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STEP1 > biochem/genetics > Flashcards

biochem/genetics Flashcards

1
Q

nucleoside =

nucleotide =

A

nucleoside = base + sugar

nucleotide = base + sugar + phosphate

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2
Q

deamination:

guanine -> _____
5-methylcytosine -> _____
cytosine -> ______
adenine -> ______

A

guanine -> xanthine
5-methylcytosine -> thymine
cytosine -> uracil
adenine -> hypoxanthine

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3
Q

methylation of _____ -> thymine

A

uracil

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4
Q

Lesch Nyhan syndrome is due to absent _____ which converts _________

inheritance pattern?

A

HGPRT. purine salvage pathway
hypoxanthine -> IMP
guanine -> GMP

x-linked recessive

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5
Q

enhancer, promotor, or operator?

can be located upstream downstream or within introns of a gene, does not have to be close to the gene

A

enhancer

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6
Q

enhancer, promotor, or operator?

must be located upstream, pretty close to the gene
directly binds RNA polymerase and transcription factors
required for transcription

A

promotor (TATA and CAAT boxes)

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7
Q

which DNA repair happens in G1 phase?

A

nucleotide escision repair

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8
Q

which DNA repair happens in S phase?

A

mismatch repair

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9
Q

which DNA repair fixes spontaneous/toxic deamination?

A

base excision repair

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10
Q

which DNA repair is defective in xeroderma pigmentosum?

A

nucleotide excision repair

pyrimidine dimers accumulate (formed from UV light)

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11
Q

which DNA repair is defective in Lynch syndrome?

A

mismatch repair

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12
Q

which DNA repair is defective in ataxia telangiectasia?

A

double strand nonhomologous end joining

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13
Q

which DNA repair is defective in breast/ovarian cancers w/ BRCA1 mutation?

A

double strand homologous recombination

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14
Q

guy eats death mushrooms. what is the problem?

A

alpha-amanitin. inhibits RNA polymerase II + sever ehepatotoxicity

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15
Q

what end does 7-methylguanosine cap go on of mRNA?

A

5’ end

A357 mnemonic

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16
Q

SLE has anti-Smith antibodies. what are these against?

A

snRNPs (spliceosomes)

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17
Q

protein synthesis is intiated by _____(reaction)

A

GTP hydrolysis

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18
Q 
lysosomal storage disorder: 
courase facial features
clouded corneas
restricted joint mvt
high plasma levels of lysosomal enzymes
often fatal in childhood

dx? pathogenesis?

A

I cell disease

defect in N=acetylglucosaminyl-1-phosphotransferase -> Golgi can’t phosphorylate mannose residues => decreased mannose-6-phosphate on glycoproteins -> proteins are secreted extracellularly rather than delivered to lysosomes

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19
Q

signs/sx of peroxisome dz?

reason for the neuro sx?

A

scaly skin, ataxia, cataracts/night blindness, shortening of 4th toe, epiphyseal dysplsia

hypotonia, seizures, hepatmegaly, early death

neuro sx are from dec synthesis of PLASMALOGENS, important for phospholipids in myelin

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20
Q

based on the primary structure of collagen, what is the best reflector of collagen synthesis? (amino acid)

A

Glycine

remember sequence is Gly-X-Y where x and y are proline or lysine

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21
Q

In Menkes dz, defective menkes protein (ATP7A) leads to what?

pattern of inheritance?

A

leads to decreased activity of lysyl oxidase, which cross links collagen in final step of synthesis -> kinky hair, growth retardation, hypotonia

x-linked recessive

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22
Q

Marfan syndrome is autosomal dominant. FBN1 gene mutation on chromosome 15 results in defective _______

can have subluxation of lenses ___ and ____

A

fibrillin

lens up and out (temporal)

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23
Q

definition of locus heterogeneity and example?

A

Albinism

mutations at different loci can produce a similar phenotype

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24
Q

definition of allelic heterogeneity and example?

A

different mutations in the same locus produce the same phenotype

B-thalassemia

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25
Q

heteroplasmy definition

A

presence of both normal and mutated mitochondrial DNA, resulting in variable expression in mitochondrially inherited dz

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26
Q

what test is used for newborn screening of Cystic fibrosis?

A

elevated immunoreactive trypsinogen

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27
Q

X-linked recessive disorders: Oblivious Female Will Often Give Her Boys Her x-Linked Disorders

A 
OTC deficiency
Fabry dz
Wiskott-Aldrich syndrome
Ocular albinism
G6PD deficiency
Hunter syndrome
Bruton agammaglobulinemia
Hemophilia A and B
Lesch-Nyhan syndrome
Duchenne and Becker muscular dystrophy
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28
Q

Lyonization definition

A

x inactivation. female carriers

variably affected depending on the pattern of inactivation of the X chromosome carrying the mutant vs normal gene.

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29
Q

in muscular dystrophies, esp Duchenne, there is increased CK and ______

A

aldolase

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30
Q

in myotonic dystrophy, there is _____ trinucleotide repeat expansion in ____ gene -> abnormal expression of ______

A

CTG

DMPK gene

myotonin protein kinase

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31
Q

in fragile X syndrome, trinucleotide repeat expansion in FMR1 gene leads to _________

A

hypermethylation -> decreased expression

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32
Q

what inherited syndromes/dz can predispose to MVP? (4)

A

fragile X
Marfan
Ehlers-Danlos
AD PKD

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33
Q

trinucleotide repeat expansion in fragile X syndrome

A

CGG

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34
Q

trinucleotide repeat expansion in Friedreich ataxia

A

GAA

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35
Q

of the trisomies, which one has increased B-hCG?

A

Downs 21. the other 2 are decreased

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36
Q

of the trisomies, which one has increased PAPP-A?

A

none. all decreased

37
Q

of the trisomies, which one has decreased inhibin A?

A

Down 21.

38
Q

of the trisomies, which one has normal levels of stuff in 2nd trimester?

A

13, Patau syndrome

39
Q

severe intellectual disability, rocker- bottom feet, microphthalmia, microcephaly, cleft liP/Palate, holoProsencephaly, Polydactyly, cutis aPlasia, congenital heart disease, Polycystic kidney disease. Death usually occurs by age 1.

which trisomy?

A

13 Patau syndrome

40
Q

Prominent occiput, Rocker-bottom feet, Intellectual disability, Nondisjunction, Clenched fists (with overlapping ngers), low-set Ears, micrognathia (small jaw), congenital heart disease. Death usually occurs by age 1.

which trisomy?

A

18, Edward syndrome

41
Q

if trisomy 21 is due to unbalanced Robertsonian translocation, which 2 chromosomes is it most commonly between?

A

14 and 21

42
Q

if a fetus has Down’s, 1st semester ultrasound will show what?

A

nuchal translucency and hypoplastic nasal bone.

43
Q

microcephaly, moderate to severe intellectual disability, VSD or other cardiac abnormality
deletion of short arm of chromosome 5

what is it?

A

Cri du chat syndrome

44
Q

Congenital microdeletion of long arm of chromosome 7 (deleted region includes elastin gene). Findings: distinctive “elfin” facies, intellectual disability, hypercalcemia ( sensitivity to vitamin
D), well-developed verbal skills, extreme friendliness with strangers, cardiovascular problems (eg, supravalvular aortic stenosis, renal artery stenosis)

dx?

A

Williams syndrome

william for will ferrel in the movie Elf (elfin facies and super friendly)

45
Q

which 2 cardiac defects are associated w/ catch22?

A

truncus arteriosis

tetralogy of fallot

46
Q

alopecia, dry skin (eg, scaliness), hepatic toxicity and enlargement, arthralgias, and pseudotumor cerebri

these are from chronic toxicity of what vitamin?

A

vit A

47
Q

4 enzymes/reactions that thiamine B1 is cofactor for

A
  1. Pyruvate dehydrogenase (links glycolysis to
    TCA cycle)
    ƒ 2. α-ketoglutarate dehydrogenase (TCA cycle)
    ƒ 3. Transketolase (HMP shunt)
    ƒ 4. Branched-chain ketoacid dehydrogenase (valine, leucine, isoleucine, maple syrup dz)
48
Q

what test confirms diagnosis of vitB1 thiamine deficiency?

A

increased RBC transketolase activity after vitB1 administration

49
Q

Wernicke-Korsakoff syndrome is due to damage to mammillary bodies and _________

A

medial dorsal nucleus of thalamus

50
Q

facial flushing, hyperglycemia, and hyperuricemia are signs of toxicity of what vitamin?

A

B3. niacin.

51
Q

Dermatitis, enteritis, alopecia, adrenal insufficiency.

are signs of deficiency of what vitamin?

A

vit B5 pantothenic acid

note: alopecia is also sign of vit A EXCESS

52
Q

vit B3 niacin is derived from ______. thus, Hartnup dz can lead to pellagra b/c ________

A

tryptophan

Hartnup dz is missing neutral amino acid transporters (tryptophan is neutral)

53
Q

which rx in TCA ccle is vit B2 (riboflavin) a cofactor for?

A 
succinate dehydrogenase (requires FAD which riboflavin is used to make)
the rxn is succinyl - > fumarate
54
Q

Converted to pyridoxal phosphate (PLP), a cofactor used in transamination (eg, ALT and AST), decarboxylation reactions, glycogen phosphorylase. Synthesis of cystathionine, heme, niacin, histamine, and neurotransmitters including serotonin, epinephrine, norepinephrine (NE), dopamine, and GABA.

is function of what vitamin?

A

B6 pyridoxine

55
Q

avidin in egg whites binds _______

sx of deficiency:

A

B7 biotin

dermatitis, alopecia, enteritis

56
Q

how does vitC facilitate iron absorption?

A

reduces it to Fe2+ state (can also be used as ancillary tx for methemoglobinemia

57
Q

which skin layer forms D3 cholecalciferol

A

stratum basale

58
Q

Hemolytic anemia, acanthocytosis, muscle weakness, posterior column and spinocerebellar tract demyelination.

signs of deficiency of what vitamin?

A

vit E

looks like B12 deficieny but is hemolytic anemia, not megaloblastic. also b12 def has increased serum methylmalonic acid

59
Q

S/Sx of Kwashiorkor dz (protein malnutrition): MEALS

A 
Malnutrition
Edema
Anemia
Liver (fatty_
Skin lesions (hyperkeratosis, dyspigmentation)
60
Q

Fomepizole inhibits ____(enzyme). use?

A

alcohol dehydrogenase

antidote for alcohol OD

61
Q

disulfiram inhibits _______ enzyme

A

acetaldehyde dehydrogenase

62
Q

where in cell does ketogenesis and acetyl-coA production occur?

A

mitochondria

63
Q

where in cell does HMP shunt, steroid synthesis, and synthesis of a lot of other things happen?

A

cytoplasm

64
Q

which vitamin is essential compononent for coenzyme A (coA) and fatty acid synthase?

A

vit B5 pantothenic acid

65
Q

hexokinase vs glucokinase:

  1. which one is mostly in liver and beta cells of pancreas?
  2. which one has higher Km aka lower affinity, but higher Vmax aka capacity for substrate?
  3. which one is NOT feedback inhibited by G6P?
  4. which one induced by insulin?
A

all glucokinase

66
Q

essential fructosuria is defect in _____ enyzyme,
where as hereditary fructose intolerance is deficiency of _______ enzyme, so _______ accumulates

tx?

A

essential fructosuria is defect in fructokinase enyzyme. benign.

hereditary fructose intolerance is deficiency of aldolase B -> fructose 1 phosphate accumulates. decreased availabel phosphate - > inhibition of glycogenolysis and gluconeogenesis

tx is decrease intake of BOTH glucose and fructose,..

67
Q

infant has neuro defects, lactic acidosis, and in creased serum alanine. dx? tx?

A

pyruvate dehydrogenase complex deficiency

tx: increase intake of ketogenic nutrients (high fat content or lysine and leucine which are the purely ketogenic amino acids)

68
Q

FAB GUT mnemonic

A

Fructose is to
Aldolase B, as
Galactose is to
UridylTransferase

missing aldolase B -> fructose intolderance
missing G1P uridyltransferase -> classic galacosemia

69
Q

galactose appears in blood (galactosemia) and urine (galactosuria); infantile cataracts. May present as failure to track objects or to develop a social smile

dx? missing what enzyme?

A

galactokinase deficiency

70
Q

Symptoms develop when infant begins feeding (lactose present in breast milk and routine formula)
and include failure to thrive, jaundice, hepatomegaly, infantile cataracts, intellectual disability. Can
predispose to E coli sepsis in neonates.

dx? missing what enzyme? tx?

A

absent galactose-1-phosphate uridyltransferase

exclude galactose and lactose (galactose + glucose) from diet

71
Q

PKU pts must avoid _______, an artificial sweetener that contains phenylalanine

A

aspartame

72
Q

PKU is missing _____ OR ________

tx? (increase intake of what?)

A

phenylalanine hydroxylase or BH4 (tetrahydrobiopterin) cofactor

tx is decreased phenylalanine and increased tyrosine + BH4 supplementation

73
Q

bluish-black connective tissue, ear cartilage, and sclerae (ochronosis); urine turns black on prolonged exposure to air. May have debilitating arthralgias (homogentisic acid toxic to cartilage)

dx? pathogenesis?

A

Alkaptonuria:
deficiency of homogentisate oxidase in the degradative pathway of tyrosine to fumarate pigment-forming homogentisic acid accumulates in tissue

aka improper tyrosine degradation

74
Q

presentation of homocystinuria: HOMOCYstinuria

A 
Homocysteine in urine,
Osteoporosis,
Marfanoid habitus, 
Ocular changes (downward and inward
lens subluxation), 
Cardiovascular effects (thrombosis and atherosclerosis stroke
and MI), 
kYphosis,

bonus: intellectual disability

75
Q

kid has cystinuria (hexagonal cystine stones). this is b/c of a hereditary defect in renal PCT and intestinal aminoa acid transporter that prevents reabsorption of _____

A 
COLA
Cystine
Ornithine
Lysine
Arginine
76
Q

diagnostic test for cystinuria

A

urinary cyanide nitroprusside test

77
Q 
glycogen storage dz:
increased glycogen in liver, hepatomegaly
increased uric acid -> gout
increased blood lactate and TAGs
severe fasting hypoglycemia

what enzyme is deficient?

A

glucose 6 phosphatase

78
Q

glycogen storage dz:
cardiomegaly, hypertrophic cardiomyopathy
hypotonia, exercise intolerance
early death

which enzyme is deficienty?

A

LYSOSOMAL acid alpha-1,4-glucosidase, alpha-1,6-glucosidase (acid maltase)

79
Q

glycogen storage dz:
milder form of type 1 (hepatomegaly, gout, etc)

what enzyme deficient?
accumulation of what structures in cytosol?

A

deficient in debranching enzyme alpha-1,6-glucosidase
GLUCONEOGENESIS IS INTACT

limit dextrin-like structures in cytosol

80
Q

glycogen storage dz:
painful muscle cramps, myoglobinuria (red urine) with exercise

2nd win phenomenon due to increase blood flow to muscles

which enzyme deficient?
are blood glucose levels high low or normal?

A

skeletal muscle glycogen phsophorylase aka myophosphorylase

blood glucose levels typically unaffected

81
Q 
lysosomal storage disorder:
progressive neurodegeneration, developmental delay
lysosomes with onion skin
cherry red macula
NO hepatosplenomegaly

deficient enzyme?
accumulated substrate?

A

Tay Sach’s

heoxsaminidase A enzyme deficient
GM2 ganglioside accumulates

82
Q

all the lysosomal storage dz are autusomal recessive except

A

fabry dz (x-linked recessive)

83
Q

fanconi anemia has what signs/sx besides aplastic anemia? what is pathogenesis?

A

problem is DNA repair defect causing bone marrow failure

incidence of tumors/leukemia, café-au-lait spots, thumb/radial defects

84
Q

lysosomal storage disorder:

deficient enzyme?
accumulated substrate?

A

Fabry dz

85
Q

lysosomal storage disorder:

deficient enzyme?
accumulated substrate?

A

metachromatic leukodystrophy

86
Q

lysosomal storage disorder:

deficient enzyme?
accumulated substrate?

A

Krabbe

87
Q

lysosomal storage disorder:

deficient enzyme?
accumulated substrate?

A

Gaucher

88
Q

lysosomal storage disorder:

deficient enzyme?
accumulated substrate?

A

Neimann Pick

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