PL cd: Nucleic acids; transcription; translation

Question 1

Give the formula for a hydrogen phosphate ion.

Answer 1

H₂PO₄^-

On the data sheet

Question 2

Describe the structure of DNA.

Answer 2

• Deoxyribose sugars + phosphate groups condense together, forming an alternating sugar-phosphate backbone
• One of 4 bases, A/T/C/G, is condensed to each deoxyribose unit
• Each sugar-phosphate-base group is one nucleotide
• Hydrogen bonds form between pairs of bases, A&T / C&G, on 2 different DNA molecules
• Further hydrogen bonding coils strands into a double helix

Question 3

The image shows the structure of DNA, which is a polynucleotide. Identify one nucleotide on the diagram.

Answer 3

Question 4

Describe briefly what occurs during transcription.

Answer 4

• Enzymes unzip a gene (section of a DNA molecule relating to one protein)
• Single DNA strand acts as a template
• Enzymes adjoin free RNA nucleotides in the nucleus in an order determined by that of the bases on the DNA template
• Once synthesis is complete, DNA double helix reforms
• mRNA molecule leaves nucleus

Question 5

How does mRNA differ from DNA?

Answer 5

• Has ribose, rather than deoxyribose
• Has uracil rather than thymine (these differ by a methyl group at a place which doesn’t affect base pairing)
• Single polynucleotide strand, rather than double helix

Question 6

What is meant when DNA is said to be degenerate?

Answer 6

More than one codon may code for each amino acid.

Question 7

Describe what occurs during translation.

Answer 7

• mRNA template molecule travels from nucleus to ribosome
• Amino acids are joined to tRNA molecules by an ester link + taken to ribosome
• tRNA anti-codon has complementary bases to mRNA codon, so they fit together
• Ribosome moves along mRNA molecule
• Amino acids are peptide-bonded into a polypeptide via tRNA molecules
• tRNAs vacate after delivering their amino acid

Question 8

Draw a diagram highlighting the hydroxyl groups which could form phosphodiester bonds in:

• Ribose
• Deoxyribose

Answer 8

The other one on the right, which they both share, condenses to bond with a base.

Question 9

Draw a diagram showing the organic product of the condensation reaction between one phosphoric acid molecule and one ribose molecule.

Answer 9

Phosphoric acid behaves like carboxylic acid. Essentially formation of an ester bond.

Question 10

Draw a diagram showing the repeating unit of DNA, using the base adenine.

Answer 10

Phosphoric acid behaves like carboxylic acid, forming a phosphodiester bond. Deoxyribose reacts by condensation with adenine.

Question 11

Draw a diagram of a DNA nucleotide containing thymine, hydrogen bonded to another containing adenine.

Answer 11

Easiest to draw the bases first, since they need to be orientated correctly for hydrogen bonding. Then add the sugar + phosphate onto each base.

Question 12

Draw a diagram of an RNA nucleotide containing cytosine, hydrogen bonded to another containing guanine.

Answer 12

Easiest to draw the bases first, since they need to be orientated correctly for hydrogen bonding. Then add the sugar + phosphate onto each base.