6.1.1 - Cellular Control

Question 1

What is a gene mutation?

Answer 1

A change in the DNA’s base sequence which can occur spontaneously during DNA replication

Question 2

What are mutagenic agents?

Answer 2

Outside factors which increase the rate of mutations

Question 3

What are the 3 types of gene mutation?

Answer 3

• Deletion
• Substitution
• Insertion

Question 4

What is deletion?

Answer 4

When a nucleotide is removed from a DNA sequence causing a frameshift which is a change to the sequence of triplets. A deletion of 3 bases will not cause a frameshift but an amino acid will be missing from the polypeptide.

Question 5

What is the effect on the polypeptide of deletion?

Answer 5

This changes the sequence of amino acids which are coded for and results in a large change to the primary structure of the resulting protein meaning it may be non-functional

Question 6

What is substitution?

Answer 6

When a base is swapped out for a different one. This only affects a single triplet in the DNA sequence.

Question 7

What is the effect on the polypeptide of substitution?

Answer 7

• Non-sense: the new sequence is a STOP codon so the polypeptide would be truncated
• Mis-sense: the triplet codes for a different amino acid having a different effect depending on the substituted amino acid and where in the protein it is found
• Silent: the substituted nucleotide still codes for the same amino acid having a neutral effect

Question 8

What is insertion?

Answer 8

When one or more nucleotides are added to a DNA sequence. This either results in a frameshift or in the addition of an extra amino acid.

Question 9

What is the effect on the polypeptide of insertion?

Answer 9

If a frameshift occurs the polypeptide will be disrupted with a different amino acid sequence. The resulting protein may be non-functional.

Question 10

Why might gene mutations be harmful?

Answer 10

Mutations which do change the protein’s primary structure alter the bonds within its tertiary structure. This can result in a non-functional protein which may be harmful for the organism.

Question 11

Why might gene mutations be beneficial?

Answer 11

Mutations which do change the protein’s primary structure alter the bonds within its tertiary structure. This can result in a new protein which is beneficial for the organism.

Question 12

What are the 3 levels of gene expression?

Answer 12

• Transcriptional
• Post-transcriptional
• Post-translational

Question 13

What is an active gene?

Answer 13

A gene which is transcribed and translated resulting in a polypeptide

Question 14

What is a structural gene?

Answer 14

A gene which codes for a protein that has a function within the cell

Question 15

What is a regulatory gene?

Answer 15

A gene which codes for a protein that controls structural genes

Question 16

What is a promoter?

Answer 16

A promoter enables the transcription of structural genes because its the binding site for the enzyme that carries out transcription which is RNA polymerase.

Question 17

How is gene expression controlled at the transcriptional level in prokaryotes?

Answer 17

• The regulatory gene produces a repressor protein
• The repressor protein binds to the operator
• RNA polymerase is then unable to bind to the promoter
• RNA polymerase can’t transcribe structural genes

Question 18

What is an operon?

Answer 18

A cluster of structural genes that is under the control of one promoter

Question 19

When is the lac operon active?

Answer 19

When lactose is present

Question 20

How is the lac operon activated?

Answer 20

• Regulatory gene produces repressor protein
• Lactose binds to repressor protein and changes its tertiary structure
• Repressor protein unable to bind to operator
• RNA polymerase binds to promoter
• RNA polymerase transcribes structural genes

Question 21

How is the lac operon inactivated?

Answer 21

• Regulatory gene produces repressor protein
• Repressor protein binds to operator
• RNA polymerase unable to bind to promoter
• RNA polymerase can’t transcribe structural genes

Question 22

Why isn’t the lac operon always on?

Answer 22

The structural genes coding for lactose digestion are only active when lactose is present which ensures that ATP isn’t wasted on expressing the genes coding for lactose digestion when lactose isn’t present.

Question 23

What does a DNA sequence in a eukaryotic cell not contain?

Answer 23

An operator

Question 24

How do transcription factors in eukaryotes stimulate gene expression?

Answer 24

• Regulatory gene produces transcription factor which stimulates gene expression
• Transcription factor binds to promoter
• Transcription factor enables RNA polymerase to bind to promoter
• RNA polymerase transcribes structural genes

Question 25

How are transcription factors activated?

Answer 25

A hormone enters the cell and diffuses into the nucleus. It then binds to the inactive transcription factor and activates it.

Question 26

What does control at the post-transcriptional level describe?

Answer 26

The changes primary mRNA goes through after transcription to ensure it is ready for translation

Question 27

What changes does primary mRNA go through to ensure it is ready for translation?

Answer 27

RNA splicing occurs where the non-coding introns are removed and RNA editing occurs where some RNA bases are substituted, deleted or added in. This creates a mature mRNA which is ready for translation.

Question 28

What does control at the post-translational level describe?

Answer 28

The changes a protein goes through after translation to ensure the protein is ready to perform a specific function in the cell. After translation a protein needs to be activated.

Question 29

How are proteins activated?

Answer 29

- Cyclic AMP binds to and activates an enzyme called protein kinase - Protein kinase then phosphorylates the protein which changes the protein's tertiary structure and activates it - The activated protein can now perform a specific function in the cell

Question 30

What is an organism's body plan?

Answer 30

The observable, spatial arrangement of an organism's body parts including any symmetry in the way the body parts are arranged

Question 31

What is a homeobox gene?

Answer 31

A type of regulatory gene which controls the initial development of an organism's body plan

Question 32

When are homeobox genes active?

Answer 32

During the embryonic stage

Question 33

What do homeobox genes contain?

Answer 33

A DNA sequence called a homeobox

Question 34

What do homeoboxes do?

Answer 34

It codes for the homeodomain which is the transcription factor's DNA binding site

Question 35

Why do biologists say homeobox genes and homeoboxes are highly conserved by natural selection?

Answer 35

This is because the homeobox found in all plants, animals and fungi is very similar

Question 36

What is a hox gene?

Answer 36

A type of homeobox gene that is only found in animals

Question 37

Which 2 cellular processes control the development of body plans?

Answer 37

Mitosis and apoptosis

Question 38

What does mitosis do?

Answer 38

Produces new cells for growth, repair and reproduction

Question 39

What does apoptosis do?

Answer 39

Removes old cells or cells that are no longer needed

Question 40

What are mitosis and apoptosis controlled by?

Answer 40

Hox genes which respond to internal stimuli such as DNA damage or external stimuli such as stress