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USMLE Step 1 > BIOCHEMISTRY > Flashcards

BIOCHEMISTRY Flashcards

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USMLE® Step 1 flashcards
1
Q

Chromatin Structure to fit into the nucleus

A

Beads on a string. Histone octamer to form a nucleosome

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2
Q

Gives positive and negative charges to DNA respectively

A

Phosphate (-) and Lysine and Arginine (+)

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3
Q

Does mitochondria utilize histones?

A

No. They have their own which is circular

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4
Q

Condensed, Transcriptionally inactive

A

Heterochromatin

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5
Q

Example of heterochromatin

A

Barr Bodies

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6
Q

Phase where DNA and histone synthesis occur?

A

S phase

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7
Q

Less condensed chromatin, transcriptionally active, sterically accessible

A

Euchromatin

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8
Q

Changes the expression of DNA segment without changing the sequence. Involved in genomic imprinting, x-chromosome inactivation, repression of transposable elements, aging, and carcinogenesis

A

DNA methylation

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9
Q

Within what gene promoter region does methylation repress gene transcription?

A

CpG

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10
Q

Usually causes reversible transcriptional suppression, but can also cause activation depending on location of methyl groups.

A

Histone methylation. (Histone Methylation Mostly Makes DNA Mute.

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11
Q

Allows transcription and relaxes DNA coiling.

A

Histone Acetylation

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12
Q

Components of nucleoside

A

Base + Deoxyribose (sugar)

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13
Q

Components of Nucleotide

A

Base + Deoxyribose + phosphate

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14
Q

Linkage of both nucleoside and nucleotide

A

3’-5’ phosphodiester bond

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15
Q

Number of rings for purine and pyrimidine respectively

A

2 and 1

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16
Q

Deamination of cytosine will form?

A

Uracil

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17
Q

Deamination of adenine will form?

A

Hypoxanthine

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18
Q

Deamination of guanine will form?

A

Xanthine

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19
Q

Deamination of 5-methylcytosine will form?

A

Thymine

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20
Q

Methylation of uracil makes what?

A

Thymine

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21
Q

Of the two base pair bonds, A-T and G-C, which is stronger?

A

G-C (3>2), higher G-C content, higher melting temperature of DNA.

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22
Q

Amino acids necessary for purine synthesis.

A

Glycine, Aspartate, Glutamine

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23
Q

Inhibits both purine and pyrimidine synthesis by inhibiting ribonucleotide reductase

A

Hydroxyurea

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24
Q

Inhibits purine synthesis by inhibiting de novo purine synthesis. Give its prodrug form also.

A

6-MP, 6-Mercaptourine (azathioprine)

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25
Q

Inhibit purine synthesis by inhibiting inosine monophosphate dehydrogenase.

A

Mycophenolate and ribavirin

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26
Q

Inhibits pyrimidine synthesis by inhibiting dihydroorotate dehydrogenase

A

Leflunomide

27
Q

Inhibits drihydrofolate reductase (lower deoxythymidine monophosphate/dTMP in humans, bacteria, and protozoa respectively

A

Methotrexate (MTX), Trimethoprim (TMP), pyrimethamine

28
Q

Where does CPS 1 usually occur?

A

Mitochondria (urea cycle)

29
Q

Where does CPS2 occur?

A

Cytosol

30
Q

Enzyme deficiency that is One of the major causes of autosomal recessive SCID. Higher dATP may cause lymphotoxicity.

A

Adenosine deaminase deficiency (ADA is required for degradation of adenosine and deoxyadenosine)

31
Q

Enzyme deficiency due to defective purine salvage due to absent HGPRT which converts hypoxanthine to IMP and guanine to GMP. Results in excess uric acid production and de novo purine synthesis. X-linked recessive

A

Lesch-Nyhan Syndrome

32
Q

Common findings of Lesch-Nyhan Syndrome

A 
Hyperuricemia
Gout
Pissed off(aggression, self-mutilation)
Retardation (intellectual disability)
Dystonia
33
Q

Clinical feature of hyperuricemia in the laboratory

A

Orange sand (sodium urate crystals) in diaper

34
Q

Treatment for Lesch-Nyhan Syndrome

A

Allopurinol or febuxostat

35
Q

Genetic code feature where each codon specifies only 1 amino acid

A

Unambiguous

36
Q

Genetic code feature where most amino acids are coded by multiple codons.

A

Degenerate/redundant

37
Q

Codons that differ in 3rd position may code for the same tRNA/amino acid. Specific base pairing is usually required only in the first 2 nucleotide positions of mRNA codon

A

Wobble/Wobble theory

38
Q

Genetic code feature where the DNA is read from a fixed starting point as a continuous sequence of bases

A

Commaless, nonoverlapping (except in some viruses)

39
Q

Genetic code features where the genetic code is conserved throughout evolution (except in humans-mitochondria)

A

Universal

40
Q

Semiconservative, involves both continuous and discontinuous (Okazaki fragments) synthesis and occurs in 5’-3’ direction

A

Eukaryotic DNA replication

41
Q

Particular consensus sequence of base pairs in genome where DNA replication begins. May be single (prokaryotes) or multiple (eukaryotes)

A

Origin of replication

42
Q

Found in promotors and origins of replication

A

AT-rich sequences (TATA box regions)

43
Q

Y-shaped region along DNA template where leading and lagging strands are synthesized

A

Replication form

44
Q

Unwinds DNA template at replication fork

A

Helicase

45
Q

Prevents strands from reannealing

A

Single-stranded binding proteins

46
Q

Create a single- or double-stranded break in the helix to add or remove supercoils

A

DNA topoisomerase

47
Q

Makes an RNA primer on which DNA polymerase III can initiate replication

A

Primase

48
Q

In eukaryotes: _________ inhibit topoisomerase I, while _______ inhibit topoisomerase II

A

Irinotecan/topotecan

Etoposide/teniposide

49
Q

In prokaryotes, _______ inhibit TOP II (DNA gyrase) and TOP IV

A

Fluoroquinolones

50
Q

Used by prokaryotes only. Elongates leading strand by adding deoxynucleotides to the 3’ end. Elongates lagging strand until it reaches primer of preceding fragment

A

DNA polymerase III

51
Q

Proofreads each added nucleotide

A

3’-5’ exonuclease

52
Q

Drugs blocking DNA replication often have a _______ thereby preventing addition of the next nucleotide (“chain termination”h

A

Modified 3’OH

53
Q

Prokaryotic only. Degrades RNA primer; replaces it with DNA. Same functions as DNA polymerase III, also excises RNA primer with 5’-3’ exonuclease

A

DNA polymerase I

54
Q

Catalyzes the formation of a phosphodiester bond within a strand of double-stranded DNA (joins Okazaki fragments)

A

DNA ligase

55
Q

Eukaryotes only. A reverse transcriptase (RNA-dependent DNA polymerase) that adds DNA TO 3’ ends of chromosomes to avoid loss of genetic material with every duplication

A

Telomerase

56
Q

Sequence of telomerase

A

TTAGGG

57
Q

Purine-purine or pyrimidine-pyrimidine

A

Transition

58
Q

Purine-pyrimidine or pyrimidine-purine

A

Transversion

59
Q

Nucleotide substitution but codes for same/synonymous amino acid; often base change in 3rd position of codon (tRNA wobble)

A

Silent Mutation

60
Q

Nucleotide substitution resulting in changed amino acid (conservative if new amino acid is similar in chemical structure). Ex. Sickle cell disease (substitution of glutamic acid with valine)

A

Missense mutation

61
Q

Nucleotide substitution resulting in early stop codon (UAA, UAG, UGA). Usually results in non-functional protein

A

Nonsense mutation

62
Q

Deletion or insertion of a number of a number of nucleotides not divisible by 3, resulting in misreading of all nucleotides downstream. Function may be disrupted or altered. Ex. (Duchenne muscular dystrophy, Tay-Sachs disease)

A

Frameshift mutation

63
Q

Retained intron in the mRNA; protein with impaired or altered function. Rare cause of cancers, dementia, epilepsy, some types of B-thalassemia

A

Splice site mutation

64
Q

Classic example of genetic response to an environmental change. Seen in the activity of E.coli in culture. Low glucose-high adenylate cyclase activity-high generation of cAMP from ATP- activation of catabolite activator protein (CAP)- increased transcription. High lactose-unbinds repressor protein from repressor/operator site-increased transcription

A

Lac operon gene activation

USMLE Step 1 (1 decks)

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