Module 2: Nucleotides & Nucleic Acids

Question 1

Describe the structure of a nucleotide

Answer 1

Pentose sugar
Nitrogenous base
Phosphate group

Question 2

DNA nucleotide structure

Answer 2

Deoxyribose sugar
Nitrogenous base (Adenine, Cytosine, Guanine or Thymine)
Phosphate head

Question 3

How is DNA stranded

Answer 3

Double stranded

Question 4

RNA nucleotide structure

Answer 4

Ribose sugar
Nitrogenous base (Adenine, Cytosine, Guanine or Uracil)
Phosphate head

Question 5

How is RNA stranded

Answer 5

Single stranded

Question 6

Describe the synthesis of a polynucleotide

Answer 6

The phosphate group of one nucleotide bonds to the sugar of another.
Phosphodiester bond is formed.
Via condensation reaction.
Produces a polynucleotide with a sugar phosphate backbone.

Question 7

Structure of ATP

Answer 7

Ribose sugar
Adenine nitrogenous base
Three phosphate groups

Question 8

Describe structure of DNA

Answer 8

Two polynucleotide chains
Hydrogen bonds between nitrogenous bases.
Complementary base pairing of nitrogenous bases.
Purine bonds to pyrimidine by Hydrogen bond (eg adenine with thymine & cytosine with guanine)
Two antiparallel strands to form double helix.

Question 9

Describe how to purify DNA by precipitation

Answer 9

1. Physically break up cells using knife.
2. Add it to a boiling tube and mush up with a stirring rod.
3. Add detergent to disrupt phospholipid bilayer and nuclear membranes to release DNA.
4. Add salt to break hydrogen bonds of DNA & clump together.
5. Place boiling tube with solution in boiling water bath. Heat denatures enzymes that would break DNA.
6. Filter mixture into another boiling tube to ensure filtrate only contains DNA and associated proteins.
7. Add protease enzyme to break down DNA bound proteins.
8. Pour ice cold ethanol into tube. Nucleic acids are insoluble in ice cold ethanol and so DNA forms a precipitate.

Question 10

Structure of purine base

Answer 10

Contains two carbon-nitrogen rings joined together
(Adenine & Guanine)

Question 11

Structure of pyrimidine base

Answer 11

Contains one carbon-nitrogen ring
(Cytosine, Thymine & Uracil)

Question 12

Describe how DNA replication occurs

Answer 12

DNA helicase breaks hydrogen bonds between nitrogenous bases on DNA strands.
Helix unzips and forms two single strands. Each strand acts as a template for a new strand.
Free floating DNA nucleotides join to exposed bases by complementary base pairing (cytosine to guanine, adenine to thymine) and form hydrogen bonds.
DNA polymerase catalyses formation of phosphodiester bonds to form sugar phosphate backbone on new nucleotide strand.
Strands twist to form a double helix,

Question 13

Why is it known as semi-conservative replication

Answer 13

Because each new DNA molecule has one original strand and one new strand.

Question 14

State the two processes that make up proteinsynthesis

Answer 14

Transcription
Translation

Question 15

Describe process of transcription

Answer 15

DNA helicase controls uncoiling of DNA molecule at beginning of gene by breaking hydrogen bonds between strands.
One of the strands is used as a template strand
RNA polymerase lines up free floating RNA nucleotides along template strand by complementary base pairing.
RNA polymerase joins nucleotides together by catalysing formation of phosphodiester bonds. This forms an mRNA molecule.
DNA molecule reforms its hydrogen bonds and recoils as RNA polymerase passes.
When RNA polymerase reaches a stop codon, it stops making mRNA and detaches from the DNA.
The mRNA leaves the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm.

Question 16

Describe process of translation

Answer 16

A strand of mRNA made in transcription attaches itself to a ribosome.
a tRNA molecule with a complementary anticodon to start codon of mRNA attaches to mRNA by complementary base pairing.
A second tRNA molecule attaches to the next codon.
rRNA in ribosome catalyses formation of a peptide bond between the two amino acids attached to the tRNA molecules.
Ribosome moves along the mRNA releasing the first tRNA molecule, leaving the amino acid behind.
This process continues, producing a polypeptide chain until a stop codon is reached on the mRNA molecule.
The polypeptide chain moves away from the ribosome.

Question 17

Explain how genes code for a specific polypeptide sequence

Answer 17

Bases in DNA are in triplets called codons.
Each codon codes for a specific amino acid.
The mRNA strand is a complementary copy of the template strand.

Question 18

Genetic code is non-overlapping, degenerate & universal. Describe what these terms mean.

Answer 18

Non-overlapping: codons are separate and don’t share any bases.
Degenerate: There are more codons than amino acids, meaning some amino acids are coded for by more than one codon.
Universal: The same codons code for the same amino acids in all living organisms.

Question 19

Comparing RNA molecules

Answer 19

mRNA: MESSENGER RNA. found in nucleus, creates a complementary template of gene
tRNA: TRANSFER RNA. found in cytoplasm, transfers amino acids to ribosome.
rRNA. RIBOSOMAL RNA. found in cytoplasm. Makes up ribosomes.

Question 20

Insertion mutation

Answer 20

An extra nitrogenous base is added to the DNA molecule.

Question 21

Deletion mutation

Answer 21

A base is removed from the DNA molecule.

Question 22

Substitution mutation

Answer 22

One base is replaced with another.