6.1.1 Cellular control

Question 1

What are the different methods of mutation?

Answer 1

1) Substitution
2) Deletion
3) Insertion

Question 2

What is a frameshift mutation?

Answer 2

A change in DNA sequence that causes the whole sequence to shift - all consecutive bases affected

Question 3

What are the possible effects of mutations?

Answer 3

1. Neutral
2. Damaging - coding for cancerous or non-functioning protein
3. Beneficial - e.g. HIV immunity, lactose digestion

Question 4

What are four factors that control gene expression at the TRANSCRIPTION level?

Answer 4

1. Chromatin remodelling
2. Histone modification
3. Lac Operon
4. cAMP and CAP (Catabolite activator protein)

Question 5

Describe the role of chromatin remodelling in gene expression

Answer 5

Heterochromatin (TIGHTLY wound DNA) can’t be transcribed - RNA polymerase can’t reach bases.
Euchromatin (LOOSELY wound DNA) are freely transcribed - only present in interphase

Question 6

Describe the role of histone modification in gene expression

Answer 6

DNA coils around histone proteins (DNA negative, histone positive).
Acetylation and Phosphorylation REDUCE positive charge on histones - bind less tightly to DNA so INCREASED transcription
Methylation makes histones more hydrophobic, bind tighter together, DNA coils tighter so DECREASED transcription

Question 7

Describe the role of the lac operon in gene expression

Answer 7

Operon of 3 structural genes - lacZ, lacY and lacA, and nearby regulatory gene (lacI) that codes for repressor protein.
Lactose present: binds to repressor protein, released from operator region and RNA polymerase binds to promoter region - transcription occurs

Question 8

Describe the role of cAMP and CAP in gene expression

Answer 8

Low glucose: cAMP levels HIGH - bind to CAP, enabling binding to CAP site on DNA - FAST transcription
High glucose: cAMP levels LOW, CAP doesn’t bind to DNA - SLOW transcription

Question 9

What two mechanisms occur at a post-transcriptional level to control gene expression?

Answer 9

1. RNA Processing

2. RNA Editing

Question 10

Describe the role of RNA Processing in gene expression

Answer 10

Modification of pre-mRNA to mature mRNA - introns removed, extrons joined together (splicing). ‘Cap’ added to 5’ end, ‘tail’ to 3’ end - helps stabilise and delay degradation of molecule

Question 11

Describe the role of RNA Editing in gene expression

Answer 11

Change in sequence via addition, insertion or substitution. Results in generation of multiple proteins from single strand

Question 12

What four modifications occur in post-translational level that control gene expression?

Answer 12

1. Addition of non-protein groups
2. Modification of amino acids and bond formation
3. Folding or shortening proteins
4. Modification/activation via cAMP

Question 13

Define homeobox genes, and state their role

Answer 13

Codes for a part of a protein that’s highly conserved in plants, animals and fungi (homeodomain). Protein can bind to DNA to switch genes on/off.
E.g. pax6 controls underdevelopment of retina - causes blindness in humans, mice and fruit flies

Question 14

Describe the role of hox genes

Answer 14

Group of homeobox genes responsible correct positioning of body parts - appear along chromosomes in the order of body parts.
Regulate mitosis and apoptosis.

Question 15

Define radial symmetry

Answer 15

Organism only has a top and bottom

e.g. diploblastic animals (jellyfish)

Question 16

Define bilateral symmetry

Answer 16

Organism with a left and right side, as well as head and tail
e.g. most animals

Question 17

Give an example of an asymmetrical organism

Answer 17

Sponges

Question 18

Describe the role of apoptosis and mitosis in controlling body form development

Answer 18

Regulated by hox genes
Apoptosis: Removal of unwanted cells and tissues to shape body parts e.g. hands, toes, brain cells
Mitosis: Increase cell count for growth. Cells undergoing apoptosis release chemicals to stimulate mitosis to remodel tissues afterwards

Question 19

What external stimuli could influence gene regulation?

Answer 19

1. Temperature

2. Light Intensity

Question 20

What internal stimuli could influence gene regulation?

Answer 20

1. Hormone release
2. Psychological stress
3. Intake of drugs

Question 21

Give an example of a drug affecting gene regulation

Answer 21

Thalidomide given to pregnant women for morning sickness - caused birth defects (shortened limbs)
Currently used as cancer treatment - prevents formation of capillary networks that aid tumour growth

Question 22

Define a nonsense mutation

Answer 22

Stop codon coded for mistakenly - results in shortened, usually non-functional protein

Question 23

Define a missense mutation

Answer 23

Incorporation of incorrect amino acid(s) into protein sequence

Question 24

Define epigenetics

Answer 24

Controlling gene expression through modifying the DNA sequence

Question 25

Define an operon

Answer 25

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

Question 26

Define morphogenesis

Answer 26

Regulation of the pattern of anatomical development within organisms

Question 27

What’s the difference between diploblastic and triploblastic organisms?

Answer 27

Diploblastic - two primary tissue layers

Triploblastic - three primary tissue layers