Final Review Flashcards
Which enzyme of the citric acid cycle closely resembles the pyruvate dehydrogenase complex in terms of its structure, organization and the reaction it performs?
a) isocitrate dehydrogenase
b) alpha-ketoglutarate dehydrogenase
c) succinate dehydrogenase
b) alpha-ketoglutarate dehydrogenase
In going from acetyl-CoA to succinate, two carbons have entered the cycle and two have been released as CO2. Why is the cycle not considered as complete at this point?
a) Not enough NADH has been generated
b) The cell requires FADH2 produced in subsequent reactions of the cycle
c) The oxaloacetate used to initiate the cycle must be regenerated
c) Regeneration of oxaloacetate
Of the enzymes of the citric acid cycle, which is not a freely soluble enzyme?
a) citrate synthase
b) succinate dehydrogenase
c) malate dehydrogenase
b) succinate hydrogenase
Although not present in animals, many plants and microorganisms can use a modified form of citric acid cycle known as the glyoxylate cycle. This is benefit in that it:
a) It allows the organisms which process it to convert acetyl CoA into glucose precursors
b) It provides a source of glyoxylate which is an essential molecule in biosynthetic pathways in these organisms
c) It does not release CO2 which is toxic to these organisms
a) glucose precursors
Which two enzymes within the citric acid cycle are allosterically inhibited by ATP?
a) citrate synthase and aconitase
b) isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase
c) fumerase and malate dehydrogenase
b) alpha-ketogluterate dehydrogenase
isocitrate dehydrogenase
Which intermediates in the citric acid cycle are used for the biosynthesis of amino acids?
a) citrate
b) succinyl CoA
c) alpha-ketogluterate and oxaloacetate
c) alpha-ketogluterate and oxaloacetate
The purpose of anaplerotic reactions is:
a) to divert materials out of the citric acid cycle for use in biosynthesis
b) to produce pyruvate to initiate the cycle when glucose degradation is not occuring
c) to replenish the citric acid cycle if it becomes depleted of intermediates by biosynthetic demands
c) replenishing citric acid cycle intermediates
What is the rate limiting enzyme in the citric acid cycle?
alpha-ketogluterate dehydrogenase
Which intermediates in the citric acid cycle are used for the biosynthesis of glucose?
oxaloacetate
Which intermediates in the citric acid cycle are used for the biosynthesis of fatty acids?
citrate
Where are the electron transport chain proteins located?
Bound to the inner membrane of the mitochondria
What characteristic indicates a compound will prefer to donate electrons?
a) A positive delta E’
b) A negative delta E’
b) negative delta E’
Which of the following is not a mobile or diffusible electron carrier in the mitochondrial ETC?
a) FAD
b) Ubiquinone
c) Cytochrome C
a) FAD
Of the electron transfer complexes associated with the inner mitochondrial membrane, which is not involved in generation of a proton gradient?
a) cytochrome c oxidase
b) cytochrome bc1
c) succinate-Q reductase
c) succinate-Q reductase - Complex II
What is the role of superoxide dismutase?
a) catalyzes the conversion of 2 H2O2 –> O2 + 2 H20
b) catalyzes the conversion of 2O2- + 2H+ –> O2 + H2O2
c) catalyzes the formation of superoxide anion and peroxide from O2
b) 2O2- + 2H+ –> O2 + 2H2O2
Which of the following statements does NOT apply to the ATP synthase mechanism?
a) The pH gradient causes a series of histidine residues to become protonated, thus driving the protein complex to rotate and release ATP
b) The pH gradient causes an aspartic acid residue to become protonated and powers the rotation of transmembrane subunit in the c ring of the ATP synthase
c) The F0 subunit of AtP synthase spans the inner mitochondrial membrane whereas the F1 protrudes into the mitochondrial matrix
a) NOT histidine residues (could be glutamate)
How many net ATP molecules are produced upon the reoxidation NADH and FADH2 in the ETC?
- 5 ATP / NAD+ formed
1. 5 ATP / FAD formed
Describe the direction of proton movement relative to electron transfer and phosphorylation?
Electron transfer pumps protons out of the matrix. As the protons reenter through the ATP synthase, ATP is produced in the mitochondrial matrix
The process of glycolysis occurs in the cytoplasm. The electrons from the NADH generated during glycolysis:
a) enter the mitochondrial ETC directly because NADH freely enters the mitochondria
b) cannot be used by the mitochondrial ETC because NADH cannot enter the mitochondria
c) may enter the ETC either at the level of NADH or FADH2, depending on the shuttle system used to transport them into the mitochondria
c) 3-phosphate shuttle allows e- from cytoplasmic NADH to enter at level of FADH2
malate-aspartate shuttle at the level of NADH
The glycogen molecule has two types of linkages between the glucose molecules of which it is comprised. Of these, the _________ linkage is broken by the glycogen phosphorylase enzyme; the _________ linkage is NOT broken by glycogen phosphorylase
alpha 1-4
alpha 1-6
The glycogen phosphorylase enzyme carries out a phosphorolysis reaction resulting in the formation of:
glucose 1-phosphate
The fact that liver tissue contains glucose 6-phosphatase while muscle tissue does not is physiologically important because:
a) one of the major functions of the liver is to maintain the blood glucose level
b) the muscle tissue does not use glucose as an energy source
c) glycogen is found only in the liver and not in muscle tissue
a) glucose 6-phosphatase produces glucose
Glycogen degradation in muscle is mainly stimulated by what?
epinephrine
Glycogen degradation in the liver is mainly stimulated by what?
glucagon and epinephrine
Glycogen synthase adds glucose units to growing glycogen molecules using what molecule?
UDP-glucose
Glycogen degradation and synthesis are said to be reciprocally regulated. This means that:
the same effectors affect both processes but in opposite directions
In order for regulation of glycogen metabolism to function, there must also be a means to reverse the regulatory effects of the various kinases. This is accomplished by protein phosphatase 1, which:
a) transfers the phosphate from a modified enzyme back to ADP
b) hydrolyzes the phosphate from the modified enzyme
c) recombines cyclic AMP and pryophosphate to turn off the signal activating the kinases
b) hydrolyzes the phosphate from the modified enzyme
Which of the following is true about Type II diabetes?
a) called insulin-dependent diabetes mellitus
b) usually occurs in children, not in adults
c) individuals have a normal amount of insulin in their blood
c) normal insulin levels
The major use of NADPH generated by the pentose phosphate pathway is?
serve as a reductant in biosynthetic pathways
For the pentose phosphate pathway, which of the following best summarizes the reversible reaction catalyzed by transaldolase?
a) C5 + C5 C3 to C7
b) C3 + C7 C6 + C4
c) C4 + C5 C6 + C3
b) C3 + C7 C6 + C4
For the pentose phosphate pathway, which of the following best summarizes the reversible reactions catalyzed by transketolase?
a) C5 + C5 C3 to C7
b) C3 + C7 C6 + C4
c) C4 + C5 C6 + C3
d) a + c
d)
Which of the following enzymes operates in the oxidative phase of the pentose phosphate pathway?
a) lactonase
b) phosphopentose isomerase
c) phosphopentose epimerase
a) lactonase
The ovary and testes have active pentose phosphate pathway because their tissues:
a) are actively involved in fatty acid and cholesterol biosynthesis
b) are actively involved in steroid biosynthesis
c) maintain a very large pool of reduced glutathione in their cells to prevent oxidative damage
b) involved in steroid biosynthesis
Which of the following is true regarding NADP+?
a) NADP+ and NAD+ are interchangeable cofactors for most enzymes
b) both the oxidative and nonoxidative branches of the pentose phosphate pathway convert NADP+ to NADPH
c) The ratio amounts of NADP+ and NADPH are important for protecting cells from oxidative stress
c) protects cells from damage from ROS
only the oxidative branch converts NADP+
Under conditions where NADPH is NOT needed, how are five-carbon sugars, such as ribose 5-phosphate, generated?
a) Through normal pentose phosphate pathway
b) By withdrawing 3 and 6-carbon units from the glycolytic pathway and converting them into 5-carbon sugar via the non-oxidative branch of the pentose phosphate pathway
c) It is not possible to produce 5-carbon sugars under these conditions
b)
The cleavage of triglycerides into glycerol and fatty acids is performed by lipases. The signalling process initiating the activation of lipases is the same at that which signals what process?
glycogen degradation
The glycerol produced during the lipolysis of triglycerides:
a) is a waste product
b) is stored within the cell for future synthesis of triglycerides
c) can be used as either a source of energy or for gluconeogenesis
c)
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:
a) crosse the inner mitochondrial membrane freely due to its hydrophobic character
b) is reconverted to the free fatty acid on the inner mitochondrial membrane, where it is also reattached to coenzyme A on the other side of the membrane
c) is transferred to another molecule that is involved in transport of the fatty acid into the mitochondrial matrix
c)CoA exchanged for carnitine (catalyzed by carnitine acyltransferase I (CAT I) ) and then transferred back via (CAT II)
The degradation of an 18-carbon saturated fatty acid would be expected to yield how many NADH and FADH2 / fatty acid molecule?
eight
During the degradation of unsaturated fatty acids, the double bonds must be reduced. The reductant for this process is?
NADPH
For untreated diabetics, how can the switch to ketone bodies as a fuel source become a dangerous metabolic state?
release of ketone bodies produces acidosis of the blood
The brain normally uses ______ as its major fuel; but during extended periods of starvation, the brain gets its energy from ______
glucose, ketone bodies
Fatty acid biosynthesis depends on the presence of CO2 to generate malonyl-coenzyme A from acetyl-coenzyme A. If a culture of cells grown in the presence of 14C-labeled bicarbonate, which carbons of the newly synthesized fatty acids would be expected to be radiolabeled?
a) even-number carbons
b) odd-number carbons
c) none of the carbons
none of the carbons
Acetyl groups to be used for fatty acid biosynthesis are transferred across the mitochondrial membrane in what form?
Citrate
The NADPH used in the reductive steps of fatty acid biosynthesis comes from?
one NADPH being generated per citrate leaving the mitochondria and the degradation of glucose via the pentose phosphate pathway
Which enzyme catalyzes the committed step in fatty acid synthesis?
acetyl CoA-carboxylase
Which of the following does NOT apply to prostaglandins?
a) derived from arachidonic acid
b) members of the eicosanoid family
c) systemic hormones, with long-lasting physiological effects
c) they are short-term
Each of the following conditions will enhance the activity of acetyl CoA carboxylase except:
a) release of insulin
b) phosphorylation of the enzyme, via AMPK
c) high levels of citrate
b) phosphorylation of the enzyme, via AMPK
In the synthesis of triglycerides and phospholipids, fatty acids are first attached to glycerol 3-phosphate. Which of the following is NOT a source of glycerol 3-phosphate?
a) phosphorylation of glycerol by ATP
b) reduction of an intermediate in the glycolysis pathway
c) acetyl-coenzyme A
c) acetyl-coenzyme A
In the synthesis of triglycerides and phospholipids, fatty acids are attached to the glycerol 3-phosphate in the form of?
a) free fatty acids
b) fatty acyl-coenzyme A
c) fatty acyl-carrier protein complexes
fatty acyl-coenzyme A
In the synthesis of triglycerides, the third fatty acid:
a) is added by displacing the phosphate group of phosphatidate
b) is added by diacylglycerol after removal of the phosphate group from phosphatidate
c) is added to a CDP-diacylglycerol
b)
The synthesis of cholesterol involves condensations of 5-carbon units from isopentenyl pyrophosphate. Which of the following summarizes the sequence of these condensations?
a) 5-carbon units are added sequentially to give a 30-carbon molecule that is cyclized to form cholesterol
b) Two 5-carbon units are condensed to form a 10-carbon unit, three of which are combined to yield a 30-carbon molecule that is cyclized to form cholesterol
c) Three 5-carbon units are condensed to form a 15-carbon unit, two of which are combined to yield a 30-carbon molecule that is cyclized to form cholesterol
c)
The major sites of cholesterol synthesis are the liver and small intestine. The primary way by which cholesterol is transported from these organs to other tissues is?
via LDL that is taken up by a receptor-mediated endocytosis
Most terrestrial vertebrates excrete excess nitrogen as what simple chemical compound?
Urea
During the degradation of many amino acids, the first step involves transfer of the amino group to what citric acid cycle intermediate?
alpha-ketogluterate
Terrestrial vertebrates use the urea cycle to convert the ammonium ion to urea such that it 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
Which of the following is NOT true regarding phenylketonuria?
a) Untreated PKU can lead to severe mental retardation
b) Carriers of this genetic disease have a decreased level of phenylalanine hydroxylase
c) PKU is treated with a diet completely void of any phenylalanine
c) they can have small amounts
In de novo synthesis, the framework of ______ bases is assembled prior to attachment to ribose, while in the case of ______ bases, the framework is assembled on the ribose structure
pyrimidines
purines
During the synthesis of pyrimidine nucleotides, the pyrimidine ring framework that is attached to the ribose is?
orotate
The synthetic pathways leading to AMP and GMP are:
a) linearly related with AMP being produced first and then converted to GMP
b) linearly related with GMP being produced first and then converted to AMP
c) branched at the level of an intermediate which can be converted to either AMP or GMP
c)
Deoxyribonucleotides are required for the synthesis of DNA. They are:
a) made by the attachment of the purine and pyrimidine bases to deoxyribose phosphates
b) made by the reduction of the ribose component of ribonucleotide phosphates
c) synthesized in the same manner as ribonucleotides except that a 5-phosphodeoxyribosyl-1-pyrophosphate is used instead of a 5-phosphoribosyl-1-pyrophosphate
b)
DNA is more resistant to hydrolysis than RNA. What feature of DNA is responsible for this characteristic?
Absence of the 2’-hydroxyl group
In eukaryotes, DNA is present in a chromatin structure. Chromatin is made up of?
DNA that is highly ordered by wrapping around histones
Which is the dominant form of DNA found under physiological conditions?
B-DNA
Which of the following is NOT a structural theme in RNA structures:
a) supercoiling
b) formation of stem-loop structures through base-pairing
c) stabilization through binding of divalent cations
a) supercoiling
Which polymerase is key to replication?
polymerase III
In order for DNA replication to occur, the two strands of the double helix must be physically separated. This is accomplished through the use of?
helicase enzymes using energy from hydrolysis
What is the function of the primase enzyme?
synthesizes a short stretch of RNA complementary to a part of the template DNA strand
Which of the following is NOT a difference between RNA and DNA synthesis?
a) The nature of the nucleotide used
b) The need for a primer
c) The direction of synthesis
c) direction of synthesis
Gene regulation in eukaryotes involves reorganization of the chromatin structure such that DNA binding is weakened in regions to be transcribed. This is accomplished how?
chemical modification of histone proteins
Steroid hormones regulate gene expression by binding where?
To DNA-binding receptor proteins which in turn regulate gene expression
Many eukaryotic genes are divided into mosaics of exons and introns with only the exon portions containing the coding sequence for a protein. Are the introns transcribed? Translated?
Introns are transcribed but NOT translated
What RNA polymerase is involved in the synthesis of pre-mRNAs?
RNA polymerase II
Of the 64 triplet codons in the genetic code, ___ code for the 20 amino acids and ____ serve as signal to terminate protein synthesis
61
3
Where on the tRNA does the amino acid become covalently attached?
At the 3’-terminus, which is not phosphorylated
What statement best describes ribosomes?
a) The ribosome is a ribonucleoprotein, with most of its mass due to three different sized RNAs
b) Most bacterial cells have only a few ribosomes that are responsible for translating mRNA into protein
c) The majority of the proteins in the ribonucleoprotein particle serve as catalysts in protein synthesis
a) ribonucleoprotein with 3 RNAs
