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Medical Biochemistry > Medical Genetics > Flashcards

Medical Genetics Flashcards

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USMLE® Step 1 flashcards
1
Q

How many hydrogen bonds are between each pair?

A

A-T: 2

C-G: 3

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2
Q

What are the major characteristics of B DNA?

A
  • Right handed twist
  • 2 Nm diameter
  • 0.34 Nanometers btwn base pairs
  • Each turn is 10 base pairs —> every 3.2 nm

*Human DNA

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3
Q

How does actinomyocin work?

A

Intercalating into the narrow groove of DNA double helix and interfering with synthesis of RNA

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4
Q

What is Theta replication?

A

Circular DNA (E. Coli) replication with a single origin and is bidirectional

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5
Q

Differentiate functions of the five polymerase enzymes.

A

DPIII - Performs DNA replication (Both 5-3/3-5)

DPI - Remove RNA primers Both 5-3/3-5 activity

DP II/IV/V - DNA repair

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6
Q

What is the primary function of Pol I?

A

Repair any damage with DNA and connect Okazaki fragments by deleting RNA primers and replacing with DNA

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7
Q

What are the four enzymatic activities of DPI?

A
  1. 5-3’ DNA-Dependant activity and require a 3’ primer site and template strand
  2. 3-5’ (Reverse) exonuclease which mediates proofreading
  3. 5-3’ exonuclease activity mediating nick translation during repair
  4. 5-3’ RNA-Dependant activity (Very limited due to low binding capacity)
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8
Q

What is the primary enzyme responsible for DNA replication?

A

DP III

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9
Q

What is the Klenow fragment?

A
  • Large protein produced when DPI from E. Coli is enzymatically cleaved
  • Retains activity of DPI except reverse exonuclease activity
  • Used for: Double strains synthesis from templates, Digesting away 3’ overhangs, Preparing radioactive DNA probes, and Filling in receded 3’ DNA ends to make 5’ overhang blunt
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10
Q

What is DnaA?

A

The initiator protein for DNA replication in E. Coli

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11
Q

What is DNA Gyrase?

A

A topoisomerase which binds to chromosome ahead of replication for and relieves tension

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12
Q

Differentiate the two types of topoisomerase.

A

TPI I: Relax negative supercoils in E. Coli; Pos/neg in other types of prok; No ATP Use; Create Nick III DNA and reseal

TPI II: Create transient breaks in both strands; Requires ATP; Introduce Net supercoils to relieve pos supercoils; Can fix neg and pos supercoils

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13
Q

What is Quinoline?

A
  • Antibiotic against gram-negative bacteria with minor gram positive activity
  • Inhibits subunit of DNA gyrase and TPI IV in bacteria
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14
Q

What is DnaG?

A

Primase- synthesizes short strands of RNA

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15
Q

What is the primosome?

A

The prepriming complex of proteins on the Okazaki fragments and Primase enzyme

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16
Q

What is the role of DNA Ligasee?

A
  • Join Okazaki fragments

- Joins DP I strand to DP III strand

17
Q

What are the two main differences in Eukaryotic and prokaryotic DNA replication?

A
  1. # ORCs (Euk have multiple sites vs 1)

2. # DNA polymerases (Bacteria have 5; Euk can have to to 13 different ones)

18
Q

What is the function of Telomerase?

A

Maintains length of Telomere in Euls

19
Q

What causes histones to be positive as physiological pH?

A

High amounts of Lysine and Arginine

20
Q

What is DNA Polymerase y?

A
  • Replicative polymerase in mitochondrial DNA
21
Q

What is most significant about Polymerase y?

A

It contains a 3’-5’ exonuclease domain which acts to proofread newly synthesized DNA strand

22
Q

Which enzymes initiates mtDNA termination?

A

DNA Ligase III

23
Q

What does the strand displacement model say?

A

MtDNA Replication is initiated at Theo distinct locations; OH and OL

24
Q

What make sup the non coding region of mtDNA?

A

HSP - Heavy strand promoter

LSP - Light strand promoter

3 conserved sequence boxes

H-strand OR

TAS - Termination associated sequence

25
Q

Where is the primer for Pol-y to begin synthesis at OH?

A

LSP

26
Q

What does OL do in mtDNA synthesis?

A

Forms a stem-loop

27
Q

What is the role of POLRMT in mtDNA synthesis?

A

Initiates primer synthesis from single stranded loop region

28
Q

Why is MtDNA more likely to mutate?

A
  • Reactive Oxidation f/ OXPHOS

- No DNA repair mechanism

29
Q

Describe pathology of MERRF.

A

Myoclonic eplepsy and ragged red fiber disease

  • Lack of muscular coordination (Myoclonus)
  • Secondary features: Dementia, peptic atrophy, deafness, lipomata
  • Ragged red fibers in skeletal muscle
  • History in maternal transmission
30
Q

Describe pathology of LHON

A
  • Fast, sudden, painless loss of vision in both eyes in late teens
  • LHON exhibit reduced penetrance; MEn have 40% and women have 10% chance of developing symptoms if they have mutation

Medical Biochemistry (26 decks)

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