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Biochemistry USMLE > Biochemistry > Flashcards

Biochemistry Flashcards

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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
What is the difference between the leading and lagging strand in replication
Lagging strand goes in the opposite direction of the replication fork. Requires okazaki fragments.
26
What function do the following have in replication? - Helicase - Single stranded DNA binding protein - Primase - Ligase - Topoisomerase (Gyrase)
- 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.
27
What causes thymine dimers, and which disease is associated to its enzyme deficiency?
``` UV radiation. Xeroderma pigmentosum (Excision endonuclease) - UV sensitivity - Freckling - Skin cancer - Corneal ulceration. ```
28
If there is a problem in the Mismatched base DNA repair what disease is present?
Lynch Syndrome, Hereditary nonpoliposis colorectal cancer | hMSH2 and hMLH1
29
p53 tumor suppresor gene Stops cell to enter S phase, its mutation is associated to:
Li fraumeni syndrome and solid tumors.
30
Retinoblastima gene caracteristics
Tumor suppresor, stops cell cycle and S phase. | Bind to transcription factor. E2F
31
Causes of DNA damage that require DNA repair
Thymine dimers Mismatch base Cytosine deamination
32
Caracteristics of the telomerase
1- Present in stem , germ embryonic and tumor cells 2. Has a RNA template 3. telomerase reverse transcriptase activity.
33
Which is the most abundant RNA type?
Ribosomal RNA
34
Is the promoter region transcribed?
No. | Transcription initiates at the +1 site.
35
Eat a mushroom found outside con kill you because
It has alfa amanitin, that stops the RNA polymerase
36
What drugs inhibit the prokaryotic RNA polymerase
Rifampin (TBC/meningitis profilaxis) Orange color change | Actinomycin D
37
Caracteristics of the transcription unit in prokaryote
Prokaryote: 1. Polycistronic (more than 1 gene) 2. NO introns 3. Coupled with translation 4. Shine Dalgarno sequences
38
Caracteristics of the transcription unit in eukaryotic
1. Monocistronic 2. Maturation: Capping, Splicing, Poly Adenylation 3. No coupling.
39
mRNA maturation process
1. Cap in 5´ end (7-methylguanosine) 2. Splicing: spliceosome = snRNA + snRNPs 3. Poly A: AAAA in the 3´ end
40
How can a cell produce different types of proteins from 1 single gene?
Alternative splicing. | hnRNA is a pre mRNA, before being spliced.
41
Prokaryote ribosome subunits:
70s unit 50s + 30 s subunits. 16s recognizes the shine dalgarno sequence
42
Eukaryotic ribosome subunits:
80s unit 60s + 40s subunits 18s recognizes 7methylguanosine
43
Components of the promoter region for transcription?
TATA box CAAT box Some transcription factors
44
Shiga toxin action
Cleaves ribosomal RNA in the 60s subunit, stopping protein synthesis.
45
Start and Stop codons?
AUG start Methyonine | UAG, UGA, UAA stop
46
What is a silent mutation?
Single nucleotide change, that doesnt change the aminoacid. The protein is normal. Example: Normal UUA = Leu Mutation: UUG = Leu
47
What is a missense mutation? | Biggest example
One nucleotide change in the gene, a different aminoacid. | - Sickle cell anemia: Glu to Valine.
48
What is a nonsense mutation?
Nucleotide change to a stop codon, short and truncated protein. Not common, incompatable with life.
49
Wht is a frameshift mutation? | Disease example:
There is a deletion of nucleotides. Incorrect aminoacids downstream. Duchenne Muscular dystrophy
50
Alfa thalassemia is related to what kind of mutation
Large segmental deletion. Unequeal crossover in meiosis.
51
Triplet repeat expansion diseases. | Name 5.
``` Huntington corea (CAG) Fragile X syndrome Myotonic dystrophy Friedrich Ataxia Spinobulbar muscular atrophy ``` Remember anticipation phenomenon.
52
B thalassemia, Tay Sachs and Gaucher are related to what kind of mutation?
Splice site mutation.
53
What is activation of aminoacyl tRNA. | What enzyme is involved
Adding an aminoacid to the 3´ end of the tRNA | Aminoacyl tRNA synthetase
54
antimicrobialthat e bind to the 30s subunit, inhibiting the recognition of the shine dalgarno sequence. What side effects?
Aminoglycosides. | Ototoxicity / Nefrotoxicity
55
Phases in elongation during translation of proteins
1. Aminoacyl tRNA binds to a site 2. peptide bond forms (peptidil transferase) 3. Traslocation of the ribosome 3 unit downstream.
56
Anitbioticos that act in translation elongation?
1. Tetracycline: 30s subunit 2. Cloramphnicol 50s peptidil trasnferase. (Grey baby syndrome , aplasic anemia) 3. Macrolides/clindamycin 50s.
57
Inhibitor of protein synthesis?
30s : aminoglycoside / tetracycline. | 50s : macrolides / chloranfenicol.
58
What enzyme is mutated in Tay sachs disease? | What type of mutation causes it?
Hexosaminidase A. | Splice site mutation.
59
What accumulates in Tay Sachs disease?
GM2 ganglioside
60
Type 2A hyperlipidemia, mutation type and molecule affected
Splice site mutation | LDL receptor
61
What does de the prokayotic ribosome recognize in the mRNA to initiate translation
Shine dalgarno sequence
62
What does the eukaryotic ribosome recognize in the mRNA to initiate translation
7 methylguanosine cap.
63
Example of proteins that undergo alternative splicing?
1. Inmunoglobulins bound to the membrane vs Ig secreted 2. Tropomyosin and troponin 3. Dopamine receptors.
64
Where can I have modified bases? Why do they have them?
In tRNA.
65
What is there on the 3´ end of tRNAm | What sequence is there?
The aminoacid is bound with a covalent bond. | 5´ CCA 3´
66
whwy is the genetic code considered degenerate/redundant?
Multiple codons for a single aminoacid.
67
Nonsense mutation example
Hemophilia. | Factor VIII deficiency.
68
Cystic Fibrosis is caused by what kind of mutation.
3 nucleotide deletion, without frameshift. | delta F508. CFTR
69
What is peptidyl tranferase and what does it do?
Its a ribozyme. | Make peptide bonds.
70
In translation, why is elongation factor 2 (eEF-2) important?
It can be inihibtied by ADP ribosylation pseudomonas and diphteria toxin
71
Binds tot he 50s subunut and inhibits initiation of translation
Linezolid.
72
TOXINs mechanism of action
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
How does the cell destory missfolded proteins?
1. Poliubiquitination of the protein | 2. Directed to the proteosome.
74
If the ribosome is related to the RER, what kind of proteins are being made
Secreted proteins Membrane Bound proteines Lisosomal enzymes
75
What signal makes the proteins be directed to the RER, what molecule recognizes it?
A hydrofobic aminoacido signal sequence in the N terminal. | SRP signal recognition particle
76
What is attached to the protein while being made in the R.E. reticulum
N-glycosilation | Asparagine
77
Which proteins are in the bloodstream and DONT are not Glycosilated?
Albumin Insulin Glucagon
78
In protein synthesis, what happens in the golgi.
Postranslational modification: | O linked glycosilation
79
How are proteins destined to the lysosomes?
Phosphorilation of mannose by the enzyme Phosphotrasnferase.
80
Phosphotransferase mutation. | Hallmark of the disease:
I cell disease. Lysosomal enzyme are secreted. - Generalized inflammation. - Big lysosomes
81
Osteogenesis imperfecta
- Mutation in collegen type 1. - Blue sclera - skeletal defrmities and fractures.
82
What role does vitamin C have in the production of collagen?
The hydroxilation of proline and lysine is Vit C dependent.
83
Lysyl oxidase function in collagen formation
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
Menckes disease
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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