Translation

Translation is the process by which mRNA transcripts are converted into the amino acid sequences of proteins. A cell uses special organelles called ribosomes to translate RNA messages into protein. Ribosomes are themselves composed of RNA and protein, and consist of two components, a large subunit and a small subunit. Together, these form a complex that moves along the messenger RNA molecule and decodes its sequence. The translation process begins as the small ribosomal subunit, depicted in pink, binds to proteins called initiation factors, shown here as green and yellow spheres. Then, the small subunit binds to an mRNA molecule, shown here as a blue strand, near its 5’ end. Two important structures called the P site and the A site are located within the small subunit. As shown, the segment of the mRNA positioned at the P site binds to a molecule called an initiator tRNA that is attached to the amino acid methionine. This is almost always the first amino acid of a protein sequence and is depicted here as the blue sphere. The initiator tRNA carries three nucleotides, most often U, A, and C. These are shown here as the small green, red, and yellow cylinders and are collectively called an anticodon. The anticodon forms base pairs with a set of three complementary nucleotides on the mRNA which are referred to as the start codon and most commonly have the sequence AUG. Next, the large subunit binds to the complex, and a second tRNA carrying another amino acid enters the A site of the ribosome. The second tRNA base pairs with the next set of three mRNA nucleotides, or codon, as before. Note that a peptide bond forms between the first amino acid and the second amino acid, and that the first initiator tRNA begins to leave the ribosome as a third tRNA approaches. The third tRNA adds its amino acid to the growing peptide chain, depicted here as the linked blue spheres, and the second tRNA exits the ribosome. This process continues until the ribosome recognizes a set of three specific nucleotides called a stop codon along the sequence of the mRNA and releases the completed polypeptide chain. As shown here, when one ribosome moves away from the initiation site, other ribosomes are free to bind to the mRNA and begin translation. Many ribosomes will oftentimes simultaneously bind to and translate the same mRNA molecule in a configuration called a polyribosome or polysome.

Question 1: What is the basic concept of translation?
  1. The process by which mRNA transcripts are converted into the amino acid sequences of proteins.
  2. Conversion of RNA into DNA.
  3. Conversion of DNA into RNA.
  4. Folding of nucleotides to make them useful.


Answer 1 Answer - (a) The process by which mRNA transcripts are converted into the amino acid sequences of proteins.

Question 2: Which organelle in Eukaryotes is responsible for translating RNA messages into protein?
  1. Mitochondria
  2. Golgi apparatus
  3. Ribosomes
  4. Liposomes


Answer 2 Answer – (c) Ribosomes

Question 3: How many subunits does a ribosome have?
  1. 1
  2. 2
  3. 3
  4. 4


Answer 3 Answer – (b) 2

Question 4: Which amino acid is usually coded for by the first codon in mRNA?
  1. Adenine
  2. Thymine
  3. Methionine
  4. Methanol


Answer 4 Answer – (c) Methionine

Question 5: The segment of the mRNA on the P-site of the small ribosomal subunit binds to a(n) _____________ that is attached to methionine.
  1. methionine RNase
  2. initiator tRNA
  3. methionase
  4. tRNA


Answer 5 Answer – initiator tRNA

Question 6: What are anticodons, and where are they located?
  1. negative codons, nucleus
  2. RNA codons, membrane
  3. nucleotides, small ribosomal subunit
  4. nucleotides, large ribosomal subunit


Answer 6 Answer – (c) nucleotides, small ribosomal subunit

Question 7: The sequence of the start codon is often _____________.
  1. AUG
  2. CUA
  3. UAA
  4. UAG


Answer 7 Answer – (a) AUG

Question 8: The first initiator tRNA begins to leave the ribosome when the third initiator tRNA enters the ribosome and this process continues adding amino acids in the peptide chain until the ribosome recognizes a codon called the ____________?
  1. terminator
  2. final codon
  3. end codon
  4. stop codon


Answer 8 Answer - (d) stop codon

Question 9: What is the structure called when many ribosomes simultaneously bind to and translate the same mRNA molecule?
  1. A polysome.
  2. A ribosomal cluster.
  3. A mRNA translation unit.
  4. A poly-mRNA.


Answer 9 Answer – (a) A polysome.