week 2: Enzyme function and control

Question 1

what are the components that make up a functional enzyme?

Answer 1

1. **Apoenzyme = ** protein components and provides a 3D structure.
2. **cofactors = ** non-protein molecules. 2 types: inorganic factors (metal ions), and coenzymes (organic molecules that bind to enzyme temporarily, e.g. vitamins)
3. **prosthetic groups = ** tightly bound cofactors remain associated with the enzyme through catalytic phase.
4. **active site = ** region where substrate bind to be catalysed.

Question 2

what is the interaction between enzyme and its substrate?

Answer 2

• enxyme binds with substrate = enzyme-substrate complex
• ## weak non-covalent interactions (e.g. hydrogen bonds)

Question 3

what is a non-regulated enzyme?

Answer 3

• not controlled by regulators produced by cells.
• depend on substrate conc.
• follows Michaelis-Menten Kinetics.
• have Km and Vmax
• activity can be controlled by drugs (e.g. pain killers, blood pressure, antibiotics, chemo)

Question 4

what is a regulated enzyme?

Answer 4

• activity changes depending on the presence of a regulator.

Question 5

which kinetics do regulated enzymes follow?

Answer 5

• they contain 2 subunits and an active site therefore, follow Signmoidal kinetics.

Question 6

what is feedback inhibition?

Answer 6

• mechanism used by cells to control enzyme activity.
• inhibition of an enzyme in a pathway by the end product of that pathway.
• regulate the rate of a metabolic pathway and maintain homeostasis by preventing the overproduction of certain substances.

Question 7

3 types of regulations which affect regulated enzyme activity?

Answer 7

1. covalent modification = formation of a covalent bond via adding an atom/molecule to enzyme (PTM - post translational modification)
2. Zymogens = removing a small piece of proteins activates the enzyme.
3. isozymes = enzymes that catalyse the same reaction but have different tertiary or quaternary structures.

Question 8

can zymogens be controlled after activation?

Answer 8

• zymogens involves irreversible regulations but can be controlled by cellular inhibitors.
• irreversible inhibition of the actovated zymogen can only occur by binding an inhibitor to enzyme active site.

Question 9

where are isozymes found?

Answer 9

heart, liver, skeletal muscles.

Question 10

what is covalent modification and is it reversible?

Answer 10

• type of PTM
• addition or removal of a hydroxile or phosphate group via covalent attachement or removal (e.g. phosphorylation)
• can result in enzyme activation or inhibition
• in activation –> change enzyme structure –> alteration in catalytic activity.
• reversibility depends on the specific modification and the availability of the enzyme responsible for adding or removing the modifying group.

Question 11

which isozyme appears in the blood after a heart attack

Answer 11

• following a heart attack, the damaged heart muscles secrete lactate dehydrogenase (LDH) isozyme into the blood stream. LDH-1 and LDH-2.
• LDH isozymes are diff forms of LDH enzyme –> structurally diffeerent.
• therefore detection of elevated LDH-1 and LDH-2 can clinically serve as an indication of myocardial damage - :. diagnosis of heart attack.

Question 12

how does the appearence of LDH isozymes in the blood indicate acute hepatitis?

Answer 12

LDH-5 (specific to the liver) are released into bloodstream when liver cells are damaged due to acute hepatitis.
- but important to consider other clinical laboratory findings to confirm diagnosis.

Question 13

what is the role penicillin

Answer 13

• penicillin is a mechanism based inactivator, an irriversible suicide inhibitor.
• inhibits transpeptidase (enzyme) –> transpeptidase is a bacterial enzyme, essential in the synthesis of bacterial cell wall.

Question 14

how does penicillin inhibit transpeptidase?

Answer 14

• penicillin has a reactive peptide bond between 2 amino acids which causes it to bind/destroy a functional group on the transpeptidase
• :. complementary substrate cannot bind to transpeptidase as the enzyme is destroyed.
• if bacterial cell was can’t be synthesised, bacteria cannot reproduce or maintain their cell wall –> :. bacterial death
• :. penicillin is an antibiotic.

Question 15

what are 2 exmples of suicide inhibitors?

Answer 15

• penicillin
• some chemotherapy drugs

Question 16

how can a drug that is an enzyme inhibitor chaange the activity of a non-regualted enzyme without destroying it

Answer 16

through ____ inhibition:
- competitive
- uncompetitive
- noncompetitive

Question 17

how can methanol poisoning be reduced by administering ethanol?

Answer 17

• ethanol acts as a competitive inhibitor for alcohol dehydrogenase to stop the conversion of methanol to its toxic metabilite - formate.
• by administerin ethanol which preferentially binds to alcohol dehydrogenase via competitive inhibition, fewer toxic products are produced –> acting as a treatment for methanol poisoning.

Question 18

what is a competitve inhibitor

Answer 18

• type of reversible inhibitor.
• Vmax takes longer to reach
• Km increases.

Question 19

non-competitive inhibitors

Answer 19

• type of reversible inhibition
• binds to allosteric site –> changing shape of active site

Question 20

uncompetitive inhibitors

Answer 20

• type of reversible inhibition
• stops substrate from being converted to a product, taking longer –> :. active sites are occupied for longer periods of time.