Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
41 Cards in this Set
- Front
- Back
|
Differences between DNA and RNA
|
(1) double-stranded vs. single-stranded
(2) thymine vs. uracil (3) deoxyribose vs. ribose |
|
|
Three (3) types of RNA
|
(1) mRNA
(2) tRNA (3) rRNA |
|
|
RNA polymerase
|
enzyme that transcribes DNA to RNA (Eukaryotes have I, II, and III)
bacterial: 4 subunits > α2 (2 copies) > β > β' > ω > σ (binds RNAP to promoter) |
|
|
Three (3) Phases of Transcription
|
(1) initiation
(2) elongation (3) termination |
|
|
Initiation of Transcription
|
RNAP needs no primer
(1) sigma (σ) binds to promoter in DNA (-10 and -35) (2) RNAP unwinds DNA (3) sigma (σ) factor released |
|
|
Promoters
|
specific DNA sequences indicating start site of transcripton
in Bacteria: -35 -10 (Pribnow box) |
|
|
Sigma (σ) Factors
|
S70 (most commonly used, binds to most genes)
S32 (heat-shock response, active when stressed by heat) |
|
|
Transcription Elongation
|
> RNA strand is made 5' to 3' (same as DNA)
> RNAP moves down template DNA from 3' to 5' |
|
|
Transcription Termination
|
polymerase slows at pause site (GC rich sequence, forms stem loop)
Rho-dependent termination- Rho (ρ) factor binds to mRNA, slides along to polymerase, breaks RNAP and mRNA off of DNA Rho-independent termination: series of U residues downstream of pause site (DNA-RNA UA base pairs less stable, even less so if stalled) |
|
|
Transcription factors
|
help eukaryotic RNAP bind to promoters
(since do not have sigma factors) |
|
|
Operon
|
DNA containing a cluster of genes under the control of a single promoter
> genes transcribed together into a polycistronic mRNA strand and: (1) translated together in the cytoplasm (2) trans-splicing to mRNAs translated separately EX: lac operon (3 lactose utilization enzymes) |
|
|
lac operon
|
lacZ: β-galactosidase
lacY: lac permease lacA: transacetylase |
|
|
Operon
|
DNA containing a cluster of genes under the control of a single promoter
> genes transcribed together into a polycistronic mRNA strand and: (1) translated together in the cytoplasm (2) trans-splicing to mRNAs translated separately EX: lac operon (3 lactose utilization enzymes) |
|
|
lac operon
|
lacZ: β-galactosidase
lacY: lac permease lacA: transacetylase |
|
|
Translation
|
process of making a polypeptide chain from mRNA
|
|
|
Codons
|
a group of 3 RNA bases which codes for an individual amino acid
(20 amino acids found in proteins) |
|
|
Degenerate Genetic Code
|
64 possible codons
(several codons code for a single amino acid; 1st 2 bases same, 3rd different) |
|
|
The "Wobble" Concept
|
base pairing between tRNA and mRNA is flexible for third base pair
> some tRNA can recognize more than one codon |
|
|
"Wobble" concept
|
base pairing between tRNA and mRNA is more flexible for the third base pair
|
|
|
tRNA
|
transfer RNA- composed of:
(1) binding site for codon (anticodon: 3'->5') (2) binding site for amino acid 61 sense codons; 3 nonsense codons (no tRNA exist) |
|
|
aminoacyl-tRNA synthetases
|
attached amino acid to a tRNA
|
|
|
anticodon
|
sequence on tRNA which binds to codon on mRNA
written 3' -> 5' |
|
|
start codon
|
AUG
Met (methionine) |
|
|
ORF
|
open reading frame
from start to stop codon |
|
|
Nonsense codons
|
do not have tRNA (stop codons)
UAG UGA UAA |
|
|
Ribosome
|
large complex of proteins and RNA that links amino acids together to form proteins
Two (2) subunits in prokaryotes: 30s + 50s = 70s |
|
|
Svedberg unit
|
a measure of mass and shape
used in describing ribosomes |
|
|
Three (3) Sites on Ribosome
|
A (acceptor) site: tRNA first binds
P (peptide) site: growing peptide held E (exit) site |
|
|
Ribosome binding site in prokaryotes
|
Shine-Dalgarno sequence (mRNA sequence allowing binding of mRNA to ribosome)
|
|
|
Translation Initiation
|
30s subunit: mRNA attaches
50s: three holes (PAE) (1) initiation factors (2) 2 tRNAs hydrogen bind to P and A site (3) ribosome forms peptide bond b/w amino acids (4) P site tRNA released, chain hooked to tRNA in A site |
|
|
Initiation Factors
|
In translation initiation:
initiation factors bind ribosome to mRNA so 1 codon in P and 1 codon in A |
|
|
Only tRNA which can bind to P site
|
tRNA carrying methionine
|
|
|
Translation Elongation
|
ribosome moves up the mRNA by 1 codon so chain of AAs is in P site
Elongation factors (EF-Ts, EF-Tu, EF-G) bring GTP energy required to move ribosome along mRNA |
|
|
Translation Termination
|
occurs when a nonsense codon is in the A site
> releasing factors unlock ribosome from mRNA |
|
|
Difference between Eukaryotic and Prokaryotic Translation
|
in eukaryotes, occurs in cytoplasm separated from transcription
in prokaryotes, transcription and translation occur simultaneously (coupled) |
|
|
Polysome
|
several ribosomes translating a single mRNA simultaneously forming a complex
|
|
|
Protein Modification
|
enzymes modify translated proteins
> fMet (formal methionine) removed from N-terminus > proteins cleaved > groups added to amino acids > protein folding (spontaneous or chaperoned) |
|
|
Types of small groups added to amino acids
|
(1) phosphoryl
(2) methyl (3) adenylate |
|
|
Protein Secretion
|
(1) Sec-dependent pathway
- delivers proteins to periplasm (2) Type I secretion system - secretes protein out of bacterium (total of 6) |
|
|
What characteristics determine protein half-life?
|
(1) sequence
(2) shape (3) function |
|
|
Protein Degradation
|
- survive from minutes to days
(1) amino acids reused (2) cells constantly rebuilding (3) PROTEASES cut proteins (4) PROTEASOMES degrade proteins In eukaryotes, ubiquitin tag signals degradation |
