Biological Molecules - Protein Synthesis

Question 1

Contrast the structures of mRNA and DNA molecules to give three differences (3)

Answer 1

• DNA is double stranded and mRNA is single-stranded
• DNA (very) long and RNA is short
• Thymine/T in DNA and uracil/U in RNA

Question 2

If the DNA base sequence is TGC, what what the codon and anti-codon be?

Answer 2

• The codon: ACG
• The anti-codon: UGC

Question 3

What is a ribosome?

Answer 3

• It is the site of protein synthesis
• It’s an organelle made of 2 sub-units
• It can be found floating in the cytoplasm or attached to membranes of the rough Endoplasmic Reticulum
• The mRNA produced in transcription binds to the ribosome for translation

Question 4

What is the process of transcription (DNA –> mRNA)?

Answer 4

• An enzyme, DNA helicase breaks hydrogen bonds to separate the DNA strands
• Only one DNA strand needs to act as a template
• RNA nucleotides are attracted & align to complementary exposed bases (on template strand)
• According to the base pairing rule (A –> U, T –> A, C –> G, G –> C)
• RNA polymerase joins adjacent RNA nucleotides together with a phosphodiester bond to form pre-mRNA
• Pre-mRNA spliced to remove introns (non-coding DNA)

Question 5

What is the process of translation (mRNA –> protein)?

Answer 5

• mRNA associates with a ribosome / ribosome attaches to mRNA
• Ribosome moves to the start codon (AUG)
• tRNA carries specific amino acid
• Anticodon (on tRNA) is complementary to codon (on mRNA)
• Ribosome moves along to next codon
• The process is repeated and amino acids join by peptide bonds in a condensation reaction (to form a polypeptide using energy from ATP)

Question 6

What is a codon?

Answer 6

A triplet / three bases on mRNA that code for an amino acid

Question 7

Describe the part played by RNA in protein synthesis (3)

Answer 7

• Carries coded information about the sequence of amino acids
• Copied from DNA
• Code is in a sequence of bases
• Codes for one amino acid
• Moves out of nucleus and goes into cytoplasm