chapter 19

Question 1

RNA polymerase and DNA polymerase are both enzymes. RNA polymerase is involved in the action of some control elements, whereas DNA polymerase is not.

Describe and explain the difference between the functions of these two enzymes.

Answer 1

RNA polymerase
makes (m / messenger / t / transfer / r / ribosomal) RNA ;
2 transcription ;
3 one strand (DNA) used / short section used / one strand formed ;

DNA polymerase
4 DNA replication ;
5 semi-conservative / both strands used /
whole length used / 2 strands formed ; 6 before , nuclear / cell , division ;

Question 2

State what is meant by a homeobox gene.

Answer 2

homeotic / regulatory, (gene) ;
contains, 180 base pairs / homeobox, sequence ; that codes for homeodomain (on protein) ; (gene product) binds to DNA ;
initiates transcription / switch genes, on / off ; control of, development / body plan ;

Question 3

Homeobox genes show ‘astonishing similarity across widely different species of animal’.

Explain why there has been very little change by mutation in these genes.

Answer 3

these genes very important ;
mutation would, have big effects / alter body plan ; many other genes would be affected / knock-on effects ; mutation likely to be, lethal / selected against

Question 4

State the stage(s) in which the following events occur:

independent assortment
formation of the spindle apparatus separation of sister chromatids formation of nuclear membranes chromosomes pulled to opposite poles

Answer 4

metaphase I and metaphase II ; prophase I ;
anaphase II ;
telophase II ;
anaphase I ;

Question 5

Explain why meiosis needs to have twice as many stages as mitosis.

Answer 5

to, halve chromosome number / reduce from 2n to n ;

to separate homologous pairs (of chromosomes)
and sister chromatids ;

because, DNA (previously) replicated /
chromosomes are two chromatids at start ;

Question 6

Meiosis is a source of genetic variation. Mutation is another source of variation.
(i) What feature of the DNA molecule is changed as a result of mutation

Answer 6

sequence / order, of bases / nucleotides ;

Question 7

Discuss the possible effects that mutation can have on the structure and function of a
protein.

Answer 7

different, primary / secondary / tertiary, structure ;
(protein ) shorter due to, deletion / stop codon

OR

longer due to, insertion / duplication ;
(protein) unchanged due to, silent mutation / non-coding DNA altered ;
for ‘silent’

or a description of more than one triplet coding for one amino acid
(function is) lost / worse / better

Question 8

Suggest two purposes of a plant collection in a modern botanic garden.

Answer 8

conservation / keep rare plants / save endangered plants ; 2 gene bank OR genetic resource / store of alleles ;
3 teaching / education ;
4 leisure / amenity / visitor attraction / aesthetic value ;

Question 9

State what is meant by gene mutation.

Answer 9

change to , DNA / base(s) / nucleotide(s)

Question 10

Distinguish between the terms ‘regulatory gene’ and ‘structural gene’.

Answer 10

regulatory
idea that makes , repressor protein / transcription factor or
idea that product switches (structural / another) gene , on / off ;

‘structural
idea that makes , enzyme / polypeptide / protein ;

relationship between the 2
idea that regulatory gene , controls / affects ,the expression of structural gene ;

Question 11

The control of the expression of the lac operon genes, which allow uptake and digestion of lactose in the bacterium Escherichia coli, is well known.
Fig. 1.2 shows the arrangement of the elements of the lac operon.
Fig. 1.2
Describe how genes Z and Y are switched on in bacteria that are moved to a nutrient medium
that contains lactose.

Answer 11

lactose binds to repressor protein ;

2 changes , shape / structure (of protein) ;

3 removes it from / stops it binding to , operator ;

RNA polymerase binds to promoter ;

5 idea that (so that Z and Y) are , transcribed / mRNA made ;

CREDIT lactose permease and β-galactosidase for Z and Y

Question 12

What is an operon?

Answer 12

A cluster of genes under the control of a promoter.

Question 13

What feature of a pathogen such as Mycobacterium tuberculosis could be altered by a mutation, making a vaccine ineffective?

Answer 13

(shape of), proteins / glycoproteins / glycocalyx / antigens of the plasma / cell surface, membrane (1)

Question 14

State what structural detail of a polypeptide is altered by gene mutations

Answer 14

sequence / order, of amino acids

Question 15

Explain how it is possible for a mutation to have no effect on the protein produced from that gene.

Answer 15

some triplets, code for same amino acid / are degenerate (1)
(so) the amino acid sequence is not altered (1)
some alternative amino acids will not alter the shape of the protein (1)
mutation occurs in intron (1)

Question 16

Explain how a mutation could alter the protein so that it no longer performs its correct function in the cell.

Answer 16

an insertion / deletion will cause frame shift (1)

all triplets downstream will be different (1)

the protein will have a different sequence of amino acids (downstream of the mutation) (1)

the, tertiary structure / three dimensional shape will be different (1)

Question 17

describe how transcription can be controlled in eukaryotes with lac operon

Answer 17

hormone enters cell and binds to a transcription factor (1)
transcription factor activated (1) binds to, site A / promoter region (1) RNA polymerase able to bind (1)

Question 18

Describe how gene expression can be regulated after transcription.

Answer 18

primary mRNA is modified (1)
removal of introns to produce mature mRNA (1)
Alternative splicing can produce different versions of mRNA (1)
protein must be activated by cAMP / phosphorylation (1)
binding (of cAMP) alters shape of protein (1)