biochemistry questions

For every molecule of glucose that enters glycolysis, there is an initial investment of 2 molecules of ____ before the subsequent generation of ____ .

• ATP, ATP

What is the purpose of glucagon?

• It slows down glycolysis when blood sugar is low and stimulates the formation of more glucose.

An enzyme that catalyzes the phosphorylation of a molecule using ATP is called ____

• Kinase

Name two molecules that carries electrons from glycolysis and Krebs Cycle to the electron transport system.

• NADH and FADH2

Phosphofructokinase-1 (PFK-1) is an enzyme in glycolysis. It’s activity is controlled by a complex allosteric regulation.

What is the function of AMP in the PFK-1 regulation?

• AMP allosterically activates PFK-1

There are three irreversible reactions in the glycolysis. What are the corresponding enzymes that catalyze those reactions?

• Hexokinase or Glucokinase

• Phosphofructokinase 1 or PFK-1

• Pyruvate Kinase

Hexokinase is allosterically inhibited by its product Glucose 6 phosphate. The hexokinase in the liver is called glucokinase. However, glucokinase is not subject to product inhibition by glucose-6-phosphate. What the benefit of this characteristics of glucokinase?

• Liver will take up & phosphorylate glucose even when liver glucose-6-phosphate concentration is high.

During the Cori cycle, _____ is transported to the liver to regenerate glucose which is returned to muscle tissue.

• Lactic acid or lactate

Insulin is produced when blood glucose is high. How does insulin regulate the transcription of the glycolysis enzyme in liver,

glucokinase?

• Insulin activates of transcription of Glucokinase in liver.

In the liver, the most important coordinating modulator is fructose 2,6-bisphophate (F2,6BP). It is formed from F6P by the enzyme domain, phosphofructokinase-2 (PFK-2), and broken down by the same enzyme, but at a different domain called fructose 2,6-bisphosphatase (FBPase-2). How does the balance of PFK-2 to FBPase-2 activity controlled by glucagon?

• Glucagon causes the enzyme phosphorylation. Phosphorylation of the enzyme results in the inactivation of the phosphofructokinase-2 activity and activation of the fructose-2,6-bisphosphatase activity.

The last product of glycolysis is ____ while the first reactant of Krebs cycle is ____.

• Pyruvate, Acetyl Co-A

Briefly explain the Cori cycle which is a linked metabolic pathways.

• The glucose can enter the blood and be carried to muscles.

• Lactic acid is produced by anaerobic glycolysis in the muscles

• The lactic acid is sent in the blood to the liver which can convert it back to glucose through gluconeogenesis.

What is epinephrine’s role in glycogen and glucose metabolism?

• Epinephrine markedly stimulates glycogen breakdown and glycolysis.

Palmitic acid, CH3(CH2)14COOH, can maximally yield ____ acetyl-CoAs through ____ cycles of beta-oxidation.

• Eight, seven

Why can acetone be detected on breath of diabetic patients?

• Acetone breath in diabetics is caused by an excess production of ketone bodies.

• Glucose is abundant in blood, but uptake by cells in muscle, liver, and adipose cells is low. Cells, metabolically starved, turn to gluconeogenesis and fat/protein catabolism

• However, due to excess gluconeogenesis, oxaloacetate is low, so acetyl-CoA from fat/protein catabolism does not go to TCA, but rather to ketone body production.

High cholesterol diet leads to ____ (promotion/repression) of LDL receptor synthesis.

• repression

Chylomicrons are vesicles found in the blood and lymphatic fluid where they serve to transport lipid from the intestine to the liver and to adipose tissue. Of what are the chylomicrons composed? List at least 3 components.

• Triglycerides

• Cholesterols

• lipoproteins

• phospholipids

• Cholesteryl ester

What is the effect of epinephrine and glucagon on triglyceride metabolism?

• Epinephrine and glucagon trigger the mobilization of stored triglycerides

What is oxidative phosphorylation?

• Answer1: Oxidative phosphorylation transfers energy from NADH to ATP. (via chemiosmosis)

• Answer2: Oxidative phosphorylation is the process of converting this high redox potential into energy-rich ATP molecules.

Oxidative phosphorylation is accomplished via two separate systems in the mitochondrion. What are those two systems?

• Electron transport chain system and ATP synthesis system.

ATP synthesis is driven by proton motive force. What are the two types of gradient associated with proton motive force?

• a proton gradient or pH gradient

• a electrical gradient or ion gradient

Metabolism of amino acids differs, but all of them require the removal of amino groups. What are the two types of reactions to remove amino groups?

• Transamination

• Deamination

Disposal of ammonia from amino acid metabolism as _____ in most tissues especially in the brain and kidneys, as _____ in the liver, and as _____ in the skeletal muscles.

• Glutamine, urea, alanine

Based on the catabolic fates of carbon skeleton of amino acids, the amino acids can be classified as ____ or _____.

• Glucogenic, ketogenic

Dietary nucleotides _____ (do/do not) contribute energy as an energy source material and _____ (are/are not) incorporated into RNA or DNA.

• Do not, are not

The purine nucleotides are synthesized via two pathways in the body. One is ____ synthesis pathway while the other is ____ pathway.

• De novo, salvage

The purine synthesis is _____ by PRPP, _____ by IMP, _____ by AMP, and _____by GMP. Fill the blank with activated or inhibited.

• Activated, Inhibited, Inhibited, Inhibited,

What are the carbohydrate and fat metabolic events occurred in liver during fasting?

• The liver first starts glycogen degradation, then gluconeogenesis to maintain blood glucose levels.

• The fatty acid oxidation and ketone body production are increased.

Insulin promotes the translocation of ______ to the plasma membrane.

• GLUT or glucose transporter

Why do we say that DNA replication is semiconservative?

• The new strands composed of one original strand and one daughter strand

DNA polymerases cannot initiate synthesis of a polynucleotide; they can only add nucleotides to the 3’ end. Therefore, a short _____ is required to initiate nucleotide synthesis.

• RNA primer

Eukaryotic chromosomal DNA molecules have special nucleotide sequences at their ends called ______.

• telomeres

Why is DNA replication semi- discontinuous?

• DNA strands are antiparallel. And, replication process obeys the principle that DNA is synthesized from the 5´ end to the 3´end.

• Leading strand synthesized continuously while lagging strand synthesized discontinuously

replication transcription

template double strands single strand

substrate dNTP NTP

primer yes no

Enzyme DNA polymerase RNA polymerase

product dsDNA ssRNA

base pair A-T, G-C A-U, T-A, G-C

List at least 3 differences between replication and transcription.

The whole genome of DNA needs to be replicated, but only small portion of genome is transcribed

• Template, coding

During transcription, one of the DNA strands called ______ strand is the strand from which the RNA is actually transcribed. The other strand called _____ strand is the strand whose base sequence specifies the amino acid sequence of the encoded protein.

• Only the template strand is used for the transcription, but the coding strand is not.

• The transcription direction on different strands is opposite.

5'

3'

3'

5'

What is asymmetric transcription?

The mRNA start codon is ___ in most cases.

• AUG

Deoxyribonucleotides are formed from their corresponding _____.

• ribonucleotides

• During splicing, introns are removed from the strand, and the exons that remain are assembled into a finished strand of mRNA that is ready for translation. 

Explain mRNA splicing

What is the consequence of frameshift mutation?

• Frameshift mutations result in all subsequent reading frames (codons) being shifted by one or two nucleotides. These shifted frames will code for different amino acids than before, and will result in the creation of a malfunctioning protein.

The GUU GUA transition still codes for Val and it therefore called to be ______ mutation.

• nonsense

The insertion or deletion of a nucleotide into a gene results in a _____ mutation.

• frameshift

An incoming aminoacyl-tRNA enters the ribosome at the ___ site.

• A

____ are synthesized as inactive precursors that require proteolysis for activation.

• zymogen or proenzyme

In the operon system, tryptophan acts as a ____ by binding the trp repressor.

• Co-repressor