DNA, genes and chromosomes

Question 1

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

Answer 1

locus/loci;

Question 2

describe how a gene is a code for the production of a polypeptide. do not include information about transcription or translation in your answer. (3)

Answer 2

1. (because) base/nucleotide sequence;
2. (in) triplet(s);
3. (determines) order/sequence of amino acid sequence/primary structure (in polypeptide);

Question 3

define the term exon. (1)

Answer 3

base/nucleotide/triplet sequence coding for polypeptide/sequence of amino acids/primary structure;

Question 4

describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule. (2)

Answer 4

1. condensation (reaction)/loss of water;
2. (between) phosphate and deoxyribose;
3. (catalysed by) DNA polymerase;

Question 5

name the protein associated with DNA in a chromosome. (1)

Answer 5

histone;

Question 6

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

Answer 6

1. DNA that does not code for protein/polypeptides
   OR
   DNA that does not code for (sequences of) amino acids
   OR
   DNA that does not code for tRNA/rRNA;
2. (positioned) between genes;

Question 7

give three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell. (3)

Answer 7

plant Vs prokaryote
1. (associated with) histones/proteins v no histones/proteins;
2. linear v circular;
3. no plasmids v plasmids;
4. introns v no introns;
5. long(er) v short(er);

Question 8

the nucleus and a chloroplast of a plant cell both contain DNA.
give three ways in which the DNA in a chloroplast is different from DNA in the nucleus. (3)

Answer 8

in chloroplasts
1. DNA shorter;
2. fewer genes;
3. DNA circular not linear;
4. not associated with protein/histones, unlike nuclear DNA;
5. introns absent but present in nuclear DNA;

Question 9

give one other difference between the structure of a DNA nucleotide and the structure of an RNA nucleotide. (1)

Answer 9

deoxyribose in DNA and ribose in RNA;

Question 10

label:
1. the top of tRNA molecule
2. the bottom of tRNA molecule

Answer 10

1. amino acid binding site;
2. anticodon;

Question 11

not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide.
give two reasons why. (2)

Answer 11

1. triplets code for same amino acid;
2. occurs in introns/non-coding sequence;

Question 12

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

Answer 12

comparisons
1. nucleotide structure is identical;
2. nucleotides joined by phosphodiester bond;
OR
deoxyribose joined to phosphate (in sugar, phosphate backbone);
3. DNA in mitochondria/chloroplasts same/similar (structure) to DNA in prokaryotes;

contrast
4. eukaryotic DNA is longer;
5. eukaryotic DNA contains introns, prokaryotic DNA does not;
6. eukaryotic DNA is linear, prokaryotic DNA is circular;
7. eukaryotic DNA is associated with/bound to protein/histones, prokaryotic DNA is not;

Question 13

suggest one way the structure of the chromosome could differ along its length to result in the stain binding in some areas. (1)

Answer 13

difference in base sequences;
OR
differences in histones/interactions with histones;
OR
differences in condensation/(super)coiling;

Question 14

what is a homologous par of chromosomes? (1)

Answer 14

(two chromosomes that) carry the same genes;