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Biochemistry USMLE > Biochemistry > Flashcards

Biochemistry Flashcards

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USMLE® Step 1 flashcards
1
Q

In which cell cycle phase ocurrs replication

A

S phase

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2
Q

In which phase of the cell cycle ocurrs trancription and translation

A

Interphase = G0 - G1- - S - G2

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3
Q

What cell cycle phase does methrotrexate target, and how does it work?

A

S phase

Dihydrofolate reductase

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4
Q

Vincristine, vinblistine, Paclitaxel target what cell cycle phase?

A

M phase, mitosis.

Prevent the microtubular assembly.

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5
Q

Where in the cell does transcription occur ?

A

In the nucleus during interphase

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6
Q

Where does translation ocurr in the cell?

A

Cytoplasm

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7
Q

Which are the Purines?

A

Adenine, Guanine

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8
Q

Which are the pyrimidine?

A

Cytosine, Uracil, Thymine

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9
Q

Whats the difference between Adenine and guanine, and what enzyme participates in the process.

A

Adenine is Deaminated to guanine

ADA = Adenosine deaminase

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10
Q

How do I get a thymine from a Uracil?

A

Metilation of uracil, enzyme: Thymidylate synthase

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11
Q

Chargaffs rule is?

A

In a double stranded DNA the

Amount of A = T and amount of C = G

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12
Q

Which bonds link between the nitrogen bases in the DNA strand?
How many do A-T have and C-G

A

Hydrogen Bonds
A- T has 2
C-G has 3

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13
Q

How is the sequence of a DNA conventionaly read?

A

From 5´ phosphate to 3´ hydroxyl

Asume its the coding sequence.

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14
Q

How con DNA be denaturated

A

Heat, pH, Urea, Formamide

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15
Q

What is a nucleosome made of?

A

DNA + histone octamer

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16
Q

Which are the histones that compose the octamer?

A

H2a H2b H3 H4 x2

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17
Q

Histones are positivly charged because they are rich in positive charged aminoacids which are:

A

In histones: Rich in Arginine, Lysine

Histidine is positive charge, not common in histones

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18
Q

What does the H1 histone do?

A

Helps pack the DNA to a 30nm nucelofilament

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19
Q

What does DNA methylation do?

A

Inactivates DNA (heterochromatin)

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20
Q

What does Histone acetylation / phosphorylation do?

A

Actives DNA (euchromatin)

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21
Q

Which cells have telomerase activity

A

Germ cells, stem cells, and tumor cells (activity stimulated)

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22
Q

Prokaryotic and eukaryotic replication caracteristics?

A

Prokaryots

  1. Only one origin of replication
  2. Creates a circular DNA

Eukaryotic:

  1. Mulitple origins
  2. Creates sister chromatids.
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23
Q

In replication, the enzyme used is DNA polymerase.

what does DNA polymerase need to initiate replication?

A

An RNA primer

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24
Q

Which polymerase have proofread actiity

A

DNA polymerase in replication.

Exonuclease 3´ - 5´ activity.

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25
Q

What is the difference between the leading and lagging strand in replication

A

Lagging strand goes in the opposite direction of the replication fork. Requires okazaki fragments.

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26
Q

What function do the following have in replication?

  • Helicase
  • Single stranded DNA binding protein
  • Primase
  • Ligase
  • Topoisomerase (Gyrase)
A
  • Helicase: separates the dsDNA
  • SSB: prevent degradation
  • Primase: RNA primer to start polymerase activity
  • Ligase: connects the fragements at the end.
  • Topoisomerase II: relaxes the DNA in front of the replication fork.
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27
Q

What causes thymine dimers, and which disease is associated to its enzyme deficiency?

A 
UV radiation. 
Xeroderma pigmentosum (Excision endonuclease)
- UV sensitivity
- Freckling
- Skin cancer
- Corneal ulceration.
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28
Q

If there is a problem in the Mismatched base DNA repair what disease is present?

A

Lynch Syndrome, Hereditary nonpoliposis colorectal cancer

hMSH2 and hMLH1

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29
Q

p53 tumor suppresor gene Stops cell to enter S phase, its mutation is associated to:

A

Li fraumeni syndrome and solid tumors.

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30
Q

Retinoblastima gene caracteristics

A

Tumor suppresor, stops cell cycle and S phase.

Bind to transcription factor. E2F

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31
Q

Causes of DNA damage that require DNA repair

A

Thymine dimers
Mismatch base
Cytosine deamination

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32
Q

Caracteristics of the telomerase

A

1- Present in stem , germ embryonic and tumor cells

  1. Has a RNA template
  2. telomerase reverse transcriptase activity.
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33
Q

Which is the most abundant RNA type?

A

Ribosomal RNA

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34
Q

Is the promoter region transcribed?

A

No.

Transcription initiates at the +1 site.

35
Q

Eat a mushroom found outside con kill you because

A

It has alfa amanitin, that stops the RNA polymerase

36
Q

What drugs inhibit the prokaryotic RNA polymerase

A

Rifampin (TBC/meningitis profilaxis) Orange color change

Actinomycin D

37
Q

Caracteristics of the transcription unit in prokaryote

A

Prokaryote:

  1. Polycistronic (more than 1 gene)
  2. NO introns
  3. Coupled with translation
  4. Shine Dalgarno sequences
38
Q

Caracteristics of the transcription unit in eukaryotic

A
  1. Monocistronic
  2. Maturation: Capping, Splicing, Poly Adenylation
  3. No coupling.
39
Q

mRNA maturation process

A
  1. Cap in 5´ end (7-methylguanosine)
  2. Splicing: spliceosome = snRNA + snRNPs
  3. Poly A: AAAA in the 3´ end
40
Q

How can a cell produce different types of proteins from 1 single gene?

A

Alternative splicing.

hnRNA is a pre mRNA, before being spliced.

41
Q

Prokaryote ribosome subunits:

A

70s unit
50s + 30 s subunits.
16s recognizes the shine dalgarno sequence

42
Q

Eukaryotic ribosome subunits:

A

80s unit
60s + 40s subunits

18s recognizes 7methylguanosine

43
Q

Components of the promoter region for transcription?

A

TATA box
CAAT box
Some transcription factors

44
Q

Shiga toxin action

A

Cleaves ribosomal RNA in the 60s subunit, stopping protein synthesis.

45
Q

Start and Stop codons?

A

AUG start Methyonine

UAG, UGA, UAA stop

46
Q

What is a silent mutation?

A

Single nucleotide change, that doesnt change the aminoacid.
The protein is normal.
Example:
Normal UUA = Leu Mutation: UUG = Leu

47
Q

What is a missense mutation?

Biggest example

A

One nucleotide change in the gene, a different aminoacid.

- Sickle cell anemia: Glu to Valine.

48
Q

What is a nonsense mutation?

A

Nucleotide change to a stop codon, short and truncated protein.
Not common, incompatable with life.

49
Q

Wht is a frameshift mutation?

Disease example:

A

There is a deletion of nucleotides.
Incorrect aminoacids downstream.
Duchenne Muscular dystrophy

50
Q

Alfa thalassemia is related to what kind of mutation

A

Large segmental deletion. Unequeal crossover in meiosis.

51
Q

Triplet repeat expansion diseases.

Name 5.

A 
Huntington corea  (CAG)
Fragile X syndrome 
Myotonic dystrophy
Friedrich Ataxia
Spinobulbar muscular atrophy

Remember anticipation phenomenon.

52
Q

B thalassemia, Tay Sachs and Gaucher are related to what kind of mutation?

A

Splice site mutation.

53
Q

What is activation of aminoacyl tRNA.

What enzyme is involved

A

Adding an aminoacid to the 3´ end of the tRNA

Aminoacyl tRNA synthetase

54
Q

antimicrobialthat e bind to the 30s subunit, inhibiting the recognition of the shine dalgarno sequence.
What side effects?

A

Aminoglycosides.

Ototoxicity / Nefrotoxicity

55
Q

Phases in elongation during translation of proteins

A
  1. Aminoacyl tRNA binds to a site
  2. peptide bond forms (peptidil transferase)
  3. Traslocation of the ribosome 3 unit downstream.
56
Q

Anitbioticos that act in translation elongation?

A
  1. Tetracycline: 30s subunit
  2. Cloramphnicol 50s peptidil trasnferase. (Grey baby syndrome , aplasic anemia)
  3. Macrolides/clindamycin 50s.
57
Q

Inhibitor of protein synthesis?

A

30s : aminoglycoside / tetracycline.

50s : macrolides / chloranfenicol.

58
Q

What enzyme is mutated in Tay sachs disease?

What type of mutation causes it?

A

Hexosaminidase A.

Splice site mutation.

59
Q

What accumulates in Tay Sachs disease?

A

GM2 ganglioside

60
Q

Type 2A hyperlipidemia, mutation type and molecule affected

A

Splice site mutation

LDL receptor

61
Q

What does de the prokayotic ribosome recognize in the mRNA to initiate translation

A

Shine dalgarno sequence

62
Q

What does the eukaryotic ribosome recognize in the mRNA to initiate translation

A

7 methylguanosine cap.

63
Q

Example of proteins that undergo alternative splicing?

A
  1. Inmunoglobulins bound to the membrane vs Ig secreted
  2. Tropomyosin and troponin
  3. Dopamine receptors.
64
Q

Where can I have modified bases? Why do they have them?

A

In tRNA.

65
Q

What is there on the 3´ end of tRNAm

What sequence is there?

A

The aminoacid is bound with a covalent bond.

5´ CCA 3´

66
Q

whwy is the genetic code considered degenerate/redundant?

A

Multiple codons for a single aminoacid.

67
Q

Nonsense mutation example

A

Hemophilia.

Factor VIII deficiency.

68
Q

Cystic Fibrosis is caused by what kind of mutation.

A

3 nucleotide deletion, without frameshift.

delta F508. CFTR

69
Q

What is peptidyl tranferase and what does it do?

A

Its a ribozyme.

Make peptide bonds.

70
Q

In translation, why is elongation factor 2 (eEF-2) important?

A

It can be inihibtied by ADP ribosylation pseudomonas and diphteria toxin

71
Q

Binds tot he 50s subunut and inhibits initiation of translation

A

Linezolid.

72
Q

TOXINs mechanism of action

A
  1. Search for NAD in the cell.
  2. The cut of the NIACIN of NAD, remaining ADP-Ribose
  3. Then they Add ADP-ribose to the G PROTEIN they target.
  4. This inactivates the G PROTEIN.
73
Q

How does the cell destory missfolded proteins?

A
  1. Poliubiquitination of the protein

2. Directed to the proteosome.

74
Q

If the ribosome is related to the RER, what kind of proteins are being made

A

Secreted proteins
Membrane Bound proteines
Lisosomal enzymes

75
Q

What signal makes the proteins be directed to the RER, what molecule recognizes it?

A

A hydrofobic aminoacido signal sequence in the N terminal.

SRP signal recognition particle

76
Q

What is attached to the protein while being made in the R.E. reticulum

A

N-glycosilation

Asparagine

77
Q

Which proteins are in the bloodstream and DONT are not Glycosilated?

A

Albumin
Insulin
Glucagon

78
Q

In protein synthesis, what happens in the golgi.

A

Postranslational modification:

O linked glycosilation

79
Q

How are proteins destined to the lysosomes?

A

Phosphorilation of mannose by the enzyme Phosphotrasnferase.

80
Q

Phosphotransferase mutation.

Hallmark of the disease:

A

I cell disease. Lysosomal enzyme are secreted.

  • Generalized inflammation.
  • Big lysosomes
81
Q

Osteogenesis imperfecta

A
  • Mutation in collegen type 1.
  • Blue sclera
  • skeletal defrmities and fractures.
82
Q

What role does vitamin C have in the production of collagen?

A

The hydroxilation of proline and lysine is Vit C dependent.

83
Q

Lysyl oxidase function in collagen formation

A

The oxidation enables the formation of cross linked so the collagen fibrils can join and make the collagen fiber.
This requieres Cu (cooper) and O2.

84
Q

Menckes disease

A

x linked, proetin that absorbes copper. The deficiency of Cu
Limits the action of lysyl oxidase.
Impaired collagen fiber function.

Biochemistry USMLE (1 decks)

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