L3 - ENZYMES

Question 1

Enzyme DEF and structural features

Answer 1

PROTEINS
Biological catalyst - speed up a reaction
ACTIVE SITE - where substrate molecules bond to ACTIVATE the enzyme

Highly specific -produce particular product from certain substrate

NB; remain unchanged chemically after the reaction

E & S —-ES(C) —-E & P

Question 2

Activation Energy

Answer 2

Energy needed to start a chemical reaction

Question 3

enzymes affect on AE

Answer 3

• lowers it (even tho overall energy delta G remains unchanged)
• reaction can take place at lower temperature & less energy needed
• ROR increases

Question 4

What forms when an enzyme & substrate molecule forms

Answer 4

ENZYME - SUBSTRATE COMPLEX

Question 5

How ESC can catalyze a reaction (join or breakdown)

Answer 5

if 2 molecules need to be joined, the joining of the substrate molecule to the active site of the enzyme reduces FORce of repulsion and strengthens their bond (closer together)

breakdown reaction;

• joining of the substrate to the AS of the enzyme puts STRAIN on the substrate bonds & weakens them
• substrate molecule breaks down more easily

Question 6

INDUCED FIT MODEL

Answer 6

• how E & S combine
• AS of E has a particular shape
• special substrate fits it
• 0 ES(C) forms (enzyme - substrate - complex forms)
• BUT protein & AS change shape to accomadate

Question 7

How enzyme concentration affects ROR

Answer 7

• increase in EC means lots of enzymes to bind to substrate molecules - MORE ACTIVE SITES
• will happen more easily than usual AT START
• BUT, - SATURATION POINT - where there are loads of enzymes but no substrate molecules left - no more ES can be formed
• SUBSTRATE IS THE LIMITING FACTOR

Question 8

How substrate concentration affects ROR

Answer 8

ES form at start lots of Substrate molecules
very high at start (ROR)
Then it ill decrease from the time we start to run out of enzymes

Question 9

6 Main Classes of Enzymes (name)

Answer 9

Oxidoreductase
Transferase 
Hydrolase
Lyase
Isomerase
Ligase

Question 10

Classes of enzymes - function/action, common names

OXIDOREDUCTASE

Answer 10

A; Oxi and Reduc reactions
N; oxidase, reductase.
PEROXIDASE, DEHYDROGENASE

Question 11

TRANSFERASE

Answer 11

A- transfer of chemical groups like amino, carboxyl, methyl groups to dif. molecules
N; TRANSAMINASE, TRANSCARBOXYLASE

Question 12

HYDROLASE

Answer 12

A; clevage/ separation of bonds by inerting water– HYDOLYSIS = separation of bonds by adding water
N; PEPSIN, AMYLASE. TRYPSIN

Question 13

LYASE

Answer 13

A; SEPARATION OF C-C, C-S & C-N bonds but not peptide bonds = removal of atoms w/o hydrolysis
N; decarboxylase, aldolase

Question 14

ISOMERASE

Answer 14

A; re-arrangement of bonds

N; epimerase, mutase

Question 15

LIGASE

Answer 15

A; formation of bonds between C, 02, S, N. = rearrangement of atoms within a molecule
N; SYNTHETASE, carboxylase

Question 16

Vmax

Answer 16

Max rate - occurs when all enzymes AS are full

Enzymes are saturated

Question 17

Km

Answer 17

• Substrate concentration when the rate is HAlf Vmax
• Measure of Affinity of the substrate to bind to the enzyme

Low Km - means substrate binds to enzyme easily
Bonded tightly

High Km means affinity is low
A lot of energy would be needed for this substrate to bind to the enzyme

Question 18

Competitive inhibitor
what is it
how does it affect Km and Vmax

Answer 18

• Inhibitor stops or slows down a chemical reaction
• Competitive means it’s competes with the substrate for the AS.
• Thus if u want to over come this the substrate Conc must be very very high
• Thus Km increases : as much higher conc of substrate is need to overcome the inhibitor
• Vmax is unchanged

Question 19

Non compétitive inhibitor

Answer 19

• Does Not compete with substrate for AS of enzyme
• Instead it bonds to another site of the enzyme - Allosteric site ( can do this even if substrate molecule is in AS)
• thus Km remains the same
• Vmax decreases : as even if substrate molecule is perfectly binded the inhibitor will reduce the enzyme activity thus reducing Vmax

Question 20

Reversible vs Ireversible Inhibitors

bond wise what’s different about them

Answer 20

Reversible- they bind to enzyme but can Release enzyme also

• NO COVALENT BONDS
• Once inhibitor is removed enzyme can be used again 100%

Irreversible - no going back

• Substrate and enzyme are permanently combined
• Enzyme is inactive and loses its function
• Cell will have to reccreate the protein in order to regain function
• COVALENT BONDS

Question 21

How enzymes are regulated in cells - Short term

Answer 21

• Neg- Feedback loops
  1) - Controlled variable, receptor, processor, set point, effector mechanism

Note: a product of a metabolic pathway often inhibits an enzyme early on
This prevents wasting energy &; wasteful overproduction of a metabolite = END POINT INHIBITION (I think)

2) - Allosteric regulation - means that the inhibitor binds to site other than AS ie the REGULATORY site

Can switch between activating & deactivating enzyme

3)- Post-translation regulation like Phosphorylation

Question 22

Regulation of enzymes long term

Answer 22

NB enzymes are proteins

• Change in gene expression.
• Proteolysis: breakdown of proteins

Question 23

Rate of reaction is affected by what?

Answer 23

Temperature
pH
Conc of enzyme & substrate