DNA Replication and Protein Synthesis recall Q

Question 1

Describe the structure of DNA. (5 marks)

Answer 1

1.Polymer of nucleotides;
2. Each nucleotide formed from deoxyribose, a
phosphate (group) and an organic/
nitrogenous base;
3.Phosphodiester bonds (between nucleotides);
4.Double helix/2 strands held by hydrogen
bonds;
5.(Hydrogen bonds/pairing) between adenine,
thymineandcytosine, guanine;

Question 2

Explain how the structure of DNA is related to its functions (6 marks)

Answer 2

1.Sugar-phosphate (backbone) is double
stranded into a helix so provides strength
& stability (protects bases);
2.Long / large molecule so can store lots of
information;
3.Helix / coiled so compact;
4.Base sequence allows information to be stored
(protein formation);
5.Double stranded so replication can occur
semi-conservatively as existing strands can act
as templates via complementary base pairing
6.Weak hydrogen bonds for replication and
strand separation OR many hydrogen bonds
so stable/strong;

Question 3

Describe and explain how the structure of DNA results in accurate replication (4 marks)

Answer 3

1.Two strands therefore semi-conservative
replication;
2.Base pairing held together by hydrogen bonds
3.Hydrogen bonds weak so easily broken, which
allows strands to separate;
4.Bases exposed and act as a template;
5.A with T, C with G;
6.DNA made has one parent strand and one
new strand

Question 4

Describe how the structure of a protein depends on the amino acids it contains. (5 marks)

Answer 4

1. Structure is determined by (relative) position of R group
   2.Primary structure is sequence/order of amino
   acids
   3.Secondary structure formed by hydrogen bonding (between amino acids);
   4.Tertiary structure formed by interactions
   (between R groups);
   5.Creates active sites in enzymes
   6.Quaternary structure contains more than 1
   polypeptide chain

Question 5

Messenger RNA (mRNA) is used during translation to form polypeptides. Describe how mRNA is produced in the nucleus of a cell. (5 marks)

Answer 5

1.DNA Helicase;
2.Breaks hydrogen bonds between base pairs,
exposing them;
3.Only one DNA strand acts as a template;
4.RNA nucleotides attracted to exposed bases;
5.(Attraction) according to base pairing rule (A –
U & C – G);
6. RNA polymerase joins the RNA nucleotides
together, to form pre-mRNA;
7.Pre-mRNA is spliced to remove introns,
forming mRNA

Question 6

Starting with mRNA in the nucleus of a cell, describe how a molecule of protein is synthesised. (6 marks)

Answer 6

1.mRNA leaves the nucleus through nuclear
pore;
2.Enters the ribosome;
3.tRNA molecules bring amino acids to the
ribosome;
4.A specific tRNA molecule exists for a specific
amino acid;
5.Anticodon of tRNA complementary to codon
on mRNA;
6.Peptide bonds form between adjacent amino
acids;
7.tRNA detaches and leaves to collect another
amino acid;
8.Ribosome moves along mRNA

Question 7

Explain how a mutation can result in the production of a non-functional protein receptor (4 marks)

Answer 7

1. Change in DNA base sequence;
2. Change in amino acid sequence;
   3.This alters position of hydrogen/ionic/disulfide
   bonds;
   4.And causes a change in the tertiary structure
   (of receptor);