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 things called that increase the chance of a mutation happening (non-genetic)

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,
resulting in all amino acids being coded for downstream to change
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 2 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, as the genetic code is degenerate

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.

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

Majority of DNA is non-coding regions
So a mutation is most likely to occur in non-coding regions of DNA
This will have no effect on the proteins coded for and the organism’s phenotype as introns are removed from mRNA when it is spliced

Question 14

define operon

Answer 14

a section of DNA that contains a cluster of genes that are transcribed together as well as control elements and a regulatory gene.

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 - lac- regulatory gene that 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- lac A codes for acetyl transferase

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

What are the 3 stages gene expression can 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
• post-translation - proteins can be modified after synthesis which changes their function- role of cAMP

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 and reordered to make mature mRNA
The different order of mature mRNA changes the sequence of amino acids it codes for resulting in a different protein being produced.

A cap is added to the 5’ end of the mRNA strand and a tail is added to the 3’ end of the mRNA strand.
This prevents degradation of the mRNa stand in the cytoplasm so it stays in the cytoplasm for longer
This means more of it can be translated resulting the production of more protein

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

what was first found in fruit flies

Why are fruit flies used in scientific research rather than another organism

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 sequence

define homeobox genes

Answer 24

The homeobox sequence :
Is a 180 bp long sequence which codes for 60 amino acid long homeodomain and is involved in regulating the development and body plan of plant animals and fungi.
The homeobox sequence is highly conserved within the plants animal and fungi kingdoms

Homeobox genes:
Group of regulatory genes that contain a homeobox sequence which codes for a homeodomain which acts as a transcription factor by controlling gene expression of an organism’s body plan.

Question 25

homeodomain proteins

Answer 25

proteins that acts as transcription factors by binding to DNA and activating or repressing genes that regulate the cell cycle, mitosis and apoptosis.

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) Enzymes break down the cytoskeleton causing the cell to shrink
2) Cell begins to bleb and nucleus disintegrates
3) Small fragments are produced with the cell membrane intact and containing organelles
4) Phagocytes engulf the fragments by phagocytosis
5) Hydrolytic enzymes break down cell fragments

Question 36

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

Answer 36

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

Question 37

Define Hox genes

Answer 37

Hox genes are a subset of homeobox genes found only in animals. They are involved in the formation of anatomical features in correct location of an animal’s body plan. They code for homeodomain proteins.

Question 38

What internal factors affect rate of appoptosis

Answer 38

Release of Hormones

Mutations

Question 39

What external factors affect the rate of apoptosis

Answer 39

Physiological Stress- People lose hair and weight
Drugs
Lack of nutrients/food
Infection
Light- In plants, leaf fall occurs during winter due to lower light intensities

Question 40

Give examples of mutagens

Answer 40

Carcinogens
X-rays
UV Light