DNA REPLICATION AND PROTEIN SYNTHESIS

Question 1

describe the structure of DNA (5)

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)

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

Question 3

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

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 hows the structure of a protein depends on the amino acids it contains (5)

Answer 4

1.Structure is determined by (relative) position of amino acid/R

group/interactions/bonds;
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 site in enzymes OR Creates complementary/specific shapes in
antibodies/carrier proteins/receptor (molecules);
6.Quaternary structure contains >1 polypeptide chain

Question 5

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

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, describe how a molecule of protein is synthesised (6)

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)

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);