Biochemistry Exam 5

This is a substrate for the pentose phosphate pathway

Glucose 6 phosphatase

This is the key source of biosynthetic reducing equivalents

NADPH/ pentose phosphate pathway

The second phase of the pentose phosphatase pathway is the ___ phase

Nonoxidative

Excess of the pentose phosphate pathway are shunted to what other metabolic pathway?

Glycolysis

___ and transketolase are the enzymes that link glycolysis and the pentose phosphate pathway

Transaldolase

Ribulose 5-phosphate is the result of the ___ phase

Oxidative

This results in a C3 and a C7 carbohydrate from two C5 carbohydrate precursors

Transketolase

Two molecules of _____ are formed in phase 2 of the pentose phosphate pathway

Fructose 6-phosphate

A deficiency of glucose 6-phosphate can cause hemolytic anemia. This is due to a loss in activity in which enzyme in red blood cells?

Glutathione reductase

The prosthetic group _____ is tightly bound to the enzyme transketolase

Thiamine pyrophosphate

Glucose-6-phosphate can be utilized by either the glycolytic or the pentose phosphate pathway. What is the major factor regulating how the use of glucose-6-phosphate is distributed between these two pathways?

The relative levels of NADP+ and NADPH

Under conditions in which NADPH is not needed, how are five-carbon sugars, such as ribose-5-phosphate, generated?

By withdrawing 3-carbon units from the glycolytic pathway and converting them into 5-carbon sugars via the nonoxidative branch of the pentose phosphate pathway

Possible fates for the glucose 5-phosphate produced during glycogen breakdown include...

(All of the listed)
Entering glycolysis, entering the pentose phosphate pathway, formation of glucose through the action of glucose 6-phosphatase

Glutathione combats ___ in the organism

Reactive oxygen species (ROS)

The first phase of the pentose phosphate pathway involves the ___ generation of ___

Oxidative, NADPH

Under what conditions might the pentose phosphate pathway produce large amounts of NADPH without significant net production of ribose 5-phosphate?

Synthesis of fatty acids in the liver

Triacylglycerols are stored in these cells in animals

Adipose

The approximate energy yield from complete oxidation of palmitate is

106 ATP

The hormone __ stimulates lipolysis when energy reservoirs are low

Glucagon

The enzyme ___ is activated by hormones and is responsible for the first hydrolysis of triaglycerol

Hormone-sensitive lipase

The transfer of an acyl group to coenzyme A is driven by the hydrolysis of ___

Pyrophosphate

The pathway by which an acyl CoA is degraded to acetyl CoA is ___

Beta oxidation

Another name for vitamin B12 is

Cobalamin

The availability of the metabolite ___ determines whether acetyl CoA, made from fatty acids, can enter the citric acid cycle

Oxaloacetate

The compound ___ is considered one of the "ketone bodies"

Beta hydroxybutyrate

Increases in acetyl CoA during starvation inhibit this enzyme

Pyruvate dehydrogenase

The degradation of an 18-carbon saturated fatty acid would be expected to yield how many NADH and FADH2 per fatty acid molecule?

8

Fatty acids are activated by attachment to coenzyme A at the outer mitochondrial membrane, but the resulting fatty acyl-coenzyme A is not degraded until it reaches the mitochondrial matrix. The fatty acyl-coenzyme A...

is transferred to another molecule that is involved in transport of the fatty acid into the mitochondrial matrix

Animals are not capable of converting fatty acids into glucose because...

Fatty acid degradation through the citric acid cycle does not lead to a net increase in oxaloacetate

During the degradation of unsaturated fatty acids the double bonds must be reduced. The reductant for this process is

NADPH

Enzymes that digest the triacylglycerols into free fatty acids and monoacylglycerol are called

Lipases

The hormone ___ induces lipolysis, whereas the hormone ___ inhibits the process

Glucagon, insulin

Triacylglycerol stored in adipose tissue is used by the liver and other tissues for...

(All of the listed)
Glycerol for pyruvate and glucose in liver,
ATP production via the citric acid cycle in muscle,
conversion to acetyl CoA and ketone bodies during starvation for the brain

The purpose of the pentose phosphate pathway is to...

Generate NADPH and synthesize five-carbon sugars

ATP is called the energy currency. The currency of reducing power is

NADPH

Which biosynthetic pathway requires NADPH?

(All of the listed)
Fatty acid, cholesterol, nucleotide

The two key components required for growth are ___ and biochemical reducing power

Ribose sugars

In the nonoxidative stage of the pentose phosphate pathway, intermediates of ___ are produced

Glycolysis

The enzyme transketolase transfers a ___-carbon fragment from a ketose to an aldose

Two

Glucose 6-phosphate dehydrogenase is inhibited by low levels of...

NADP+

Under what conditions might the pentose phosphate pathway produce large amounts of NADPH without significant net production of ribose 5-phosphate?

Synthesis of fatty acids in the liver

The function of the enzyme acyl CoA synthetase is...

ATP-dependent activation of fatty acids using CoA

Triacylglycerol stored in adipose tissue is used by the liver and other tissues for...

(All of the listed)
Glycerol for pyruvate and glucose in liver, ATP production via the citric acid cycle in muscle, conversion to acetyl CoA and ketone bodies during starvation for the brain

The hormone ___ induces lipolysis, whereas the hormone ___ inhibits the process

Glucagon, insulin

Three rounds of fatty acid oxidation results in...

Three acetyl CoA molecules

How many rounds of beta-oxidation would be required for a 16-carbon fatty acyl chain to be degraded to acetyl CoA?

7

Enzymes that digest the triacylglycerols into free fatty acids and monoacylglycerol are called...

Lipases

Acetoacetate spontaneously decarboxylates to form...

Acetone

In eukaryotes, the degradation of fatty acids occurs in the...

Mitochondrial matrix

Which of the following is an essential fatty acid?

Linoleate

The reaction that catalyzes the addition of an activated two-carbon compound with an activated three-carbon compound is

beta-ketoacyl synthase

What enzyme catalyzes the committed step in fatty acid synthesis?

Acetyl CoA carboxylase

Insulin leads to...

An activation of fatty acid synthesis

Enzymes from which of the following pathways are utilized for fatty acid synthesis

(All of the listed)
The citric acid cycle, the pentose phosphate pathway, glycolyis

Acetyl CoA carboxylase is globally regulated by

Phosphorylation and dephosphorylation

Chronic ethanol ingestion alters carbohydrate metabolism and leads to a fatty liver due to an increase in which of the following?

NADH

Which compound inhibits the entry of fatty acyl CoA into the mitochondria as a function of the cell being in the high-energy state?

Malonyl CoA

The carrier of an acyl chain through the synthetic protein complex is

ACP

How are fatty acids larger than 16 carbons formed?

By elongation reactions catalyzed by enzymes on the endoplasmic reticulum

Which of the following is the common precursor for both the phosphatidyl inositols and triaglycerols?

Phosphatidate

HMG-CoA is synthesized from acetyl CoA and

Acetoacetyl CoA

The role of lipoprotein particles is to

Solubilized hydrophobic lipids and contain cell-targeting signals

Respiratory distress syndrome is caused by a failure in the biosynthetic pathway of

Dipalmitoyl phosphatidyl choline

Hydrolyzation of cholesterol by cytochrome P450 requires

NADPH and activated O2

Phosphatidate is formed from

Glycerol-3-phosphate and two fatty acyl CoAs

The major carriers of dietary fat from the intestine is/are

Chylomicrons

Feedback regulation of cholesterol synthesis is mainly controlled at the step catalyzed by the enzyme

3-hydroxy-3-methylglutaryl (HMG) CoA reductase

Which of the following is/are major component(s) of low-density lipoprotein particles (LDLs)?

(All of the listed)
Cholesteryl ester, phospholipid, apoprotein B-100

Which of the following combines withe cholic acid to form a major bile salt?

Glycine

Ketogenic amino acids are degraded to which of the following metabolites?

Acetyl CoA and acetoacetate

Which amino acid is converted to tyrosine in the degradative pathway?

Phenylalanine

Surplus amino acids are...

Used as metabolic fuel

In the urea cycle, free NH4+ is coupled with carboxyphosphate to form

Carbamic acid

In the urea cycle, the carbon skeleton of aspartate is preserved as

Fumarate

Which of the following amino acids is ketogenic?

Lysine

Which of the following amino acids is glucogenic?

(All of the listed)
Asparagine, methionine, valine

The rate of synthesis of amino acid metabolic pathways often depends on the...

(All of the listed)

The carbon skeletons for amino acids are intermediates found in...

(All of the listed)
Glycolysis, the citric acid cycle, the pentose phosphate pathway

Essential amino acids are synthesized by...

Microorganisms and plants

S-adenosylmethionine carries which groups?

Methyl

Essential amino acids differ from nonessential amino acids in that...

Nonessential amino acids are synthesized in simple reactions compared to many for most essential amino acids

The activated methyl cycle involves the production and use of

Homocystine

The initial step in the degradation of phenylalanine is its conversion to another of the 20 common amino acids in a reaction catalyzed by phenylalanine hydroxylase. This reaction...

Adds a phenolic OH group producing tyrosine

Terrestrial vertebrates use the urea cycle to convert the ammonium ion to urea such that the urea can be excreted. In the production of urea, only one of the nitrogens in the product comes from ammonium ions. What is the source of the other nitrogen?

Aspartate

Urea can be said to directly originate from which single amino acid?

Arg

so provides the means by which ammonium ions are first incorporated into amino acids during their biosynthesis. Th carbon skeleton that accepts the ammonia to form glutamate is...

Alpha-ketogluterate

Nitrogen fixation is a means by which what type of organisms convert nitrogen into ammonium ions?

Bacteria

Which of the following is not a source of carbon skeletons for amino acid biosynthesis?

Beta-oxidation pathways of fatty acids

For humans, 11 amino acids are referred to as being "nonessential". This means that...

We have the capability of synthesizing these amino acids and thus do not need them in the diet.

What cofactor or prosthetic group serves as a carrier for activated one-carbon units during the synthesis of amino acids and other biological molecules?

Tetrahydrofolate or S-adenosylmethionine

Which of the following is an allosteric activator of mammalian carbamoyl phosphate synthetase?

N-acetylglutamate

The making of carbon-carbon bonds requires energy. How does the activated methyl cycle provide energy for methyl group transfer to a wide variety of acceptors?

The methyl group of methionine is activated by the transfer of an adenosyl group to the sulfur atom of methionine

(Essay question) Outline the control of triacylglycerol mobilization

Glucagon and epinephrine trigger 7TM receptors in adipose tissue that activated adenylate cyclase. The increased level of cyclic AMP then stimulates protein kinase A, which phosphorylates two key proteins: perilipin, a fat-droplet-associated protein, and hormone-sensitive lipase. The phosphorylation of perilipin restructures the fat droplet so that the triacylglycerols are more readily mobilized, and it triggers the release of a coactivator for the adipose triglyceride lipase (ATGL). Activated ATGL then initiates the mobilization of triacylglycerols by releasing a fatty acid from triacylglycerol, forming diacylglycerol. Diacylglycerol is converted into a free fatty acid and monoacylglycerol by the hormone sensitive lipase. Monoacylglycerol lipase completes the mobilization of fatty acids with the production of a free fatty acid and glycerol.

(Essay question) Explain why people with a hereditary deficiency of carnitine acetyltransferase 2 have muscle weakness. What are the symptoms

Fatty acids cannot be transported into mitochondria for oxidation. The muscles cannot use fats as a fuel. Muscles can use glucose derived from glycogen. However, when glycogen stores are depleted, as after a fast, the effect of the deficiency is especially apparent.

(Essay question) Insulin-dependent diabetes is often accompanied by high levels of triaglycerols in the blood. Suggest a biochemical explanation for the high blood levels of triaglycerols.

In the absence of insulin, lipid mobilization will take place to an extent that it overwhelms the ability of the liver to convert the lipids into ketone bodies.

(Essay question) Glucose is normally completely oxidized to CO2 in the mitochondria. Under what circumstance can glucose be completely oxidized to CO2 in the cytoplasm?

When much NADPH is required. The oxidative phase of the pentose phosphate pathway is followed by the nonoxidative phase. The resulting fructose 6-phosphate and glyceraldehyde 3-phosphate are used to generate glucose 6-phosphate through gluconeogenesis, and the cycle is repeated until the equivalent of one glucose molecule is oxidized to CO2.

(Essay question) Noted psychiatrist Hannibal Lecter once remarked to FBI Agent Clarice Starling that he enjoyed liver with some fava beans and a nice Chianti. Why might this diet be dangerous for some people?

Fava beans contain vicine, a pyrimidine glycoside that can lead to the generation of peroxides (ROSs) that can damage membranes as well as other biomolecules. Glutathione is used to detoxify the ROS. The regeneration of glutathione depends on an adequate supply of MADPH, which is synthesized by the oxidative phase of the pentose phosphate pathway. People with low levels of the dehydrogenase activity are especially susceptive to vicine toxicity.

(Essay question) Why do deficiencies in glucose 6-phosphate dehydrogenase frequently present as anemia?

Because RBCs do not have mitochondria and the only mans to obtain NADPH is through the pentose phosphate pathway. There are biochemical means to convey mitochondrial NADH into cytoplasmic NADPH.

(Essay question) Red blood cells lack mitochondria. These cells process glucose to lactate, but they also generate CO2. What is the purpose of producing lactate? How can RBCs generate CO2 if they lack mitochondria?

Lacking mitochondria, RBCs metabolize glucose to lactate to obtain energy in the form of ATP. The CO2 results from extensive use of the pentose phosphate pathway coupled with gluconeogenesis. This coupling allows the generation of much NADPH with the complete oxidation of glucose by the oxidative branch of the pentose phosphate pathway.

(Essay question) Indicate whether each of the following statements is true or false.
a. Biotin is required for fatty acid synthase activity
b. The condensation reaction in fatty acid synthesis is powered by the decarboxylation of malonyl CoA
c. Fatty acid synthesis does not depend on ATP
d. Palmitate is the end product of fatty acid synthesis
e. All of the enzyme activities required for fatty acid synthesis in mammals are contained in a single polypeptide chain
f. Fatty acid synthase in mammals is active as a monomer
g. The fatty acid arachidonate is a precursor for signal molecules
h. Acetyl CoA carboxylase 1 is inhibited by citrate

a. False-- Biotin is required for acetyl CoA carboxylase activity
b. True
c. False-- ATP is required to synthesize malonyl CoA
d. True
e. True
f. False-- Fatty acid synthase is a dimer
g. True
h. False-- Acetyl CoA carboxylase 1 is stimulated by citrate, which is cleaved to yield its substrate acetyl CoA