Chapter 3: Bioenergetics, Enzymes, and Metabolism

Question 1

Compare Justus von Liebig, Louis Pasteur, and the Büchner brothers’ conclusions

Answer 1

Justus von Liebig: fermentation is no different than the types of organic reactions studied in test tubes

Louis Pasteur: fermentation can only take place within the confines of a living cell

Büchner brothers: fermentation doesn’t require a living cell but only a unique set of catalysts that have no counterpart in the non-living world (enzymes)

Question 2

Crystallization of urease

Answer 2

James Sumner

Question 3

Discuss the structure of enzymes

Answer 3

conjugated proteins: contain non-protein components known as cofactors

Question 4

What are cofactors?

Answer 4

Cofactors are inorganic (metals) or organic (coenzymes) factors that play an important role in the functioning of the enzyme by carrying out activities that the protein cannot

Question 5

Provide the cofactors of the following:

1. Hemoglobin
2. Chlorophyll
3. Carboxypeptidase

Answer 5

1. Iron
2. Magnesium
3. Zinc

Question 6

What is the function of the enzyme carboxypeptidase?

Answer 6

Catalyzes the cleavage of peptide bonds in proteins attracted to carbohydrates

Question 7

List the properties of enzymes

Answer 7

1. Required in only small amounts
2. Are not altered irreversibly throughout the course of a reaction - can participate repeatedly
3. Do not change the thermodynamic of the reaction, only accelerate the rate at which a favorable reaction occurs
4. Increase the reaction speed by 10^8-10^13 fold
5. Occur at mild pH and temperatures within the cell
6. Highly specific

Question 8

Differentiate between the types of inhibitors

Answer 8

There are irreversible and reversible enzyme inhibitors

Irreversible inhibitors form a covalently linked complex with the enzyme and thus cannot be removed

Reversible inhibitors form a weaker bond and can be removed, this can be further subdivided into two

1) Competitive
2) Non-competitive

Question 9

Give an example of an irreversible inhibitor and the resulting effect of inhibition

Answer 9

Diisopropylphosphofluoridate inhibits acetylcholinesterase

Acetylcholinesterase catalyzes the breakdown of acetylcholine

Acetylcholine is the neurotransmitter that controls muscle contraction

If acetylcholinesterase is inhibited by diisopropylphosphofluoridate then acetylcholine accumultaes in the nerve cells and sends the body into a prolonged state of contraction thus leading to death

Question 10

Give an example of competitive reversible inhibition and the effecting result of inhibition

Answer 10

Teprotide and Captopril inhibit Angiotensin converting-enzyme (ACE)

ACE catalyzes the breakdown of angiotensin I into angiotensin II

Elevated levels of angiotensin II leads to hypertension

If ACE is inhibited then angiotensin II will not accumulate in the blood thus lowering the risk of high blood pressure

Question 11

Differentiate between competitive and noncompetitive inhibition

Answer 11

Competitive: inhibitor resembles substrate and competes for the active site, degree of inhibition depends on relative affinity for enzyme and can be reduced by increasing substrate concentration

Noncompetitive: inhibitor occupies a different site on the enzyme but binding to it causes conformational change in the active site, degree of inhibition depends solely on the concentration of the inhibitor

Question 12

Explain the importance of the structure of the active site of an enzyme

Answer 12

The different amino acids present within the active site gives rise to the specificity of the enzyme and its catalytic activity

Question 13

What are the mechanisms for enzyme catalysis?

Answer 13

1. Substrate orientation
2. Changing the reactivity of the substrate
3. Inducing strain in the substrate

Question 14

Explain the mechanism for enzyme catalysis involving substrate orientation

Answer 14

Substrates are held close together in the correct orientation when bound to the surface of an enzyme

Question 15

Explain the mechanism for enzyme catalysis involving changing the reactivity of the substrate

Answer 15

When bound to the active site the distribution of electrons is influenced by the side chains in the active site and the substrate is made more reactive and the transition-state complex is stabilized

Question 16

Explain the mechanism for enzyme catalysis involving inducing strain in the substrate

Answer 16

Conformational shifts cause the fit of the enzyme and the substrate to improve.

Destabilizes the substrate to induce it to adopt the transition-state

Question 17

What are the targets of the following antibiotics? How do they function

1. Penicillin
2. Streptomycin
3. Ciprofloxacin
4. Daptomycin

Answer 17

1. Inhibits the transpeptidases responsible for the formation of the bacterial cell wall
2. Binds to bacterial ribosomes
3. Inhibits DNA gyrase
4. Inhibits bacterial membrane function

Question 18

What are the main targets of antibiotics?

Answer 18

1. Enzymes involved in the formation of the bacterial cell wall
2. Enzymes involved in the replication, transcription, and translation of bacterial genetic information
3. Enzymes involved in metabolic activities