MODULE 6 - controlling gene expression

Question 1

what are the four ways to control gene expression?

Answer 1

transcriptional, post-transcriptional, translational, post-translational

Question 2

what does transcriptional gene control do?

Answer 2

turns genes on or off in order to control what is transcribed

Question 3

what impacts how easily the DNA can be transcribed?

Answer 3

how tightly the DNA coils around the histones

Question 4

when is DNA harder to transcribe?

Answer 4

when the DNA is coiled tightly around the histones

Question 5

when is DNA easier to transcribe?

Answer 5

when the DNA is coiled loosely around the histones

Question 6

what makes DNA coil tightly around the histones?

Answer 6

methylation - the addition of methyl groups to the histones - so they become more hydrophobic

Question 7

what makes DNA coil loosely around the histones?

Answer 7

acetylation or phosphorylation - both reduce the positive charge on the histones so they become more negative. this means that the DNA, a negative molecule, is less attracted to the histone

Question 8

what is an operon? are they more common in eukaryotes or prokaryotes?

Answer 8

a sequence of DNA containing a cluster of genes under the control of a single promoter. more common in prokaryotes

Question 9

when does lac operon occur?

Answer 9

when glucose in not available to metabolise for respiratory purposes

Question 10

what is lac operon?

Answer 10

the metabolisation of lactose in the place of glucose when it not available for metabolic purposes in respiration
- Lactase breaks down the substrate lactose so that it can be used as an energy source in the bacterial cell

Question 11

what are the components of a lac operon gene in order

Answer 11

• regulatory gene
• promotor region
  -operator region
• lac Z, lac Y, lac A

Question 12

lac operon is a relatively slow process. what can be done to speed this up

Answer 12

cAMP receptor protein can bind to the promotor, making it easier for RNA polymerase to bind to the promotor region

Question 13

what does a repressor protein do in lac operon?

Answer 13

it binds to the operator region and prevents RNA polymerase binding to the DNA, therefore preventing transcription

Question 14

what are the two processes involved in post-transcriptional control?

Answer 14

RNA processing and RNA editing

Question 15

what does RNA processing entail?

Answer 15

the modification of pre-RNA to form mature mature mRNA before it binds to the ribosome

Question 16

what is splicing in terms of RNA processing?

Answer 16

when RNA is cut at specific points to remove introns and join exons together

Question 17

why are introns removed in splicing during RNA processing?

Answer 17

because they are non-coding regions meaning they do not code for any amino acids

Question 18

where does splicing occur?

Answer 18

the nucleus

Question 19

what is a cap in terms of RNA processing?

Answer 19

a modified nucleotide

Question 20

where is a cap added to the pre-RNA during RNA processing?

Answer 20

to the 5’ end

Question 21

what is a tail in terms of RNA processing?

Answer 21

a long chain of adenine nucleotides

Question 22

where is a tail added to the pre-RNA during RNA processing?

Answer 22

to the 3’ end

Question 23

what is RNA editing

Answer 23

the change of the nucleotide sequencing in mRNA

Question 24

how is RNA editing done?

Answer 24

through the addition/deletion/substitution of bases

Question 25

what is the benefit of RNA processing?

Answer 25

it increases the range of proteins that can be produced from a single mRNA molecule or gene

Question 26

what 3 mechanisms regulate protein synthesis in translational gene expression control?

Answer 26

- mRNA degradation - the binding of inhibitory proteins to the mRNA - the activation of initiation factors

Question 27

which of the three mechanisms regulating translational gene control decrease translation?

Answer 27

- mRNA degradation - the binding of inhibitory proteins to the mRNA

Question 28

which of the three mechanisms regulating translational gene control increase translation?

Answer 28

- the activation of initiation factors

Question 29

what does mRNA degradation mean in terms of translational gene control?

Answer 29

a less resistant molecule will last a shorter time in the cytoplasm , so a smaller amount of the protein is synthesised

Question 30

what does the binding of inhibitory proteins to the mRNA do in translational gene control?

Answer 30

inhibitory proteins prevent mRNA binding to the ribosome, therefore preventing protein synthesis

Question 31

what does the activation of initiation factors do in translational gene control?

Answer 31

it aids the binding of mRNA to the ribosome

Question 32

what is the main aim of post translational gene control?

Answer 32

to modify synthesised proteins

Question 33

what four protein modifications are involved in post-translational gene control?

Answer 33

- the addition of non-protein groups like carbs, lipids, phosphates - modifying amino acids to form bonds like disulphide bridges - affecting the folding/shortening of proteins - modification by cAMP

Question 34

what are protein kinases?

Answer 34

proteins which catalyse the addition of phosphate groups to rpoteins

Question 35

why are protein kinases important?

Answer 35

many enzymes are activated by phosphorylation

Question 36

what secondary messenger often activates protein kinases?

Answer 36

cAMP

Question 37

what is an operon?

Answer 37

a group or a cluster of genes that are controlled by the same promoter

Question 38

what does it mean that lactase is an inducible enzyme? what does this prevent?

Answer 38

it is only synthesized when lactose is present - This helps prevent the bacteria from wasting energy and materials

Question 39

where does the lac repressor protein bind to on the lac operon gene? what happens when it bind to the operator?

Answer 39

the operator - When it binds to the operator it prevents the transcription of the structural genes as RNA polymerase cannot attach to the promoter

Question 40

what happens when the lac repressor protein binds to lactose?

Answer 40

When it binds to lactose the shape of the repressor protein distorts and it can no longer bind to the operator

Question 41

describe the five steps which take place in the lac operon when lactose is absent

Answer 41

- The regulatory gene is transcribed and translated to produce lac repressor protein - The lac repressor protein binds to the operator region upstream of lacZ - Due to the presence of the repressor protein RNA polymerase is unable to bind to the promoter region - Transcription of the structural genes does not take place - No lactase enzyme is synthesized

Question 42

describe the five steps which take place in the lac operon when lactose is present

Answer 42

- There is an uptake of lactose by the bacterium - The lactose binds to the second binding site on the repressor protein, distorting its shape so that it cannot bind to the operator site - RNA polymerase is then able to bind to the promoter region and transcription takes place - The mRNA from all three structural genes is translated - Enzyme lactase is produced and lactose can be broken down and used for energy by the bacterium

Question 43

what are transcription factors?

Answer 43

proteins that bind to specific regions of DNA to control the transcription of genes

Question 44

how do transcription factors work?

Answer 44

- Some transcription factors bind to the promoter region of a gene - This binding can either allow or prevent the transcription of the gene from taking place

Question 45

how is mature mRNA created?

Answer 45

through splicing. this is when: - introns are first removed from the pre-mRNA molecule - then exons are fused together to form a continuous mRNA molecule called mature mRNA that is ready to be translated

Question 46

what would happen if introns were not removed from the mRNA molecules?

Answer 46

the resulting protein would not be formed properly and may not function as it should

Question 47

where do post translational modifications take place?

Answer 47

- cytosol - Golgi apparatus

Question 48

how might proteins be modified at a post-translational level?

Answer 48

- folded - cut - have sugars or phosphates added

Question 49

why is cAMP needed in post translational gene expression?

Answer 49

Some proteins are made in an inactive form and must be activated. One way to activate them is using cAMP.

Question 50

what is cAMP made from?

Answer 50

ATP

Question 51

which enzyme converts ATP into cAMP?

Answer 51

adenyl cyclase

Question 52

what does cAMP activate?

Answer 52

protein kinases - It is made in an inactive form - cAMP binds to it and activates it - Once active, PKA can activate many other proteins

Question 53

how do protein kinases switch proteins on?

Answer 53

by adding phosphate groups to other proteins