From gene to protein
24 important questions on From gene to protein
What is a primary transcript?
What is a triplet code?
Where does the flow of information from gene to protein base on?
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What is a template strand?
What is a promoter?
What is a transcription unit?
What happens in initiation of transcription?
than a transcription initiation complexs is formed.
What happens in elongation of the RNA strand?
•As RNA polymerase moves along the DNA, it untwists the double helix, 10 to 20 bases at a time
•Transcription progresses at a rate of 40 nucleotides per second in eukaryotes
•A gene can be transcribed simultaneously by several RNA polymerases •Nucleotides are added to the 3¢ end of the growing RNA molecule
What happen at the termination of transcription?
•In bacteria, the polymerase stops transcription at the end of the terminator and the mRNA can be translated without further modification •In eukaryotes, RNA polymerase II transcribes the polyadenylation signal sequence; the RNA transcript is released 10–35 nucleotides past this polyadenylation sequence
In which particular way is each end of a pre-mRNA molecule modified?
–The 3' end gets a poly-A tail
Which functions do pre-mRNA modifications (alteration) share?
–They seem to facilitate the export of mRNA to the cytoplasm
–They protect mRNA from hydrolytic enzymes –They help ribosomes attach to the 5' end
What are interons (or intervening sequences)?
What kind of molecule helps a cell translates an mRNA message into a protein?
Why is a molecule of tRNA not identical?
–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
Which two steps requires accurate translation?
2. a correct match between the tRNA anticodon and an mRNA codon.
What three binding sites for tRNA has a ribosome, and which function has these sites?
- the A site holds the tRNA that carries the next amino acid to be added tot the chain.
- the E site is the exit site, where discharged tRNAs leave the ribosome.
What happens in the initiation stage?
a small subunit moves along the mRNA until it reaches the start codon (AUG).
What happens during the elongation stage?
•Each addition involves proteins called elongation factors and occurs in three steps: codon recognition, peptide bond formation, and translocation
•Translation proceeds along the mRNA in a 5′ to 3′ direction
What happens during the termination stage?
•Termination occurs when a stop codon in the mRNA reaches the A site of the ribosome
•The A site accepts a protein called a release factor
•The release factor causes the addition of a water molecule instead of an amino acid •This reaction releases the polypeptide, and the translation assembly then comes apart
What is a polyribosome?
polyribosomes enable a cell to make many copies of a polypeptide very quickly.
In which two categories can a point mutations within a gene be divided?
one or more nucleotide-pair insertions or deletions.
What effect has a silent mutation?
What is an inserion and deletion?
What effect does an isertion and deletion have?
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