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USMLE Biochemistry > Molecular > Flashcards

Molecular Flashcards

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USMLE® Step 1 flashcards
1
Q

Why does DNA exists in the chromatin form?

A

To fit in the nucleus

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2
Q

What does the chromatin structure look like?

A

Negatively charged DNA loops twice around the positively charged histone octomer to form a nucleosome bead

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3
Q

What amino acids are chromatin rich in?

A

Lysine and arginine

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4
Q

What does H1 part of chromatin do?

A

It binds to the nucleosome and to a linker DNA stabilizing the chromatin fiber

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5
Q

Which histone is not in the nucleosome core?

A

H1

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6
Q

When does DNA and histone synthesis occur in miosis?

A

S phase

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7
Q

What is heterochromatin?

A

Condensed, transcriptionally inactive, sterically inaccessible

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8
Q

What is euchromatin?

A

Less condensed, transcriptionally active, sterically accessible

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9
Q

What is DNA methylation?

A

Template strande cytosine and adenine are methylated in DNA replcation allowing for mismatch reapair enzymes to distinguish between old and new strands

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10
Q

What to CPG islands do?

A

Repress transcription

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11
Q

What is histone methylation?

A

Usually reversibly repressing DNA transcription but can activate sometimes

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12
Q

What is histone acetylation

A

Relaxes DNA coiling, allowing for transcription

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13
Q

What are the nucleotide purines?

A

A and G

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14
Q

What are the nucleotide pyrimidines?

A

C, U, and T

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15
Q

Which nucleotide has a methyl group?

A

Thymine

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16
Q

Which nucleotide is exclusive to RNA?

A

Uracil

17
Q

Which nucleotide is exclusive to DNA?

A

Thymine

18
Q

How many H bonds does a G-C bond have?

A

3

19
Q

How many H bonds does an A-T bond have

A

2

20
Q

What are the amino acids needed for purine synthesis?

A

Glycine, Aspartate and Glutamine

21
Q

What is a nucleoside?

A

Base + deoxyribose

22
Q

What is a nucleotide?

A

Base + deoxyribose + phosphate

Linked by 3’-5’ phosphodiester bond

23
Q

What is adenosine deaminase deficiency?

A

Excess ATP and dATP imbalances nucleotide pool via feedback inhibition of ribonucleotide reducatase which prevents DNA synthesis and thus decreases lymphocyte count
A major cause of autosomal recessive SCID

24
Q

What is Lesch-Nyhan syndrome?

A

Defective purine salvage due to HGPRT
Results in excess uric acid production and de novo purine synthesis
X-linked recessive

25
Q

What does HGPRT do?

A

Converts hypoxanthine to IMP and guanine to GMP

26
Q

What are the findings of Lesch-Nyhan sydrome?

A

Intellectual disability, self-mutilation, aggression, hyperuricemia, gout, and dystonia

27
Q

What is the treatment for Lesch-Nyhan syndrome?

A

Allopurinol or febuxostat (2nd line)

28
Q

What does an unambiguous genetic code feature mean?

A

Each codon specifics only 1 amino acid

29
Q

What does a degenerate/redundant genetic code feature mean?

A 
Most amino acids are coded by multiple codons
except methionine (AUG) and tryptophan (UGG)
30
Q

What does a commaless or nonoverlapping genetic code feature mean?

A

Read from a fixed starting point as a continuous sequence of bases
except some viruses

31
Q

What does a universal genetic code feature mean?

A

Genetic code is conserved through evolution except in mitochondria

32
Q

Describe the process of DNA replication (prokaryotes and eukaryotes);

A

Semiconservative and involves both continuous and discontinuous synthesis

33
Q

What is the origin of replication?

A

A particular consensus sequence of base pairs in genome where DNA replication begins
May be single (prokar) or multiple (eukar)

34
Q

What is a replication fork?

A

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

35
Q

What is the action of helicase?

A

Unwinds DNA template at the replication fork

USMLE Biochemistry (1 decks)

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