M6, C19 Genetics Of Living Systems

Question 1

define mutation

Answer 1

changes (amount or arrangement) to the base (nucleotide) sequence of DNA

Question 2

define chromosome mutation

Answer 2

changes to parts of or whole chromosomes

Question 3

define DNA mutation

Answer 3

changes to genes due to changes in nucleotide base sequence

Question 4

what are the things called which cause mutations

Answer 4

mutagens

Question 5

what are the 6 types of gene mutations

Answer 5

point or substitution - only one nucleotide is affected
insertion - inserting a base which shifts nucleotides to the right
deletion - base or triplet removed
nonsense - stop codon being coded for due to substitution
missense - different amino acid being coded for, which will alter primary structure of polypeptide and probably change its tertiary structure
silent/neutral - same amino acid being coded for, as genetic code is degenerate, therefore polypeptide will be unaltered

Question 6

what are the different ways mutations can affect an organism (both beneficially and harmfully)

Answer 6

Beneficial - mutation produces an advantage to the organism, so increase chance of survival
- these are passed onto offspring, by the process of natural selection

Harmful - mutation produces a disadvantage, so decrease chance of survival
- organism may not survive or mate

Question 7

what is a conservative mutation

Answer 7

when the amino acid change leads to an amino acid being coded for which has similar properties to the original, this means the effect of the mutation is less severe

Question 8

what is non-conservative mutation

Answer 8

when the new amino acid coded for has different properties to the original

Question 9

what are frameshift mutations

Answer 9

adding or deleting a base causes a sift in bases that follow
the base sequence is read differently
the earlier the frameshift, the greater the effect on the protein

(it is NOT a frameshift if a triplet is added)

Question 10

what are the 4 types of chromosome mutations

Answer 10

Deletion - a section of chromosome breaks off and is lost within the cell

Duplication - sections get duplicated on a chromosome

Translocation - a section of chromosome breaks off and joins another non-homologous chromosome

Inversion - a section of chromosome breaks off, is reversed and then joins back onto the chromosomes

Question 11

give 3 ways in which a mutation gives a neutral effect on the protein

Answer 11

If the mutation changes a base sequence in a triplet, but the amino acid the triplet codes for doesn’t change

If the mutation produces a triplet that codes for a different amino acid, but the amino acid is chemically similar to the original so it functions like the original amino acid.

If the mutated triplet codes for an amino acid not involved in the proteins function.

Question 12

Give one example of how a mutation can lead to a protein not being produced

Answer 12

A mutation at the start of a gene could result in RNA polymerase not being able to bind to the gene, which would mean that the protein coded for by the gene wouldn’t be produced.

Question 13

Outline why the majority of mutations do not have an influence on phenotype

Answer 13

Mutations are random.
Mutations are more likely to occur in non-coding regions.
Majority of DNA is non-coding.
But a mutation on a non-coding region doesn’t affect the phenotype.

Question 14

define operon

Answer 14

a section of DNA that contains a cluster of structural genes that are transcribed together

Question 15

what are factors that start transcription called?

what are factors that stop transcription called?

Answer 15

start - activators

stop -repressors

Question 16

The image for lac operon in E.coli is represented with the letter IPOZYA
what do they all stand for

Answer 16

I - lacI produces lac repressor, which is the transcription factor
P - promoter - RNA polymerase binds here to start transcription of structural genes
O - repressor binds here, switch structural genes on and off
Z - lacZ - beta-galactosidase - hydrolyse lactose to glucose and galactose
Y - lacY - lactose permease - allows cell to take up lactose
(A - lacA - enzyme that transfers an acetyl group from acetyl-CoA to beta-galactosides, precise function not known)

Question 17

in the lac operon in E. coli, what happens when lactose is NOT present

Answer 17

• lacI produces the lac repressor which is the transcription factor
• it binds to the operator site
• this also covers the promoter which blocks transcription because the RNA polymerase can’t bind to the promoter

Question 18

in the lac operon in E. coli, what happens when lactose is present

Answer 18

• the lactose binds to the repressor which is on the operator site
• this changes the shape of the repressor meaning it can no longer bind to the operator site
• RNA polymerase can now begin transcription of the structural genes

Question 19

at what stages can gene expression be controlled

Answer 19

• transcriptional - genes can be turned on/off
• post-transcription - mRNA can be modified which regulates translation and the types of protein produced
• translational - translation can be stopped/started
• post-translation - proteins can be modified after synthesis which changes their function

Question 20

how is protein production controlled at the post-transcriptional level

Answer 20

After transcription

• mRNA is edited because it contains sections that don’t code for amino acids (introns)
• the primary mRNA transcript has introns in it so they have to be removed by the process of splicing
• exons (bits that do code for amino acids) and joined together to make mature mRNA

Question 21

define introns and exons

Answer 21

introns - genes in eukaryotic DNA that don’t code for amino acids

exons - bits that do code for amino acids

Question 22

how is protein production controlled at the post-translational level

Answer 22

-some proteins aren’t functional straight away (they need to be activated to become functional)
-protein activation is controlled by molecules (hormones and sugars)
-the molecules bind to the cell surface membrane and trigger the production of cAMP (cyclic-AMP) inside the cell
-cAMP activates proteins inside the cell by altering their 3D structure
(-by altering the 3D structure the active site changes shape making it more or less active)

Question 23

give some details about fruit flies

what was first found in them

Answer 23

Genes that control body development first found in fruit flies
Very small (2mm), easy to keep, short life cycle
Reproduce quickly
Cheap
Feed on rotting fruit

Question 24

define homeobox

define homeobox genes

Answer 24

The homeobox:
Is a section of DNA, 180 base pairs long coding for a part of the protein, 60 amino acids long that is very similar in plants, animals and fungi
Homeobox genes:
Group of genes that contain a homeobox

direct the formation of many body structures during early embryonic development

Question 25

define homeobox domain

Answer 25

Homeobox domain:

The part of the protein that binds to DNA and switches other genes on or off

Question 26

what type of genes are homeobox genes

Answer 26

regulatory genes

Question 27

what are gene clusters

Answer 27

homeobox genes are found in clusters

Question 28

why do humans have lots of Hox genes

Answer 28

Humans have 39 Hox genes, due to duplication and accumulated mutations

Question 29

what does it mean when it’s said that homeobox sequences are highly conserved

Answer 29

they haven’t changed much during evolution of different organism

Question 30

how do homeobox sequences work

Answer 30

• They code for a part of the protein called the homeobox domain
• The homeobox domain binds to specific sites on DNA, enabling the protein to work as a transcription factor
• The proteins bind to DNA at the start of developmental genes, activating or repressing transcription, so altering the production of proteins involved in the development of body plans

Question 31

what types of symmetry can be seen in organisms

Answer 31

Radial symmetry – in diploblastic animals like jellyfish – they have no right/left sides, only a top and bottom

Bilateral symmetry – seen in most animals, have left/right symmetry and a head/tail rather than top/bottom

Asymmetry – seen in sponges – no lines of symmetry

Question 32

define apoptosis

Answer 32

programmed cell death

Question 33

what type of genes regulate mitosis and apoptosis

Answer 33

hox genes

Question 34

how does apoptosis shape us when we’re developing

Answer 34

Removing unwanted cells and tissues can cause different body parts to be shaped
Cells undergoing apoptosis can release chemical signals which stimulate mitosis and cell proliferation, causing the remodelling of tissues.

Question 35

what is the step-by-step process of apoptosis

Answer 35

1) Cell shrinks, enzymes break down cytoskeleton
2) Cell membrane changes, blebs form
3) Chromatin condenses, nuclear envelope breaks and the DNA breaks into fragments
4) The cell breaks up into vesicles
5) Phagocytes engulf the vesicles
6) The cellular debris is either disposed of or reused.

Question 36

what internal factors can affect regulatory genes

Answer 36

Psychological stress
Release of hormones, growth factors
Cytokines

Question 37

what external factors can affect regulatory genes

Answer 37

temperature change

light intensity

Question 38

give an example of a drug which affects regulatory genes and prevented mitosis and apoptosis from working

Answer 38

thalidomide
prevented the expression of a particular Hox gene
resulted in shortened limbs in babies