Cellular Control

Question 1

How can mutations arise

Answer 1

They can be spontaneous
They can be from random changes to genetic code
There is an increased frequency from mutagens

Question 2

What are the 3 types of mutagens

Answer 2

Physical
Chemical
Biological

Question 3

Give an example(s) of physical mutagens

Answer 3

UV light - Break strands of DNA

X-Ray/Gamma radiation - Cause pyrimidine dimers

Question 4

Give an example(s) of Chemical mutagens

Answer 4

Deaminating agents - Cytosine to Uracil

Clastogens - eg Benzene cause deletion or addition

Question 5

Give an example(s) of biological mutagens

Answer 5

Alkylating agents - Attaching an ethyl or methyl group
Base anaglogs - Used in place of a base
Viruses - Inserts itself into the genome

Question 6

What are the three impacts of a mutation

Answer 6

Neutral
Deleterious
Beneficial

Question 7

How can a mutation’s impact be neutral

Answer 7

It can be silent due to the degenerate nature of code

It can occur on the non coding DNA (introns)

Question 8

How can a mutation’s impact be deleterious

Answer 8

There won’t be a protein made
Shorter protein made
Key αα missing

Question 9

Explain how a mutation leads to cystic fibrosis

Answer 9

Cystic fibrosis is the production of excess mucus
This is due to the deletion of three bases
As a result the protein folds incorrectly

Question 10

Give an example of a beneficial mutation

Answer 10

Lactose persistence - The ability of adults to digest the lactose in milk
This is a recent mutation
The lactose promoter still works so lactase gene is still transcribed

Avoid osteoporosis
Additional food source

Question 11

What are the types of chromosome mutations

Answer 11

Deletion - Gene is deleted
Duplication - Gene is duplicated
Translocation - A gene is cut off and attaches to a non homologous chromosome
Inversion - A section of the gene inverts itself

Question 12

What are the time of point mutations

Answer 12

Original AAA
Substitution - AAT
Deletion - AA
Insertion - AAAA

Question 13

What is a codon

Answer 13

3 bases that code for an amino acid

Question 14

What does degenerate code mean

How many possible combinations are there

Answer 14

More than one codon codes for the same amino acid

4^3

Question 15

What type of mutation is this
TTC TTT
Lys Lys

Answer 15

Silent mutation - A base change still codes for the same amino acid

Question 16

What type of mutation is this
TTC ATC
Lys Stop

Answer 16

Nonsense - Base change results in the formation of a stop codon

Question 17

What type of mutation is this
TTC TGC
Lys Thr

Answer 17

Missense - Change in base results in a different amino acid being coded for
Can be conservative or non conservative depending on αα being code

Question 18

What is a frameshift

Answer 18

Every codon after the mutation is affected

It’s much more harmful then a insertion/deletion of 3n bases

Question 19

How is gene regulated at a transcriptional level

Answer 19

Genes can be turned permanently on or off

Can be up or down regulated by affecting promoter (transcription factors)

Question 20

How is gene regulated at a post transcriptional level

Answer 20

Pre mRNA is formed and this undergoes splicing to remove the introns leaving the exons

This is then protected by a modified nucleotide cap and a tail of adenine

Mature mRNA is formed then mRNA editing or further splicing can occur to code for different genes

Question 21

How is gene regulated at a translational level

Answer 21

Translation can be stopped or started

Question 22

How is gene regulated at a post transcriptional level

Answer 22

Usually done by phosphorylating proteins to active them

A signalling molecule binds to a complimentary and specific receptor on cell surface membrane
This activates a gene protein which activates adenylyl cyclase
This catalyses the reaction of ATP to form cAMP
This activates protein kinase A (PKA)
Goes to phosphorylates of various proteins

Question 23

What is an operon

Answer 23

A cluster of genes under the influence of one promoter - energy saving

Question 24

Describe the lac operon in E.coli if there isn’t lactose present

Answer 24

A regulatory gene at the stand of the operon codes for a repressor protein
This protein binds to an operator region which masks the promoter region
RNA polymerase can’t code for the structural genes

Question 25

Describe the lac operon in E.coli if there is lactose present

Answer 25

Lactose binds to the repressor protein and it unbinds from the operator region
This unmasks the promoter region and so RNA polymerase can start transcribing the genes
These genes are lactose permease and β galactosidase

Question 26

What are homeobox genes

Answer 26

Regulatory genes that control body development
Made of 180bp and code for a protein called the homeodomain
They are highly conserved so between species there is very little difference
Involved in mitosis and apoptosis

Question 27

What are Hox genes

Answer 27

They are a set of homeobox genes only found in animals

They regulate the development of an embryo such as head orientation and limb position

Question 28

Why do we use fruit flies to look at mutations

Answer 28

They have a short life cycle
Rapid growth rate
Mutations can be observed under a light microscope

Question 29

How can body plans be controlled

Answer 29

Normal body cells can divide around 50 times - Hayflick limit
Apoptosis is a programmed cell death
Controls body development plans such as separation of fingers, toes and harmful T-lymphocytes
Is the opposite of necrosis

Question 30

Describe the sequence of events during apoptosis

Answer 30

Enzymes break down the cytoskeleton
Cytoplasm becomes tightly densed with organelles
Blebs form as cell surface membrane changes
Chromatin condense, nuclear envelope breaks down and DNA breaks into fragments
Cells break into vesicles that are ingested by phagocytic cells

Question 31

What is an internal and external signalling moelcuels

Answer 31

Internal - Hormone

External - Thalidomide