3.5 Transcription And Translation

Question 1

Compare the structure of DNA and RNA

Answer 1

DNA
	• Deoxyribose pentose sugar
	• Thymine base
	• Double stranded
	• Long molecule
RNA
	• Ribose pentose sugar
	• Uracil
	• Single stranded
	• Shorter molecule
Both
        • Both have a pentose sugar, a phosphate group and a nitrogenous base

Question 2

List the three forms of RNA

Answer 2

• Messenger RNA (mRNA)
  
  • Transfer RNA (tRNA)
  • Ribosomal RNA (rRNA)

Question 3

Describe a ‘codon’ and outline its function

Answer 3

• A codon is a triplet of bases which codes for a particular amino acid
  
  • The order of codons determines the amino acid sequence for a protein
  • The coding region always begins with the START codon (AUG) and terminates with a STOP codon

Question 4

Describe the genetic code

Answer 4

• Universal - every living thing uses the same code (there are a few rare and minor exceptions)
• Degenerate - more than one codon may code for the same amino acid
– e.g. GGT and GGG = glycine

Question 5

Explain the relationship between one gene and one polypeptide

Answer 5

• One gene codes for one polypeptide
  
  • The gene sequence is converted into a polypeptide via translation (mRNA synthesis) and transcription (polypeptide synthesis)
  • Some proteins consist of a number of polypeptide chains, and so will need multiple genes