From gene to protein

24 important questions on From gene to protein

What is a primary transcript?

the initial RNA transcript from any gene prior to processing.

What is a triplet code?

a serie of nonoverlapping, three-nucleotides words.

Where does the flow of information from gene to protein  base on?

triplet code
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What is a template strand?

one of the two DNA strands that provides a template for ordering the sequence of complementary nucleotides in an RNA transcript.

What is a promoter?

the DNA sequence where RNA polymerase attaches.

What is a transcription unit?

the stretch of DNA that is transcribed.

What happens in initiation of transcription?

the promoter has a TATA box, transcription factors bind to the DNA (TATAbox).
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 5' end receives a modified nucleotide 5' cap
–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)?

Most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that lie between coding regions. (noncoding regions are interons).

What kind of molecule helps a cell translates an mRNA message into a protein?

transfer RNA (tRNA)

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?

1. a correct match between a tRNA and an amino acid, done by the enzyme aminoacyl-tRNA synthetase.
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 P site holds the tRNA that carries the growing polypeptide chain.
- 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?

the initiation stage of translation brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits.
a small subunit moves along the mRNA until it reaches the start codon (AUG).

What happens during the elongation stage?

amino acids are added one by one to the preceding amino acid at the C-terminus of the growing chain.
•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?

a number or ribosomes can translate a single mRNA simultaneously
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?

nucleotide-pair substitutions.
one or more nucleotide-pair insertions or deletions.

What effect has a silent mutation?

they have no effect on the amino acid produced by a codon, because of redundancy in the genetic code.

What is an inserion and deletion?

are additions or losses of nucleotide pairs in a gene.

What effect does an isertion and deletion have?

these mutations have a disastrous effect on the resulting protein more often than substitutions do. insertion or deletion of nucleotides may alter the reading frame, producing a frameshift mutation.

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