Cellular control Module 6

Question 1

What do all cells in an organism carry?

Answer 1

The same genes

Question 2

How come the structure and function of different cells varies if they all have the same genes?

Answer 2

Not all genes in a cell are expressed (transcribed and used to make functional proteins), they are selectively switched on and off

Question 3

What does cells having different gene expression lead to?

Answer 3

Different proteins made

Different cell structure and processes

Question 4

What levels can gene expression (and therefore protein synthesis) be controlled at?

Answer 4

Transcriptional
Post-transcriptional
Post-translational

Question 5

How can gene expression be controlled at transcriptional level?

Answer 5

Altering the transcription of genes

This is controlled by transcription factors

Question 6

What are transcription factors?

Answer 6

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

Factors which increase rate = activators
Factors which decrease rate = repressors

Question 7

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

Answer 7

The shape, can be altered by hormones and sugars

Meaning the amount of certain molecules in an environment or cell can control translation

Question 8

In eukaryotes where do transcription factors bind to?

Answer 8

Specific DNA sites near the start of the target genes

Question 9

In prokaryotes where do the transcription factors bind to?

Answer 9

The operon

Question 10

What’s an operon?

Answer 10

A section of DNA which contains a cluster of structural genes, that are transcribed together as well as control elements and sometimes a regulatory gene

Question 11

What do structural genes code for?

Answer 11

Useful proteins such as enzymes

Question 12

What do the control elements consist of?

Answer 12

Promoter (a DNA sequence located before the structural genes that RNA polymerase binds to)
An operator (a DNA sequence that transcription factors bind to)

Question 13

What does the regulatory gene do?

Answer 13

Codes for an activator or repressor

Question 14

For an example of example of an operon, explain the lac operon in E.coli?

Answer 14

The lac operon has 3 structural genes which lacZ, lacY and lacA which produce proteins which allow the bacteria to digest lactose (including B-galactosidase and lactose permease)

Lactose not present:
The regulatory gene prodcues the lac repressor, which is a transcription factor which binds to operator site when there’s no lactose present. This blocks transcription because RNA polymerase can’t bind to the promoter

Lactose present:
When lactose is present, it binds to the repressor, changing the repressors shape so it can no longer bind to the operator site.
RNA polymerase can now begin transcription of the structural genes

Question 15

What is E.coli?

Answer 15

Bacterium that respires glucose, but it can use lactose if glucose isn’t available

The genes that produce the enzyme needed to respire lactose are found on the operon, called the lac operon

Question 16

What is edited at post-transcriptional level?

Answer 16

mRNA

Question 17

What’s an intron?

Answer 17

Section of DNA which doesn’t code for amino acids?

Question 18

What’s an exon?

Answer 18

Section of DNA which does code for amino acids

Question 19

What’s happens in transcription in relation to introns and exons?

Answer 19

Introns and exons are both copied into mRNA forming primary mRNA transcripts

Then in a process called splicing, the introns are removed and the exons join together, forming mature mRNA strands, this occurs in the nucleus

The mature mRNA then leaves the nucleus for the next stage of protein synthesis (translation)

Question 20

Why do some proteins need to activated?

Answer 20

They aren’t functional straight after they have been synthesised

Question 21

What is protein activation controlled by?

Answer 21

Molecules eg. hormones and sugars

Question 22

How does protein activation work?

Answer 22

Molecules such as hormones or sugars bind to the cell membrane, triggering the production of cyclic AMP within the cell

Cyclic AMP then activates proteins within the cell, by altering their 3D strucuture

Question 23

What is PKA?

Answer 23

An enzyme made of 4 subunits

Question 24

How does cyclic AMP activate PKA?

Answer 24

When cyclic AMP isn’t bonded the 4 units are held together and it’s inactive

However, when cyclic AMP binds, it causes a change in the enzymes 3D structure, releasing the active subunits, PKA is now active

Question 25

What the body plan of an organism?

Answer 25

The general structure, it’s controlled by proteins created from hox genes

Question 26

What are similar hox genes found in, and what does this mean?

Answer 26

Found in animals, plants and fungi, meaning body development is controlled in a similar way

Question 27

What are homeobox sequences?

Answer 27

Regions in hox genes which are highly conserved, so have changed very little in the evolution of different organisms

Question 28

How do hox genes control development?

Answer 28

Homebox sequences code for a part of the protein called the homeodomain

The homedomain binds to specific sites on DNA, enabling the protein to work as transcription factor

The protein binds to DNA at the start of developmental genes, activating or repressing transcription and so altering the production of proteins involved in the development of the body plan

Question 29

What’s apoptis?

Answer 29

Programmed cell death

Question 30

What are the steps of apoptis?

Answer 30

Enzymes in the cell break down important cell components such as proteins in the cytoplasm and DNA in the nucleus

As the cell’s contents are broken down, it shrinks and breaks into fragments

The cell fragments are engulfed by phagocytes and digested

Question 31

Bried description how a body part is formed?

Answer 31

Mitosis and differentiation provide the bulk of body parts, apoptosis then refines them by removing unwanted structures
Eg digits on hands and feet formed via this

Question 32

What happens during development to the genes that control apoptosis and mitosis?

Answer 32

Switched on/off in appropriate cells

Question 33

What internal stimulus can the genes that regulate apoptosis respond to?

Answer 33

DNA damage

Question 34

What external stimulus can the genes that regulate apoptosis respond to?

Answer 34

Attack from a pathogen

Question 35

Any change to the base (nucleotide) sequence is know as a?

Answer 35

Mutation

Question 36

3 types of mutation?

Answer 36

Substitution
Deletion
Insertion

Question 37

What’s substitution?

Answer 37

One or more bases are swapped for another

Question 38

What’s deletion?

Answer 38

Where one or more bases are removed

Question 39

What’s insertion?

Answer 39

Where one or more bases are added

Question 40

What do mutations do?

Answer 40

Change in the order of DNA bases, will change the order of amino acids and therefore the primary structure of the protein formed

This may change the final 3D shape of the protein, so it doesn’t work properly

Question 41

Why can a mutation have a neutral affect on a protein?

Answer 41

Mutation has changed a base in a triplet, but the amino acid that that triplet codes for doesn’t change, as some amino acids are coded for by more than 1 triplet

Mutation produces a triplet code which codes for a different amino acid, however it’c chemically similar to the original so it functions like the original

The mutated triplet codes for an amino acid not involved in the proteins function

Question 42

Mutations with beneficial effects?

Answer 42

Bacterial enzymes break down certain antibiotics, mutations in the genes could allow them to break down a wider range of antibiotics

Question 43

Mutations with harmful effects?

Answer 43

cycstic fibrosis can be caused by deletion of bases in genes which code for CFTR protein, leads to excess mucus production