GENE REGULATION

Question 1

Gene regulation is

Answer 1

Gene regulation is a process turning genes on an off. It regulates the rate in which genes are transcribed to form proteins by 𝑅𝑁𝐴 polymerase

Question 2

Operons

Answer 2

operons are site of gene regulation in prokaryotes.

Question 3

Operons are composed of

Answer 3

• Promoter – place for 𝑅𝑁𝐴 polymerase to bind and start transcription of a gene.
• Operator – region of 𝐷𝑁𝐴 that repressor protein can bind to and prevent the transcription process.
• Structural – genes that are regulated by the operon that codes for the protein interest.
• Regulator – not always includes in the operon, constantly expressed gene that codes for repressor
  protein.

Question 4

Kinds of operons

Answer 4

There are two kinds of operons:

• Inducible operons – prevent transcription until a specific condition.
• Repressible operons – allow transcription until a specific condition.

Question 5

Inducible Operon are

Answer 5

A repressor protein is bond to the operator region of a specific gene. This prevents transcription from
occurring. When an inducer molecule arrives, it binds to the repressor protein, changes its shape and
prevents it from binding the operator. This allows the transcription of the target gene.

Question 6

The lac operon ,,,

Answer 6

lactase is an enzyme that breaks down lactose. In absence of glucose,
prokaryotes will utilize lactose by breaking in down into its compounds.

The lac operon regulates the synthesis of enzymes responsible for breaking down lactose (lactase for
example).

• Structural – lactose utilization genes – lac 𝐴, lac 𝐵 and lac 𝐶.
• Regulator – lac 1 gene that encodes for the repressor protein.

Question 7

In high levels of glucose

Answer 7

(𝑐𝐴𝑀𝑃 deactivated) – lac 1 produces a repressor protein that binds to the operator,
preventing transcription of enzymes that break lactose.

Question 8

In Low level of glucose

Answer 8

(𝑐𝐴𝑀𝑃 activated) – lactose acts as an inducer molecule by binding to the repressor
protein, which prevents it from binding to the operator. Thus. The transcription occurs, allowing the
prokaryote to break down lactose.

Question 9

Repressible Operon

Answer 9

The repressor protein is usually not bond to the operator, and therefore, the target gene is usually
expressed. Only when a co-repressor molecule arrives, it binds to the repressor protein that then binds to
the operator. This prevents transcription of the same gene.

Question 10

The 𝑇𝑅𝑃 operon…

Answer 10

𝑇𝑅𝑃 operon – tryptophan in an amino acid synthesized by prokaryotes.
𝑇𝑅𝑃 operon – regulates the synthesis of tryptophan.
* Structural – tryptophan genes 𝑇𝑅𝑃 𝐴−𝐸.
* Regulator 𝑇𝑅𝑃 𝑅 gene encodes for the repressor protein.

Question 11

In low level of tryptophan…

Answer 11

𝑇𝑅𝑃 𝑅 produces a repressor protein that is non active. Therefore, in can’t bind
to the operator, resulting in the transcription of the tryptophan synthesis.

Question 12

In high levels of tryptophan

Answer 12

Tryptophan acts as a co-repressor in activating the receptor protein. It binds the protein, and allows it to bind the operator. This results in the suppressing the transcription of tryptophan synthesis.

Question 13

𝑇𝐴𝑇𝐴 Box

Answer 13

Nucleotide sequence at the promoter. Composed mostly of thiamine and adenine. It is a binding site
for transcription factors of histones.
* Binds 𝑅𝑁𝐴 polymerase and transcription factors.
* It is a core sequence of a promoter.

Question 14

Tailing and Capping

Answer 14

Messenger 𝑅𝑁𝐴 has a tail and a cap. This allows the cell to recognize it as a molecule that needs to be
translated.

Question 15

Enhancers and Transcription Factors

Answer 15

Enhancers are sequences of 𝐷𝑁𝐴 that can be found away from genes, and still enhance their expression.
Transcription factors are proteins that bind to enhancers and to promotors. In this way, they fold the 𝐷𝑁𝐴 in a way that attracts 𝑅𝑁𝐴 polymerase.

Question 16

Methylation

Answer 16

Addition of methyl groups to nucleotides in the 𝐷𝑁𝐴. Methylated regions in the 𝐷𝑁𝐴 are silenced. Meaning, they are not expressed, due to the 𝐷𝑁𝐴 polymerase that cant bind and translate them.

Question 17

Histone Occupancy

Answer 17

𝐷𝑁𝐴 molecules are wrapped around proteins called histones. Regions that are tightly packed are not
accessible, and therefore, not expressed. Such places are called heterochromatin.

Question 18

Significance of Gene Regulation

Answer 18

Cells that are not tightly regulated may eventually develop into cancerous ones.

Question 19

Oncogenes

Answer 19

family of genes that promote mitosis. When a mutation occurs in these genes, it may cause
cancer.

• Most normal cells undergo apoptosis (programmed death).
• Mutated oncogenes can cause cells that ought to survive instead. This causes proliferate of these
  cells that may lead to cancer.

Question 20

Tumor suppressor genes

Answer 20

family of genes that suppress mitoses. When mutation occurs in this genes, it may cause cancer by not stopping mitosis when needed.