2.3 Nucleotides And Nucleic Acids

Question 1

Name the three components of a nucleotide.

Answer 1

A nitrogenous base (Adenine, Thymine, Cytosine, Guanine, Uracil).
Pentose sugar (Ribose or deoxyribose).
A phosphate group.

Question 2

How are adjacent nucleotides joined together?

Answer 2

Via a condensation reaction between the pentose sugar of one nucleotide and the phosphate group of the next. This forms a phosphodiester bond between C3 and C5

Question 3

Describe the differences between a DNA and an RNA molecule.

Answer 3

DNA contains the nitrogenous bases A,T,C,G and RNA contains A,U,C,G
DNA is double stranded, RNA is single stranded
DNA contains a deoxyribose sugar and RNA contains a ribose sugar

Question 4

Describe the structure of ATP (Adenine triphosphate)

Answer 4

Comprised of a ribose pentose sugar, an adenine nitrogenous and has 3 phosphate groups. ATP can be hydrolysed resulting in ADP and energy.

Question 5

Describe the structure of DNA.

Answer 5

Two antiparallel strands, double helix, 3 H-bonds between C & G, 2 H-bonds between A & T, a purine (A/G) always binds to a pyrimidine (C/T), complementary base pairing

Question 6

Describe semi-conservative replication

Answer 6

• Enzyme helicase breaks the hydrogen bonds between complementary base pairs.
• Double helix uncoils/unwinds
• Each strand acts as a template
• Free DNA nucleotide assembled in complementary base pairing.
• Hydrogen bonds reform
• DNA polymerase joins nucleotides forming a new sugar phosphate backbone.

Question 7

Define semi-conservative

Answer 7

Each daughter DNA molecule contains one original/parent strand and one new strand of DNA.

Question 8

What is a gene? Define allele.

Answer 8

A gene is a section of DNA that codes for the sequence of amino acids in a polypeptide.
Alleles are different versions of the same gene.

Question 9

Define triplet code

Answer 9

Each sequence of 3 bases (codon) determines one amino acid

Question 10

What does non overlapping mean?

Answer 10

The code is always read in one direction. The code is only ever read on one DNA strand.

Question 11

Define degenerate

Answer 11

Some amino acids have more than one triplet code.

Question 12

Define universal

Answer 12

Used across all organisms

Question 13

Describe the practical investigation to precipitate DNA

Answer 13

• Crush using a pestle and mortar to break down the cellulose cell wall.
• Add detergent to dissolve the cell surface membrane.
• Add protease enzyme to break down histones associated with DNA.
• Filter to remove solids.
• Add salt to clump DNA.
• Add Ice cold ethanol to precipitate.

Question 14

Describe transcription

Answer 14

• Break hydrogen bonds (DNA helicase)
• Free RNA nucleotides form a complementary mRNA strand which is a copy of the DNA coding strand.
• RNA polymerase helps form 3-5 phosphodiester bonds between RNA nucleotide (sugar phosphate backbone).
• mRNA leaves the nucleus via nuclear pores and DNA helix reforms.

Question 15

Describe translation

Answer 15

• mRNA attaches to a ribosome made of two rRNA subunits.
• anticodon on tRNA will bind to complementary mRNA codon bringing a corresponding amino acid.
• amino acids joined by peptide bonds (primary structure which gives rise to secondary and tertiary structure)