Prokaryote + Eukaryote gene expression

Question 1

why do bacteria alter gene expression pattern?

Answer 1

because their environemnt is constantly changing. Nutrient avaliability can increase, decrease
- eg. bacteria cells in our intestines responding to mcribiome envrionemnt

Question 2

what is a reason for genes to be adjacent?

Answer 2

the proteins that the genes code for are functionally coneccted.
so the regulation of these genes are coordinated

Question 3

what is the funciton of operator + repressor

Answer 3

Operator = short stretch of DNA that the repressor protein binds

repressor = protein that binds to operator / DNA sequence..
- it has an ALLOSTERIC site for INDUCER molecule to bind

Question 4

describe the lac operon model

Answer 4

includes:
1) CAP site = CAP binds to promote RNA polymerase binding
2) Promoter ( where RNA polymerase binds)
3) Operator (overlaps w promoter, where lac repressor binds)
4) Lac genes Z, Y , A
lac Z = beta galactosidase gene
lac Y = beta galactoside permease gene
lac A = beta galatosides transacetylase gene

Question 5

lacl gene properties

Answer 5

• transcribes lac repressor= continually so lac repressor always present
• found near the lac operon, but not part of it, transcribed separately
• under control from its own promoter
• lac repressor has allosteric site on it for ALLOLACTOSE (Inducer) to bind

Question 6

describe what happens when lactose is absent + present

Answer 6

Lactose absent
- lac repressor (continually transcribed) binds to operator –> prevents RNA polymerase from transribing structural genes

lactose present
- ALLOLACTOSE (rearranged lactose ) binds lac repressor –> loses ability to bind DNA –> floats off operator & allows RNA polymerase to transcribe lac genes

Question 7

what is the role of allolactose

Answer 7

• acts as inducer

Question 8

what are transcription factors

Answer 8

• regulatory proteins
• repressor = negative regulators
• activators = positive regulator

Question 9

what happens when tryptophan presnet vs absent?

Answer 9

• bacteria (e.coli) need amino acids (tryptophan) to survive + build proteins

Tryptophan avaliable in environemnt = trp operon switched off by trop repressor (E.coli doesnt need to make trptophan by itself) = E.coli will take it up & use it to make proteins

Tryptophan absent = trp operon expressed (turn on)

• TRYPTOPHAN synthesis also regulated by ATTENUATION (coupling of transcription + translation)
• E.coli can make their own tryptophan using enzymes encoded by 5 genes
• 5 genes located next to ea other on the trp operon

Question 10

what happens when tryp (low levels) not in environemnt

Answer 10

• switches operon ON

low tryptophan = trp repressor is inactive = doesnt binds trp operon = allows RNA polymerase to transcribing trp enzymes needed for tyrptophan synthesis

Question 11

what is attention

Answer 11

• it is a way that tryptophan synthesis is regulated

- coupling of transcription + translation

Question 12

what happens when trypt is in environemnt (high levels)

Answer 12

switches operon OFF

• high levels of tryptophan in environment activate trp repressor
• gene trpr transcribes trp repressor –> binds to trp operon –> blocks RNA polymerase = dont get transcription of enzymes

Question 13

what is the trp operon

Answer 13

• trp operon = group of genes that encode enzymes to make tryptophan
• when trypt is not in environent so E.coli bacteria must make it itself using 5 genes located next to trp operon

Question 14

what regulates tryptophan synthesis

Answer 14

repressor

Question 15

what does gene trpr do

Answer 15

GENE trpR transcribes trp repressor that binds to trp operon to prevent RNA polymerase transcribing enzymes
- not part of trp operon
located somewhere else on bacteria chromosome
has own promoter + other regulatory sequences

Question 16

allocate inducible/ repressing system + anabolic / catabolic to lac + trp operon

Answer 16

lac operon

• inducible system
• catabolic

trp operon

• repressible system
• anabolic

Question 17

how do eukaryotes coordinate the regulation of gene expression

Answer 17

• promoters share regulatory DNA sequences that bind SAME transcription factors
  ie: SAME transcription factors will activate –> bind to same regulatory DNA sequences in DIFFERENT regions of genome = coordinate gene expression

Question 18

how does corticosteroids induce gene transcription

Answer 18

corticosteroids enter cell –> bind to glucocorticoid receptors GR in cytoplasm –> together translocate into nucleus –> GR interacts w Glucocorticosteroid response element (on the promoter) –> induce gene transcription

Question 19

what 2 things do u need to maintain glucose + lipid metabolism

Answer 19

1) hormonal regulation
2) metabolites need to have direct effect on gene transcritpion = to code for enzymes involved in maintaining glucose + lipid homeostasis

Question 20

how does body react to high carbohydrate diet (in terms of gene transcription)

Answer 20

high carb diet induces transcription of enzymes, that are responsible to convert sugars into stored macromolecules (glycolysis, lipogenesis + pentose pathway)

1) for glycolysis:
- Glucokinase GK
- pyruvate kinase

2) for lipogenesis
- ATP citrate lyase
- acetyl CoA carboxylase
- fatty acid synthase FASN
- stearoyl CoA desaturase 1 SCD1

3) for pentose pathway
- G6P dehydrogenase