chapter three: enzymes - regulation of biochemical pathways

Question 1

equation for photosynthesis

• state the inputs (reactants) and outputs (products)

Answer 1

carbon dioxide + water —> glucose +oxygen

• CO2 + H2O —> C6 H12 O6 + O2
• inputs - carbon dioxide and water
• outputs - glucose and oxygen

Question 2

equation for cellular respiration

• state the inputs (reactants) and the outputs (products)

Answer 2

glucose + oxygen —> carbon dioxide + water

• C6 H12 O6 + O2 —> CO2 + H2O
• inputs - glucose and oxygen
• outputs - carbon dioxide and water

Question 3

what are biochemical pathways

Answer 3

a chemical reaction that occurs in living things

• a biochemical pathway is a series of interconnected biochemical reactions
• each step requires a specific enzyme

Question 4

what are the role of enzymes in biochemical pathways

• why are enzymes important

Answer 4

enzymes catalyses chemical reactions, in which:

• speed up chemical reactions
• works best in certain conditions
• are not used up in reactions

enzymes are important as it allows for chemical reactions to occur at a greater rate by lowering the activation energy of the reactions

• chemical reaction occurs when reactants must collide with enough energy to react as well as reactants must be in the correct orientation

Question 5

what does NADP+ and ADP do in photosynthesis

Answer 5

NADH and ADP bing with the hydrogen from the H2O, and while O2 is released, the H is carried over to the light independent stage and provides the electron for ATP production

Question 6

what does ADP, FAD, and NAD+ do in cellular respiration

Answer 6

ADP, FAD and NAD+ are the carriers that carry the hydrogen from one stage to the other
->

Question 7

what happens to coenzymes once they have delivered their energy to H+

Answer 7

once the coenzymes have delivered the H+ to the other stage, they are reverted back to their original form and are used in another cycle

Question 8

list the loaded and unload forms of NADP+, ADP, NAD and FAD

Answer 8

• NADP+ —>NADPH
• ADP —> ATP
• NAD —> NADH
• FAD —> FADH

Question 9

state the factors affect enzyme activity

Answer 9

• temperature
• pH
• concentration of enzyme
• concentration of substrate
• competitive and non-competitive enzymes inhibitors

Question 10

state and explain how does temperature affect the RATE of photosynthesis and cellular respiration

Answer 10

when temperature changes, so does the movement of molecules

low temperature means less movement

• less chance of molecules colliding
• lower reaction rate

high temperature means more movement

• higher chance of molecules colliding
• BUT ALSO a higher change of bonds breaking
• if bonds within an enzyme break it will change shape (denature)

as temperature increases, the kinetic energy of the enzyme and substrate increases in which collisions are more likely to occur = reactions more likely to occur

• above the optimum temperature the kinetic energy becomes too high, and the bonds that hold the enzyme begin to break
• from here, the enzymes starts to change shape = means that the active site is disrupted and the enzyme activity quickly starts to drop
• this change of shape of the enzyme is denaturation = irreversible

Question 11

state how pH affects the rate of photosynthesis and cellular respiration

Answer 11

if the surrounding pH is too high or low (from the optimal pH level) it can alter intra- and inter- molecular bonds of the active site and substrate complex

• change the shape of the active site
• reduce/stop function
• e.g. denature the protein

when pH is below or above the optimum range for the enzyme, the groups between the active site of the enzyme and the substrate are no longer able to form a bond causing the enzyme activity to decline and eventually stop

Question 12

state how changing the SUBSTRATE CONCENTRATION affects the action of enzymes and therefore the rate of photosynthesis and cellular respiration

Answer 12

a higher substrate concentration will result in a higher reaction rate provided there is unlimited enzyme to a point

• after, adding a substrate causes no significant change
• with a finite amount of enzyme, the rate will increase until all enzymes are working at their maximum —> the rate will plateau

Question 13

state and explain how/why changing the ENZYME CONCENTRATION impacts the rate of photosynthesis and cellular respiration

Answer 13

a higher concentration of enzymes will result in a higher rate of reaction provided there is unlimited substrate and optimum conditions

• continues to increase

Question 14

explain how competitive inhibitors reduce the action of enzymes

Answer 14

the inhibitors has a similar shape to the substrate

• blocks the formation of enzyme-substrate complex = fewer substrates can bind to the enzymes, rate of reaction decreases
• the effect of competitive inhibitors reduces as substrate concentration increases

Question 15

explain how non-competitive inhibitors reduce the action of enzymes

Answer 15

the inhibitors binds to a region other than the active site

• the allosteric site

this changes the shape of the active site, so the substrate has difficulties binding

• as substrate increases, the rate of reaction begins to plateau once it has reached its optimum range

Question 16

state the differences between reversible and irreversible inhibitors

• (in terms of strength of chemical bonds and the effect on the organism)

Answer 16

reversible inhibitors

• the inhibitors can dissociate from the enzyme
• can be competitive or non-competitive

irreversible inhibitors

• specific molecules can form a strong covalent bond with an enzyme at its active site, so that the normal substrate is permanently blocked from accessing the active site
• these are often poisons
• e.g. cyanide binds to an enzyme needed for cellular respiration
• e.g. penicillin acts as an enzyme inhibitor in bacteria
• these are irreversible as the strength of the bond cannot be reversed by the addition of more substrate

Question 17

types of reactions

• anabolic
• catabolic

Answer 17

anabolic reaction:

• occurs when smaller substances are joined to form a larger product
• energy is used (e.g. photosynthesis)

catabolic reaction:

• occurs when a large substrate is broken down into smaller products
• energy is released (e.g. cellular respiration)

Question 18

representing enzyme action

Answer 18

substrate/s —> product/s

• enzyme + substrate —> enzyme-substrate complex —> enzyme +products

Question 19

inhibition of enzyme action

Answer 19

changes to optimal conditions can inhibit enzyme activity

• chemicals can also inhibit enzyme activity - these are called inhibitors
• they can be competitive or non-competitive

these can be irreversible or reversible

• reversible inhibitors bind non-covalently (weakly)
• irreversible inhibitors bind covalently (strongly)