Cellular Control

Question 1

Suggest why this mutation reduces the effectiveness of salmeterol.

Answer 1

(mutation) change in (DNA) nucleotide/ base, sequence ;
(mutation causes) change in,
amino acid sequence / primary structure
(of protein) ;
change in , tertiary structure/ 3D shape / binding site , of
receptor ;
salmeterol unable to bind ;
idea that no response triggered in cell /
no second messenger system activated ;

Question 2

After one year, the children taking montelukast had better control of their asthma and were able to reduce their use of montelukast. Suggest why these children responded better to montelukast than to salmeterol.

Answer 2

(mutation resulted in) receptor having
complementary shape to montelukast ; 
montelukast able to bind ; 
(whereas) salmeterol cannot ; 
montelukast may have a different receptor ;

Question 3

State the number of DNA nucleotide bases that code for a single amino acid.

Answer 3

3.

Question 4

There is a maximum of 64 different base combinations in DNA that could each code for an amino acid.How is this number of combinations calculated?

Answer 4

4^3

Question 5

Twenty different amino acids are commonly used for protein synthesis. In theory, this would need only 20 different base combinations.
Explain the uses of the remaining 44 combinations.

Answer 5

Several, triplet(s) / codon(s) ,
code for one amino acid ; 
(some are used as) start / stop / termination ; 
idea that mutation may , 
not result in change in amino acid / 
have a neutral effect / 
result in silent mutation ;

Question 6

Describe how a nucleotide base sequence in a gene is used to synthesise a polypeptide.

Answer 6

transcription
1 DNA / gene , copied / transcribed , into mRNA ;
2 free / activated ,
(RNA) nucleotides / (RNA) nucleoside triphosphates ;
3 (line up by) complementary base-pairing / described ;
4 (to) one / template / reference / sense , (DNA) strand ;
5 (catalysed by) RNA polymerase ;
translation
6 (mRNA moves to) ribosomes ;
7 tRNA (molecules) bind to mRNA ;
8 anticodon(s) , match / pair with / bind to , codons ;
9 specific / correct , amino acid attached to tRNA ;
10 formation of peptide bond between amino acids;

Question 7

Meiosis is used in many organisms for the production of gametes.
Explain why meiosis needs to have twice as many stages as mitosis.

Answer 7

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 8

What feature of the DNA molecule is changed as a result of mutation?

Answer 8

sequence / order, of bases / nucleotides ;

Question 9

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

Answer 9

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 ;
(function is) lost / worse / better ;

Question 10

Explain why dwarfism can be described as a genetic condition.

Answer 10

inherited / passed to offspring /
passed (down) from parents ;
(caused by) mutation / allele ;

Question 11

Describe one other example of genes being switched on or being switched off by a molecule that binds directly to DNA.

Answer 11

EITHER
1 (lac) repressor protein ;
2 (repressor protein) changes shape when bound to
lactose ;
3 (with lactose) lifts off operator allowing,
transcription / gene expression /
binding of RNA polymerase to promoter ; ORA
4 β-galactosidase / enzyme(s) / structural gene(s) ;
OR
5 homeotic / homeobox / hox (genes) ;
6 gene product / protein / transcription factor,
binds to DNA ;
7 gene product / protein, starts transcription / is a
transcription factor ;
8 many genes affected / controls body plan ;

Question 12

Outline the events that lead to genetic variation in gametes and in the plants grown from seed.

Answer 12

1 mutation ;
2 meiosis ; 
3 cross(ing)-over ; 
4 between non-sister chromatids ; 
5 (in) prophase I ; 
6 independent / random , assortment / segregation ; 
7 (in) metaphase ; 
8 idea of random , fertilisation / fusion of gametes ;

Question 13

Suggest two ways in which the varieties may differ from one another biochemically to account for the difference in the length of the cold period required by each.

Answer 13

they have different (qualitatively or quantitatively)
1 genes / DNA / alleles / genotypes ;
2 repressor proteins ;
3 enzymes ;
4 protein folding / tertiary structure / thermostability ;
5 (plant) growth regulators / hormones ;

Question 14

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 14

RNA polymerase
1 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 15

The panda crystallin protein obtained was 175 amino acids long, corresponding to a 528 base pair cDNA gene.
Explain why a protein that is 175 amino acids long is coded for by 528 base pairs of DNA.

Answer 15

triplet code or 3 bases = 1 amino acid ;
525 ;
3 bases are , stop / (chain) termination , codon ;

Question 16

State what is meant by a homeobox gene.

Answer 16

homeotic / regulatory, (gene) ;
contains, 180 bp / 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 17

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 17

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 18

List two cellular processes that must occur during the development of a tadpole into a frog.

Answer 18

protein synthesis / transcription and translation 
respiration ;
DNA replication ;
mitosis ;
cytokinesis ;
apoptosis ;
differentiation / gene switching ;

Question 19

Name another kingdom of organisms, other than animals, that have similar homeotic genes.

Answer 19

fungi / plants ;

Question 20

State the name of the stage of protein synthesis and name the organelle in the cell where this takes place.

Answer 20

translation ;

ribosome / rough ER / RER ;

Question 21

State what is meant by gene mutation.

Answer 21

idea of change to , DNA / base(s) / nucleotide(s) ;

Question 22

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

Answer 22

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 23

Describe how genes lacZ and lacY are switched on in bacteria that are moved to a nutrient medium that contains lactose.

Answer 23

1. lactose binds to repressor protein ;
2. changes , shape / structure (of protein) ;
3. removes it from / stops it binding to , operator ;
4. RNA polymerase binds to promoter ;
5. idea that (so that Z and Y) are transcribed / mRNA made ;

Question 24

Name the type of gene which, if mutated, gives rise to dramatic changes in body plan.

Answer 24

homeotic / homeobox / hox ;

Question 25

Describe how the information coded on genes is used to synthesise polypeptides and how these polypeptides control the physical development of an organism.

Answer 25

1 synthesis
2 DNA, copied into mRNA 
3 transcription / transcribed ;
4 one strand copied ;
5 complementary base-pairing 
6 triplet code / code read in threes / codon is 3 bases ;
7 base sequence determines amino acid sequence ;
8 translation ;
9 ribosomes

roles of polypeptides:
10 actin/collagen/keratin
11 enzymes / catalyse reactions / control metabolism 
12 hormones / growth factors ;
13 receptor proteins ;
14 adenyl cyclase / cAMP ;
15 idea of switching genes, on / off ;
16 homeotic / homeobox, genes
or homeodomain proteins ;
17 idea of master switch gene /
 one gene turns on/off whole set of other genes /
 cascades of gene switching ;
18 apoptosis ;

Question 26

Three alleles of DRD4 have the following alterations:
• a single base-pair substitution
• a 21 base-pair deletion
• a 13 base-pair deletion.
Suggest which of the three mutations will have the most serious consequences for the structure of the protein receptor. Give a reason for your choice.

Answer 26

13 b-p deletion (has most serious consequences) ;
frameshift / alter reading frame ;
genetic code is triplet / read in groups of 3 bases ;
alters all amino acids (coded for) after the mutation ;
21 b-p deletion causes 7 amino acids to be lost ;
substitution changes, one / no, amino acids ;