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Flashcards in Energetics and Enzymes Deck (18):
1

Define enzyme

A protein that acts aas a catalyst to induce chemical changes in other substances, remaining apparently unchanged.

2

What is the first Law of thermodynamics?

Energy is neither CREATED nor DESTROYED and is only converted from one form to another.

3

What is the Second Law of Thermodynamics?

In any ISOLATED system the degree of disorder only increases, entropy increases.

4

What do reactions process spontaneously towards?

Products with greater entropy

5

What is free energy?

(Gibb's) Free Energy (G) is the amount of energy in a molecule that can perform useful work at a constant temperature. (KJ/Mole)

6

Why are there coupled reactions?

Generally pathways synthesising molecules are energetically unfavourable, e.g. peptide synthesis, so they are coupled with a favourable one so overall DG is negative. Most energetically unfavourable biochemical reactions depend on hydrolysis of high energy Phosphate bonds e.g. ATP.

7

What does change in free energy measure?

Amount of disorder resulting from a reaction

8

When can a reaction occur spontaneously?

If DG ( Free energy of products - free energy of reactants) is negative

9

How does ATP act as a carrier of free energy?

Phosphoanhydride bonds have a large negative DG of hydrolysis and so are called "high energy" bonds.

10

What is the structure of ATP?

Adenosine TriPhosphate has Adenine, ribose, and on 5th C has the triphosphate chain, where P-O bond is a phosphoanhydride bond

11

Why does glucose not spontaneously combust?

As it needs an activation energy, energy supplied before the reaction takes place.

12

How does an enzyme act as a catalyst in the example of lysozyme?

Lysozyme is a component of tears and nasal secretions, a first line of defence against bacteria.
CATALYSES HYDROYSIS OF SUGAR MOLECULES WITHIN BACTERIAL CELL WALL NECESSARY FOR THEIR STRUCTURE. When the bond is broken, bacteria lyse and die.
hydrolyses alternating polysaccharide copolymers of N-Acetyl glucose(NAG) and N-acetyl Muramic acid (NAM) (The unit of many cell walls)
Cleaves at the Beta(1-4) glycosidic link, C1 of NAM to C4 of NAG
The acidic residues Glu 35 and asp 52 are needed for catalysis.
- Glu 35 protonates O in glycosidic link between 2 sugars, breaking the bond
- water enters, deprotonated by Glu 35
- Asp 52 stabilises positive charge in transition state
- Hydroxide ion attacks remaining sugar molecule, adds OH to it.
- Proton transferred to Glu 35 to return to original state.

13

How does the enzyme glucose-6-phosphatase work as a catalyst?

Speeds up reaction of Glucose 6 phosphate to Glucose + inorganic phosphate in presence of water.

14

Graphically demonstrate the effects of substrate concentration, temp, pH on reactions catalysed by enzymes.

Substrate conc- Max value reached, then enzyme conc becomes limiting factor
Temp- Denaturing
pH- Optimum pH


15

What is the role of the coenzyme NAD+ in reactions catalysed by dehydrogenase?

Nicotinamide adenine dinucleotide.
Used to catalyse DEHYDROGENATION REACTIONS, by readily accepting a proton and two electrons. (two H atom attached at end)
As it is a coenzyme it has no catalytic activity of its own and only functions after binding to an enzyme.
E.g. Lactate dehydrogenase
Pyruvate -> Lactate
Generates free NAD+
Lactate movwwes to liver, high level of NAD+ used to convert lactate back to pyruvate through dehydrogenation.

16

How can enzyme activity be measured using spectrophotometry?

Measures hoe much light absorbed by a chemical substance

17

How can experimental values of reaction velocity at different substrate concentrations be used to derive Km and Vmax for an enzyme?

Graph shows Rate of reaction and substrate conc
Km is substrate conc allowing enzyme to achieve half Vmax (Maximum reaction velocity)
Enzymes with high Km have lower affinity for substrates.

18

What is the effect of competitive and non competitive inhibitors on Km and Vmax?

Competitive competes with substrate for active site. So Higher Km needed,Same Vmax can be reached eventually.
Non competitive- reacts with enzyme substrate complex and slows the rate of forming the product. Increasing substrate makes no difference. Km unchanged, Vmax reduced.