L05 Translation Flashcards
________________ received a nobel prize for deciphering the genetic code.
A. Wilhelm Johannsen B. Johann Mischer C. Marshall Nirenburg D. Frederick Griffith E. Oswald Avery F. Chase and Hershey G. Erwin Chargaff H. Meselson and Stahl G. Kornberg
C. Marshall Nirenburg
Review:
Wilhelm Johannes - coined the term “gene”
Friedrich Miescher - isolated “nuclein” from salmon sperm (now known as nucleic acid)
Griffith discovered a “transforming factor” using rough and smooth strains of Pneumococcus
Avery reasoned DNA was transforming factor from treatment of virulent/non-virulant bacteria with deoxyribonuclease
Chase and Hershey used bacteriophages to reason that DNA is the genetic material
Charges quantified nucleotides (A,T,G,C)
Meseleson and Stahl produced evidence that DNA replicates in a semi-servative fashion
Kornberg received a nobel prize for his research studying the enzyme responsible for DNA replication
Why is the genetic code considered degenerate?
Because the code is redundant. With the exception of AUG (methionine) and UGG (tryptophan), more than one codon occurs for each amino acid.
The code is unambiguous meaning each code codes for one amino acid.
Chemical changes in just one base pair of a gene is called?
A. Frameshift mutations B. Nucleotide-pair substitution C. Silent mutations D. Missense mutations E. Nonsense mutations F. Point mutations
F. Point mutations
In a point mutation, one nucleotide is swapped out for another. Therefore, the mutation occurs at a single point or location within the DNA strand. Point mutations usually only affect the codon that contains the altered nucleotide. Frameshift mutations are due to either insertions or deletions of nucleotides.
Which replaces one nucleotide and its partner with another pair of nucleotides?
A. Frameshift mutations B. Nucleotide-pair substitution C. Silent mutations D. Missense mutations E. Nonsense mutations F. Point mutations
B. Nucleotide-pair substitution
Which has no effect on the amino acid produced by a codon because of redundancy in the genetic code?
A. Frameshift mutations B. Nucleotide-pair substitution C. Silent mutations D. Missense mutations E. Nonsense mutations F. Point mutations
C. Silent mutations
Which change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein?
A. Frameshift mutations B. Nucleotide-pair substitution C. Silent mutations D. Missense mutations E. Nonsense mutations F. Point mutations
E. Nonsense mutations
Which still code for an amino acid, but not the correct amino acid?
A. Frameshift mutations B. Nucleotide-pair substitution C. Silent mutations D. Missense mutations E. Nonsense mutations F. Point mutations
D. Missense mutations
What mutation is responsible for sickle-cell disease?
Point mutation
The wild type hemoglobin sequence is changed from CTT to CAT which transcribes GUA mRNA instead of GAA mRNA. The normal hemoglobin is translated from Glu and sickle-cell disease is translated from VAL.
Which may alter the reading frame due to an insertion or deletion of nucleotides?
A. Frameshift mutations B. Nucleotide-pair substitution C. Silent mutations D. Missense mutations E. Nonsense mutations F. Point mutations
A. Frameshift mutations
What is on each end of the tRNA?
Each carries a specific amino acid on one end
Each has an anticodon on the other end
the anticodon base-pairs with a complementary codon on mRNA
Describe base-pairing wobble and why is it used?
Wobble is a property that allows an identical tRNA to bind to different codons at the third base. It allows some tRNAs to bind to more than one codon.
It’s important because sometimes cells do not carry tRNAs for all codons.
Which site holds the tRNA that carries the growing polypeptide chain?
P site
Which site is the exit site, where discharged tRNAs leave the ribosome?
E site
Which site holds the tRNA that carries the next amino acid to be added to the chain?
A site
what are the 3 initiation steps of translations and what are the components that are brought together?
The initiation stage of translation brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits.
1) First, a small ribosomal subunit binds with mRNA and a special initiator tRNA
2) Then the small subunit moves along the mRNA until it reaches the start codon (AUG)
3) Proteins called initiation factors bring in the large subunit that completes the translation initiation complex
During the initiation of protein synthesis in eukaryotes, the fMet initiator tRNA binds to the start codon AUG on the 30s ribosomal unit. (T/F)
False, this happens in prokaryotes
A 30S ribosomal subunit, complexed with initiation factors and GTP binds to mRNA and fMet initiator tRNA to form a 30S initiation complex.
Where is the Shine-Dalgarno sequence found?
The 30S ribosome “binds to a specific mRNA sequence” called the Shine-Dalgarno sequence (typically
5’ - AGGAGG - 3’)
In eukaryotes, the small ribosomal subunit first binds to the methylated cap at the 5’ end of the mRNA. It then migrates to the initiation site - usually the first AUG it encounters. (T/F)
True
What are the steps of the elongation cycle of translation?
Each addition involves proteins called elongation factors and occurs in three steps:
1) codon recognition
2) peptide bond formation
3) translocation
A group of proteins called _____________ and ____________ usher the appropriate tRNA into the A site of the ribosome.
elongation factors (EF-Tu) and GTP
What is peptidyl transferase responsible for?
Peptide bond formation between the two adjacent amino acids by peptidyl transferase.
The formation of a peptide bond between the first two amino acids (fMet and Ser) of a polypeptide chain is catalyzed on the ribosome by peptidyl transferase.
During termination of translation, the A site accepts a protein called a release factor which causes the addition of a water molecule instead of an amino acid. This reaction releases the polypeptide, and the translation assembly then comes apart. The releasing factor in eukaryotes is called ___________.
A. RF1 B. RF2 C. RF3 D. eRF1 E. eRF2 F. eRF3 G. none of the above
G. None of the above. Eukaryotes possess a single releasing factor - eRF.
Prokaryotes possess three releasing factors: RF1 (recognizes UAA and UAG), RF2 (recognizes UAA and UGA) and RF3 which stimulates termination
During termination of translation, prokaryotes possess three releasing factors. Identify the correct pairs.
A. RF1 recognizes UAA and UGA B. RF1 recognizes UGA and UAG C. RF1 recognizes UAA and UAG D. RF2 recognizes UAA and UGA E. RF2 recognizes UGA and UAG F. RF2 recognizes UAA and UAG G. RF3 stimulates termination
C. RF1 recognizes UAA and UAG
D. RF2 recognizes UAA and UGA
G. RF3 stimulates termination
What is a polyribosome?
A number of ribosomes can translate a single mRNA simultaneously, forming a polyribosome (or polysome)
Polyribosomes enable a cell to make many copies of a polypeptide very quickly.
What happens to polypeptides destined for the ER?
Polypeptides destined for the ER or for secretion are marked by a signal peptide. A signal-recognition particle (SRP) binds to the signal peptide and brings the signal peptide and its ribosome to the ER.
