6.1 cellular control

Question 1

What is a mutation

Answer 1

a random change to the genetic material. It involves changes to the structure or number of chromosomes. They occur spontaneously during DNA replication before cell division

Question 2

what are the two main classes of DNA mutation

Answer 2

-point mutation- one base pair replaces another
-Indel mutation- one or more nucleotides are inserted or deleted from a length of DNA- may cause a frameshift

Question 3

what are the 3 types of point mutation

Answer 3

-silent
-missense
-nonsense

Question 4

what is often called the redundancy or degeneracy of genetic code

Answer 4

As all amino acids, apart from methionine, have more than one base triplet code, it reduces the effect of point mutations as they do not always cause a change to the sequence of amino acids in a protein.

Question 5

what is a silent mutation

Answer 5

a mutation involving a change to the base triplet, where that triplet still codes for the same amino acid. The primary, secondary and tertiary structure of a protein is not altered.

Question 6

what is a missense mutation

Answer 6

a change to the base triplet sequence that leads to a change in the amino acid sequence in a protein. It alters the primary structure therefore the tertiary structure of a protein, which alters its shape and prevents it from carrying out its usual function.

Question 7

what does sickle cell anaemia result from

Answer 7

a missense mutation on the 6th base triplet of the gene for the B-polypeptide chains of haemoglobin. Valine is inserted in this position instead of glutamic acid. This results in deoxygenated haemoglobin crystallising within erythrocytes, causing them to become sickle shaped, blocking capillaries and depriving tissues of oxygen

Question 8

what is a nonsense mutation

Answer 8

when a point mutation alters a base triplet so that it becomes a termination (stop) triplet. This results in a truncated protein that will not function

Question 9

what are the types of indel mutations

Answer 9

-insertions
-deletions

Question 10

what is an insertion or deletion

Answer 10

If nucleotide base pairs, not in multiples of 3, are inserted or deleted in the gene, as the code is non overlapping and read in groups of 3 bases, all the subsequent base triplets are altered. This is a frameshift.

Question 11

What happens when there is a frameshift in a gene

Answer 11

when the mRNA from a mutated gene is translated, the amino acid sequence after the frameshift is severely disrupted. The primary and tertiary structure is much altered. The protein cannot carry out its normal function. If it is very abnormal, it will be rapidly degraded within the cell.

Question 12

what happens when there is an insertion or deletion of a triplet of base pairs

Answer 12

it results in an addition or loss of amino acid and not in a frameshift

Question 13

how can mutations be harmful/beneficial

Answer 13

-blue eyes may be harmful in areas where sun intensity is high as the lack of iris pigmentation could lead to lens cataracts/in more temperate zones, it could enable people to see better in less bright light
-humans in Africa would have black skin, the high concentrations of melanin protecting them from sunburn and cancer
-when humans migrated to temperate regions, a paler skin would be an advantage, enabling vitamin D to be made with a lower intensity of sunlight- vitamin D protects from heart disease and cancer

Question 14

what mutations can be considered neutral

Answer 14

-inability to smell certain flowers, including freesias and honeysuckle
-differently shaped ear lobes

Question 15

define exon

Answer 15

the coding, or expressed, region of DNA

Question 16

define intron

Answer 16

the non-coding region of DNA

Question 17

define operon

Answer 17

a group of genes that function as a single transcription unit

Question 18

define transcription factor

Answer 18

protein or short non-coding RNA that can combine with a specific site on a length of DNA and inhibit or activate transcription of the gene

Question 19

what is the lac operon

Answer 19

the control sites and structural genes of E coli

Question 20

what are the control sites of the lac operon

Answer 20

the promoter region (P)
the operator region (lacO)

Question 21

what are the structural genes of the lac operon

Answer 21

lacZ- codes for b-galactosidase
lacY- codes for lactose permease

Question 22

what is I in the lac operon

Answer 22

regulatory gene

Question 23

describe what happens when E-coli is grown on glucose

Answer 23

when ecoli is grown on glucose, the regulatory gene codes for the repressor protein. The repressor protein binds to the operator region which prevents the RNA polymerase from binding to the promoter region. This means that the mRNA for lactase permease and b-galactosidase cannot be transcribed and therefore cannot be translated meaning the enzymes for lactose metabolism are not made. The genes lacZ and lacY are off. As the e-coli is grown on glucose, it can use it as a respiratory substrate therefore it would be a waste of amino acids and energy to create the enzymes when it can already respire.

Question 24

describe what happens when E-coli is grown on lactose

Answer 24

when ecoli is grown on lactose, molecules of lactose bind to the lacI repressor protein molecules which alters the shape of the lacI repressor protein therefore preventing it from binding to the operator. Because of this, RNA polymerase can bind to the promoter region and begin transcribing the structural genes into mRNA that will then be translated into B-galactosidase and lactose permease. Lactose Permease increases the uptake of lactose and b-galactosidase hydrolyses lactose to glucose and galactose. Therefore, the ecoli can respire the glucose

Question 25

why is lactose an inducer

Answer 25

it changes the shape of the repressor protein which prevents it from binding to the operator region