enzymes

Question 1

what is the importance of km

Answer 1

• describes the affinity of an enzyme for susbstrate
• concentrations of substrates in cells = approx km

Question 2

what are isozymes

Answer 2

• active forms of an enzye with slightly different amino acid sequences
• catalyse the same reaction
• often found in different tissues/locations
• tailor repsonse to specific cellular response (diff affinity snf regulation)

Question 3

what is enzyme inhibition`

Answer 3

• enzyme inhibitors bind to enzyme and decrease activity
• competitive or non-competitive
• irreversible or reversible
• important means by which metabolic pathways are regulated

Question 4

discuss reversible competitive inhibition

Answer 4

• mimics the substrate or transition state analogue
• substance competes directly with substrate for active site
• not transformed into product
• reversible

Question 5

what is non-competitive inhibition

Answer 5

• substrate an inhibitor bind at different site
• little or no resemblance to substrate
• able to bind to enzyme in any state
• causes change to the 3D structure
• enzyme able to bind both inhibitor and substrate

Question 6

what is irreversible inhibition

Answer 6

• forms a covalent bond to amino acid near/at active site
• permanently inactivates enzyme
• susceptible amino acid residues

Question 7

what factors are considered in enzyme assay design

Answer 7

• temp
• pH
• concentration
• detection and standardisation

Question 8

why are enzymes important

Answer 8

• key molecule in metabolism
• enzyme deficiencies = problem (glycogen branching enzyme def leads to neonatal mortality in horses)
• pathological diseases often associated with abnormal enzyme activity
• opportunities to treat infections (many anti-microbials are anzyme inhibitors)

Question 9

what are enzymes

Answer 9

proteins that function by accelerating chemical reactions in biological systems

Question 10

what are key features of enzymes

Answer 10

• higher reaction rates
• milder reaction conditions
• greater reaction specificity
• capactiy for regulation

Question 11

how do enzymes speed up reactions

Answer 11

helping to lower the activation energy needed to start a reaction.

Question 12

discuss the active site

Answer 12

• small on the surface of enzyme
• 3D cleft
• often non-polar
• binds susbtrate (complementary)
• highly conserved (same speciesto species)
• functional residues like His, Ser, asp and lys found in active sites

Question 13

discuss substrate binding

Answer 13

• multiple weak non covalent reactions
• 2 models: lock and key vs induced fit

Question 14

what is induced fit substrate binding

Answer 14

• substrate binding induces conformation change in enzyme
• optimal orientation for formation of transition state
• stabilisation of transition state
• excludes water

Question 15

mechanism of enzyme catalysis steps

Answer 15

1. susbtrate orientation
2. changing substrate reactivity
3. inducing substrate strain
4. exculde water

Question 16

how is substrate reactivity changed

Answer 16

• acid base catalysis (removal/addition of protons)
• covalent catalysis (nucleophilic/electrophilic substition

Question 17

what are cofactors

Answer 17

• trace elements
• present in 30% of enzymes
• 2 classes:
• metalloenzymes: tightly bound usually transition metal ions (zinc, iron, copper)
• metal activated: loosely bound usually alkali element (magnesium, calcium)

Question 18

what are co-enzymes

Answer 18

• orgnic molecules (vitamins)
• high affinity for enzyme
• couple reactions together