to perform work All organisms require energy which is defined as the capacity to do work Kinetic energy is the energy of motion Potential energy is stored energy and can be converted to kinetic energy Figure 5.1A C

19 5.2 Two laws govern energy transformations Thermodynamics is the study of energy transformations The First Law of Thermodynamics According to the first law of thermodynamics Energy can be changed from one form to another Energy cannot be created or destroyed Figure 5.2A

20 The Second Law of Thermodynamics The second law of thermodynamics states that energy transformations increase disorder or entropy, and some energy is lost as heat Heat Glucose + Oxygen Chemical reactions ATP ATP Energy for cellular work Carbon dioxide + water Figure 5.2B

21 Potential energy of molecules 5.3 Chemical reactions either store or release energy Endergonic reactions absorb energy and yield products rich in potential energy Products Energy required Amount of energy required Reactants Figure 5.3A

22 Exergonic reactions release energy and yield products that contain less potential energy than their reactants Potential energy of molecules Reactants Figure 5.3B Energy released Amount of energy released Products Cells carry out thousands of chemical reactions the sum of which constitutes cellular metabolism Energy coupling uses exergonic reactions to fuel endergonic reactions

23 5.4 ATP shuttles chemical energy and drives cellular work ATP powers nearly all forms of cellular work The energy in an ATP molecule lies in the bonds between its phosphate groups Adenosine Triphosphate Adenosine diphosphate Phosphate groups H 2 O Adenine P P P Hydrolysis P P + P + Energy Ribose ATP ADP Figure 5.4A

24 ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to make molecules more reactive ATP Chemical work Mechanical work Transport work Membrane protein Solute P + Motor protein P Reactants P P P Product P Molecule formed Protein moved Solute transported ADP + P Figure 5.4B

25 Cellular work can be sustained because ATP is a renewable resource that cells regenerate ATP Energy from exergonic reactions ADP + P Energy for endergonic reactions Figure 5.4C

26 5.21 Chloroplasts and mitochondria make energy available for cellular work Enzymes are central to the processes that make energy available to the cell Chloroplasts carry out photosynthesis using solar energy to produce glucose and oxygen from carbon dioxide and water Mitochondria consume oxygen in cellular respiration using the energy stored in glucose to make ATP

27 Bozeman: Enzymes

28 Enzyme HOW ENZYMES FUNCTION 5.5 Enzymes speed up the cell s chemical reactions by lowering energy barriers For a chemical reaction to begin reactants must absorb some energy, called the energy of activation E A barrier Figure 5.5A Reactants Products 1 2

29 A protein catalyst called an enzyme can decrease the energy of activation needed to begin a reaction Energy Reactants E A without enzyme E A with enzyme Net change in energy Products Figure 5.5B Progress of the reaction

30 5.6 A specific enzyme catalyzes each cellular reaction Enzymes have unique three-dimensional shapes that determine which chemical reactions occur in a cell The catalytic cycle of an enzyme 1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Substrate binds to enzyme with induced fit Glucose Enzyme (sucrase) Fructose 4 Products are released H 2 O 3 Substrate is converted to products Figure 5.6

31 5.7 The cellular environment affects enzyme activity Temperature, salt concentration, and ph influence enzyme activity Some enzymes require non-protein cofactors such as metal ions or organic molecules called coenzymes

32 5.8 Enzyme inhibitors block enzyme action Inhibitors interfere with an enzyme s activity A competitive inhibitor Takes the place of a substrate in the active site A noncompetitive inhibitor Alters an enzyme s function by changing its shape Substrate Active site Enzyme Normal binding of substrate Competitive inhibitor Noncompetitive inhibitor Figure 5.8 Enzyme inhibition

33 CONNECTION 5.9 Many poisons, pesticides, and drugs are enzyme inhibitors EX: Cyanide is a inhibitor in the cellular respiration reaction in the mitochondria. It causes a build-up of O 2 in the blood and ultimately results in suffocation