Nucleic acids questions

Question 1

Describe the structure of DNA.

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, thymine and
   cytosine, guanine;

Question 2

Describe how a phosphodiester bond is formed between two nucleotides
within a DNA molecule.

Answer 2

1. Condensation (reaction)/loss of water;
2. (Between) phosphate and deoxyribose;
3. (Catalysed by) DNA polymerase;

Question 3

Describe the role of DNA polymerase in the semi-conservative replication
of DNA

Answer 3

1. Joins (adjacent DNA) nucleotides;
2. (Catalyses) condensation (reactions);
3. (Catalyses formation of) phosphodiester bonds (between adjacent
   nucleotides);

Question 4

Use your knowledge of semi-conservative replication of DNA to suggest:
1. the role of the single-stranded DNA fragments
2. the role of the DNA nucleotides

Answer 4

Role of single-stranded DNA fragments
1. Template;
2. Determines order of nucleotides/bases;

Role of DNA nucleotides
3. Forms complementary pairs / A – T, G - C
OR
Forms complementary (DNA) strand;

Question 5

Give two features of DNA and explain how each one is important in the
semi-conservative replication of DNA.

Answer 5

1. Weak / easily broken hydrogen bonds between bases allow two
   strands to separate / unzip;
2. Two strands, so both can act as templates;
3. Complementary base pairing allows accurate replication;

Question 6

Describe the role of two named enzymes in the process of semiconservative replication of DNA.

Answer 6

(DNA) helicase causes breaking of hydrogen/H bonds (between DNA
strands);
DNA polymerase joins the (DNA) nucleotides;
Forming phosphodiester bonds;

Question 7

The arrows in Figure 2 show the directions in which each new DNA strand is
being produced.
(d) Use Figure 1, Figure 2 and your knowledge of enzyme action to explain
why the arrows point in opposite directions.
(PAGE 15 IN NUCLEIC ACIDS QP)

Answer 7

1. (Figure 1 shows) DNA has antiparallel strands / described;
2. (Figure 1 shows) shape of the nucleotides is different /
   nucleotides aligned differently;
3. Enzymes have active sites with specific shape;
4. Only substrates with complementary shape / only the 3’ end
   can bind with

Question 8

QUESTION 11 B IN NUCLEIC ACIDS QP AND GET 11 C WHILE UR AT IT

Answer 8

FIND IT YOU BUM

Question 9

During replication, the two DNA strands separate and each acts as a
template for the production of a new strand. As new DNA strands are
produced, nucleotides can only be added in the 5’ to 3’ direction.
Use the figure in part (a) and your knowledge of enzyme action and DNA
replication to explain why new nucleotides can only be added in a 5’ to 3’
direction

Answer 9

1. Reference to DNA polymerase;
2. (Which is) specific;
3. Only complementary with / binds to 5’ end (of strand);
4. Shapes of 5’ end and 3’ end are different / description of how
   different.