3.4.1 - 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. do not include information about transcription or translation (3)

Answer 2

1. because bases
2. in triplets
3. determines the order of the amino acid sequence that makes up the primary structure of a polypeptide

Question 3

define the term exon (1)

Answer 3

base triplet sequence coding for a sequence of amino acids

Question 4

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

Answer 4

1. condensation reaction
2. between phosphate group and deoxyribose
3. catalysed by DNA polymerase

Question 5

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

Answer 5

histone

Question 6

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

Answer 6

plant DNA: associated with histones, linear, no plasmids, introns, longer

prokaryotic DNA: no histones, circular, plasmids, no introns, shorter

Question 7

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

Answer 7

1. DNA that does not code for sequences of amino acids
2. found between genes

Question 8

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

Answer 8

DNA in chloroplasts: shorter, fewer genes, circular, no histones, no introns

Question 9

some DNA nucleotides have the organic base thymine, but RNA nucleotides do not. RNA nucleotides have uracil instead of thymine.

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

Answer 9

• deoxyribose sugar in DNA
• ribose sugar in RNA

Question 10

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 10

1. multiple triplets code for the same amino acid (code is degenerate)
2. the mutation occurs in the introns

Question 11

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

Answer 11

comparisons:
1. nucleotide structure is identical
2. nucleotides joined by phosphodiester bond
3. DNA in mitochondria and chloroplasts is similar structure to prokaryotic DNA

contrasts:
4. eukaryotic DNA is: longer, contains introns, linear, associated with histones

Question 11

the dark stain used on the chromosomes binds more to some areas of the chromosomes than others, giving the chromosome a stripped appearance.

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

Answer 11

differences in base sequences

Question 11

what is a homologous pair of chromosomes? (1)

Answer 11

two chromosomes that carry the same genes
OR
same loci

Question 12

what is a gene? (1)

Answer 12

a sequence of DNA bases that code for either a polypeptide or functional RNA

Question 13

what is a proteome? (1)

Answer 13

the full set of proteins a cell can produce