Unit 1 - Chemistry of Life

Question 1

what do heterotrophs require energy for?

Answer 1

• mechanical work
• active transport
• macromolecule synthesis

Question 2

what are the four major macromolecules and how are they synthesised?

Answer 2

• carbohydrates
• lipids
• proteins
• nucleic acids
  synthesised by condensation reactions

Question 3

what is an amphibolic pathway? - give an example

Answer 3

biochemical pathway that involves both catabolism and anabolism
- krebs cycle: cat of carbs/fatty acids/ ana amino acids synthesis

Question 4

what is catabolism?

• what type of reaction is it?
• give an example

Answer 4

degradative phase of metabolism - breaking down of macromolecules

• oxidation reaction which yields energy
• e.g. glycolysis

Question 5

what is anabolism?

• what type of reaction is it?
• give an example

Answer 5

biosynthetic phase of metabolism - formation of macromolecules

• reduction reaction requiring energy from ATP hydrolysis
• gluconeogenesis

Question 6

what is a futile cycle?

Answer 6

a substrate cycle, occurs when two metabolic pathways run simultaneously in opposite directions and have no overall effect other than to dissipate energy in the form of heat
- uneconomical process

Question 7

what is gibbs free energy?

Answer 7

maximum amount of energy obtained from reaction at constant temperature/ pressure

Question 8

what are the principles of gibbs free energy?

Answer 8

No indication of reaction rate
- If (-) value, reaction occurs spontaneously - exothermic reactions more likely to occur spontaneously
- Energy is Independent of path/mechanism of reaction (still same)
Changes are additive - use energy yielding reaction to drive an unfavourable one - make gibbs negative so will be spontaneous

Question 9

how can ATP be described?

Answer 9

• central metabolic currency

- primary/ universal energy carrier

Question 10

why does hydrolysis of ATP yield large negative change in free energy?

Answer 10

contains two phosphoanhydride linkages - high energy bonds

Question 11

why are nucleoside phosphate groups good energy donors?

Answer 11

• multiple phosphates
• strong tendency to repel due to high concentration of negative charge in oxygen atoms
• when enzyme is present - force transfers phosphates to other molecules

Question 12

what is ATP coupling?

Answer 12

allows biosynthetic reactions to be thermodynamically favourable due to ‘group transfer potential’ of ATP in which transfer of phosphate primes reaction with energy

Question 13

give an example of a common molecule that provides transfer potential

Answer 13

creatine phosphate  (-43.1 kJ/mol)
- coupled with formation of ATP (30.5 kJ/mol) produces a spontaneous reaction

Question 14

where are electron carriers tend to be derived from and give examples

Answer 14

derived from essential vitamins

• carriers which fuel oxidation: NAD (vitamin b3 niacin) and FAD (vitamin B2 riboflavin)
• carriers involved in biosynthesis: NADPH

Question 15

what are the six most common reactions and the enzymes involved in the processes?

Answer 15

1) redox - dehydrogenases
2) ligation - ligases
3) isomerisation - isomerases
4) group transfer - kinases
5) hydrolysis - hydrolases
6) elimination - lyases

Question 16

what is a lyase?

Answer 16

enzyme that catalyses the cleavage of C-C, C-O, C-N bonds by other means than by hydrolysis and the resulting product is the formation of a double bond or a new ring.

Question 17

name three ways in which pathways are regulated

Answer 17

• enzymes - proteases slow pathways/ gene expression
• accessibility of substrates beta oxidation/ FA synthesis
• regulation of catalytic activity - allosteric/ covalent modification/ adenylate control/ rate limiting steps