Exam 4 Flashcards
The majority of transaminases exhibit a specificity for L-glutamate and alpha-ketoglutarate.
True.
Urea is synthesized in mammalian kidneys.
False.
Nitrogen fixation, catalyzed by the enzyme nitrogenase, is a process that requires energy.
True.
Nitrogen fixation via nitrogenase produces hydrogen gas as well as ammonia.
True.
Glutamine is a nitrogen donor in several biosynthetic reactions and represents a means of carry nitrogen between tissues.
True.
Each of the 20 common amino acids can be described as being either glucogenic or ketogenic.
False.
Arginase is an enzyme found at high activity levels in nearly all mammalian organs and tissues.
False.
Because of the importance of their function, regulatory proteins have long half-lives.
False.
Like most catabolic processes, the protein hydrolysis that occurs during turnover is not energy consuming.
False.
The urea cycle requires 4 ATP equivalents per molecule of urea that is produced.
True.
A transaminase enzyme would convert alanine to _________ while converting ___________ to glutamate.
pyruvate
alpha ketoglutarate
When there is excess ammonia and little aspartate available for the urea cycle, ammonia combines with ___________ to produce glutamate, which then undergoes transamination with _____________ to produce the necessary oxaloacetate.
alpha ketoglutarate
oxaloacetate
Amino acids whose carbon chains are catabolized to form acetyl CoA are said to be _____________. Those that form intermediates of glycolysis or the citric acid cycle are said to be ___________.
ketogenic
glucogenic
In the biosphere, the two major sources of nitrogen ultimately used for amino acid synthesis are ____________ and _____________.
atmosphere N2
soil NO3-
The sources of the two nitrogen atoms and the carbon atom of urea are ___________, __________, and __________, respectively.
NH4+
aspartate
HCO3-
One of the nitrogen atoms and the carbon atom of urea enter the urea cycle as a single molecule, namely ________________.
carbamoyl phosphate
The urea cycle requires energy to form urea. The equivalent of ________ ATP molecules is required.
4
The exchange of glucose and alanine between muscle and liver is called the __________.
glucose-alanine cycle
Several molecules of the protein ____________ are attached to proteins targeted for degradation.
ubiquitin
The multiprotein complex that hydrolyzes targeted proteins to peptides during the turnover process is called the _______________.
proteasome
The nitrogenous bases of nucleotides and nucleosides are of two types - the purines, which are heterocycles containing six atoms, and the pyrimidines, which are heterobicycles containing nine atoms.
False.
Nucleotide biosynthesis occurs only in cells that undergo replication.
False.
To synthesize the purine ring, liver cells require metabolic sources of glycine, formate, glutamine, CO2, and aspartate.
True.
In purine nucleotide synthesis, the purine ring is synthesized and then attached to ribose-5-phosphate to make nucleotides. In pyrimidine nucleotide synthesis, the components of the pyrimidine ring are assembled on ribose-5-phosphate.
False.
Inosine 5’-monophosphate (IMP) is an intermediate from which both 5’-AMP and 5’-GMP are synthesized.
True.
To synthesize GMP from IMP, ATP is required, whereas to synthesize AMP from IMP, GTP is required.
True.
To synthesize the pyrimidine ring, liver cells require asparagine, glutamate and bicarbonate.
False.
The first step in the pyrimidine ring biosynthesis involves formation of carbamoyl phosphate, catalyzed by carbamoyl phosphate synthetase. This is the same enzyme that operates in the urea cycle.
False.
Uric acid, an avian excretion product, is a pyrimidine.
False
Orotate is the end product of the pyrimidine biosynthetic pathway and is the derivative from which the pyrimidine nucleosides and nucleotides are made.
False.
The disease gout is the result of excess amounts of uric acid.
True.
dTMP is formed by the reduction of the ribose moiety of ribothymidylate.
False.
Most free purine and pyrimidine molecules are salvaged, but some are catabolized. Catabolism of both purine and pyrimidine molecules leads to the excretory product uric acid.
False.
The components of a nucleotide are a/an _____________, a/an ______________, and _____________.
purine or pyrimidine base
ribose or deoxyribose
1 or more phosphate groups
The active form of ribose 5-phosphate required for nucleotide biosynthesis is ____________.
PRPP
In liver cells, the location of purine biosynthesis is ____________.
the cytosol
During purine nucleotide synthesis, the first reaction of 5-phosphoribosyl 1-pyrophosphate is the addition of nitrogen to the ribose residue. The source of nitrogen is ___________.
glutamine
Carbamoyl phosphate is involved in the biosynthesis of which type of nucleotides, the pyrimidines or the purines.
pyrimidines
The recycling of products from the normal cellular breakdown of nuclei acids is an energy-conserving process called ____________.
salvage
A common treatment for gout, allopurinol works by inhibiting xanthine oxidase. Instead of producing ______________, the two more soluble products of purine metabolism _____________ and _____________.
uric acid
xanthine
hypoxathine
CTP is formed from UTP by transformation of the keto group at C-4 of the pyrimidine ring to an amino group. The source of the nitrogen for this amino group is __________ that is converted to __________.
glutamine
glutamate
Anticancer drugs such as 5-fluorouracil and methotrexate prevent the synthesis of ____________.
dTMP
Nucleotides are molecules that contain only a sugar and a nitrogenous base.
False.
Nucleosides are obtained as breakdown products of nucleic acids and contain a pentose and a nitrogenous base bonded to the pentose by a beta-N-glycosidic bond.
True.
Uracil and thymine are members of the pyrimidine family and are typically found as components of DNA.
False.
The nucleoside moieties of nucleic acids exist predominantly in the anticonformations due to steric hindrance present in the syn conformation.
True.
When incorporated into DNA, thymine and adenine each contain one hydrogen bond donor and one hydrogen bond acceptor.
True.
Chargaff determined that the molar ratios of adenine to thymine and of guanine to cytosine in DNA are about one. This means that the sum of the adenine + thymine bases will be equal to the sum of the guanine + cytosine bases.
False.
The Watson-Crick model of DNA is a right-handed helix of two separate chains, both oriented in the same direction.
False.
When incorporated into DNA, guanine and cytosine each contain two hydrogen bond donors and two hydrogen bond acceptors.
False.
Endonucleases are enzymes that catalyze the cleavage of phosphodiester linkages in the interior of nucleic acid polymers.
True.
DNA can be hydrolyzed in the laboratory by dilute (less than 0.5 M) NaOH.
False.
Hydrolysis of RNA by the catalytic action of pancreatic ribonuclease or by dilute NaOH involves formation of a 2’,3’-cyclic nucleoside monophosphate intermediate.
True.
Under physiological conditions, nucleic acids are polyanions.
True.
A-DNA, B-DNA, and Z-DNA all exist in vivo.
True.
2,4-Dioxopyrimidine is more commonly known as ____________.
uracil
2-Oxo-4-aminopyrimidine is more commonly known as ______________.
cytosine
Deoxythmidine-5’-triphosphate is commonly abbreviated as ________________.
dTTP
DNA polymerase requires ______________ as substrates for the extension of a DNA chain.
deoxynucleoside triphosphates
The hydrated, more common form of DNA is ______________.
B-DNA
The type of DNA that exists as a left-handed helix is _____________.
Z-DNA
The allowed base pairing in DNA is thymine with ___________ and cytosine with ___________.
adenine
guanine
The process of using heat to dissociate duplex DNA into separate single strands is called ________________. The temperature at which half of the DNA has become single stranded is called the __________________.
melting
Tm (melting temperature)
Enzymes that break DNA, unwind or overwind the double helix, and rejoin the strands are called ________________.
topoisomerases
RNA molecules that carry information from DNA to the ribosomes for protein synthesis are called _________.
mRNA
When certain bases in DNA are methylated for protection from the cell’s own restriction endonucleases, the -CH3 group is supplied by __________________.
s-adenosyl methionine
A technique that utilizes restriction endonucleases to analyze samples of DNA and identify individuals from a large population is called _________________.
DNA fingerprinting
The conservative model of DNA replication is supported by experimental evidence.
False.
In E. coli, replication is unidirectional.
False.
Bacterial replication requires dAMP, dTMP, dGMP, and dCMP.
False.
Both eukaryotic and prokaryotic cells have several different DNA polymerases that are involved in replication and repair of DNA.
True.
Kornberg’s enzyme (DNA polymerase I) catalyzes the synthesis of DNA if provided with only the four deoxyribonucleoside triphosphates.
False.
DNA polymerase III performs the major role in prokaryotic replication.
True.
DNA polymerase III requires only a single-stranded DNA template for replication.
False.
The reaction by which deoxyribonucleotides are added during replication is a near-equilibrium process.
False.
Eukaryotic Okazaki fragments are smaller than prokaryotic Okazaki fragments.
True.
DNA ligase plays a role in normal DNA replication as well as in repair of damaged DNA.
True.
The location at which duplex DNA is unwound during replication and at which new DNA is being synthesized is called the ___________________.
replication fork
During replication, proteins that bind to individual unwound DNA strands to prevent them from re-forming as a double helix are called _______________.
single strand binding protein (SSB)
The DNA strand that serves as a complementary pattern along which a new DNA strand is synthesized is called the ____________ strand.
template
Short segments of RNA required for synthesis of DNA on a template are called _____________ which are removed from the product DNA by the _____________ activity of DNA polymerase I.
primers
5’-3’ exonuclease
The DNA strand formed as a continuous strand during replication is called the _________________ and the strand formed in a discontinuous process is called the ______________.
leading strand
lagging strand
DNA sequencing is best done by using _____________ to effect termination of the growing DNA molecule, followed by _____________ to separate the resulting DNA fragments to determine their size.
dideoxyribonucleotides
electrophoresis
Short segments of lagging-strand DNA formed by the discontinuous process are called _______________.
okazaki fragments
_______________ is the name of the process by which DNA polymerase I catalyzes the formation of DNA segments to replace the RNA primer segments required by DNA polymerase III during replication.
Nick translation
The direction of RNA synthesis is the same as that of DNA synthesis.
True.
The unusual bases, such as N6-methyladenylate, inosinate, and dihydrouridylate, found in tRNA molecules are incorporated during transcription of the gene.
False.
Promoter regions are found exclusively on the DNA template strand.
False.
The RNA product of transcription is sequentially the same as that of the DNA coding strand, except that U replaces T.
True.
Not all genes that encode enzymes are inducible.
True.
Protein synthesis of prokaryotic mRNA molecules begins before synthesis of the mRNA molecule is complete.
True.
It is common for eukaryotic mRNA molecules to have poly A tails.
True.
Eukaryotic mRNA molecules are capped by the addition of a 7-methylguanylate group to the 3’ end of the mRNA molecule.
False.
The 18S, 5.8S, and 28S rRNA molecules that are part of the human ribosomes are all present in a single precursor rRNA molecule.
True.
The five classes of RNA include ___________, __________, __________, ___________, and __________.
transfer RNA
ribosomal RNA
small RNA molecules
regulator RNA
The most abundant class of RNA in the cell is ___________.
ribosomal RNA
The DNA region that acts as a transcription initiation signal is called the ___________, which is the site for the enzyme ___________ to bind.
promoter
RNA polymerase
The prokaryotic RNA polymerase holoenzyme contains a ________________ that is responsible for the elongation of RNA and the ______________ that aids with initiation.
core polymerase
sigma factor
Once a newly synthesized RNA molecule is approximately 10 nucleotides long, RNA polymerase undergoes the transition from ____________ to ___________ mode.
initiation
elongation
_________ is the hexameric protein that aids in certain prokaryotic termination processes.
Rho factor
The eukaryotic enzyme that catalyzes the synthesis of mRNA precursors is _____________.
RNA polymerase II
During splicing of eukaryotic mRNA molecules, internal sequences called __________ are removed from the primary RNA transcript. Sequences present in the primary RNA transcript and also in the mature RNA molecules are called ____________.
introns
exons
The RNA molecules that combine with proteins to form the spliceosome are called ______________.
snRNAs
Every cell must contain at least 20 different tRNA species.
True.
tRNA molecules are relatively small molecules composed of less than 100 nucleotides.
True.
A particular aminoacyl-tRNA synthetase will recognize a specific amino acid, but will bind and aminoacylate any tRNA.
False.
The formation of an aminoacyl tRNA requires the input of 1 ATP equivalent.
False.
Protein synthesis always begins at the amino terminus in prokaryotic systems.
True.
Transfer RNA molecules are charged by the covalent attachment of the amino acid for which they are specific at the 5’ end of the tRNA.
False.
N-Formylmethionyl-tRNA initiates protein synthesis in both prokaryotic and eukaryotic systems.
False
Base pairing between aminoacyl-tRNA anticodon and an mRNA codon occurs in an antiparallel fashion.
True.
When an aminoacyl tRNA synthetase acts to remove an amino acid mistakenly joined to a tRNA, the enzyme is exercising its _____________ activity.
proof reading
The process by which the ribosome is shifted by one codon relative to mRNA is called ____________.
translocation
The activation and incorporation of an amino acid into a growing peptide chain requires energy equivalent to the hydrolysis of ____ phosphoanydride bonds; ____ equivalents are used during amino acid activation while ____ equivalents are used during elongation.
4
2
2
Proteins destined for secretion are synthesized with an N-terminal sequence, called the _________, which assists in transport of the protein into the lumen of the endoplasmic reticulum, as the protein is being synthesized. This sequence may be removed at a later time.
signal peptide
Modification of protein chains is categorized as either ____________ or ____________ with regard to when they occur.
cotranslational
posttranslational
