enzymes (bio)

Question 1

what are enzymes

Answer 1

• biological catalysts
• speed up rate of chemical reactions without themselves being chemically changed at the end
• hence can be reused and are effective in small concentrations

Question 2

define catabolic reactions

Answer 2

break up complex molecules into simpler molecules

Question 3

define anabolic reactions

Answer 3

build up simpler molecules into complex molecules

Question 4

explain the structure of enzymes

Answer 4

most enzymes are proteins with unique 3D structure

Question 5

explain what a substrate, active site and specificity of an enzyme is

Answer 5

substrate: molecule which enzyme acts on
active site: where substrate binds, can only allow specific substrate(s) to fit in
Specificity: attributed to complementary shape between substrate and active site

Question 6

deifine activation energy

Answer 6

energy that must be supplied to the reactant molecules for them to react

Question 7

how does activation energy help molecules react

Answer 7

• often supplied in the form of heat
• absorption of thermal energy increases the speed of the reactant molecules –> collide more frequently and forcefully in the correct orientation
• thermal agitation of atoms within the molecules oso make bonds more likely to break

Question 8

Heating speeds up chemical reaction, but is inappropriate for a biological system. Why?

Answer 8

High temp dentaure proteins and kill cells. Heating oso speed up all chemical reactions, not just intended ones

Question 9

explain enzymatic reaction

Answer 9

1. effective collision between specific substrate(s) and enzyme at the correct orientation causes substrate molecules to enter active site of enzyme
2. substrate molecules bind to the activie site of the enzyme –> enzyme-substrate complex
3. formation lowers activation energy
4. chemical reaction –> products formed
5. products dissociate from enzyme and the chemically unchanged enzyme is ready for another cycle of chemical reaction

Question 10

explain the lock-and-key hypothesis [5]

Answer 10

• substrate is “key” and enzyme is “lock”
• substrate has a shape complementary ro the shape of active site (x same shape)
• with active site of enzyme having a specific shape into which the substrate fits exactly
• substrate binds to the active site of enzyme, forming ES-complex
  once products formed, no longer fit into active site if the enzyme and released into surrounding medium

Question 11

explain the induced fit model [5]

Answer 11

• active site of enzymes is complementary in shape but not a perfect fit to substrate it catalyses
• when substrate binds to active site of enzyme, induces a change in shape of active site
• allows substrate to fit more tightly into active site
• binding of substrate to active site of enzymes occurs and ES-complex forms
• chemical reaction occurs –> forming products –> released into the surrounding medium as they no longer fit into active site of enzyme

Question 12

characteristics of enzymes [4]

Answer 12

• speed up chemical reactions by lowering activation energy (extremely effiecient –> speed up by 10^3 to 10^8 times faster than uncatalysed reactions) and remain chemically unchanged
• (since can be reused, required in small concentrations)
• specific in action (due to 3D shape, with active site complementary in a shape to a specific substance)
• affected by temp and pH

Question 13

factors affecting rate of enzyme-catalysed reaction

Answer 13

temp
pH
enzyme concentration
substrate concentration

Question 14

what is an optimum temp

Answer 14

temperature at which the rate of enzyme activity is at its maximum

Question 15

explain what happens to enzyme reactions as temp rises

Answer 15

1. as temp rises, kinetic energy of substrate and enzyme molecules increase
2. enzyme becomes more active
3. substrate and enzyme molecules collide more often –> increases no. of effective collisions and formation of enzyme-substrate complexes –> rate of reaction increases
4. reaction rate doubles for every 10 degrees rise in temp until optimal temp is reached

Question 16

explain what happens to enzyme reactions beyond optimum temp

Answer 16

1. rate starts to decrease
2. enzyme loses 3D shpe (as high temp breaks weak hydrogen bonds between amino acids) and active site no longer able to bind to substrate. enzyme said to be denatured (irreversible)
3. as temp continues to increase, more enzyme molecules become denatured –> rate of reaction decreases further

Question 17

explain what happens to enzyme reactions beyond optimum pH

Answer 17

1. rate starts to decrease
2. enzyme loses 3D shpe and active site no longer able to bind to substrate. enzyme said to be denatured (irreversible)
3. as pH continues to increase, more enzyme molecules become denatured –> rate of reaction decreases further

Question 18

define limiting factor

Answer 18

factor that directly affects rate of a chemical reaction if its quantity is changed

Question 19

explain the effects of varying enzyme concentration

Answer 19

• lower enzyme concentrations –> adding more enzyme increases the rate of chemical reaction – enzyme concentration said to be limiting
• enzyme concentration increase –> more effective collisions occur, resulting in formation of more ES-complexes
• rate of reaction increases until a point where further increase in enzyme concentration will no longer the rate of reaction – rate of reaction becomes constant and reaches a plateau
• enzyme concentration no longer limiting factor
• not enough substrates to occupy active sites of enzymes – substrate concentration becomes limiting factor

Question 20

explain the effects of varying substrate concentration

Answer 20

• low substrate concentrations –> few substrate molecules present –> many available enzyme actives sites for effective collisions to occur
• adding more substrate increases rate of chemical reaction – substrate concentration is limiting
• substrate concentration increases –> more effective collisions occur –> formation of more ES complexes
• rate of reaction increase until a point where further increase in substrate concentration will no longer increase rate of reaction – rate if reaction becomes constant and reaches a plateu
• all active sites of enzyme molecules saturated with substrate molecules, concentration of product formed per unit time remains the same – enzyme concentration is now limiting factor

Question 21

how to determine rate of reaction

Answer 21

measure:
- amt of product formed per unit time
- amt of substrate used per unit time

Question 22

what do control-boiled reactants do

Answer 22

denature enzymes, all other factors kept constant

Question 23

what do factors that affect enzyme activity do

Answer 23

alter rate of enzyme-catalysed reaction