Regulation of Gene Expression (4)

Question 1

genes are regulated …

Answer 1

… by proteins that bind to regulatory sequences that are upstreams or downstreams of the transcribed sequence

Question 2

what is the name of the units that prokaryotic genes are organized in?

Answer 2

operons

Question 3

what are prokaryotic genes regulated by?

Answer 3

metabolites binding to proteins that recognize and bind to operators

Question 4

where does regulation of gene expression in eukaryotes occur?

Answer 4

various levels like transcriptional, post-transcriptional, translational, and post-translational

Question 5

what does the bacterial genome include?

Answer 5

chromosomal DNA and episomes (extrachromosomal DNA in plastids)

Question 6

transduction

Answer 6

transfer of a part of a chromosome from one bacterium to another through a phage
- can be general or specific

Question 7

transfection

Answer 7

experimental method to introduce dna fragments into bacterial using phage as vectors

Question 8

transformation

Answer 8

introduction of dna from an external medium into the bacterial

Question 9

gene expression

Answer 9

-synthesis of RNA from a DNA template
- includes translation of mRNA into specific proteins resulting in specific genotypes
- constitutive or regulated

Question 10

constitutive genes

Answer 10

expressed without much regulation
- expressed continuously

Question 11

Transposable elements (Transposons)

Answer 11

• mobile genetic elements/ jumping genes
• move from one chromosome to another part of a different chromosome
• important in new combinations of genes, mutations, and microevolution of bacteria

Question 12

How is bacterial dna introduced from one bacterium to another?

Answer 12

conjugation, transduction, and transformation

Question 13

conjugation

Answer 13

sexual mating of bacterial through f-pili and the genes present in the F-factor are transferred from an F+bacteria to an F-bacteria

Question 14

what does an operon constitute?

Answer 14

• the coding sequences of the genes in that unit
• a promoter
• operator

Question 15

what does the promoter in an operon do?

Answer 15

determine tha accuracy of transcription

Question 16

what does the operator in an operon do?

Answer 16

determine the amount of transcription
- serves as the on/off switch to regulate transcription in response to an enviromental stimuli

Question 17

polycistronic

Answer 17

many transcripts are made from one operon simultaneously as a single mRNA in a single transcription

Question 18

operons can be …

Answer 18

induced (positive regulation) or repressed (negative regulation)

Question 19

Inducible operon

Answer 19

• mostly turned off
• turned on only when necessary
• present to control catabolic pathways used to break down compounds

Question 20

inductible operon example

Answer 20

lac operon
- induced when lactose is present with glucose or alone
- expression of genes for lactose-utilizing enzymes is activated by removing a repressor that is bound to the operator of the lac operon
- the lactose binds to the repressor molecule, and the operon is derepressed to start transcription
-If there is no glucose and only lactose is present, it results in an increase of cyclic AMP (cAMP) levels in the cells. The cAMP binds to a catabolite activator protein (CAP) and that binds to the promoter to further enhance the activity of the lac operon much more than the basal level at derepression alone

Question 21

repressible operon

Answer 21

• used for anabolic pathways to synthesise compounds
• mostly turned on

Question 22

repressible operon example

Answer 22

trp-operon to synthesize tryptophan
- the enzymes in the Trp biosynthetic pathway are expressed only when Trp is absent
- when trp is absent a repressor protein is inactive and it does not bind to the operator to repress transcription
- when sufficient levels of Trp are made, it binds to the repressor molecule and makes it an active repressor that now binds to the operator and stops transcription
- feedback inhibition at gene level

Question 23

sigma factors

Answer 23

• can control gene regulation
• can bind to the regulatory elements of bacteria and activate transcription
• several types of sigma factors and other DNA-binding proteins that regulate prokaryotic gene expression
• factors can transmit environmental signals to the genes to express the needed proteins immediately in response to the stimulus

Question 24

how is chromatin made?

Answer 24

the double helix of dna wraps around histone proteins to form nucleosomes, which condenses further to make chromatin

Question 25

Repetitive sequences

Answer 25

found near the telomere - useful in dna replication because they fold onto themselves to provide a -OH group for dna synthesis

Question 26

gene families

Answer 26

- result of gene replication during crossing over - genes essential for survival are highly duplicated

Question 27

coordinated gene expression

Answer 27

expression of multigene family members is regulated by common cis-acting elements recognized by crommon trans-acting factors specific for that gene family

Question 28

how are eukaryotic genes regulated?

Answer 28

by a set of regulatory DNA sequences/ cis-acting elements (recognized by trans-acting factors)

Question 29

in prokaryotes there are no introns to be removed (T/F)

Answer 29

T

Question 30

Where can gene expression be regulated in eukaryotes?

Answer 30

transcriptional level, translational level, posttranslational level

Question 31

the rate of transcription is regulated at the ____ level

Answer 31

gene with diff mechanisms for long and short term controls

Question 32

Long term controls (2)

Answer 32

- compaction - methylation

Question 33

Compation

Answer 33

- chromosomes condensed during cell division and later uncoil to chromatin - but some chromatin remain condensed and not accesible by RNA polymerase

Question 34

Methylation

Answer 34

- to control transcription on selected chromosomes - by DNA methylase - adds methyl group to the C and A bases, preventing regions form being transcribed - helps DNA polymerase distinguish the old strand from the new

Question 35

short-term control

Answer 35

- some regions of chromosomes are actively transcribed - some factors directly bind to RNA polymerase or other DNA binding proteins and can affect transcription through protein-protein interaction

Question 36

regulatory elements

Answer 36

- promoter (upstream of the start site) - enhancers - repressors

Question 37

transcription factors

Answer 37

- have unique secondary structures (motifs) - helix-turn (or loop) - helix proteins - zinc finger proteins - leucine zippers

Question 38

All these DNA binding proteins act as _____, which interact with each other along with these _____ (unique secondary/tertiary strictures) and with DNA to regulate _____.

Answer 38

All these DNA binding proteins act as dimers, which interact with each other along with these motifs (unique secondary/tertiary strictures) and with DNA to regulate transcription.

Question 39

Some _____ can bind to these transcription factors in the ____ and then migrate to the nucleus, bind with specific ____-acting elements, and activate the ____ of certain genes.

Answer 39

Some hormones can bind to these transcription factors in the cytoplasm and then migrate to the nucleus, bind with specific cis-acting elements, and activate the transcription of certain genes.

Question 40

Post-transcriptional regulation

Answer 40

- limited regulation - alternate splicing - mRNA stability

Question 41

alternate splicing

Answer 41

- during mRNA processing (where introns and exons ...) - some exons are joined differently to yield different proteins

Question 42

mRNA stability

Answer 42

- some mRNA are long-lived, and some short-lived - mRNA stability is altered by RNA binding proteins that can degrade the mRNA

Question 43

Translational regulation

Answer 43

- in eukaryotes in the cytoplasm - involves initiation factors and elongation factors - blocks translation of processed mRNA until need arises

Question 44

Examples of translational regulation

Answer 44

- mRNA storage - hormonal regulation - effect of cofactor on translation

Question 45

Post-translational modification

Answer 45

- last stage of controlling gene expression at protein level - zymogen activation - selective targeting - chemical modification - glycosylation

Question 46

Totipotency

Answer 46

single-cell having the potential to become a whole new organism - zygotes