Gene Expression & Regulation

Question 1

Define Epigenetics

Answer 1

The study of heritable phenotype changes that do not involve alterations in the DNA sequence.

Question 2

Define Operon

Answer 2

A functioning unit of DNA containing a cluster of genes under the control of a single promoter.

An operon consists of a promoter, an operator, and structural genes.

Question 3

Define Promoter

Answer 3

The site where RNA polymerase attaches, signaling the start of the gene.

Question 4

Define Operator

Answer 4

The site where a repressor binds, stopping the transcription of that gene.

Question 5

Define Structural Genes

Answer 5

Genes coding for an enzyme that are transcribed as a unit.

Question 6

Define Inducible Gene

Answer 6

A gene that needs to be “turned on” or activated in order to be expressed.

Question 7

Define Repressible Gene

Answer 7

A gene that needs to be “turned off” or deactivated in order to stop being expressed.

Question 8

Define Enhancer

Answer 8

A DNA sequence that promotes transcription. Each enhancer is made up of short DNA sequences called distal control elements.

Question 9

Define Single-Nucleotide Polymorphism (SNP)

Answer 9

A DNA sequence variation occurring when a single nucleotide in the genome differs between members of a species or paired chromosomes in an individual.

Question 10

Define Homeotic Genes (HOX)

Answer 10

Master regulator genes that direct the development of particular body segments or structures.

When HOX are changed by mutations, body plans may undergo drastic changes.

Question 11

Describe the evolution of gene regulation in prokaryotes

Answer 11

Prokaryotes are single-celled. They evolved to grow and divide rapidly, and must respond quickly to changes in external environment.
Gene regulation:
• turn genes on and off rapidly
• flexibility and reversibility
• adjust levels of enzymes for synthesis and digestion

Question 12

Describe the evolution of gene regulation in eukaryotes

Answer 12

Eukaryotes are multicellular. They evolved to maintain constant internal conditions while facing changing external conditions, and regulate the body as a whole. They have long term processes for growth and development.
Gene regulation:
• turn on and off a large number of genes
• coordinate the body as a whole rather than serve the needs of individual cells

Question 13

What are the points of control in gene expression?

Answer 13

The control of gene expression can occur at any step in the pathway from gene to functional protein.
•  packing/unpacking DNA
•  transcription
•  mRNA processing
•  mRNA transport
•  translation
•  protein processing
•  protein degradation

Question 14

How does DNA packing regulate gene expression?

Answer 14

DNA packing regulates transcription. If DNA is wrapped tightly around histones, the gene isn’t transcribed.

Question 15

How do histones contribute to gene regulation?

Answer 15

Histones are eight protein molecules containing positively charged amino acids. These amino acids bind tightly to the negatively charged DNA, regulating transcription.

Question 16

How does DNA methylation regulate gene expression?

Answer 16

The methylation of DNA blocks transcription factors. The gene doesn’t get transcribed into protein.

DNA methylation attaches methyl groups (—CH3) to cytosine, and is a nearly permanent inactivation of genes.

Question 17

How does histone acetylation regulate gene expression?

Answer 17

The acetylation of histones unwinds DNA, turning on the gene and enabling transcription.

Histone acetylation attaches acetyl groups (—COCH3) to histones, enabling transcription factors to have easier access to genes.

Question 18

What are the control regions on DNA?

Answer 18

Promotor: nearby control sequence on DNA where RNA polymerase and transcription factors bind. “Base” rate of transcription.
Enhancer: distant control sequences on DNA where activator proteins bind. “Enhanced” rate of transcription.

Question 19

How do proteins interact with DNA control regions to regulate gene expression?

Answer 19

Activator proteins bind to enhancer sequences and stimulate transcription, increasing the rate. Silencer proteins bind to enhancer sequences and block gene transcription.

Question 20

How does post-transcriptional control regulate gene expression?

Answer 20

Alternative RNA splicing causes variable processing of exons and creates a family of proteins.

Question 22

How does mRNA interference regulate gene expression?

Answer 22

Small interfering RNAs (siRNA) are short segments of RNA (21-28 bases) that bind to the mRNA template. They create sections of double-stranded mRNA that acts as a tag for degradation of that mRNA. This causes gene “silencing.”

Question 24

How does translation control regulate gene expression?

Answer 24

The initiation of the translation stage is blocked by regulatory proteins attached to the 5’ end of mRNA. This prevents the attachment of ribosomal subunits and initiator tRNA, which blocks the translation of mRNA into protein.

Question 25

How does protein processing regulate gene expression?

Answer 25

Proteins are folded, cleaved, and have sugar groups added, targeting them for transport or destruction.

Question 25

How does protein degradation regulate gene expression?

Answer 25

Ubiquitin tagging: a 76 amino acid polypeptide called ubiquitin acts as a “death tag” to mark unwanted proteins for destruction.

Proteasome degradation: breaks down any proteins into 7-9 amino acid fragments.

Question 26

Francois Jacob and Jacques Monod

Answer 26

Conducted experiments in 1961 with E. Coli bacteria that offered insight into the process of gene regulation.

Question 26

How do distal control elements regulate gene expression?

Answer 26

Activators bound to the distal control elements interact with mediator proteins and transcription factors. Two different genes may have the same promoter but different distal control elements, enabling differential gene expression.