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

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

Answer 3

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

Question 4

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

Answer 4

histone

Question 5

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

Answer 5

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

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

Question 6

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

Answer 6

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

Question 7

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

Answer 7

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

Question 8

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 8

• deoxyribose sugar in DNA
• ribose sugar in RNA

Question 9

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 9

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

Question 10

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

Answer 10

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 10

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 10

differences in base sequences

Question 10

what is a homologous pair of chromosomes? (1)

Answer 10

two chromosomes that carry the same genes
OR
same loci

Question 11

what is a gene? (1)

Answer 11

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

Question 12

what is a proteome? (1)

Answer 12

the full set of proteins a cell can produce

Question 13

other than being smaller, give two ways in which prokaryotic DNA is different from eukaryotic DNA (2)

Answer 13

1. prokaryotic DNA is circular
2. prokaryotic DNA is not associated with histones
3. prokaryotic DNA does not contain any introns

Question 14

describe how the production of mRNA in a eukaryotic cell is different from the production of mRNA in a prokaryotic cell (2)

Answer 14

1. pre-mRNA only produced in eukaryote cell
2. splicing only occur in eukaryote cell
3. introns removed in eukaryote OR no introns in prokaryote

Question 15

scientists produced a short, single-stranded, artificial nucleic acid called PNA. the PNA binds to a small section of DNA.

the scientists introduced PNA into cells and discovered that these cells produced less mRNA than the cells that did not contain it.

suggest how PNA affected the transcription of the section of DNA (2)

Answer 15

1. PNA is complementary to DNA
2. preventing RNA nucleotides binding OR reducing transcription

Question 16

this question is about the genetic code.

define universal, non-overlapping and degenerate (3)

Answer 16

1. universal = the same codon always codes for the same amino acid
2. non-overlapping = each base is only part of one codon OR adjacent codons do not overlap
3. degenerate = more than one codon codes for each amino acid

Question 17

describe one difference between the structure of DNA in a prokaryotic cell and in a eukaryotic cell (1)

Answer 17

1. in prokaryotes DNA circular not linear
2. in prokaryotes DNA not associated with histones
3. in prokaryotes DNA has no introns

Question 18

describe the mechanism of breathing that causes air to enter the lungs (3)

Answer 18

1. diaphragm muscle contract and diaphragm is pulled down/flattens
2. external intercostal muscles contract and ribcage is pulled up/out
3. causes volume increase and pressure decrease in lungs to below atmospheric pressure

Question 19

name two biological molecules that can be coded for by a gene. do not include a polypeptide or protein in your answer (1)

Answer 19

1. rRNA
2. tRNA
3. mRNA