note
- Review: Translation involves the synthesis of a polypeptide as dictated by a mRNA nucleotide sequence. During translation, a messenger RNA strand, tRNA molecules, and ribosomal subunits come together. Nucleotide codons on the mRNA strand specify tRNA anticodons. The tRNA molecules donate specific amino acids. The ribosomal subunits provide a physical site where translation occurs. The product of translation is a newly synthesized polypeptide strand.
• Review: Translation takes place in three stages, initiation, elongation, and termination.
• During translation nucleotide codons on the messenger RNA strand are converted into amino acids. The amino acids are bonded together to form a polypeptide strand. Proteins are polypeptide strands in a three-dimensional form. The events of translation, therefore, enable protein synthesis.
The events of translation result in protein (polypeptide)
synthesis:
- A messenger RNA strand reading 5’ AUGGAUCAACGUUAA 3’ is used to translate a new polypeptide strand.
- A specific type of tRNA molecule possesses the anticodon 3’ UAC 5’ and the amino acid methionine. The tRNA moves into the A site of the ribosome and bonds with 5’ AUG 3’ on mRNA.
- With each new incoming tRNA, the complex of molecules shifts, and the result is that the ribosomal subunits move toward the 3’ end of the mRNA strand.
- A second tRNA molecule comes in and has the anticodon 3’ CUA 5’ and the aminoacid aspartine. It moves into the A site and binds with the mRNA codon 5’ GAU 3’. The first tRNA molecule moves into the P site. A peptide bond forms between the two amino acids.
The events of translation result in protein (polypeptide)
synthesis, continued:
- A third tRNA molecule attaches to the A site bearing the anticodon 3’ GUU 5’ and the amino acid valine. It binds with the mRNA codon 5’ CAA 3’. The first and
second tRNA molecules move into the E and A sites, respectively. The growing polypeptide is now three amino acids long. - A fourth tRNA molecule attaches to the A site carrying the anticodon 3’ GCA 5’ and the amino acid arginine. It binds with the mRNA codon 5’ CGU 3’. The second and third tRNA molecules move into the E and
A sites, respectively. The chain is now four amino acids longs. - A fifth tRNA molecule moves to the A site. It has the anticodon 3’ AUU 5’ and does not carry an amino acid. Looking at the genetic dictionary, you can see that the
corresponding mRNA codon, 5’ AUU 3’ is a stop codon. The tRNA’s exit via the E
Which of the following ranks the structures in order of size from largest to smallest?
- Chromosome, gene, codon, nucleotide
In protein synthesis, __________ provides the energy necessary to form a peptide bond.
- GTP
The following section of a DNA molecule codes for a four amino acid polypeptide. Using the genetic dictionary, determine where the gene is on the molecule and what the correct amino acid sequence is.
3′ AGTTTGATCTTTGTA 5′
5′ TCAAACTAGAAACAT 3′
- Methionine, phenylalanine, leucine, valine.
Initiation of protein synthesis begins when the __________ of the mRNA binds with __________ at __________ of the ribosome.
- start codon; UAC tRNA; P site
Which of the following statements about polyribosomes is not true?
- When polyribosomes occur, as soon as one copy of a polypeptide is complete, the next copy can be started.
In the first step of protein synthesis the initiation tRNA binds to the P site of the large ribosomal subunit. Next a __________ with proper __________ comes into the __________ of the ribosome and binds with mRNA.
- tRNA; anticodon; A site.
A gene is a portion of a DNA molecule that determines the sequence of amino acids in a __________.
- Polypeptide