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usmle: biochem I


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what are the three posttranscriptional modifications
1. 7-methyl guanine cap on 5' end
2. addition of the 3' poly-A tail
3. removal of introns
what aa is the major carrier of N byproducts from most tissues in the body
what two aa have a pKa of 4
aspartic acid and glutamic acid
how many acetyl CoAs per glucose enter into the TCA cycle
2 acetyl CoA per glucose
12 ATPs per acetyl Coa
what topoisomerase makes ssDNA cuts, requires no ATP, relazes supercoils, and acts as the swivel in front of the replication fork
topoisomerase I (relaxase)
in prokaryotes , what is the name of the RNA sequence that ribosomes bind to so translation can occur
name the pattern of genetic transmission; both M and F are affected; M-to-M transmission may be present; both parents must be carriers; the trait skips generations; two mutant alleles are needed for disease; and affected children may be born of unaffecte
autosomal recessive
what factors are needed for translation of prokaryotes
elongation factor G and GTP
what three aa must patients w/ maple syrup urine disease not eat
(I Love Vermont maple syrup)
dec alpha-ketoacid dehydrogenase
how many high energy bonds are used to activate an aa
2 ATPs via the amino-acyl tRNA synthase enzyme
what water-soluble vitamin deficiency results in pellagra
niacin (B3)
what glycolytic enzyme has a high Vmax, high Km, and low affinity for glucose
how many ATPs are generated per acetylCoA
what cytoplasmic pathway produces NADPH and is a source of ribose-5-phosphate
HMP shunt
what is the main inhibitor of pyruvate dehydrogenase
AcCoA (pyruvate to AcCoA)
where on the codon and anticodon does the wobble hypothesis take place
3' end of the codon (3rd position) on mRNA and 5' end on anticodon (first position) on tRNA
what DNA excision and repair enzyme is deficient in patients with xeroderma pigmentosum
excision endonuclease- removes thiamine dimers
what form of bilirubin is carried on albumin
unconjugated (indirect)
what are the
two ketogenic AAs
leucine and lycine
which organisms have polycistronic mRNA
as what compound do the carbons for fatty acid synthesis leave the mito
citrate via the citrate shuttle
what four substances inc the rate of gluconeogenesis
1. glucagon
3. AcCoA
4. ATP
with what three enzymes is TPP assoc
1. alpha-ketoglutarate dehydrogenase
2. pyruvate dehydrogenase
3. transketolase
what test uses very small amounts of DNA that can be amplified and analyzed without the use of southern blottin gor cloning
what apoprotein is required for the release of chylomicrons from the epithelial cells into the lymphatics
what enzyme catalyzes the covalent bonding of the aa's carboxyl grouop to the 3' end of tRNA
aminoacyle-tRNA synthetase uses 2 ATPs
what must be supplemented in patients with medium-chain acyl CoA dehydrogenase (MCAD) deficiency
short chain fatty acids
what form of aa is found only in collagen
in a diabetic patient, to what does aldose reductase convert glucose
sorbitol (-> cataracts)
what enzyme catalyzes the rate-limiting step in cholesterol metabolism
what is the term for the pH at which the structure carries no charge
what enzyme catalyzes the rate-limiting step in gluconeogenesis
what is the dug of choice in treating a patient with hyperuricemia due to underexcretion of uric acid
probenecid, a uricosuric agent
what enzyme deficiency results in darkening of the urine when exposed to air
homogentisate oxidase deficiency is seen in patients w/ alcaptonuria
in eukaryotes, what transcription factor binds to the tATA box before RNA pol II can bind
transcription factor IID
what enzyme produces an RNA primer inthe 5'-3' direction and is essential to DNA replication because DNA polymerase are unable to synthesize DNA without an RNA primer
what enzyme catalyzes the rate-limiting step in fatty acid synthesis
AcCoA carboxylase
name the eukaryotic DNA polymerase based on the following info
1. replicates mito DNA
2. synthesizes lagging strand
3. synthesizes leading strand
1. dna pol-gamma
2. dna pol-alpha
2. dna pol-delta
what is the order of fuel use in a prolonged fast
glucose from liver glycogen
glucose from gluconeogenesis
body protein
body fat
which way will the O2 dissociation curve shift with the addtion of 2.3BPG to adult Hb
what enzyme of pyrimidine synthesis is inhibited by the following
1. 5-FU
2. methotrexate
3. hydroxyurea
1. thymidylate synthase
2. dihydrofolate reductase
3. ribonucleotide reductase
what is found in the R group if the aa is acidic?
if a carboxyl group is the R group- acidic
if an amino group is the R group- basic
what gluconeogenic mitochondrial enzyme rquires biotin
pyruvate carboxylase
what factors are needed fro translocation in eukaryotes
ef-2 and GTP
DNA replication occurs during what phase of the cell cycle
S phase
what is the end product of purine catabolism
uric acid
what causes transcription to stop in eukaryotes
the termination sequence on the DNA

stop codons stop translation
what enzyme of the TCA cycle catalyzes ...
1. FADH2
2. GTP
1. succinate dehydrogenase
2. succinyl CoA synthetase
3. isocitrate dehydrogenase
alpha-ketoglutarate dehydrogenase
malate dehydrogenase
what form of alcohol causes blindness
methanol (wood alcohol)
how many base pairs upstream is the TATA box promoter

there is another promoter -35
what are the two essential fatty acids
linoleic and linolenic acid
during a prolonged fast, why is the brain unable to use FAs
FAs can't cross the bbb, therefore they can't be used as an energy source
what type of jaundice is seen in Rotor's syndrome
conjugated (direct)
if a sample of DNA has 30% T, what is the percent of C
(chargaff's rule)
from where is the energy for gluconeogenesis derived
beta-oxidation of FAs
name the type of mutation
1. deletion or addition of a base
2. new codon specifies a different aa
3. unequal crossover in meiosis w/ loss of protein function
4. new codon specifies for the same aa
5. new codon specifies for a sto
1. frameshift
2. missense
3. large segment deletion
4. silent
5. nonsense
what form of bilirubin can cross the bbb
unconjugated free bili
what aa is brokin down into N2O causing an inc in cGMP of sm mm, hence vasodilation
what is needed to produce a double bond in a fatty acid chain in the ER
NADPH, O2, cythochrome b5
what are the vitamin K dependent coagulation factors
protein C and S
is the hydroxyl (-OH) end of DNA and RNA at the 3' or 5' end
how many codons code for aa?
how many for termination of translation?
(you go away, you are away, you are gone)
what is the enzyme for the oxidative reaction in glycolysis
glyceraldehyde dehydrogenase
what substrate builds upin Tay-Sachs disease
Gm2 ganglioside
what pattern of genetic transmission is characterized by no transmission from M, maternal inheritance, and the potential for the disease to affect both sons and daughters of affected F
what is the rate limiting step of glycogen synthesis
glycogen synthase
what sphingolipid is formed by the union of serine and palmitoyl CoA
what causes an inc in bone mineralization and Ca along with PO4 absorption from the GI tract andkidney tubules
vitamin D
what two sugars can be used to produce cerebrosides
glucose and galactose
what group of eukaryotic regulatory proteins has a major factor in controlling the gene expression embryonically
homeodomain proteins
what causes the lysis of RBCs by oxidizing agents in G-6-PD deficiency
lack of glutathione peroxidase activity -> dec in NADPH -> leaves glutathione reduced
all aa's have titration plateaus at what pH values
2 and 9
what cytoplasmic organelle carries the enzymes for elongation and desaturation of fatty acyl CoA
what is the binding site for RNA pol
the promoter indicates where transcription will begin
what vitamin is necessary for epithelial health
what lipoprotein is formed if an IDL particle acquires cholesterol from a HDL particle
what structure or a protein describes the interaction among subunits
what is the only factor of enzyme kinetics that the enzyme affects
Ea (activation energy)
is the lac operon activated or inactivated in the presence of both glucose and lactose
glucose results in dec cAMP and therefore blocks protein binding between cAMP and CAP
at the end of each round of beta-oxidation, what is released
what is the rate limiting step of glycolysis
PFK1 and costs 1 ATP
what enzyme of heme synthesis is deficient in autosomal dominant disorder acute intermittent porphyria
uroporphyrinogen-I synthase
what enzyme is blocked by disulfiram
aldehyde dehydrogenase
deficiencies in what enzyme result in insoluble glycogen synthesis formation
what eukaryotic translation enzyme is associated w/...
1. initiation
2. elongation
3. termination
1. eIF-2 in the P-site
2. eEF-1
3. no enzymes are needed
what aa undergoes N-glycosylation
what enzyme, induced by insulin and activated by apo C-II, is req for chylomicron and VLDL metabolism
Lipoprotein lipase
what is the most common genetic deficiency resulting in hemolytic anemia
G-6-PD deficiency,
2nd is pyruvate kinase def
are the following condtions assoc w/ neg or pos N balance
1. aa def
2. growth
3. preg
4. uncontrolled DM
5. starvation
6. infection
7. recovery from injury
8. kwashiorkor
1. neg
2. pos
3. pos
4. neg
5. neg
6. neg
7. pos
8. neg
why is the liver unable to metabolize ketone bodies
hepatocytes lack the succinyl CoA acetoacetyl CoA transferase (thiophorase)
what enzyme, induced by insulin and activated by apo C-II is required for chylomicron an dVLDL metabolism
lipoprotein lipase
what is the MC genetic deficiency resulting in hemolytic anemia
G-6-PD def
pyruvate kinase is 2nd
are the following conditions associated with a negative or pos N balance
1. aa def
2. growth
3. preg
4. uncontrolled DM
5. starv
6. infec
7. recovery from injury
8. kwashiorkor
1. neg
2. pos
3. pos
4. neg
5. neg
6. neg
7. pos
8. neg
what toxin ADP-ribosylates via Gs protein to inc cAMP
cholera toxin
what two viatmins are inactivated when they come in contact with acetaldehyde
thiamine and folate
name the end product of FA synthesis?
FA oxidation
AcCoA and propionyl Coa (odd chain FAs)
what is the term for production of a DNA copy from an RNA molecule
reverse transcription
what mineral is req for cross-lining of collagen molecules into fibrils
lysyl oxidase requires Cu and O2
how many high energy bonds does the cycle of elongation cost
2 from ATP in aa activation
2 from GTP
what enzyme of purine synthesis is inhibited by allopurinol and 6-mercaptopurine
PRPP aminotransferase
t or f
the urea cycle takes place in both the cytoplasm and the mito
carbamoyl phosphate synthtesase and ornithine transcarbamoylase are mito enzymes
what is the only FA that is gluconeogenic
propionic acid
what enzyme has 5' to 3' synth of okazaki fragments
3' exonuclease activity
5' exonuclease activity
dna pol I
in what organelle does the TCA cycle occur
what enzyme is deficient in selective T cell immunodeficiency
purine nucleoside phosphorylase
t or f
adipose tissue lacks glycerol kinase
adipose depends on glucose uptake for dihydroxyacetone phophate (DHAP) production for TG synthesis
in what form is excess folate stored in the body
N-5-methyl THF
what is the term for taking an mRNA molecule and arranging the aa sequence forming a protein
what enzyme is blocked by hydroxyurea
ribonucleotide reductase
what protein carries free fatty acids to the liver
what substrate is built up in Neimann-Pick
t or f
methylation of bacterial DNA prevents restriction endonuclease from cutting its own chromsomes
what two aa's have a pka of 10
lysine and tyrosine
what is the only enzyme in the body that uses N-5-methyl folate
homocysteine methyl transferase
how can you differentiate vitamin K from vitamin C deficiency
K- nl bleeding time, inc PT
C- inc bleeding time, nl PT
what is the term for a unit of DNA that encodes a particular protein or RNA molecule
a gene
is the coding or the template strand of DNA identical to mRNA (excluding the T/U diff)
coding strand
the template strand is complementary and antiparallel)
what enzyme is deficient in acute intermittent porphyria
uroporphyringoen I synthetase
what five cofactors and coenzymes are required by pyruvate dehydrogenase
1. B1: thyamine -> TTP
2. B2: riboflavin -> FADH2
3. B3: niacin -> NAD(H)
4. B5: pantothenate -> CoA
5. lipoic acid

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