Biochemistry Problem Session

Question 1

A teenage girl is brought to the medical center because of her complaints that she gets too tired when asked to participate in gym class. A consulting neurologist finds muscle weakness in the girl’s arms and legs. When no obvious diagnosis can be made, biopsies of her muscles are taken for tests. Chemistries reveal greatly elevated amounts of triacylglycerols esterified with primarily long fatty acids. Pathology reports the presence of significant numbers of lipid vacuoles in the muscle biopsy. What is her most likely diagnosis.

Answer 1

carnitine deficiency

individuals have a problem with the oxidation of fatty acids.
for lipoprotein lipase deficiency, heparin can be given.

Question 2

Ketone bodies include

Answer 2

B hydroxybutyrate and acetone

Question 3

During the first week of a diet of 1500 calories per day, the oxidation of glucose via glycolysis in the liver of a normal 59 kg (130 lb) woman is inhibited by the lowering of which of the following?

a. citrate
b. ATP
c. fatty acyl CoA
d. ketone bodies
e. fructose- 2,6- bisphosphate

Answer 3

e. fructose- 2,6- bisphosphate

Question 4

After a well- rounded breakfast, which of the following would be expected to occur?

a. increased activity of pyruvate carboxylase
b. decreased activity of acetyl CoA carboxylase
c. decreased rate of gylcogenolysis
d. decreased rate of protein synthesis
e. increased activity of phosphoenolpyruvate carboxykinase

Answer 4

c. decreased rate of glycogenolysis

Question 5

In the resting state what is the primary condition that limits the rate of respiration?

Answer 5

Availability of ADP

Question 6

Oxidative phosphorylation couples generation of ATP with which of the following?

a. proton translocation
b. substrate level phosphorylation
c. electron flow through cytochromes
d. reduction of NADH
e. reduction of water

Answer 6

A. proton translocation

Question 7

Many compounds poison the respiratory chain by inhibiting various steps of oxidation or phosphorylation. Which of the following steps is inhibited by carbon monoxide and cyanide?

a. oxidation step between cytochrome and coenzyme Q and distal cytochromes
b. oxidation step involving direct reduction of oxygen
c. uncoupling of oxidation from phosphorylation
d. oxidation step between cytochrome c and b
e. oxidation step of flavin cytochromes to coenzyme Q

Answer 7

b. oxidation step involving direct reduction of oxygen

Question 8

What is an important difference between respiratory chain inhibitors and uncouplers?

Answer 8

Uncouplers do not inhibit electron transport but respiratory chain inhibitors do.

Question 9

Individuals with disorder s of the respiratory chain are often placed on supplements containing riboflavin and coenzyme Q. What is the role of coenzyme Q (ubiquinone) in the respiratory chain?

Answer 9

It links flavoproteins to cytochrome b, the cytochrome of lowest redox potential.

Question 10

Why is the yield of ATP from the complete oxidation of glucose lower in muscle and brain than in kidney, liver and heart?

Answer 10

Different shuttle mechanisms operate to transfer electrons from the cytosol to the mitochondria in the two sets of tissues.

Question 11

The greatest buffering capacity at the physiologic pH would be provided by a protein rich in which of the following amino acids?

a. lysine
b. histidine
c. aspartic acid
d. valine
e. leucine

Answer 11

b. histidine

Question 12

Water, which constitutes 70% of body weight, may be said to be the “cell solvent”. The property of water that most contributes to its ability to dissolve compounds is the

Answer 12

hydrogen bond formed between water and biochemical molecules

Question 13

What hemoglobin designations best describes the relationship of subunits in the quaternary structure of adult hemoglobin?

Answer 13

e. (alpha 1 beta 1) (alpha 2 beta 2)

Question 14

Which of the following amino acids is most compatible with an alpha helical structure?

a. tryptophan
b. alanine
c. lysine
d. proline
e. cysteine

Answer 14

b. alanine because it is hydrophobic

Question 15

which of the following statements about solutions of amino acids at physiological pH is true?

a. all amino acids contain both positive and negative charges
b. all amino acids contain positively charged side chains
c. some amino acids contain only positive charges
d. all amino acids contain negatively charged side chains
e. some amino acids contain only negative charges

Answer 15

a. all amino acids contain both positive and negative charges

Question 16

In which molecule can the highest concentration of cystine be found?

Answer 16

Keratin (rich in cystine)

Question 17

Certain amino acids are not part of the primary structure of proteins but are modified after translation. In scurvy, which amino acid that is normally part of collagen is not synthesized?

Answer 17

Hydroxyproline

Question 18

Which enzyme catalyzes high-energy phosphorylation of substrates during glycolysis?

Answer 18

e. glyceraldehyde-3- phosphate dehydrogenase

Question 19

Which enzyme is common to both glycolysis and gluconeogensis?

Answer 19

phosphoglycerate kinase

Question 20

Familial fructokinase deficiency causes no symptoms because

Answer 20

hexokinase can phosphorylate fructose

Question 21

Which enzyme catalyzes phosphorylation with the use of inorganic phosphate?

Answer 21

Glyceradldehyde 3 phosphate dehydrogenase

Question 22

Which metabolite is involved in glycogenolysis, glycolysis and gluconeogensis?

Answer 22

glucose 6 phosphate

Question 23

A comatose 25 year old Asian female is brought by ambulance to the emergency room from a campus chem lab where she worked as a TA. She has high temperature, rapid hear and respiratory rate. Along one arm is a yellow stain and her blood pressure is unobtainable. Two students accompany her and report that she was giving a demonstration on metabolic inhibitors and had an accidental spill on her face. She had blurred vision, headaches and shaking movements then passed out. What is her toxin?

Answer 23

Dinitrophenol was the toxin.

Question 24

Which redox pair (because of high redox potential) is crucial for glutathione reduction?

Answer 24

NADP+/ NADPH or NAD+/NADH

Question 25

Inhibition of ATP synthase required for ox phos has a consequence of ____.

Answer 25

disruption of proton flow across the inner mitochondrial membrane

Question 26

It has been noted that infants placed on extremely low-fat diets for a variety of reasons often develop skin problems and other symptoms. This is most often due to

Answer 26

Deficiency of fatty acid desaturase greater than delta9.

these infants are not getting essential fatty acids like linoleic acid, etc. and then you cant make ricodonic acid and since these acids are important in phospholipids, then it causes skin problems.