Intro to Metabolism Campbell Chapter 8

Transcription

1 Intro to Metabolism Campbell Chapter 8

2 Section 8.1 An organism s metabolism transforms matter and energy, subject to the laws of thermodynamics PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

3 Metabolism is the sum of an organism s chemical reactions Metabolism is an emergent property of life that arises from interactions between molecules within the cell

4 A metabolic pathway begins with a specific molecule and ends with a product Each step is catalyzed by a specific enzyme BIOCHEMICAL PATHWAY VIDEO

5 Enzymes Macromolecules that serve as catalysts, a chemical agent that changes the rate of a reaction without being consumed by the reaction Mechanisms that regulate them balance metabolic supply and demand Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

6 Metabolism Manages the material and energy sources of the cell. Two types of metabolic pathways: 1. Catabolic 2. Anabolic Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

7 CATABOLIC PATHWAY (CATABOLISM) Break down pathway Release of energy by the breakdown of complex molecules to simpler compounds EX: digestive enzymes break down food Cellular respiration ions/ eng-nz/chemical_reactions_involve_making_new_combinations_full_size_landscape.jpg

8 ANABOLIC PATHWAY (ANABOLISM) Biosynthetic pathways consumes energy to build complicated molecules from simpler ones EX: synthesis of amino acids to form proteins Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

9 Energy from catabolic pathways can be stored and used later to drive anabolic pathways i.e. Krebs Cycle connects the catabolic and anabolic pathways

10 Forms of Energy ENERGY = capacity to cause change Energy exists in various forms (some of which can perform work) The work of life depends on the ability of the cell to transform energy from one form into another

11 KINETIC ENERGY energy associated with motion HEAT (thermal energy) is kinetic energy associated with random movement of atoms or molecules Light is kinetic energy harnessed from light to perform work i.e. Photosynthesis

12 POTENTIAL ENERGY - energy that matter possesses because of its location or structure CHEMICAL energy is potential energy available for release in a chemical reaction i.e. glucose is high in chemical energy Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

13 On the platform, the diver has more potential energy. Diving converts potential energy to kinetic energy. Climbing up converts kinetic energy of muscle movement to potential energy. In the water, the diver has less potential energy.

14 THERMODYNAMICS = the study of energy transformations CLOSED system (EX: liquid in a thermos) = isolated from its surroundings OPEN system =energy + matter can be transferred between the system and its surroundings Organisms are open systems

15 The First Law of Thermodynamics energy of the universe is constant Energy can be transferred and transformed Energy cannot be created or destroyed The first law is also called the principle of conservation of energy

16 The Second Law of Thermodynamics During every energy transfer or transformation entropy (disorder) of the universe INCREASES some energy is unusable, often lost as heat

17 First law of thermodynamics Chemical energy Second law of thermodynamics Heat CO 2 H 2 O ORGANISMS are energy TRANSFORMERS! Spontaneous processes occur without energy input; they can happen quickly or slowly For a process to occur without energy input, it must increase the entropy of the universe

18 Section 8.2 The free energy change of a reaction tells us whether or not the reaction occurs spontaneously PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

19 Free-Energy Change ( G) can help tell which reactions will happen spontaneously Portion of a system s energy that can perform work when temperature and pressure are uniform G = H - T S G = change in free energy H = change in total energy (enthalpy) S = change in entropy (randomness) T = temperature (K) Only processes with a negative G are spontaneous Spontaneous processes can be harnessed to perform work

20 Free Energy and Metabolism Classification of Chemical Reactions based on Free-Energy Changes: 1. Exergonic 2. Endergonic Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

21 Exergonic Reactions in Metabolism Release energy (- G) are spontaneous The magnitude of G represents the maximum amount of work the reaction can perform The greater the decrease in free energy, the greater amount of work that can be done Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

22 Endergonic Reactions in Metabolism Absorb free energy from their surroundings Stores free energy in molecules + G Are non-spontaneous

23 Equilibrium and Metabolism Reactions in an isolated system eventually reach equilibrium Metabolic reactions are reversible and they would reach equilibrium if they occurred in isolation Systems at equilibrium are at minimum G and can NOT do work a cell that reaches metabolic equilibrium is dead! The constant flow of materials keeps metabolic pathways from reaching equilibrium and the cell continues to do work throughout its life. Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

24 Section 8.3 ATP powers cellular work by coupling exergonic reactions to endergonic reactions PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

25 A cell does three main kinds of work: Mechanical Transport Chemical In the cell, energy coupling, the use of exergonic processes to drive an endergonic one occurs.

26 ATP (adenosine triphosphate) is the cell s renewable and reusable energy shuttle ATP provides energy for cellular functions Energy to charge ATP comes from catabolic reactions Adenine Phosphate groups Ribose

27 LE 8-9 Bonds between PO 3 are broken by hydrolysis It becomes ADP and releases energy P P P Adenosine triphosphate (ATP) H 2 O The reaction is exergonic P i + P P + Energy Inorganic phosphate Adenosine diphosphate (ADP)

28 Because hydrolysis releases energy, the PO 3 bonds of ATP are referred to as high-energy PO 3 bonds. The release of energy comes from the chemical change to a lower state of free energy ATP is useful because the energy it releases is greater that the energy most other molecules could deliver Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

29 Endergonic reaction: G is positive, reaction is not spontaneous NH 2 Glu + NH 3 Glu G = +3.4 kcal/mol Glutamic acid Ammonia Glutamine Exergonic reaction: G is negative, reaction is spontaneous ATP + H 2 O ADP + P i G = 7.3 kcal/mol Coupled reactions: Overall G is negative; Together, reactions are spontaneous G = 3.9 kcal/mol

30 LE 8-11 ATP drives transport and mechanic al work it causes changes in shape and binding affinities of proteins ATP P Motor protein Mechanical work: ATP phosphorylates motor proteins Membrane protein Solute P P i Protein moved P i Solute transported ADP + P i a.) directly by phosphoryl ation Transport work: ATP phosphorylates transport proteins P Glu NH 2 + NH 3 + Glu P i b.) indirectly by binding of ATP Reactants: Glutamic acid and ammonia Product (glutamine) made Chemical work: ATP phosphorylates key reactants

31 ATP Energy for cellular work provided by the loss of phosphate from ATP Energy from catabolism (used to charge up ADP into ATP ADP + P i

32 Section 8.4 Enzymes speed up metabolic reactions by lowering energy barriers PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

33 Every chemical reaction between molecules involves bond breaking and bond forming ACTIVATION ENERGY = amount of energy required to get chemical reaction started Activation energy is often supplied in the form of heat from the surroundings Free energy animation IT S LIKE PUSHING A SNOWBALL UP A HILL... Once you get it up there, it can roll down by itself

34 LE 8-14 Free energy The Activation Energy Barrier A B C D Transition state A B E A C D Reactants A C B D G < O Products Progress of the reaction

35 CATALYST = a chemical agent that speeds up a reaction without being consumed by the reaction ENZYMES = biological catalysts, most enzymes are PROTEINS Exception = ribozymes (RNA) Ch 17 & 26

36 Free energy Course of reaction without enzyme Reactants E A without enzyme E A with enzyme is lower Course of reaction with enzyme G is unaffected by enzyme Products Progress of the reaction ENZYMES work by LOWERING ACTIVATION ENERGY;

37 ENZYMES LOWER ACTIVATION ENERGY BY Orienting substrates correctly Straining substrate bonds Providing a favorable microenvironment Enzymes change ACTIVATION ENERGY but NOT energy of REACTANTS or PRODUCTS

38 ENZYMES Most are proteins Lower activation energy Specific Shape determines function Reusable Unchanged by reaction Image from:

39 The REACTANT that an enzyme acts on = SUBSTRATE Enzyme + substrate = ENZYME-SUBSTRATE COMPLEX Region on the enzyme where the substrate binds = ACTIVE SITE Substrate held in active site by WEAK interactions (i.e. hydrogen and ionic bonds)

40 TWO MODELS PROPOSED: LOCK & KEY Active site on enzyme fits substrate exactly INDUCED FIT Binding of substrate causes change in active site so it fits substrate more closely

41 Enzyme Activity can be affected by: General environmental factors: 1. Temperature 2. ph 3. salt concentration 4. Chemicals that specifically influence the enzyme Choose narrated See a movie

42 TEMPERATURE & ENZYME ACTIVITY Each enzyme has an optimal temperature at which it can function (Usually near body temp)

43 Increasing temperature increases the rate of an enzyme-catalyzed reaction up to a point. Above a certain temperature, activity begins to decline because the enzyme begins to denature.

44 ph and ENZYME ACTIVITY Each enzyme has an optimal ph at which it can function

45 COFACTORS = non-protein enzyme helpers EX: Zinc, iron, copper COENZYMES = organic enzyme helpers Ex: vitamins

46 SUBSTRATE CONCENTRATION & ENZYME ACTIVITY V MAX Adding substrate increases activity up to a point

47 Section 8.5 Regulation of enzyme activity helps control metabolism PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

48 REGULATION OF ENZYME PATHWAYS GENE REGULATION cell switches on or off the genes that code for specific enzymes

49 REGULATION OF ENZYME PATHWAYS FEEDBACK INHIBITION end product of a pathway interacts with and turns off an enzyme earlier in pathway FEEDBACK INHIBITION prevents a cell from wasting chemical resources by synthesizing more product than is needed

50 NEGATIVE FEEDBACK An accumulation of an end product slows the process that produces that product A Enzyme 1 Negative feedback A Enzyme 1 B B Enzyme 2 C C Enzyme 3 D D D D D D D D D D D Example: sugar breakdown generates ATP; excess ATP inhibits an enzyme near the beginning of the pathway

51 POSITIVE FEEDBACK (less common) The end product speeds up production W W Enzyme 4 Enzyme 4 X Positive feedback X Enzyme 5 Enzyme 5 Y Y Z Enzyme 6 Z Z Z Z Z Z Z Z Z Z Z Z Z Z Enzyme 6 Z Z Z Z EXAMPLE: Chemicals released by platelets that accumulate at injury site, attract MORE platelets to the site.

52 REGULATION OF ENZYME ACTIVITY ALLOSTERIC REGULATION = protein s function at one site is affected by binding of a regulatory molecule at another site can inhibit or stimulate an enzyme s activity Allosteric enzyme inhibition

53 SOME ALLOSTERIC ENZYMES HAVE MULTIPLE SUBUNITS Each enzyme has active and inactive forms The binding of an ACTIVATOR stabilizes the active form The binding of an INHIBITOR stabilizes the inactive form

54 COOPERATIVITY = form of allosteric regulation that can amplify enzyme activity Binding of one substrate to active site of one subunit locks all subunits in active conformation

55 Enzyme Inhibitors COMPETITIVE inhibitor = REVERSIBLE; Mimics substrate and competes with substrate for active site on enzyme ENZYME ANIMATION

56 Enzyme Inhibitors NONCOMPETITIVE inhibitors = bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective ENZYME ANIMATION