Metabolism and enzymes

Transcription

1 Metabolism and enzymes

2 What is a chemical reaction? A chemical reaction is a process that forms or breaks the chemical bonds that hold atoms together Chemical reactions convert one set of chemical substances, the reactants, into another set, the products

3 Chemical energy Primary energy source for metabolism is chemical energy stored in bonds In animals = food molecules In plants = photosynthesis More bonds means more energy stored Why fat is high in calories

4 Photosynthesis and cellular respirantion Photosynthesis generates glucose Sun energy transformed to energy carrier molecules like ATP and NADPH Cellular respiration consumes glucose Eating glucose and breathing oxygen uses the energy in the bonds to generate energy carrier molecules

5 Types of chemical reactions All chemical reactions either release energy or require a net input of energy Exergonic: releases energy Endergonic: requires a net input of energy The terms exothermic and endothermic relate to the overall exchange of heat during a process

6 Exergonic reactions Reactants have more energy than products Energy is released in these reactions Ex: Sugar + O 2 CO 2 + H 2 O Releases energy and heat

7 Endergonic reactions Reactants have less energy than products Synthesizing complex biological molecules requires energy

8 Another way of seeing the reactions

9 Metabolic pathways The sum of all the chemical reactions inside a cell is its metabolism Series of interconnected biochemical reactions Convert a substrate molecule or molecules, through a series of metabolic intermediates, into a final product

10 Initial reactant Intermediates End products PATHWAY 1 enzyme 1 enzyme 2 enzyme 3 enzyme 4 PATHWAY 2 enzyme 5 enzyme 6

11 Peppermint

12 Types of pathways Anabolic require an input of energy To synthesize complex molecules from simpler ones Catabolic generates energy To break down complex molecules to simpler ones

13 Potential energy Chemical reactions in the body Metabolic reactions are an uphill battle Energy must be put in to drive reaction True even if energy is released in reaction Minimum energy required = activation energy (E a )

14 Chemical reactions in the body E a can be overcome by increasing temperature But we would cook! At body temperature, metabolic reactions proceed too slowly to sustain life And yet we live! Nature has found a way around this

15 What are catalysts? Catalysts are molecules that speed up the rate of reaction w/out being used up or permanently altered

16 What do catalysts do? Catalysts speed up the reaction by lowering up the activation energy required for the reaction to begin

17 Activation energy A small amount of energy needed for exergonic reactions to occur (E A ) Bonds that will break and release energy need to get into the correct state This contorted state is called the transition state High-energy Unstable

18 What are enzymes? Biological catalysts Mainly proteins They speed up only exergonic reactions The majority catalyze one single reaction Leaving similar substrates unchanged enzymesubstrate enzymeproduct(s

19 Video

20 Enzyme structures allow them to catalyze specific reactions Each enzyme has a pocket called an active site into which one or more reactant molecules, called substrates, can enter

21 Enzyme structures allow them to catalyze specific reactions The amino acid sequence + folding of the protein chains distinctive shape and distribution of electrical charge

22 Enzyme structures allow them to catalyze specific reactions The distinctive shape of the active site is both complementary and specific to the substrate

23 Enzyme structures allow them to catalyze specific reactions In summary, active site amino acids bind to the substrate and distort bonds to facilitate a reaction

24 Enzymes are proteins, so What is it called when a protein looses its shape and hence its function? What can cause that?

25 substrates active site of enzyme product enzyme Substrates enter the active site in a specific orientation The substrates, bonded together, leave the enzyme; the enzyme is ready for a new set of substrates The substrates and active site change shape, promoting a reaction between the substrates

26 Cofactors and coenzymes Many enzymes don t work optimally, or even at all, unless bound to cofactors or coenzymes Binding to these molecules promotes optimal conformation proper function Cofactors are inorganic ions such as iron (Fe++) and magnesium (Mg++) DNA polymerase requires zinc ions (Zn++) to function Coenzymes are organic helper molecules The most common sources of coenzymes are dietary vitamins Some vitamins are precursors to coenzymes and others are coenzymes Vitamin C is a coenzyme for multiple enzymes when building collagen

27 Enzyme activity regulation ph Enzyme structure is distorted (denatured) when ph is too high or low

28 Enzyme activity regulation Salt concentration Salt ions can bind with key amino acids in enzymes, influencing three-dimensional structure and destroying function

29 Enzyme activity regulation Temperature Low temperatures slow down molecular movement High temperatures cause enzyme shape to be altered, destroying function Most enzymes function optimally only within a very narrow range of these conditions

30 fast For pepsin, maximum activity occurs at about ph 2 For trypsin, maximum activity occurs at about ph 8 rate of reaction For most cellular enzymes, maximum activity occurs at about ph 7.4 slow Effect of ph on enzyme activity

31 fast rate of reaction For most human enzymes, maximum activity occurs at about 98.6 F (37 C) slow temperature 140 ( F) 60 ( C) Effect of temperature on enzyme activity

32 Enzyme activity regulation Amount of substrate Genes that code for enzymes may be turned on or off Specific stages in the life of an organism Enzymes synthesized in inactive form, become active when enzyme is in its final location Trypsin Inhibition

33 Enzyme activity regulation - inhibition In competitive inhibition, a substance that is not the enzyme s normal substrate binds to the active site of the enzyme A competitive inhibitor molecule occupies the active site and blocks entry of the substrate Competitive inhibition

34 Enzyme activity regulation - inhibition In noncompetitive or allosteric inhibition, a molecule binds to a site on the enzyme distinct from the active site The active site changes shape so the substrate no longer fits when a noncompetitive inhibitor molecule binds the enzyme Noncompetitive inhibition noncompetitive inhibitor molecule

35 Allosteric activation

36 Feedback inhibition The use of a reaction product to regulate its own further production

37 ENERGY

38 First Law of Thermodynamics It states that this total amount of energy is constant Energy may be transferred from place to place or transformed into different forms But it cannot be created or destroyed Light bulbs transform electrical energy into light energy Gas stoves transform chemical energy from natural gas into heat energy Plants convert the energy of sunlight into the chemical energy stored within organic molecules

39 Second Law of Thermodynamics No energy transfer is completely efficient In every energy transfer, some amount of energy is lost in a form that is unusable In most cases, it is lost as heat

40 Entropy The more energy that is lost by a system to its surroundings, the less ordered and more random the system is This measure of randomness or disorder is known as entropy High entropy means high disorder and low energy

41 Energy summary Energy is the ability to do work Kinetic energy objects in motion Potential energy potential to do work

42 Energy summary Energy in bonds is also potential energy The energy released from bonds is chemical energy

43 Energy summary A measurement of free energy is used to quantitate these energy transfers Gibbs free energy specifically refers to the available chemical energy after entropy is accounted for Usable energy or energy that is available to do work

44 The free energy of endergonic and exergonic reactions Endergonic reactions Reactions that require energy have ΔG>0 Exergonic reactions Reactions that release energy have ΔG<0

45 ATP is the currency of the cell A nucleoside with three phosphate groups Phosphoanhydride bonds are high energy the products, ADP and one P i, have considerably lower free energy than the reactants, ATP and a water molecule

46 ATP is the currency of the cell ATP is a highly unstable molecule Unless quickly used, ATP spontaneously dissociates into ADP + P i Energy is lost as heat

47 How does the body do endergonic reactions? The body couples endergonic reactions with exergonic reactions This is mainly done by cleaving a phosphate group off ATP Glucose + Pi --> glucose-6-phosphate + water (ΔG of +14 kj/mol) ATP --> ADP + Pi (ΔG of -31 kj/mol) Combining these two reactions, we get Glucose + ATP --> glucose-6-phosphate + water + ADP (ΔG of -17 kj/mol)