Exam 2 Lecture #1 (Intro to Enzymes)

Question 1

What are enzymes?

What are the six major classess of enzymes?

Answer 1

Enzymes are proteins that perform catalytic function (they cause reactions to proceed more quickly)

The six major classes of enzymes:

1. Oxioreductases: oxidative chemistry
2. Transferases: transfer functional groups
3. Hydrolases (breaking bonds using water)
4. Lyases (break bonds not using water)
5. Isomerases: rearrange groups
6. Ligases: Make bonds

Question 2

What kind of enzyme is the SERCA pump?

Answer 2

Phosphotase (in the hydrolase family) because it breaks ATP to ADP and Pi with water

Question 3

Why do we need enzymes?

Answer 3

Because we would get tired of waiting. Most reactions proceed too slowly on their own to be useful. This is because of energy barriers.

(The reduce the delta E)

Question 4

Explain how lactose intolerance relates to enzymes

Answer 4

Lactose intolerance: enxyme defect in an intestinal enzyme that breaks down the disaccharide lactose (milk sugar) to monosaccharides galactose and glucose. If the lactose is not digested it cannot be taken up by the intestines, and it is converted by bacteria into toxic products that cause intestinal cramps and diarrhea.

Question 5

Explain how Tay-Sachs disease is related to enzymes

Answer 5

Tay-Sachs: a defect of hexosaminidase A, an enzyme in the lysosome that breaks down ganglioside lipids, removing sugar head groups. Lipids accumulate in the lysosomes of the brain cells, causing progressive retardation, paralysis, blindness, and death by age 3

The pt can’t break down ganglioside lipids

Question 6

Explain how phenylketonuria is related to enzymes

Answer 6

Phenylketonuria: a defect of phenylalanine hydroxylase that prevents conversion of Phe to Tyr, resulting in excretion of excess phenylketones in the urine (phenylketonuria). Incidence is around 1/10,000 but it varies significantly between country to country. Scrrened at birth because untreated PKU results in severe neurological symptoms and low IQ. Treatment is a special diet avoiding phenylalanine and aspartame (Nutrasweet)

Question 7

Explain how antitrypsin deficiency relates to enzyme defects

Answer 7

Antitrypsin Deficiency: a defect in an inhibitor of proteases including trypsin and elastase

Too much elastase activity breaks down the structural proteins in the lungs, increasing the risk of emphysema

Smoking exacerbates this condition

Question 8

What are the two possible mechanism for binding of a substrate by an enzyme?

Answer 8

1. Lock and Key Model: only one specific substrate fits into the enzyme’s binding pocket
2. Induced Fit Model: the enzyme changes shape slighyl as the substrate bunds

Both mechanisms may contribute to substrate recognition. The induced fit mechanism may account for the stabilization of the transition state.

Question 9

Allosteric effect:

Answer 9

When something binds at a site other than the active site and then effects the active site binding to substrate

Question 10

What can enzymes do with substrate enantiomers?

Answer 10

Enzymes can actually distinguish between L and D enantiomers and bind the correct ones that it needs.

Enzymes are stereoselective, so the substrates and products are specific.

Question 11

Explain what cofactors, coenzymes, and cosubstrates are.

Answer 11

Cofactors: a small molecule (not protein) that is bound to the enzyme and assists in the catalytic reaction. These include:

• Inorganic Elements: (like Mg++ helps kinase to hold the phosphate on ATP as it transferred from the ATP to a substrate)
• Coenzyme: a small organic model that assists in catalysis (some vitamins are coenzymes, such as niacin or riboflavin)

Cosubstrates: a secondary substrate that is modified at the same time as the primary substrate. They can provide energy to drive an otherwise unfavorable reaction. For example, ATPis hydrolyzed to cause transport of ions the wrong way against a concentration gradient.

Note: ATP can also serve as an allosteric effector- it binds to a distant site and regulates the enzyme function without participating in the reaction.

Question 12

How is thermodynamics determined by kinetics?

Answer 12

Thermodynamics is about energy. Which way will a reaction proceed basically

Kinetics is about rates. How fast a reaction will proceed.

The kinetics determines the thermodynamics.

Reactant A becomes product B, but this is a reversible reaction.

The speed of a reaction is determined by the kinetics (k+, k-) The final amounts of A and B depend of the balance of the rate constants.