Protein Synthesis

Question 1

Describe how translation leads to the production of a polypeptide.

Answer 1

• mRNA attaches to a ribosome
• Ribosome reads the first codon (start codon)
• tRNA with complementary anticodon attaches to the codon on mRNA.
• The tRNA carries a specific amino acid
• A second tRNA and amino acid arrives at the ribosome and binds to the next codon.
• The two amino acids form a peptide bonds via a condensation reaction. The formation of peptide bonds require ATP.
• This process continues until stop codon is reached.

Question 2

Describe how mRNA is produced (transcription)

Answer 2

• DNA helicase attaches to a specific DNA sequence at the start of the gene (promoter region)
• DNA helicase breaks hydrogen bonds and the DNA “unwinds” exposing the bases
• RNA polymerase attaches to specific section of DNA called a start sequence.
• Free floating RNA nucleotides attach to the template strand DNA. A-U and G-C
• RNA polymerase joins adjacent nucleotides together creating phosphodiester bonds
• The RNA polymerase moves down the DNA molecule until it reaches a stop sequence.
• As RNA polymerase moves down the DNA strand, hydrogen bonds reform between complementary bases and strands coil back together.
• The pre-mRNA strand is spliced to remove introns and non-coding repeats. Exons are joined together forming mature mRNA.
• Mature mRNA leaves via a nuclear pore.

Question 3

Compare and contrast mRNA and tRNA.

Answer 3

Both are made of RNA and have nucleotides have a phosphate group, ribose sugar and the bases A, U, C and G; mRNA does not have hydrogen bonds, whereas tRNA does; mRNA does not have an amino acid binding site, whereas tRNA does; mRNA is usually longer (has more nucleotides) than tRNA; mRNAs can be different lengths, whereas tRNA are all a similar length;
mRNA has codons, whereas tRNA has anticodons;

Question 4

A polypeptide is this many amino acids long, what is the minimum number of bases needed to code for this polypeptide?

Answer 4

This x 3 = answer

Question 5

A gene is this many nucleotides long, what is the maximum number of amino acids it could code for?

Answer 5

This ÷ 3 = answer

Question 6

6. What is a ribosome made of?

Answer 6

A molecule of ribosomal RNA and a protein.

Question 7

7. Explain the term non-overlapping.

Answer 7

Each base is part of only one triplet code.

Question 8

Explain the term degenerate.

Answer 8

More than one triplet code (or codon) codes for each amino acid.

Question 9

9. Explain how the genetic code is universal.

Answer 9

All organisms DNA triplet code in every organism codes for the same amino acid.

Question 10

Explain the difference between transcription in prokaryotes and eukaryotes.

Answer 10

Eukaryotic DNA contains introns with genes whereas prokaryotes don’t; These regions are removed from the pre-mRNA in eukaryotes whereas this isn’t necessary in prokaryotes;

Question 11

Describe the genome.

Answer 11

The complete set of genes in a cell/organism;

Question 12

Describe the proteome.

Answer 12

The full range of proteins a cell is able to produce;

Question 13

Describe the role of RNA polymerase in producing mRNA

Answer 13

RNA polymerase joins adjacent RNA nucleotides in a condensation reaction to form a phosphodiester bond. Repeating this process produces mRNA.

Question 14

Describe the role of ribosomes in translation.

Answer 14

mRNA binds to ribosome; there are two codons binding sites; Allows tRNA with anticodons to bind; Catalyses formation of peptide bond between amino acids held by tRNA molecules; Moves along mRNA to the next codon;

Question 15

Describe the role of tRNA in translation.

Answer 15

The anticodon is complementary to codon on mRNA; each tRNA has a specific amino acid; carried to ribosome; this gives the correct sequence of amino acids along polypeptide;

Question 16

Describe the role of ATP in translation.

Answer 16

ATP is hydrolysed to release the energy needed for the two amino acids on tRNA to be joined by a peptide bond. This is catalysed by an enzyme.