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USMLE 1 > Biochemistry- Molecular > Flashcards

Biochemistry- Molecular Flashcards

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USMLE® Step 1 flashcards
1
Q

Heterochromatin

A

HeteroChromatin = Highly Condensed.

Barr bodies

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2
Q

Euchromatin

A

Eu = true, “truly transcribed.”

Euchromatin is Expressed

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3
Q

DNA methylation

A

CpG Methylation Makes DNA Mute.

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4
Q

Histone acetylation

A

Histone Acetylation makes DNA Active.

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5
Q

Purinas

A

PURines (A,G)—2 rings

PURe As Gold.

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6
Q

Pirimidinas

A

PYrimidines (C,U,T)—1 ring.

CUT the PY (pie).

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7
Q

NucleoSide

NucleoTide

A

base + (deoxy)ribose (Sugar).

base + (deoxy)ribose + phosphaTe;

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8
Q

Amino acids necessary for purine

synthesis:

A

GAG:
Glycine
Aspartate
Glutamine

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9
Q

Leflunomide

A

pyrimidine synthesis: inhibits dihydroorotate

dehydrogenase

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10
Q

Methotrexate (MTX), trimethoprim (TMP),

and pyrimethamine:

A

pyrimidine synthesis: inhibit dihydrofolate

reductase

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11
Q

5-fluorouracil (5-FU)

A

pyrimidine synthesis: inhibits thymidylate synthase

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12
Q

6-mercaptopurine (6-MP) and its prodrug

azathioprine:

A

inhibit de novo purine synthesis

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13
Q

Mycophenolate and ribavirin:

A

purine synthesis: inhibit inosine

monophosphate dehydrogenase

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14
Q

Hydroxyurea:

A

purine and pyrimidine synthesis: inhibits ribonucleotide

reductase

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15
Q

Adenosine deaminase

deficiency

A

dATP 􀁰 toxicity in lymphocytes. autosomal recessive

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16
Q

Lesch-Nyhan

syndrome

A 
Defective purine salvage due to absent HGPRT
HGPRT:
Hyperuricemia
Gout
Pissed off (aggression, self-mutilation)
Retardation (intellectual disability)
DysTonia
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17
Q

Lesch-Nyhan

syndrome Treatment

A

allopurinol or febuxostat (2nd line).

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18
Q

Most amino acids are coded by multiple codons, Exceptions:

A

methionine and tryptophan encoded

by only 1 codon (AUG and UGG

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19
Q

Genetic code features

A

Unambiguous
Degenerate/redundant
Commaless, nonoverlapping
Universal

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20
Q

DNA replication is

A

semiconservative, involves both continuous and discontinuous (Okazaki fragment) synthesis, and
occurs in the 5′ 􀁰 3′ direction

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21
Q

Origin of

replication A

A

AT-rich sequences (such as TATA box regions)
are found in promoters and origins of
replication.

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22
Q

Replication fork

A

Y-shaped region along DNA template where

leading and lagging strands are synthesized.

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23
Q

Helicase

A

Unwinds DNA template at replication fork.

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24
Q

Single-stranded

binding proteins

A

Prevent strands from reannealing.

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25
Q

DNA

topoisomerases

A

Create a single- or double-stranded break in the

helix to add or remove supercoils.

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26
Q

Irinotecan/topotecan
Etoposide/teniposide
Fluoroquinolones

A
  • inhibit eukaryotic topoisomerase I.
  • inhibit eukaryotic topoisomerase II.
  • inhibit prokaryotic topoisomerase II (DNA gyrase) and topoisomerase IV.
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27
Q

Primase

A

Makes an RNA primer on which DNA

polymerase III can initiate replication.

28
Q

DNA ligase

A

Joins Okazaki fragments

29
Q

Telomerase

A

Eukaryotes only. An RNA-dependent DNA
polymerase that adds DNA to 3′ ends of
chromosomes to avoid loss of genetic material
with every duplication.

30
Q

DNA polymerase III

A

DNA polymerase III has 5′ 􀁰 3′ synthesis and

proofreads with 3′ 􀁰 5′ exonuclease.

31
Q

DNA polymerase I

A

Same functions as DNA polymerase III, also

excises RNA primer with 5′ 􀁰 3′ exonuclease.

32
Q

Mutations in DNA

A

silent &laquo_space;missense < nonsense < frameshift.

33
Q

􀂃 Transition—

􀂃 Transversion—

A

purine to purine (eg, A to G) or pyrimidine to pyrimidine (eg, C to T).
purine to pyrimidine (eg, A to T) or pyrimidine to purine (eg, C to G).

34
Q

stop codon

A

(UAG, UAA, UGA)

35
Q

splice site mutation

A

is a genetic mutation that inserts, deletes or changes a number of nucleotides in the specific site at which splicing takes place during the processing of precursor messenger RNA into mature messenger RNA

36
Q

operón

A

una unidad genética funcional formada por un grupo o complejo de genes capaces de ejercer una regulación de su propia expresión por medio de los sustratos con los que interactúan las proteínas codificadas por sus genes.

37
Q

DNA repair

Single strand

A

Nucleotide excision repair
Base excision repair
Mismatch repair

38
Q

DNA repair

Double strand

A

Nonhomologous end joining

39
Q

Lynch syndrome

A

(hereditary nonpolyposis colorectal cancer [HNPCC]).

Mismatch repair is defective

40
Q

xeroderma pigmentosum

A

Defective Nucleotide excision repair prevents repair of pyrimidine dimers that are formed as a result of ultraviolet light exposure.

41
Q

Defect in ataxia telangiectasia, breast/ovarian
cancers with BRCA1 mutation, and Fanconi
anemia.

A

Nonhomologous end joining

42
Q

mRNA start codons

A

AUG inAUGurates protein synthesis. (methionine)

43
Q

mRNA stop codons

A 
UGA = U Go Away.
UAA = U Are Away.
UAG = U Are Gone.
44
Q

Promoter

A

Site where RNA polymerase II and multiple

other transcription factors bind to DNA

45
Q

Enhancer

A

Stretch of DNA that alters gene expression by

binding transcription factors

46
Q

Silencer

A

Site where negative regulators (repressors) bind.

47
Q

RNA polymerase I
RNA polymerase II
RNA polymerase III makes 5S rRNA, tRNA
(smallest RNA, tiny).

A 
makes rRNA (most numerous RNA, rampant).
makes mRNA (largest RNA, massive). mRNA is read 5′ to 3′.
makes 5S rRNA, tRNA (smallest RNA, tiny).
48
Q

I, II, and III

A

are numbered in the same order
that their products are used in protein
synthesis: rRNA, mRNA, then tRNA.

49
Q

Actinomycin D

A

inhibits RNA polymerase in

both prokaryotes and eukaryotes.

50
Q

α-amanitin, found in Amanita phalloides (death

cap mushrooms),

A

inhibits RNA polymerase II. severe hepatotoxicity if ingested.

51
Q

Capped, tailed, and spliced transcript is called…

A

mRNA.

52
Q

polyadenylation signal.

A

AAUAAA

53
Q

Splicing of pre-mRNA

A
  1. Primary transcript combines with (snRNPs) form spliceosome.
  2. Lariat-shaped (looped) intermediate is
    generated.
  3. Lariat is released to precisely remove intron
    and join 2 exons.
54
Q

Antibodies to spliceosomal snRNPs (anti-

Smith antibodies)

A

highly specific for SLE

55
Q

Anti-U1 RNP antibodies

A

highly associated with mixed connective tissue

disease (MCTD).

56
Q

Introns vs exons

A

Introns are intervening sequences and stay
in the nucleus, whereas exons exit and are
expressed.

57
Q

microRNAs

A

regulate gene expression by targeting the 3′ untranslated region of specific mRNAs for
degradation or translational repression

58
Q

tRNA T-arm:

A

contains the TΨC (ribothymidine, pseudouridine, cytidine. T-arm Tethers tRNA molecule to ribosome.

59
Q

tRNA D-arm:

A

contains dihydrouridine residues. D-arm Detects the tRNA by aminoacyl-tRNA synthetase.

60
Q

tRNA structure

A

Have CCA at 3′ end along. The amino acid is covalently bound to the 3′ end of the tRNA. CCA: Can Carry Amino acids

61
Q

Aminoacyl-tRNA synthetase

A

scrutinizes amino acid before and after it binds to tRNA. Is responsible for accuracy of amino acid selection.

62
Q

Elongation

A

Think of “going APE”:
A site = incoming Aminoacyl-tRNA.
P site = accommodates growing Peptide.
E site = holds Empty tRNA as it Exits.

63
Q

Ribosome
Eukaryotes:
PrOkaryotes:

A

40S + 60S 􀁰 80S (Even).

30S + 50S 􀁰 70S (Odd).

64
Q

30S + 50S 􀁰 70S (Odd).

A

Intracellular protein involved in facilitating and/or maintaining protein folding.

65
Q

Covalent alterations

A

Phosphorylation, glycosylation, hydroxylation, methylation, acetylation, and ubiquitination.

66
Q

wobble phenomenon.

A

different codons that can be created but they only code for 20 amino acids.

USMLE 1 (73 decks)

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