6.1.1 Cellular Control

Question 1

What is a mutation

Answer 1

Change in sequence of bases of DNA

Question 2

Types of mutations

Answer 2

Point mutation: only affects one nucleotide
Frameshift mutation: insertion, deletion
Substitution

Question 3

Effects of subsitution mutations

Answer 3

Changes codon, different amino acid coded for, change in primary structure
- degenerate nature of DNA means it could still code for the same amino acid
- if protein is enzyme and specific amino acid plays a role in the active site, may no longer act as a biological catalyst

Question 4

Effect of frameshift mutation

Answer 4

Changes every successive codon from point of mutation, due to non-overlapping triplet code

Question 5

Possible effects of mutations

Answer 5

No effect
Damaging: proteins no longer synthesised or are non-functional
Beneficial

Question 6

What is a mutagen

Answer 6

A chemical, physical, or biological agent which causes mutations

Question 7

Examples of physical mutagens

Answer 7

Ionising radiation, e.g. X-rays
- breaks DNA strands, some can be repaired but mutations can occur in the process

Question 8

Examples of chemical mutagens

Answer 8

Deaminating agents: chemically alter bases in DNA, e.g. convert cytosine into uracil in DNA, changes base sequence

Question 9

Examples of biological agents that causes mutation

Answer 9

Alkylating agents: methyl/ethyl groups attached to bases, incorrect pairing of bases during replication
Base analogs: incorporated into DNA in place of usual base during replication, changes base sequence
Viruses: viral DNA may insert itself into genome, changes base sequence

Question 10

Other specific examples of mutations

Answer 10

Depurination (loss of purine base) and deprymidination (loss of pyrimidine base): often occurs spontaneously and can lead to insertion of incorrect base in replication

Free radicals: oxidising agents, affect structure of nucleotides and disrupt base pairing during DNA replication, antioxidants (vitamins A, C, E) negate the effects of free radicals

Question 11

What are introns

Answer 11

Non-protein coding regions of DNA

Question 12

What are exons

Answer 12

Protein-coding regions of DNA

Question 13

Types of chromosome mutations

Answer 13

Deletion: section of chromosome breaks off
Duplication: sections get duplicated
Translocation: section of a chromosome breaks off and joins another non-homologous chromosome
Inversion: section of a chromosome breaks off, is reversed, then joins back on

Question 14

Types of gene regulation

Answer 14

Transcriptional
Post-transcriptional
Translational
Post-translational

Question 15

What is transcriptional regulation

Answer 15

Genes can be turned on or off
- chromatin remodelling
- histone modification
- lac operon

Question 16

What is post-transcriptional regulation

Answer 16

MRNA can be modified which regulates translation and types of proteins produced

Question 17

What is translational regulation

Answer 17

Translation can be stopped or started

Question 18

What is post-translational regulation

Answer 18

Proteins can be modified after synthesis with changes their functions

Question 19

Examples of transcriptional control: chromatin

Answer 19

Chromatin remodelling
- heterochromatin: tightly wound DNA, chromosomes are visible during cell division, transcription not possible
- euchromatin: loosely wound DNA, present during interphase

Question 20

Examples of transcriptional control: histones

Answer 20

Histone modification
- acetylation: addition of acetyl groups
- phosphorylation: addition of phosphate groups
- reduces positive charge on histones, makes them more negative, DNA coils less tightly, certain genes can be transcribed

-methylation: addition of methyl groups, makes histones more hydrophobic, bind more tightly to eachother, DNA coils more tightly, transcription prevented

Question 21

Examples of transcriptional control: lac operon

Answer 21

If glucose is in short supply, lactose can be used as a respiratory substrate
Lac operon: 3 structural genes (lacZ, lacY, lacA) involved in metabolism of lactose, transcribed onto one molecule of mRNA
- Regulatory gene, lacI, is located near and codes for repressor protein that prevents transcription of structural genes in absence of lactose
- repressor protein binds to the operator, prevents RNA polymerase binding to DNA at the promoter

Question 22

What is an operon

Answer 22

Group of genes under control of same regulatory mechanism, expressed at the same time

Question 23

How does the lac operon work when lactose is present

Answer 23

• lactose binds to the repressor protein, changes shape and can no longer bind to operator
• RNA polymerase can bind to promoter, structural genes are transcribed and enzymes are synthesised

Question 24

Role of cAMP in the lac operon

Answer 24

• cAMP repressor protein (CRP) binds to the promoter when it is bound to cAMP
• up-regulates transcription
• transport of glucose into E.coli cell decreases levels of cAMP, reduces transcription of genes for metabolism of lactose

Question 25

Examples of post-transcriptional control

Answer 25

RNA processing: in nucleus - pre-mRNA needs to be modified to mature mRNA before it can bind to a ribosome and code for synthesis of required protein - cap (modified nucleotide) added to 5’ end and tail (chain of adenine) added to 3’ end - stabilises mRNA, delays degradation - cap aids binding of mRNA to ribosomes - splicing, introns removed RNA editing: sequence of mRNA molecules changed through addition, deletion, or substitution

Question 26

Examples of translational control

Answer 26

Degradation of mRNA: - more resistance, lasts longer in cytoplasm, more protein synthesised Binding of inhibitory proteins: - prevents it binding to ribosomes and synthesis of proteins Activation of initiation factors: - aid binding of mRNA to ribosomes Protein kinases: - enzymes that catalyse addition of phosphate group to proteins, changes tertiary structure and function - enzymes activated by this, regulators of cell activity - often activated by secondary messenger, cAMP

Question 27

Examples of post-translational control

Answer 27

Modifications to proteins that have been synthesised: - addition of non-protein groups (carb chain, lipids, phosphate) -modifying amino acids, formation of bonds (disulphide bridges) - folding/shortening of proteins - modification by cAMP

Question 28

Why are fruit flies (drosophila) used in genetic studies

Answer 28

They’re small, easy to keep, have short life cycle

Question 29

What are homeobox genes

Answer 29

Group of genes which contain a homeobox Homeobox = section of DNA 180 base pairs long, codes for 60 AA long part of a protein, highly conserved - part of protein is a homeodomain, binds to DNA and switched other genes on or off - regulatory genes

Question 30

What are hox genes

Answer 30

One group of homeobox genes, only present in animals Responsible for correct positioning of body parts Found in gene clusters: mammals have 4 clusters on different chromosomes Order that they appear in is order that effects are expressed: humans have 39

Question 31

What does diploblastic mean

Answer 31

Animals that have 2 primary tissue layers

Question 32

What does tripoblastic mean

Answer 32

Animals that have 3 primary tissue layers

Question 33

How do hox genes work

Answer 33

Hox genes in the head control development of mouthparts Hox genes in the thorax control development of wings, limbs, or ribs Regulate mitosis and apoptosis

Question 34

What is a somite

Answer 34

Individual vertebrate and structures all develop from segments in the embryo called somites Somites directed by hox genes to develop in a particular way, depending on position in sequence

Question 35

What is radial symmetry

Answer 35

Seen in dipoblastic animals like jellyfish No left/right, only top/bottom

Question 36

What is bilateral symmetry

Answer 36

Organisms have both left/right and head/tail, most animals

Question 37

What is asymmetry

Answer 37

No lines of symmetry, e.g. sponge

Question 38

What is apoptosis

Answer 38

Programmed cell death

Question 39

Role of mitosis in body plans

Answer 39

Increases number of cells, leading to growth

Question 40

Role of apoptosis in body plans

Answer 40

Removed unwanted cells and tissues Can release chemical signals to stimulate mitosis and cell proliferation, tissues are remodelled

Question 41

What factors affect expression of regulatory genes

Answer 41

Stress: - temperature/ light intensity change - release of hormones/ psychological stress Drugs: - thalidomide, prevents normal expression of particular Hox gene, babies born with shortened limbs

Question 42

Uses of thalidomide

Answer 42

Treatment of some forms of cancer Stops development of tumours