DNA, genes, chromosomes

Question 1

name the fixed position occupied by a gene on a DNA molecule (1)

Answer 1

locus

Question 2

describe how a gene is a code for the production of a polypeptide (3)

Answer 2

1. 3 bases
2. in a triplet
3. determines order of amino acid sequence

Question 3

define exon (1)

Answer 3

base coding for polypeptide

Question 4

define non coding base sequences and describe where the non coding multiple repeats are positioned in the genome (2)

Answer 4

1. DNA that does not code for protein
2. positioned between genes

Question 5

give 3 ways in which DNA in chloroplasts is different from DNA in the nucleus (3)

Answer 5

in chloroplasts DNA is shorter,
there are fewer genes
DNA is circular not linear
DNA not associated with histones

Question 6

compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells (5)

Answer 6

comparisons:
1. nucleotide structure is identical
2. nucleotides joined by phosphodiester bonds
3. DNA in mitochondria same to DNA in prokaryotes

contrasts:
4. eukaryotic DNA is longer
5. eukaryotic DNA contain introns, prokaryotic DNA does not
6. eukaryotic DNA is linear, prokaryotic DNA is circular
7. eukaryotic DNA associated with histones, prokaryotic DNA is not

Question 7

what is a homologous pair of chromosomes (1)

Answer 7

two chromosomes that carry the same genes

Question 8

define a gene (3)

Answer 8

• a base sequence of DNA
  -that codes for a functional RNA
  -and codes for the amino acid sequence of a polypeptide chain

Question 9

define proteome (1)

Answer 9

the full range of proteins that a cell is able to produce

Question 10

define genome (1)

Answer 10

the entire set of genes in a cell

Question 11

describe how DNA is replicated (6)

Answer 11

1. DNA helicase
2. breaks hydrogen bonds to separate strands
3. both strands act as template
4. free nucleotides attach
5. by complementary base pairing
6. DNA polymerase joins nucleotides
7. hydrogen bonds reform

Question 12

what is a gene (1)

Answer 12

• a base sequence of DNA that codes for a polypeptide

Question 13

the change in proportion of DNA containing heavy N is due to the way DNA replicates- explain how (2)

Answer 13

1. strands separate
2. each acts as a template
3. 1 strand in new molecule
4. new strands made of light N

Question 14

describe the structure of DNA and the structure of a chromosome (6)

Answer 14

1. DNA is double stranded- held together by H bonds
2. DNA is a polymer of nucleotides
3. nucleotides joined together by phosphodiester bonds
4. complementary base pairing between A and T, C and G

chromosome:
5. DNA associated with histones
6. chromosomes consist of 2 chromatids joined at centromere

Question 15

define phenotype (2)

Answer 15

• an expression of the genes
• and interactions with the environment

Question 16

assess the advantages of scientists questioning a current theory rather than automatically accepting it

Answer 16

alternative theories can be explored
new facts may emerge so the existing theory may be modified or a new theory may be put forward

Question 17

explain what is meant by the term ‘hypothesis’ in the scientific sense

Answer 17

a suggested explanation of something based on logical scientific reasoning

Question 18

a new scientific discovery often presents economic, moral, ethical issues.
justify why it is necessary for society to analyse the risks and benefits of these discoveries before they are developed.

Answer 18

society will be affected by new discoveries and so is entitled to say how they can be used

Question 19

suggest what the term ‘in vivo’ means in the context of synthesising DNA

Answer 19

means ‘in life’
the synthesis of DNA by a living organism rather than in a laboratory

Question 20

explain why DNA polymerase can only attach nucleotides to the OH group on the 3 carbon molecule

Answer 20

enzymes are specific
active sites of a specific shape that fits their substrate
shape of 3’ end of the molecule with the OH fits the active site of DNA polymerase but the shape of 5’ end does not fit

Question 21

What is a gene?
[1 mark]

Answer 21

A sequence of DNA (nucleotide) bases that
codes for a polypeptide;

Question 22

Describe how the production of messenger RNA (mRNA) in a eukaryote cell is
different from the production of mRNA in a prokaryote cell.

Answer 22

1. Pre-mRNA (only) produced in eukaryote (cell);
2. Splicing (only) occurs in eukaryote (cell);

Question 23

Scientists produced a short, single-stranded, artificial nucleic acid, called PNA.
The PNA binds to a section of DNA.
The scientists introduced PNA into cells and discovered that these cells produced
less mRNA than cells that did not contain PNA.
Suggest how PNA affected the transcription of the section of DNA.
[2 marks]

Answer 23

1. PNA is complementary to DNA
2. Preventing/reducing RNA polymerase
   activity/binding