DLA 3B Translation Flashcards
What is a codon?
Each 3 consecutive mRNA bases from the genetic code for an amino acid
Codon of mRNA will complementary bond to ________
Anticodon of tRNA
Why does translation depend on adaptor molecules?
The nucleotides of mRNA do not directly recognize the amino acids they code for, so adapter molecules that recognize the nucleotides in mRNA and binds to them with an amino acid attached to another site of the molecule
Describe the regions of tRNA
Some regions of the tRNA are paired and the unpaired regions form 3 loops
Each kind of tRNA carries one of the 20 amino acids linked to the 3’ end
At one loop 3 unpaired base form an anticodon(complementary to codons)
This complementary base pairing brings the correct amino acid into the growing polypeptide
What is the function of aminoacyl tRNA synthetase?
- It couples Particular amino acid to its corresponding tRNA
- Different aminoacyl tRNA synthetase for each amino acid so the enzyme “recognizes “ the codons
How many codons do rarely used amino acids have?
They have one or 2 codons
- Tryptophan is very rare in proteins(one codon UGG)
- Methionine is always the first amino acid in protein synthesis( AUG)(very specific)
How many codons do common amino acids have?
Commonly used amino acids have multiple codons, 4 or more
What is “wobble base pairing” between codons and anticodons?
- Theory why so many amino acids have more than one codon
- there must be accurate base pairings in the first two positions of the codon, but there is tolerance for mismatch at the third base called “wobble base pairing”
What are the 3 stop codons?
UAA- U are away
UAG- U are gone
UGA - U go away
What is the start codon?
AUG
Explain the possibility of 3 reading frames for one mRNA sequence
The same mRNA can sequence and specify 3 different amino acid sequences, it depends on the reading frame
Only one is real for your protein
DNA sequencing has been used to look for genes since…
1977
How do you know if a region of DNA is a gene?
- By determining the sequence of DNA we find exons
- Determine the RNA sequence
- Scan for base pairs that will make a minimum of 50 amino acids in a row without a stop codon
- this will be our open reading frame
What scientists worked on ribosomes since the 1950’s and won theNobel prize in 1974?
- Albert Claude
- George Emil Palade
- Christian de Duve
What is common about both eukaryotic and prokaryotic ribosomes ?
- Both made of a large subunit and a small subunit
- Both subunits: rRNA plus proteins
When naming types of ribosomes, what does the “S” mean?
S= sedimentation rare from Destiny Centrifugation
What is the collective sedimentation rate and MW of prokaryotic ribosomes?
70S
MW= 2.5 million
What is the collective sedimentation rate and MW of eukaryotic ribosomes?
80S
MW= 60S and 40S
What is the. MW of the 40S ribosome subunit in eukaryotic ribosomes ?
1.4 million
Describe the rRNA and proteins in the 40S ribosome subunit in eukaryotic cells
18S rRNA with 1900 nucleotides
~ 33 proteins
What is the MW of the 60S ribosome subunit in eukaryotic cells?
2.8 million
Describe the rRNA and proteins in the 60S ribosome subunit in eukaryotic cells (comeback)
55 rRNA with 120 nucleotides
28S rRNA with 470p nucleotides
5.8S rRNA with 160 nucleotides
~49 proteins
What is the A site of a ribosome?
Site for aminoacyl tRNA
-tRNA attached with the amino acid
What is P site in ribosomes?
P for peptidyl transferase
- tRNA linked to the peptide - Enzymatic activity is called peptidyl transferase
What is the E site for in ribosomes?
E for exit
What are the mRNA binding sites of a ribosome?
E site
P site
A site
Explain the initiation of protein synthesis in eukaryotes pt. 1
- tRNA loaded with the initiator methionine binds to the small ribisomal subunit with GTP and initiation factors
- Recognizes mRNA in a circular loop structure
- The small subunit than moved 5’ to 3’ searching for the first AUG
- initiation factor is released and energy of GTP hydrolysis is used
Explain the initiation of protein synthesis in eukaryotes pt. 2
- Large ribosomal subunit will assemble with the complex and complete the ribosome
- the initiator tRNA is still bound to the P site
- the first aminoacyl tRNA binds to the A site
- The first peptide bond is formed
What are the 3 main differences between prokaryotic and eukaryotic translation?
- Initiating methionine( there is a formal group COOH attached to meth in prokaryotes)
- Ribosomal binding site (eukaryotic has a closed loop mRNA unlike prokaryotic)
- When translation occurs- prokaryotic mRNA can be translated before the transcript is synthesized unlike eukaryotic mRNA
What are the 5 steps to translating an mRNA molecule?
- P site has a growing polypeptide, aminoacyl tRNA has bound to the A site, tRNA alone exits
- The high energy from AA 3 to the 3’ end of tRNA 3 is used to form a peptide bond to amino acid 4
- The large subunit moves relative to the mRNA shifting the positions of the tRNAs
- Conformational changes moves the small subunit along mRNA exactly three nucleotides to reset ribosome
- Step 1 repeats
Explain the termination of protein synthesis
- The stop codons do not have a tRNA
- “Release factors” bind to any ribosome with a stop codon in the A-site
- The peptidyl transferase activity in the P site will catalyze the addition of water to the carboxyl end of the peptide
- The growing peptide is released into the cytoplasm
- Similar in both prokaryotes and eukaryotes
What is the kozak sequence?
The. Protein translation site in eukaryotic mRNA transcripts
