Biochemistry: Enzymes and Biological Catalysts

Question 1

what do enzymes effect and not affect

Answer 1

• speed of the reaction

- equilibrium

Question 2

in what conditions do enzymes work

Answer 2

• body temp
• near neutral pH
• in aq solutions

Question 3

how are enzymes specific

Answer 3

recognise a limited range of substrates

Question 4

how are enzymes potent

Answer 4

convert many substrates to products quickly

Question 5

what is the activation energy and why is it present

Answer 5

• energy required for enzymes to work

- stops reactions occurring in normal conditions

Question 6

transition state

Answer 6

reaction intermediate substance that contains the most free energy

Question 7

what do enzymes bind to and what do they do

Answer 7

• transition state

- lower activation energy

Question 8

describe glycogen storage disease

Answer 8

enzyme deficiency resulting in failure of glycogen to enter its phosphorylated state

Question 9

what are co-factors

Answer 9

metal ions

Question 10

what are co-enzymes

Answer 10

organic molecules

Question 11

what do co-factors form in the enzymes

Answer 11

a metallo protein - metal co-ordination centre

Question 12

how do co-enzymes associate with enzymes and what happens when they bind

Answer 12

• transiently

- change or restructure themselves

Question 13

prosthetic group

Answer 13

tightly bound co-enzymes

Question 14

apoenzyme

Answer 14

enzyme without a co-factor

Question 15

holoenzyme

Answer 15

enzyme with a co-factor

Question 16

what type of reaction are co-enzymes involved in and what do they do

Answer 16

• redox reactions

- stabilise transition states

Question 17

what are many co-enzymes derived from

Answer 17

vitamins

Question 18

what do symptoms of vitamin deficiencies reflect and what are the classes of deficiencies

Answer 18

• the loss of enzyme activity

- functional or dietary

Question 19

describe substrate binding to enzyme

Answer 19

• substrate binds to an active site

- this contains the amino acids essential for catalysis and specific interactions

Question 20

what is the lock and key model

Answer 20

the substrate and active site are complementary shapes

Question 21

what is the induced fit model

Answer 21

substrate binding induces a conformational change leading to complementary fit

Question 22

what other factors can influence enzyme activity

Answer 22

temperature and pH

Question 23

describe the active site of pancreatic serine proteases

Answer 23

contain reactive serine residues that catalyse the hydrolysis of peptides at specific sites

Question 24

isoenzyme

Answer 24

isoforms of enzymes, enzymes that catalyse the same reaction but have different properties and structure

Question 25

why can isoenzymes catalyse the same reaction but have a different make-up

Answer 25

• synthesised at different stages of development

- present in different tissues/cellular locations

Question 26

what is the clinical use for isoezymes

Answer 26

diagnostic tests

Question 27

how is lactate dehydrogenase used as a diagnostic test

Answer 27

it requires hypoxia sensitive transcription factors so a decreased presence in blood indicates tissue hypoxia

Question 28

how is creatine kinase used as a diagnostic test

Answer 28

• dimeric protein that binds to muscle sarcomeres
• M form (muscles) and B form (brain)
• heart produces both
• M form in blood suggests MI, B form in blood suggests stroke

Question 29

how does phosphorylation regulate enzyme activity

Answer 29

phosphorylation is a reversible covalent modification that converts enzymes to and in/active form

Question 30

what carries out phosphorylation reactions

Answer 30

protein kinases

Question 31

describe a phosphorylation reaction

Answer 31

fast, reversible

side groups form phosphate esters

Question 32

how do irreversible covalent modification regulate enzyme activity

Answer 32

results in an active form of enzyme irreversibly

Question 33

zymogen

Answer 33

inactive precursor of an enzyme

Question 34

what do zymogens do

Answer 34

irreversible transform into active enzymes via covalent bond cleavage

Question 35

give examples of zymogens

Answer 35

• tripsinogen to trypsin via enteropeptidase
• chymotrypsinogen to chymotrypsin via trypsin
• pancreatic enzymes, blood clotting factors, clot-dissolving enzymes