Controls over Genes

Question 1

Gene controls-

Answer 1

mechanisms that control when and how fast specific genes will be transcribed and translated, and whether gene products will be switched on or silenced

Question 2

Prokaryotic control

Answer 2

Usually exhibit transcriptional level control by organizing related groups of genes into groups that can be rapidly turned on and off (operons)

Question 3

Jacob and Monod-

Answer 3

discovered mutant E. coli strains in which a single genetic defect wiped out the activity of three enzymes that helped to digest lactose. Therefore- DNA coding sequences for all three enzymes must be linked together as a unit and controlled by a common mechanism

Question 4

Operon-

Answer 4

an arrangement in which a promoter and a set of operators control access to more than one prokaryotic gene. no operons in eukaryotes.

Question 5

Regulatory (or repressor) gene

Answer 5

produces a repressor protein- substance that can prevent gene expression by blocking the action of RNA polymerase. operon.

Question 6

Promoter region

Answer 6

is a sequence of DNA that RNA polymerase can attach to in order to begin transcription. operon.

Question 7

Operator region

Answer 7

can block the action of the RNA polymerase if the region is occupied by a repressor gene. operon.

Question 8

Structural genes

Answer 8

Structural genes contain DNA sequences that code for several related enzymes that direct the production of an endproduct. operon.

Question 9

diagram inducible operon

Answer 9

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Question 10

repressed state

Answer 10

meaning that a repressor is bound to the operator region, preventing the transcription of genes that code for enzymes that break down the substance the operon targets.

Question 11

inducible operon

Answer 11

if substance the operon targets is required to induce, or turn on the gene, this operon is said to be an inducible operon. substance is usually repressed, but when the substance is present, it acts as an allosteric regulator that combines with an allosteric site on the repressor, making the repressor inactive. When the repressor is inactive, RNA polymerase is able to transcribe the genes that produce the enzymes that break down substance.

Question 12

repressible operon.

Answer 12

usually in induced state. these genes only stop producing enzymes in the presence of an active repressor

Question 13

diagram repressible operon

Answer 13

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Question 14

induced state

Answer 14

meaning that the regulatory gene produces an inactive repressor that does not bind to the operator

Question 15

detail repressible operon

Answer 15

RNA polymerase transcribes the genes necessary to produce enzymes that synthesize substance the operon targets. However, if the bacteria is in regions of abundance of substance, it no longer needs to synthesize its own. Therefore, some substance reacts with the inactive repressor and makes it active. substance acts as a corepressor. This active repressor can now bind to the operator regions, preventing the transcription of the genes.

Question 16

Negative control-

Answer 16

regulatory proteins slow down gene activity

Question 17

Positive control

Answer 17

regulatory proteins enhance gene activities. Regulated by activator proteins that bind to DNA andstimulate more efficient transcription of the gene

Question 18

Positive control–E. coli

Answer 18

E. coli cells will not typically break down lactose that much unless there is no glucose. If no glucose- an activator called CAP will bind to cAMP, a second messenger, which allows RNA polymerase to bind more efficiently.

Question 19

Positive control diagram

Answer 19

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Question 20

Eukaryotic Control

Answer 20

Do not normally form operons- instead, each gene its own has specific regulatory sequences

Question 21

Chemical modifications

Answer 21

type of transcriptional control. methylation- methyl groups (-CH 3 ) can be “painted” on parts of DNA to block access to the genes. Acetylation- acetyl groups (-CH 3 CO–) are attached to DNA to make the genes more accessible

Question 22

UPE–

Answer 22

upstream promoter element

Question 23

Promoter (TATA box)-

Answer 23

RNA polymerase binds here to begin transcription–always TATA sequence. RNA polymerase can only initiate transcription after various regulatory proteins called transcription factors have assembled on the chromosome. part of regulatory molecules and control sites

Question 24

Transcription initiation site

Answer 24

where transcription begins. part of regulatory molecules and control sites

Question 25

regulatory molecules and control sites

Answer 25

type of transcriptional control.

Question 26

tata box diagram

Answer 26

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Question 27

Enhancers

Answer 27

DNA sequences that increase the rate of RNA synthesis. enhancer type of UPE . part of regulatory molecules and control sites

Question 28

Activators

Answer 28

(types of regulator proteins) can bind here and help activate transcription part of regulatory molecules and control sites

Question 29

enhancer/activator diagram

Answer 29

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Question 30

Silencers

Answer 30

DNA sequences that turn off transcription by binding to proteins called repressors

Question 31

terminator sequence

Answer 31

at terminator sequence, transcription is completed and mRNA is released

Question 32

Post translational control

Answer 32

Allosteric enzymes regulate rate of metabolic pathways through feedback inhibition

Question 33

Proteolytic processing-

Answer 33

Post translational control. proteins are synthesized in inactive form but become active by removal of a portion of the polypeptide chain

Question 34

Post translational control–chemical modification

Answer 34

adding or removing functional groups to alter the activity of an enzyme

Question 35

Translational control-

Answer 35

mRNA can be destroyed by ribonuclease enzymes in order to control the number of protein molecules translated from it

Question 36

Chromosome Organization

Answer 36

part of transcriptional control. DNA wound tightly around histones prevent polymerases from accessing the genes; Inactive genes lie in heterochromatin; Active genes–euchromatin.

Question 37

heterochromatin

Answer 37

Inactive genes lie in compacted chromatin called heterochromatin. Heterochromatin is not transcribed- ex- Barr bodies.

Question 38

euchromatin

Answer 38

active genes lie in loosely packed chromatin called euchromatin.

Question 39

What makes histones lose their grip? (Chromosome Organization)

Answer 39

Acetylation can make histones lose their grip

Question 40

What blocks gene’s influence on trait? (Chromosome Organization)

Answer 40

Methylation can block a gene’s influence on a trait

Question 41

Post- transcriptional control-

Answer 41

Introns are spliced out by snRNPs, Differential mRNA processing, Ribozymes, Nuclear envelope controls when mRNA reaches a ribosome

Question 42

Differential mRNA processing-

Answer 42

the same pre-mRNA can be spliced in different ways in different cells- one sequence can be an intron in one type of cell but an exon in another, producing different versions of mRNA

Question 43

Ribozyme

Answer 43

Ribozyme- some intron RNA’s can self-splice, acting as an enzyme to catalyze the splicing process

Question 44

Nuclear envelope controls when mRNA reaches a ribosome

Answer 44

mRNA can only pass through the nuclear pores if there are specific proteins attached to the mRNA, Proteins help move the mRNA to its specific location to be translated or stored, Each mRNA has its own proteins attached, coded for by the untranslated end of mRNA