Exam #4 First Aid USMLE Flashcards Preview

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Flashcards in Exam #4 First Aid USMLE Deck (57):
1

H1

- Histone that binds to the nucleosome & linker DNA
- Only Histone not in the nucleosome core

2

When does DNA & Histone synthesis occur in the cell cycle?

S-phase

3

Nucleosome Core Histones

- H2A
- H2B
- H3
- H4

4

Heterochromatin

- Highly Condensed & Inactive
- Think HeteroChromatin, Highly Condensed

5

Euchromatin

- Less condensed, transcriptionally active, sterically accessible
- Think Eu= True, truly transcribed

6

DNA Methylation

- Methylation at CpG islands represses transcription
- Think Methylation Makes DNA Mute

7

Histone Acetylation

- Relaxes DNA coiling, allowing for transcription
- Think Acetylation makes DNA Active

8

What is the production of cytosine deamination?

Uracil

9

DNA Replication Characteristics

- Semiconservative
- Involves BOTH continuous & discontinuous synthesis

10

Origin of Replication

- Consensus sequence in genome where DNA replication begins
- Single in prokaryotes, Multiple in eukaryotes

11

Replication Fork

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

12

Helicase

Unwinds DNA

13

Single-stranded binding proteins

Prevents strands from reannealing

14

Topoisomerases

Create single or double strand break in helix to relieve supercoiling

15

Fluoroquinolones

Inhibit DNA gyrase i.e. prokaryotic topoisomerase II

16

Primase

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

17

DNA Ligase

- Catalyzes the formation of phosphodiester bonds within ds-DNA
- Seals or joins Okazaki fragments

18

Telomerase

RNA-dependent DNA polymerase that adds DNA to 3' ends of chromosomes to avoid loss of genetic material during replication

19

Silent Mutation

Nucleotide substitution codes for the same amino acid

20

Missense Mutation

- Nucleotide substitution results in different amino acid
- Sickle Cell Disease

21

Nonsense Mutation

- Nucleotide substitution results in an early STOP codon
- Think STOP the Nonsense

22

Frameshift Mutation

- Insertion or deletion of nucleotides not divisible by 3 causing a misreading of DNA downstream
- Duchenne Muscular Dystrophy

23

Nucleotide Excision Repair

- Repairs bulky helex distorting lesions e.g. pyrimidine dimers from UV exposure
- Endonucleases release an oligonucleotide containing damaged bases
- DNA polymerase & ligase fill and reseal the gap

24

Xeroderma Pigementosum

Defective Nucleotide Excision Repair

25

Base Excision Repair

- Important repair for spontaneous/ toxic deamination
- Base-specific glyocsylase recognizes altered base & creates AP site
- AP-endonuclease & Lyase cleave
- DNA polymerase fills in the gap & Ligase seals it

26

Mismatch Repair

- Newly synthesized DNA strand is recognized
- Mismatched nucleotides are removed
- Gap is filled & resealed

27

HNPCC

Defective Mismatch Repair

28

Nonhomologous End Joining

- Brings together 2 ends of DNA fragments to repair ds-DNA breaks

29

Ataxia Telangiectasia

Nonhomologous End Joining

30

DNA & RNA Synthesis

- 5'-->3'
- 5' end of incoming nucleotide bears triphosphate energy source

31

Protein Synthesis

N-terminus to C-terminus

32

mRNA START Codon

- AUG
- Think AUG inAUGurates protein synthesis
- Codes for methionine, which may be removed before translation is completed

33

mRNA STOP Codons

- UGA= U Go Away
- UAA= U Are Away
- UAG= U Are Gone

34

Promoter

- Site where RNA polymerase & other transcription factors bind to DNA
- TATA box, CAAT box, GC rich regions

35

Enhancer

Stretch of DNA that alters gene expression by binding transcription factors distant from START site

36

Silencer

Site where negative regulators bind

37

Pol I

rRNA

38

Pol II

mRNA

39

alpha-amanatin

- Found is death cap mushrooms
- inhibits Pol II
- Causes hepatotoxicity

40

Pol III

tRNA

41

Characteristics of RNA polymerase

- No proofreading function
- No primers

42

pre-mRNA or hnRNA

initial transcript that will become mature mRNA

43

RNA processing steps

1) Capping 5' end (methylguanosine)
2) Polyadenylation of 3' end
3) Splicing out introns

- ALL occurs in the NUCLEUS

44

Introns vs. Exons

- Exons contain actual genetic information
- Introns are intervening noncoding segments

Think:
- INtrons are INtervening sequences and stay IN the nucleus
- EXons EXit the nucleus and are EXpressed

45

Aminoacyl-tRNA synthetase

- Charges tRNA
- Responsible for accuracy of amino acid selection

46

tRNA Wobble

- Accurate base pairing is only required in the first two nucleotide positions of an mRNA codon
- Codons differing in 3rd "wobble" position may code for the same tRNA
-Insoine

47

Translation Initiation

- GTP hydrolysis
- eIFs (eukaryotic Initiation Factors) help assemble 40S ribosomal subunit (small) with initiator tRNA & are released when mRNA & 60S subunit (large) assemble the complex

Think:
- ATP= tRNA Activation
- GTP= tRNA Gripping & Going places

48

Translation Elongation

1) Aminoacyl-tRNA binds to A-site (EXCEPT initiator methionine tRNA)
2) rRNA, "ribozyme" catalyzes peptide bond formation & transfers growing polypeptide to amino acid in A site
3) Ribosome advances 3 nucleotides, moving peptidyl tRNA to the P site

Think: APE
- A= incoming Aminoacyl-tRNA
- P= accommodates growing Peptide
- E= holds Empty tRNA as it Exits

49

Termination

- STOP codon recognized by release factor in A site
- Completed polypeptide is released from ribosome

50

Post-translational Modifications

- Trimming: Removal of N or C terminal propeptides
- Covalent Alterations: Phosphorylation, Glycosylation, Hydroxylation, Methylation, Acetylation, Ubiquitination

51

Chaperone Protein

- Intracellular protein involved in facilitating and/or maintaining folding
- Heat Shock Proteins e.g. Hsp60

52

Cyclins

- Regulatory proteins that control cell cycle events
- Phase specific
- Activate CDKs

53

Rough Endoplasmic Reticulum

- Site of synthesis of secretory (exported) proteins
- Site of N-linked oligosaccharide addition to many proteins

54

Golgi Apparatus

- Distribution center for protein & lipids from the ER to vesicles & plasma membrane
- Modifies N-oligosaccharides on asparagine
- Adds O-oligosaccharides on serine & threonine
- Adds mannose 6-phosphate to proteins for trafficking to lysosomes

55

I-cell Disease

- Inclusion Cell Disease
- Inherited lysosomal storage disorder
- Caused by defect in phosphotransferase (failure of Golgi to phosphorylate mannose)

56

SRP

- Signal Recognition Peptide
- Cytosolic Ribonucleoprotein that traffics proteins from the ribosome to the RER

57

Proteaseome

Barrel-shaped protein complex that degrades damaged or polyubiquitinated proteins