Cellular Control

Question 1

At what levels can gene expression be controlled at?

Answer 1

• The transcriptional level
• The post transcriptional level
• The post-translational level

Question 2

What controls gene expression at the transcriptional level?

Answer 2

Transcription factors

Question 3

What are transcription factors?

Answer 3

Proteins that bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription.

Question 4

What are the 2 types of transcription factors?

Answer 4

• Activators
• Repressors

Question 5

What do activators do?

Answer 5

they increase the rate of transcription

Question 6

What do repressors do?

Answer 6

They decrease the rate of transcription

Question 7

What determines whether a transcription factor can bind to DNA or not?

Answer 7

The shape of the transcription factor

Question 8

In eukaryotes, where do transcription factors bind?

Answer 8

They bind to specific DNA sites near the start of their target genes.

Question 9

In prokaryotes, where do transcription factors bind?

Answer 9

To operons

Question 10

What is an operon?

Answer 10

A cluster of structural genes that are transcribed together, and also control elements and sometimes a regulatory gene.

Question 11

What do the control elements include?

Answer 11

• A promoter
• An operator

Question 12

What is a promoter?

Answer 12

A DNA sequence located before the structural genes that RNA polymerase binds to

Question 13

What is an operator?

Answer 13

A DNA sequence that transcription factors bind to

Question 14

What does the bacteria E.coli typically respire?

Answer 14

Glucose

Question 15

What can the bacteria E.coli respire if glucose isn’t available?

Answer 15

Lactose

Question 16

Where are the genes that produce the enzymes needed to respire lactose found?

Answer 16

On an operon called the Lac Operon.

Question 17

What happens when lactose isn’t present?

Answer 17

• The regulatory gene produces the lac repressor.
• The lac repressor is a transcription factor that binds to the operator site when there’s no lactose present.
• This blocks transcription because RNA polymerase can’t bind to the promoter

Question 18

What happens when lactose is present?

Answer 18

• Lactose binds to the repressor.
• This changes the repressor’s shape so that the repressor can no longer bind to the operator site.
• RNA polymerase can now begin the transcription of the structural genes.

Question 19

what structural detail of a polypeptide is altered by gene mutations?

Answer 19

the base sequence

Question 20

how is it possible for a mutation to have no effect on the protein produced from that gene?

Answer 20

• Some triplets code for the same amino acid, so the amino acid sequence isn’t altered.
• Some alternative amino acids will not alter the shape of the protein.
• The mutation may occur in the intron.

Question 21

How could a mutation alter the protein so that it no longer performs its correct function in the cell?

Answer 21

• An insertion or deletion may result in a frameshift mutation.
• All triplets downstream will be different.
• The protein will have a different sequence of amino acids.
• The tertiary structure of the protein will be different.

Question 22

What do regulatory genes do?

Answer 22

code for proteins that control the expression of structural genes.

Question 23

What do the structural genes do?

Answer 23

codes for a protein that has a function within a cell

Question 24

How can transcription be controlled in eukaryotes?

Answer 24

• Hormone enters a cell and binds to a transcription factor.
• The transcription factor will then be activated and will bind to a promoter.
• This will allow RNA polymerase to bind to the promoter.

Question 25

How can gene expression be regulated after transcription?

Answer 25

- The primary mRNA is modified. - Introns are removed to make mature mRNA. - Alternative splicing can produce different versions of mRNA.

Question 26

Why are fruit flies chosen for research into genes controlling the development of the body plan?

Answer 26

- There’s less ethical concerns - Low cost - Rapid reproduction rate - The genetics of fruit flies is well understood. - They have a simple body plan

Question 27

Why are mice usually used or research into genes controlling the development of the body plan, despite there being some ethical concerns?

Answer 27

- low cost - share some genes with humans - more than one species is needed to demonstrate the conservation of base sequences.

Question 28

do species that have diverged recently share a similar base sequence?

Answer 28

Yes

Question 29

Why do non-coding regions of DNA show more variation?

Answer 29

Because they are not selected against

Question 30

Do homeobox genes enable proteins to work as transcription factors?

Answer 30

Yes

Question 31

What does RNA polymerase do?

Answer 31

makes RNA via transcription

Question 32

What does DNA polymerase do?

Answer 32

Allows for DNA replication, where 2 polypeptide strands are produced.

Question 33

What is programmed cell death?

Answer 33

Apoptosis

Question 34

What do hox genes do?

Answer 34

They determine the identity of embryonic body regions along the anterior-posterior axis (i.e. the head-tail axis)

Question 35

What is a homeobox gene?

Answer 35

A homeotic gene that initiates transcription and controls the development of the body plan.

Question 36

Why has there been little change by mutation in homeobox genes?

Answer 36

Because these genes are very important so any mutations are likely to be lethal

Question 37

What is the relationship between regulatory genes and structural genes?

Answer 37

Regualatory genes control the expression of structural genes

Question 38

How is gene expression regulated at the post-translational level?

Answer 38

- Certain molecules, like hormones, bind to cell membranes and trigger the production of cAMP inside the cell. - cAMP then activates proteins inside the cell by altering their 3D structure. - Altering the 3D structure can change the active site of an active site, making it more or less active.

Question 39

How does cAMP activate PKA?

Answer 39

- cAMP binds to PKA and causes the shape of the enzymes 3D structure to change, releasing the active subunits. - PKA is now active

Question 40

What are the 3 main ways a mutation can occur?

Answer 40

- Substitution - Insertion - Deletion

Question 41

What can form frameshift mutation?

Answer 41

Insertion and deletion