How Cells Work. Chapter 4

Transcription

1 How Cells Work Chapter 4

2 Energy Laws Energy is the capacity to do work The total amount of energy in the universe is constant-energy can t be created or destroyed..only transferred! Energy is flowing from high-energy forms to forms lower in energy

3 Energy Gained Energy Lost Sunlight energy reaches Earth. Producers secure some and convert it to stored forms of energy. They and all other organisms convert stored energy to forms that can do cellular work. With each conversion, there is a one-way flow of energy back to the environment Energy Lost

4 ATP nucleotide base (adenine) Main energy carrier in cells (in the phosphate groups) Can give up phosphate group to another molecule sugar (ribose) Phosphorylation primes a molecule to react 3 phosphate groups

5 The Cell s Energy Currency ATP couples energy inputs and outputs ATP/ADP cycle regenerates ATP ATP energy input ADP + P i energy output

6 Energy Changes Endergonic reactions require energy Synthesis of glucose from carbon dioxide and water during photosynthesis Exergonic reactions release energy Breakdown of glucose to carbon dioxide and water by aerobic respiration

7 Electron Transfers Oxidation: loss of an electron Reduction: gain of an electron Electron transfer chains are vital to the formation of ATP during photosynthesis and aerobic respiration

8 H 2 1/2 O 2 H 2 2H + 2e - 1. Water molecules split; hydrogen ions, electrons, oxygen released 1/2 O 2 electric spark 3. Some released energy is used to make ATP Explosive release of energy as heat cannot be harnessed for cellular work 2. Electrons transferred through an electron transfer system 2e - 2H + 1/2 O 2 H 2 O H 2 O

9 Participants in Metabolic Pathways Reactants Intermediates Products Energy carriers Enzymes Cofactors Transport proteins

10 Which Way Will a Reaction Run? Nearly all chemical reactions are reversible The direction a reaction runs depends upon Energy content of participants Reactant-to-product ratio

11 highly spontaneous equilibrium highly spontaneous

12 Metabolic Pathways Biosynthetic (anabolic) pathways Require energy inputs Assemble large molecules from subunits Photosynthesis Degradative (catabolic) pathways Release energy Breakdown large molecules to subunits Aerobic respiration

13 Enzymes Catalyze (speed up) reactions Recognize and bind specific substrates Act repeatedly Most are proteins

14 Activation Energy For a reaction to occur, an energy barrier must be surmounted Enzymes make the energy barrier smaller Figure 4.6, page 62 starting substance energy released by the reaction activation energy without enzyme activation energy with enzyme products

15 reactants A lower energy Barrier means more Product! energy barrier with no enzyme to promote reaction energy barrier with an enzyme s participation products

16 Factors Influencing Enzyme Activity Coenzymes and cofactors Allosteric regulators Temperature ph Salt concentration

17 Allosteric Control Activator or inhibitor binds to an enzyme Binding changes enzyme shape Change hides or exposes active site Feedback inhibition Product of pathway binds to and inhibits enzyme in the pathway

18 allosteric activator vacant allosteric binding site enzyme active site active site cannot bind substrate allosteric inhibitor allosteric binding site vacant; active site can bind substrate active site altered, can bind substrate active site altered, can t bind substrate Allosteric activation Allosteric inhibition

19 Feedback Inhibition enzyme 2 enzyme 3 enzyme 4 enzyme 5 enzyme 1 SUBSTRATE Excess end-product molecules bind with molecules of enzyme 1. The greater the excess, the more enzyme molecules are inhibited and the greater the decrease in tryptophan synthesis. END PRODUCT (tryptophan)

20 Effect of Temperature Small increase in temperature increases molecular collisions, reaction rates High temperatures disrupt bonds and destroy the shape of active site - denaturation

21 Figure 4.10a Page 64

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23 Concentration Gradient Means the number of molecules or ions in one region is different than the number in another region In the absence of other forces, a substance moves from a region where it is more concentrated to one where it is less concentrated: down gradient

24 oxygen, carbon dioxide, and other small, nonpolar molecules; some water molecules glucose and other large, polar, water-soluable molecules; ions (e.g., H+, Na+, K+, CA++, CI ); water molecules

25 Diffusion The net movement of like molecules or ions down a concentration gradient Although molecules collide randomly, the net movement is away from the place with the most collisions (down gradient)

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27 Factors Affecting Diffusion Rate Steepness of concentration gradient Steeper gradient, faster diffusion Molecular size Smaller molecules, faster diffusion Temperature Higher temperature, faster diffusion Electrical or pressure gradients

28 Transport Proteins-proteins that help large molecules cross a membrane Span the lipid bilayer Interior is able to open to both sides Change shape when they interact with solute Move water-soluble substances across a membrane

29 Passive and Active Transport Passive Transport Doesn t require energy inputs Solutes diffuse through a channel inside the protein s interior Net movement is down concentration gradient Active Transport Requires ATP Protein is an ATPase pump Pumps solute against its concentration gradient

30 Osmosis Water molecules tend to diffuse down water concentration gradient Total number of molecules or ions dictates concentration of water Tonicity: relative solute concentrations

31 semipermeable membrane between two compartments water molecule protein molecule

32 Figure % sucrose Page solution 69 distilled water 10% sucrose solution 2% sucrose solution Hypotonic Conditions Hypertonic Conditions Isotonic Conditions

33 Hydrostatic Pressure Also called OSMOTIC PRESSURE Pressure that a fluid exerts against structure enclosing it Increases with increased solute concentration Influences the osmotic movement of water

34 Hypotonic Solution Hypertonic Solution membrane permeable to water but not to solutes

35 Membrane Traffic Endocytosis Membrane sinks inward around a substance bringing it into the cell in a vesicle Exocytosis Vesicle carrying substance fuses with membrane releasing it into the intracellular fluid

36 Types of Endocytosis Bulk-phase endocytosis Receptor-mediated endocytosis Phagocytosis

37 Exocytosis plasma membrane cytoplasm Endocytosis cytoplasm

38 amoeba edible bacterium phagocytic vesicle