UNIT 3 - AOS1 - CH 1.5 & 1.6 - Structure of genes & Gene Regulation

Question 1

Coding region

Answer 1

part of a gene that contains the coded info for making a polypeptide chain

Question 2

flanking regions

Answer 2

regions located either downstream or upstream of the coding region of a gene

Question 3

Intron

Answer 3

regions in eukaryotes of non-coding DNA that do not contribute to the final polypeptide (removed during RNA modification)

Question 4

Extrons

Answer 4

Regions in eukaryotes and prokaryotes of coding DNA, that do contribute to final protein structure.

Question 5

Promoter

Answer 5

5’ prime end (upstream) & is TATAA box for eukaryotes

is the binding side for RNA polymerase.

Question 6

Termination sequence

Answer 6

Eukaryotes 3’ prime end (downstream flanking region)

DNA sequence that determines the end of transcription

Question 7

Leader region

Answer 7

Prokaryotes

Contains attenuators = formation of hairpin loops and the stalling and detachment of RNA polymerase when the structural genes don’t need to be transcribed & translated.

Question 8

Operator region

Answer 8

Prokaryotes

OPERATOR = a region that serves as a binding site for repressed proteins to inhibit transcription

REPRESSOR = a protein produced by a regulatory gene that can bind to the operator to prevent RNA polymerase from binding to the promoter

Question 9

Gene regulation definition

Answer 9

The conservation of energy through the process of either inhibiting or activating gene expression.

Question 10

prime ends for template, coding strand and mRNA

Answer 10

Coding strand = 5’ - 3’

Template strand = 3’ - 5’

mRNA = 5’ - 3’

Question 11

Structural genes

Answer 11

“produce proteins that are involved in the structure or function of cell”

e.g transport proteins

Question 12

Regulatory genes

Answer 12

“produce regulatory proteins that control the activity of other genes”.

e.g repressor protein

Question 13

opening definition

Answer 13

“cluster of adjacent structural genes in bacteria controlled by a single promoter and operating as a coordinated unit”

Question 14

Summary of trp operon

Answer 14

“ a series of structural genes within certain species of bacteria (e.g ecoli ) that encode for the production of tryptophan”

• when trp is present = operon is switched off and trp is not produced
• when trp is absent = operon is switched on and trp is produced

Question 15

Summarise how the trp operon is regulated through repression in the presence of tryptophan.

Answer 15

STEP ONE:
Tryptophan binds to repressor protein which caused conformational change (active repressor)

STEP TWO:
Active repressor binds to operator.

STEP THREE:
RNA polymerase cannot bind to the promoter

STEP FOUR:
Transcription does not occur & operon is turned off

Question 16

Summarise how the trp operon is regulated through repression in the absence of tryptophan

Answer 16

STEP ONE:
Repressor cannot bind to operator because it is inactive because tryptophan is not present.

STEP TWO:
RNA polymerase can bind to the promoter

STEP THREE:
Transcription of structural genes does occur & operon is turned on.

Question 17

Summarise how the trp operon is regulated through attenuation in the presence of tryptophan

Answer 17

STEP ONE:
Transcription & translation of the trp operon begin & occur simultaneously

STEP TWO:
Ribosome arrives at attenuator sequence that codes for the two tryptophan amino acids. The tRNA-bound tryptophan in cell adds to the leader peptide causing the ribosome to continue and reach the ‘stop’ codon.

STEP THREE:
This causes the mRNA leader sequence to create a terminator hairpin loop. (Domain 3&4)

STEP FOUR:
The folding of the mRNA terminator hairpin loop causes the attenuator sequence to break and seperate from he DNA.

STEP FIVE:
RNA polymerase is flicked off the DNA, causing transcription to stop before any structural genes are transcribed.

Question 18

Summarise how the trp operon is regulated through attenuation in the absence of tryptophan

Answer 18

STEP ONE:
Transcription & translation of the trp operon begin & occur simultaneously

STEP TWO:
Ribosome arrives at the attenuator sequence (in the leader) that codes for the two tryptophan amino acids. Due to no tRNA-bound tryptophan in the cell, the ribosome will pause and wait.

STEP THREE:
This causes the mRNA attenuator sequence to create a anti-terminator hairpin loop (domain 2&3)

STEP FOUR:
The anti-terminator hairpin loop does not cause the mRNA to separate from the DNA at the attenuator sequence because it has moved further along past T’s and A’s. (Cs and Gs have a stronger bond)

STEP FIVE:
RNA polymerase continues to read the DNA template strand, transcribing the structural genes for proteins involved in the synthesis of tryptophan.