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usmle: biochem II


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to what does aldose reductase convert galactose
name three purine bases that are not found in nucleic acids
uric acid
what water-soluble vitamin deficiency is associated with cheilosis and magenta tongue
riboflavin (B2)
what is the precursor of all sphingolipids
what three substances stimulate glycogenolysis
Ca:calmodulin ration
what is the primer for synthesis of the second strand in production of cDNA from mRNA
hairpin loop made by reverse transcriptase at the 3' end of the first strand is the primer
what factors are needed for elongation in prokaryotes
EF-Tu or EF-ts and GTP
what restriction endonuclease site is destroyed in sickle beta-globin allele
MstII, changing codon 6 from A to T) destroys the restriction site
what complex is needed for propionyl CoA carboxylase
what enzyme catalyzes the reversible, oxidative, deamination of glutamate and produces the TCA cycle intermediate alpha-ketoglutarate
glutamate dehydrogenase
what enzyme is deficient in congenital erythropoietic porphyria
uroporphyrinogen III cosynthase
what is the drug of choice for treating a patient with hyperuricemia due to overproduction of uric acid
what is the max rate possible w/ a given amount of enzyme
from what do catalase, superoxide dismutase, and glutathione peroxidase defend the cell
oxygen free radicals
what signals are used to direct an enzyme to a lysosome
phosphorylation of mannose residues
what enzyme catalyzes the rate-limiting step of the urea cycle
carbamoyl phophate synthetase I
what liver enzyme, for TG synthesis converts glycerol to glycerol-3-phosphate
glycerol kinase
what organ functions to keep blood glucose levels nl through both well-fed and fasting states and produces ketones in response to inc FA oxidation
what pattern of inheritance does G-6-PD deficiency follow
what is the term for conversion of a dsDNA molecule to the base sequence of an ssRNA molecule
transcription (C comes before L- transcription before translation)
via what cell surface receptor does HDL cholesterol from the periphery enter hepatoceles
scavenger receptor (SR-B1)
which shuttle is used to bring fatty acyl CoA from the cytoplasm for ketogenesis
carnitine acyl CoA transferase II
what enzyme is blocked by 5-FU
thymidylate synthetase
what disease has a genetically low low level of UDP-glucoronate transferase, resulting in elevated free unconjugated bili
what aa has a pKa of 13
what X-L-R disorder is characterized by hyperuricemia, spastic CP, mental retardation, and self-mutilation
how many ATPs per glucose are generated from glycolysis in RBCs
2 ATPs, because RBCs use only anerobic metabolism
what enzyme catalyzes rate-limiting step in glycogenolysis
glycogen phosphorylase
would a G-C or A-T rich dsDNA sequence have a higher melting point
as what aa's do mm send N to liver
alanine and glutamine
what sphingolipid can't be produced without sialic acid and amino sugars
what happens to affinity if you inc Km
affinity decreases
what type of bili is found in neonatal jaundice
unconjugated (indirect)
what two aa's don't have more than one codon
what bonds are broken by exonucleases
external 3'5' PDE bonds
how can a genetic deficiency of carbamoyl phosphate synthetase be differentiated from an ornithine transcarbamoylase deficiency
uracil and orotic acid levels inc with ornithine transcarbamoylase def
nl in carbamoyl phosphate synthetase def
name the lipoprotein based on the following...
1. apo E
2. apo B-100
3. ape E, apo B-100, apo C-II
4. apo A-1, apo E, apo C-II
5. apo E, apo C-II, apo B-48
1. IDL
2. LDL
4. HDL
5. chylomicron
t or f
there is no hormonal control to the TCA cycle
what are the three tissues where TGs are produced
what toxin ADP-ribosylates via Gi to inc cAMP
pertussis toxin
what enzyme catalyzes the rate-limiting step in heme synthesis
d-ALA synthase
what cycle is responsible for converting to glucose in the liver the lactate made in RBCs
cori cycle
what enzyme is used to remove the hairpin loop during production of cDNA from mRNA
s1 nuclease
does a saturated FA have double bonds
unsaturated does
what pyrimidine base is found...
1. only in RNA
2. only in DNA
3. in both RNA and DNA
1. U
2. T
3. C
what two aa's require vitamin C for hydroxylation
proline and lysine
what is the only organ in the body that can produce ketone bodies
liver (mito)
what determines the rate of reax
energy of activation
what is the term for the number of trinucleotide repeats increasing w/ successive generations and correlating with increased severity of disease
fragile X
what enzyme is blocked by methotrexate/trimethoprim
dihydrofolate reductase
what fructose metabolism enzyme is deficient in patients w/ vomiting, apathy, diarrhea, jaundice, proximal renal tubular acidosis, hypoglycemia, and hyperuricemia
aldolase B def- tx by eliminating fructose from diet
what enzyme catalyzes the rate-limiting step in purine synthesis
PRPP aminotransferase
what water-soluble vitamin deficiency is assoc with porr wound healing, easy brusing, bleeding gums, anemia, and painful glossitis
vitamin C
what three susbtrates control the enzyme PEPCK for the conversion of OAA to pyruvate in the cytoplasm
1. cortisol-stimulates PEPCK
2. glucagon
3. GTP
what genetic defect is characterized by coarse facial features, gingival hyperplasia, macroglossia,psychomotor and growth retardation, club foot, claw hand, cardiorespiratory failure, and death in the first decade of life
I-cell disease
genetic defect affecting the phosphorylation of mannose residues
what two glycolytic enzymes catalyze the susbtrate-level phosphorylation
3-phosphoglycerate kinase and pyruvate kinase; this produces 2 ATPs per enzyme (total 4 ATPS)
what pathway uses HMG CoA synthetase in the cytoplasm
cholesterol biosynthesis
where in the body is heme converted to bili
what protein is required by prokaryotic RNA polymerase to initiate transcription at the promoter region of DNA
sigma factor
what enzyme catalyzes the rate-limiting step in pyrimidine synthesis
aspartate transcarbamylase
what are the two actions of calcitonin
inc Ca excretion from kidney and inc bone mineralization
what enzyme of the purine salvage pathway is deficient is
1. selective T cell immunodeficiency
3. Lesch-Nyhan syndrome
1. purine nucleoside phosphorylase
2. adenosine deaminase
in what cycle does glucose go to the mm, where it is converted to pyruvate and then into ala before being taken back to the liver
alanine cycle
what is the primary end product of pyrimidine synthesis
what pyrimidine base is produced by deaminating cytosine
what aa is classified as basic even though its pK is 6.5 to 0
histidine- its imidazole ring found in the R group is basic
what enzyme is deficient in hereditary protoporphyria
what eF is inactivated by ADP ribosylation, preventing translation
eEF-2 is where pseudomonas and diphtheria toxins work
is linolenic acid and omega-3 or omega-6 fatt acid
linoleic is omega-6
how many ATPS per glucose are generated in glycolysis
8 aerobic
2 anaerobic
name the three ketone bodies
what three bases are pyrimdines
name the RNA subtype...
1. most abundant form
2. found only in nucleus of eukaryotes and functios to remove introns from mRNA
3. only type translated
4. carries aa to the ribosome for protein synthesis
5. RNA molecules w/ enzyma
1. rRNA
2. snRNA
3. mRNA
4. tRNA
5. ribozymes
6. hnRNA
what enzyme is deficient in the following glycogen storage diseases
1. von Gierke's
2. Pompe's
3. McArdles
4. Hers'
1. glucose-6-phosphatase
2. lysosomal a-1,4-glucosidase
3. mm glycogen phosphorylase
4. hepatic glycogen phosphorylase
in prokaryotes, what is the term for a set of structureal genes that code for a select group of proteins and the regulatory elements req for the expression of such gene
what are the two most common aa's found in histone
lysine and arginine
what five pathways use SAM as methyl donor
1.epi synthesis
2. phophatidyl choline
3. creatine
4. methylation of cytosine
5. N-methyl cap of mRNA
what complex of the ETC contains Cu
complex 4
how many ATPs per glucose are produced by pyruvate dehydrogenase
6 ATPs
(2 pyruvates per glucose
2 NADHs from AcCoa
= 6 ATPS)
what is the size of the prokaryotic ribosome
what type of FA is assoc w/ a dec in serum TG and CV disease
omega-3 FA
what disease is produced by a deficiency in the enzyme tyrosinase
in what form are TGs sent to adipose tissue from the liver
what determines the rate of a reaction
energy of activation
what is the rate-limiting enzyme of the HMP shunt
what vitamin is necessary for the transfer of one amino grup from a carbon skeleton to another
pyridoxal phosphate (from B6)
what is the only sphingolipid that contains choline and PO4
(lecithin does to but its not a sphinolipid)
what protein catalyzes the formation of the last PDE bond between the okazaki fragments to produce a continuous strand
DNA ligase
what type of damage to the kidneys is caused by drinking ehtylene glycol
nephrotic oxylate stones
what water-soluble vitamin deficiency may result form eating raw eggs
regarding the lac operon fro what do the following genes code...
1. Z gene
2. Y gene
3. I gene
4. A gene
1. beta-galactosidase
2. galactoside permease
3. lac repressor
4. thiogalactoside transacetylase
what attaches to protons and allows them to enter into the mito without going through the ATP generating system
1-a-hydroxylase activity is inc in response to what two physiologic states
and hypophosphatemia
what is the major ketone body produced during alcoholic ketoacidosis
what enzyme catalyzes the rate-limiting step in the TCA cycle
isocitrate dehydrogenase
what bonds are broken by endonucleases
internal 3',5' PDE bonds
name the GLUT transporter based on the following
1. found in liver and pancreatic beta cells
2. foundin sk mm and adipose tissues
3. found in most tissues, including brain and RBCs
1. GLUT2
2. GLUT4
3. GLUT3 and 4
what enzyme catalyzes the rate-limiting step in FA oxidation
carnitine acetyltransferase I
what enzyme of the TCA cycle also acts as complex II of the ETC
succinate dehydrogenase
what is the term for chemicals thatkeep the pH constant despite the formation of acids an dbases during metabolism
in the mito, what complex is needed for pyruvate carboxylase to catalyze the reax from pyruvate to OAA
biotin, ATP, CO2
how may ATPs are produced from cytoplasmic NADH oxidation using the malate shuttle
3 by oxidative phosphorylation
what is the rate limiting step
1. FA synthesis
2. beta oxidation
3. ketogenolysis
4. cholesterol synthesis
1. acetyl CoA carboxylase
2. carnitine acyltransferase I
3. HMC CoA synthase
4. HMG CoA reductase
what direction does RNA polymerase move along the template strand of DNA during transcription
3'-5' direction
synthesizing RNA in 5'- 3'
t or f
histidine activates the histidine operon
activated by low levels of histidine
what organ is responsibel for the elimination of excess N from the body
what is the only way to inc maximum velocity
inc enzyme conc
name the two purine bases foundin both DNA and RNA
adenine and guanine
what prokarytoic positioning enzyme in translation is blocked by...
1. tetracycline
2. erythromycin
3. streptomycin
1. eEF-Tu and eEF-Ts of 30S
2. eEF-G of 50S
3. eIF-2 of 30S
t or f
DNA polymerases can correct mistakes, wheras RNA polymerases lack this ability
they have 3'-5' exonuclease proofreading ability
what are the two precursosrs of heme
glycine and succinyl CoA
what two factors cause PTH to be secreted
A dec in Ca and a dec in PO4
what are teh nonoxidative enzymes of the HMP shunt?
are teh reactions they catalyze reversible?
transketolase and transaldolase
yes - reversible
what are the five aa's that re both ketogenic and glucogenic
what artifical sweetener must patients w/ PKU avoid
cri-du-chat syndrome results in a terminal deletion oof the short arm of what chromsome
what substrate gets buit up in Gaucher's diseas
glucosyl cerebroside
what protein prevents ssDNA form reannealing during DNA replication
ss DNA binding protein
what type of jaundice is seen in Dubin-Johnoson syndrome
conjugated (direct)
-a transport defect
what type of DNA library is made from the mRNA from a tissue expressing a particular gene
what is the most common cause of B12 def
isoniazid tx
what lysosomal enzye is deficient in...
1. Gauchers
2. Neimann-Pick
3. Tay-Sachs
1. glucocerebrosidase
2. sphingomyelinase
3. hexosaminidase A
what are the 3 exceptions to rule of codominant gene expression
1. Barr bodies
2. T-cell receptors loci
3. IG light and heavy chain loci
how many kilocalories per gram are produced from the degradation of fat?> CHO? protein?
fat- 9 kcal/mol
CHO- 4 kcal/mol
protein- 4 kcal/mol
from which two sustances are phospholipids made
diacylglycerols and phophatidic acid
what intermediate enables propionyl CoA to enter the TCA cycle
succinyl CoA
what vitamin is an important component of rhodopsin
vitamin A
what is the term to describe the 5'-3' sequence of one strand being the same as the opposite 5'-3' strand
what gluconeogenic enzyme is absent in mm, accounting for its inability to use glycogen as a source for blood glucose
in what disease is there a genetic absence of UDPglucoronate transferase, resulting in an inc in free unconjugated bili
what enzyme req molybdenum as a cofactor
xanthine oxidase
at what three sites can the HMP shunt enter into glycolysis
1. fructose-6-phosphate
2. glucose-6-phosphate
3. glyceraldehyde-3-phosphate
what is the term for the pH range where the dissociation of H occurs
what regulates the rate of ketone body formation
rate of beta-oxidation
what are the eight liver specific enzymes
glycerol kinase
pyruvate carbodylase
how many bases upstream is the EUKARYOTIC TATA box promoter? the CAAT box?
the CAAT box is -75
what is needed to initiate translation
IF and GTP
eIF for eukaryotes
what part of the 30S ribosome binds to the Shine-Delgarno sequence
16S subunit
what component of the ETC is inhibited by...
1. barbituates
2. antimycin A
3. cyanide
4. oligomycin
5. atractyloside
6. CO
7. rotenone
8. azide
1. complex I
2. cytochrome b/cl
3. cytochrome a/a3
4. Fo/FI complex
5. ATP/ADP translocase
6. cytochrome a/a3
7. complex I
8. cytochrome a/ae
what aa is a precursor of the folowing substances
1. serotonin
3. histamine
4. creatine
5. NAD
6. N2O
1. tryptophan
2. glutamate
3. histidine
4. glycine/arginine
5. tryptophan
6. arginine
what two enzymes are B12 dependent
homocysteine methyl transferase
methylmalonyl CoA transferase
what two post-transcriptional enzymes in collagen synthesis require ascorbic acid to function properly
prolyl and lysyl hydroxylases
what three organs participate in production of vit D
what water-soluble vitamine deficiency is associated with neural tube defects
folic acid
what phase of interphase is haploid (N)
G2 and S are diploid
what neurotransmitter inhibits the optic nerve bipolar cell and shuts off in response to light
which of the following- DNA methylating enzymes, scaffolding proteins, histone acetylases, or deacetylases- is a regulator of eukaryotic gene expression
histone acetylase is a regulator favoring gene expression
all othere favor inactivation
what fat-soluble vitamin is connected to selenium metabolism
vit E
why are eukaryotes unable to perform trasncrtiption and translation at the same time like prokaryotes
in eukaryotes transcrtiption occurs in the nucleus and translation in the cytoplasm
what is determined by secondary structure of an aa
the folding of an aa chain
what three vitamine deficiencies are assoc w/ homocystinemia
if the pH is more acidic than the pI, does the protein carry a net positive or net negative charge
net positive charge
what form of continuous DNA used in clonging has no introns or regulatory elements
cDNA, when its made from mRNA
what is the start codon, and what does it code for in eukaryotes?
AUG in eukaryotes codes for methionine
in prokaryotes codes for formylmethionine
what parasite found in raw fish can produce vitamine B12 def
diphyloobothrium latum
methylating uracil produces what pyrimidine base
name the eukaryotic RNA polymerase based on the following
1. synthesizes tRNA, mRNA, and the 5S rRNA
2. synthesizes hnRNA, mRNA, and snRNA
3. synthesizes 28S, 18S, and 5.8S rRNA
1. RNA pol III
2. RNA pol II
3. RNA pol I
what is the primary screening test used to detect HIV-infected individuals? confirmatory test?
ELISA for screening because it is very sensitive
Western Blot used for confirmation because it is very specific
how many covalent bonds per purine-pyrimidine base pairing are broken during denaturation of dsDNA
denaturation of dsDNA breaks hydrogen bonds, not covalent bonds
how many hydrogen bonds link A-T? G-C?
what DNA replication enzyme breaks the hydrogen bond of base pairing, forming two replication forks
helicase (requires ATP)

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