4-2: Translation Flashcards
What are proteins
Polypeptides
Polymers of aa connected by peptide bonds
Structure of aa…
Amino group, alpha carbon with R group, carboxyl group
What are joined by peptide bonds
Carboxylic acid group of one aa, amino group of the next
How are the aa grouped
Based off R group properties (non-polar, polar, positively or negatively charged)
What are the two rare aa
Selenocysteine, pyrrolysine
What is protein primary structure
Aa sequence in a protein
What is protein secondary structure
Simple local structure, a-helices or B sheets
H bonds of peptide backbone
What is protein tertiary structure
Full 3D structure, multiple secondary structure elemented arranged
What is protein quaternary structure
Multiple peptides come together (multimeric proteins)
What are protein domains
Structural or functional segments of a protein
What is the helix-turn-helix (HTH)
Protein domain, binds DNA. Found in hundreds of proteins of the Salmonella genome DNA binding regulatory proteins
What structures are involved in tRNA
Anticodon (binds specific three base codon)
At other end, specific amino acid corresponding to the codon
Enzymes that charge tRNAs are… What do they do
tRNA synthetases
Add amino acid to CCA at 3’ end
Does one codon encode one amino acid?
No, multiple codons can encode one aa
What are the translation start codons
Encode for first aa of ORF
Usually AUG (83%) (ATG in DNA)
Can also be GUG, UUG
What is the start codon translated to
N-formylmethionine (fMet)
Does AUG always encode fMet
No, unless it is start codon it encodes normal Met
What are the three stop codons
UAA, UGA, UAG
The prokaryotic ribosome is the… Made up of what subunits?
70S ribosome
- 30S (small) subunit
- 50S (large) subunit
What are ribosomal subunits made of?
rRNA and ribosomal proteins
What are the E coli 30S and 50S ribosome subunits made of
30S = 16S rRNA, 21 proteins
50S = 5S/23S rRNA, 31 proteins
Are the small and large subunits always together
No, associate and dissociate during translation
What carries out the main function of ribosome
rRNA
How is translation initiated
Consensus sequence of ribosomal binding site binds 16S rRNA in 30S subunit, helps ribosome locate AUG codon
30S binds RBS, fMet tRNA binds AUG
50S subunit recruited using GTP
The ribosomal binding site (RBS) is also known as…
Shine-Dalgarno sequence
What are the 3 tRNA binding sites of the ribosome
- A (aminoacyl) site
- P (peptidyl) site
- E (exit) site
What is the A site
New charged tRNA’s enter, recognize codon needing aa
Growing peptide from P site transfers to aa in A site
Translocation of RNA to P site
What is the P site
tRNA transfers growing aa chain onto new charged tRNA in the A site, becomes uncharged
What is the E site
uncharged tRNA exits
What is elongation
The growth of the peptide chain
When does translation end
Stop codon encountered, release factor protein binds, releasing peptide and mRNA. Ribosome dissociates
Multiple ribosomes on a single mRNA simultaneously is…
Polysomes
What is transcription/translation coupling
RNA is being translated as it is still being transcribed (RNAp and ribosome both attached)
How is eukaryotic translation different
No coupling (transcri in nucleus, transl in cytoplasm)
mRNA only encodes one gene
Initiation step different (5’ cap recognized)
Ribosome larger: 40S + 60S = 80S
Protein folding either occurs…
Spontaneously or uses chaperones
what are chaperones
Proteins that help other proteins adopt their properly folded/active states
Functions of chaperones
Initial folding, re-folding denatured
Energy source of chaperons?
ATP hydrolysis
When are chaperons activates
High or low temperatures to assist with folding
How do proteins get out of the cytoplasm into different locations
Translocase systems
What signals that a protein needs to go to a particular secretion system
signal sequence at the N-terminus (first 25 aa)
What are the two secretion systems
Sec secretion system
Twin arginine translocase (tat)
What does the tat pathway do
Secretes pre-folded proteins across membrane
What does the sec secretion do
Recognizes signal in first 20 aa, translocates unfolded protein
What are the two sec pathways
passed across cytoplasmic membrane (SecA)
Recognized by RNA/protein complex and inserted into membrane (SRP)
What does the SecA pathway do
Pass unfolded proteins across cytoplasmic membrane
What does the SRP sec pathway do
Protein recognized by signal recognition particle and inserted into membrane
Both SRP and SecA…
Pass unfolded protein through membrane channel
