8.1 : Metabolism

Question 1

what are metabolites/intermediates?

Answer 1

the molecules involved in metabolism

Question 2

what is anabolism & example?

Answer 2

the synthesis of complex molecules from simpler ones with the storage of energy. (energy-requiring = endergonic)

• -> e.g. photosynthesis is an anabolic process ( simple to complex)
• -> e.g. polysaccharides, proteins, lipids, hormones, etc.

Question 3

what is catabolism & example?

Answer 3

the breakdown of larger molecules to simpler ones, releasing energy. (exergonic)

• ->e.g. cellular respiration is a catabolic process (complex to simple)
• ->e.g. inorganic molecules (CO2, H20, ions, etc)

Question 4

what is ATP?

Answer 4

the energy currency linking endergonic & exergonic reactions.

Question 5

what type of reaction is ATP to ADP + Pi?

Answer 5

a hydrolysis reaction = catabolic reaction –> breaking it down to a simpler molecule.

Question 6

what type of reaction is ADP + Pi to ATP?

Answer 6

a condensation reaction = anabolic reaction –> building it up to a more complex molecule.

Question 7

what is metabolism?

Answer 7

a series of continuous reactions in which the product of one reaction is an intermediate of the next.
(intermediate - used to make the product)

Question 8

what are the two types of metabolic pathways?

Answer 8

• straight chains (linear sequences)
• cyclic processes.
• branched.

Question 9

what determines the way in which a branched metabolic pathway splits?

Answer 9

the amount of enzymes present in each direction –> chain will split in direction that has the most enzymes.

Question 10

an example of a branched metabolic reaction/pathway?

Answer 10

glucose –> activated by enzyme –> enters blood stream used for energy in respiration…
–>takes part in glycolysis
OR
–> is stored in the form of glycogen in the liver –> activated by insulin.

Question 11

how is the enzyme-substrate complex formed?

Answer 11

substrate binds to enzyme at active site –> enzyme-substrate complex (short lived & unstable) formed at transition state.
–> after it is formed –> the product is formed (energy released when substrate becomes product) & enzyme is not used up –> substrate & enzyme (unchanged) are released –> substrate will have a different shape due to chemical reactions that have occurred in active site.

Question 12

what is the transition state?

Answer 12

a short period in which the potential energy is at its highest where the molecule is no longer only a substrate but not yet a product & when the enzyme-substrate complex is formed.

Question 13

what is the active site?

Answer 13

part of enzyme where a substrate fits and binds –> site of catalytic activity.

Question 14

what occurs when the substrate becomes the product?

Answer 14

(small amount of energy needed to bring about this reaction)
–> bonds break / weaken in the substrate –> brining about the transitional state –> enzyme-substrate complex formed –> then substrate turns into product –> energy that is put in for this to occur = activation energy.

Question 15

what is activation energy & how do enzymes influence this?

Answer 15

a small but significant energy barrier that has to be overcome before the reaction can occur = exergonic (energy released when reaction takes place).
- enzymes lower the amount of activation energy –> reaction occurs faster.

Question 16

what happens to the activation energy once the substrate is in contact with an enzyme?

Answer 16

it decreases –> less energy is required for the reaction to begin –> more chance of reaction going faster & continuing

Question 17

what do enzyme inhibitors do?

Answer 17

inhibitors lower the rate of a reaction & enzyme inhibitors disable the work and function of enzymes (doesn’t function properly) –> large amount of activation energy needs to be overcome for the reaction to begin (lower reaction rate)

Question 18

what is competitive inhibition? Is it reversible? How?

Answer 18

• molecules that sufficiently resemble the substrate in shape and compete with a substrate molecule to occupy the active site –> binds to active site
• reversible –> add enough substrate (more than inhibitor) –> most enzymes present will be occupied by substrate molecule.

Question 19

what is the enzyme that catalyses the reaction between CO2 and NADP in photosynthesis? What is its competitive inhibitor?

Answer 19

• RuBisCo (Ribulose Biphosphate Carboxylase)

- competitively inhibited by oxygen in chloroplasts;

Question 20

what is non-competitive inhibition? Is it reversible? Why?

Answer 20

• molecule that binds to the enzyme in another location besides the active site, but partly blocks access for the substrate to attach or changes the shape of the active site.
• irreversible if the active shape changes site as the enzyme will never go back to its original shape –> substrate will never bind.

Question 21

explain why the shape of globular proteins that are enzymes is important in enzyme action.

Answer 21

globular proteins acting as enzymes –> must be folded such that their active sites are in the correct direction (orientation) and conformation to interact with substrates.

Question 22

what are allosteric activators?

Answer 22

substances that activate the reaction a bit more

–> binding to them –> temporarily stabilises the enzyme

Question 23

what are allosteric inhibitors?

Answer 23

substance that inhibit a reaction a bit –> ‘fine-tuning’-doesn’t completely inhibit –> only a little to find balance = homeostasis
–> binding to them –> changes enzyme shape to an inactive form.

Question 24

what is negative feedback? what is an example of this?

Answer 24

• an opposite response to a stimulus (creating the opposite reaction).
• end product inhibition

Question 25

what are allosteric regulators?

Answer 25

molecules that change the shape and activity of an enzyme by reversibly binding at a site of an enzyme.