Module 6.1 - Cellular Control

Question 1

Define mutation

Answer 1

A change in the base sequence of DNA

Question 2

3 types of mutation

Answer 2

Insertions (indel mutations)
Deletions (indel mutations)
Substitutions (point mutations)

Question 3

What happens at a point mutation?

Answer 3

One base pair replaces another

Same number of amino acids result

Question 4

What are the possible effects of a point mutation?

Answer 4

Silent mutations
Missense mutations
Nonsense mutations

Question 5

What is a silent mutation?

Answer 5

Change in base pair will still code for the same amino acid, therefore the same protein, therefore having no effect

Question 6

Why is the genetic code described as non-overlapping (unambiguous) and degenerate (redundant)?

Answer 6

Non-overlapping as no codon codes for more than one amino acid
Redundant as more than one codon codes the same amino acid

Question 7

What is a missense mutation?

Answer 7

Change in base pair causes a change in amino acid, therefore changes primary and tertiary structure of protein, therefore changes its shape/function

Question 8

What is a nonsense mutation?

Answer 8

Change in base pair causes it to become a stop codon, causing early termination of polypeptide chain, changing the shape/function of the protein

Question 9

How is a frameshift caused?

Answer 9

By indel mutations

If the number of base pairs being removed or added is not a multiple of 3, a frameshift is caused

Question 10

Effects of a frameshift

Answer 10

Alter DNA codons, causing a large change in primary and tertiary structure of codon, causing a large change in shape/function of the protein

Question 11

Define operon

Answer 11

Length of DNA made out of structural and control genes (P and lacO) that function together

Question 12

Define structural genes

Answer 12

Code for proteins

Question 13

Define regulatory genes

Answer 13

Controls the expression of structural genes by switching them on/off
Makes repressor protein/transcription factors
Not part of the operon

Question 14

Define operator region

Answer 14

Region next to structural genes that repressor binds to (lacO)

Question 15

Define promoter region

Answer 15

Binding site for RNA polymerase (P)

Question 16

Define repressor protein

Answer 16

Binds to operator region preventing RNA polymerase from binding to promoter region, preventing transcription

Question 17

Define apoptosis

Answer 17

Programmed cell death

Question 18

Stages of apoptosis

Answer 18

Cytoskeleton broken down by enzymes
Cell shrinks and cytoplasm becomes dense with tightly packed organelles
Cell surface membrane forms blebs (small protrusions)
Chromatin condenses, DNA and nuclear envelope break down into fragments
Blebs form vesicles containing organelles
Vesicles are engulfed and digested by phagocytes so the old cell and its contents can cause no damage to other cells

Question 19

How is apoptosis controlled?

Answer 19

By genes which regulate the cell cycle and apoptosis by responding to internal and external stimuli (e.g. stress)
As a result, cell signalling molecules are released: cytokines; hormones; nitric oxide

Question 20

Describe how nitric oxide can induce apoptosis

Answer 20

Makes the inner membrane of the mitochondria more permeable to hydrogen ions, dissipating the proton gradient (reducing ATP production)
Proteins are released into the cytoplasm, bind to apoptosis inhibitor proteins allowing apoptosis to occur

Question 21

Why are dead cells engulfed by phagocytes?

Answer 21

So no hydrolytic enzymes are released, destroying neighbouring cells

Question 22

What are homeobox genes?

Answer 22

Genes which control morphogenesis (anatomic development) of organisms

Question 23

What are Hox genes?

Answer 23

Subset of homeobox genes found only in animals

Control formation of anatomical features in the correct locations of the body plan

Question 24

How do homeobox genes work?

Answer 24

Contain an 180 base pair homeobox sequence that codes for a 60 amino acid sequence called a homeodomain sequence within a protein (transcription factors)
The homeodomain sequence’s shape is specific to part of the enhancer region on DNA so it binds to the DNA to initiate/stop transcription to switch genes on or off
This controls the development of the body plan
Homeobox genes are master genes - they switch many other genes on/off

Question 25

How can homeobox gene sequences be described and why?

Answer 25

Highly conserved as they are found in all plant, animal and fungal species from a common ancestor
Very similar as there are very few mutations in these genes because they are very important and mutations would have large effects on the body plan (these mutations would have been selected against as they would have killed the organisms)

Question 26

Points about Hox genes

Answer 26

Very similar across different classes of animals
Switched on in segments causing development in segments (obvious in worms and insects)
Number and arrangement of Hox genes varies among different types of animals
At some point in evolution Hox clusters have duplicated, leading to greater complexity in body structure

Question 27

Characteristics scientists look for in animals used in experiments

Answer 27

Cheap to buy and keep
Reproduce quickly
Small
Large cells
Readily available

Question 28

Why can information from model organisms be applied to humans?

Answer 28

All in the same kingdom
Have shared ancestors
Similar cells
Have shared genes and similar embryonic development/similar homeobox/Hox genes