8.17.16 Lecture

Question 1

___ gene control is the norm for eukaryotic cells.

Answer 1

Combinatorial

Question 2

Multiple different regulatory proteins can bind to ___ regulatory elements in a gene.

Answer 2

Identical

Question 3

The specific combination of proteins that bind to an element is dependent on what?

Answer 3

The cell type or physiological state of the cell

Question 4

The probability of initiating transcription results from what?

Answer 4

The net effect of all the interactions of promoter inputs

Question 5

What is the general role of Mad, Max, Myc?

Answer 5

Control genes involved in cell division

Question 6

What does the heterodimer Myc-Max do?

Answer 6

Activate transcription via histone acetylation, leading to cell proliferation

Question 7

What does the homodimer Max-Max do?

Answer 7

Repress transcription - basal level

Question 8

What does the heterodimer Mad-Max do?

Answer 8

Silence transcription via histone deacylation, leading to cell differentiation

Question 9

What type of transcription factors are Mad, Max, and Myc?

Answer 9

Basic Helix-Loop-Helix transcription factors

Question 10

What does the basic region of a transcription factor do?

Answer 10

Bind DNA

Question 11

Myc has a ___ activation domain; Max has ___ activation domain.

Answer 11

Large; no

Question 12

Myc is only expressed in…

Answer 12

…the G1 to S transition

Question 13

What are the basic methods of regulation of gene expression?

Answer 13

1. Activation of transcription factors and induction of gene expression.
2. Changes in chromatin structure
3. Epigenetic mechanisms

Question 14

What are the various methods of activation of TF?

Answer 14

1. Protein synthesis of TF
2. Ligand binding
3. Covalent modification (phosphorylation, etc.)
4. Complex between DNA-binding and activation subunits
5. Unmasking (remove inhibitor by phosphorylation)
6. Stimulation of nuclear entry by removal of inhibitor
7. Release from membrane by proteolysis

Question 15

___ can trigger signaling pathways to initiate gene expression. Give an example of this.

Answer 15

Extracellular signals; kinase cascades

Question 16

Why are cascades utilized?

Answer 16

Signal amplification

Question 17

Describe the c-Fos/c-Jun AP-1 element kinase cascade.

Answer 17

1. JNK, a terminal kinase from the cascade, phosphorylates Jun. ERK, a terminal kinase from the cascade, phosphorylates Fos.
2. Jun and Fos heterodimerize through leucine zippers and bind with the scissor motif to the AP-1 element.

Question 18

How is gene expression inhibited by changes in chromatin structure? Give an example of this.

Answer 18

Positioning a gene in heterochromatin inhibits gene expression; inactivation of the X-chromosome.

Question 19

Describe the process of inactivation of X-chromosomes.

Answer 19

1. Both X genes are active.
2. A randomly selected X is condensed and inactivated early in development (becomes a Barr Body) by deacetylase and methylase.
3. This is passed on in inheritance.

Question 20

Where does the signal for inactivation of X-chromosomes come from?

Answer 20

Placenta

Question 21

Heterochromatin structure regulates ___ gene expression on Chromosome ___.

Answer 21

Hemoglobin; 11

Question 22

Define epigenetics.

Answer 22

The passage of information from parental cells to progeny by a mechanism other than DNA sequence instructions.

Question 23

Is it possible for two alleles to have the same nucleotide sequence and give different inheritable genetic information?

Answer 23

Yes - via epigenetic information

Question 24

Epigenetic modifications occur through modification of either ___ or ___.

Answer 24

DNA or gene regulatory proteins

Question 25

What happens in a positive feedback loop?

Answer 25

1. Transient signal turns on expression of a gene.
2. Transcription factor is produced, binds to a regulatory element upstream of the gene and promotes continued transcription. This gives a cell “memory.”

Question 26

Combinatorial gene control and positive feedback loops work together in ___.

Answer 26

Embryonic cell development

Question 27

Embryonic cells receive signals from the placenta ___.

Answer 27

Asymmetrically

Question 28

What does DNA methylation do?

Answer 28

Methylation of a promoter or enhancer region usually inhibits expression (does not disrupt hydrogen bonds) by preventing TF binding.

Question 29

The methylated sequence is ___.

Answer 29

Palindromic

Question 30

How is DNA methylation inherited?

Answer 30

An established pattern of DNA methylation is continued in the progeny by methyl-directed methylating enzymes (maintenance methyl transferase), which act at hemimethyl sites.

Question 31

How does methylation upstream of a transcriptional start site block transcription?

Answer 31

By interfering with binding of TF and RNA polymerase and/or by promoting binding of inhibitory proteins

Question 32

What do CpG islands do?

Answer 32

Protect essential genes from DNA methylation; areas with a high concentration of C and G are resistant to methylation.

Question 33

How is histone acetylation maintained?

Answer 33

Maintenance acetylases acetylate histone proteins of nucleosomes that are hemi-acetylated in progeny cells.

Question 34

What is imprinting?

Answer 34

Retention of methylation in progeny cells

Question 35

Genomic imprinting occurs in ~___ genes.

Answer 35

50

Question 36

Usually, the ___ gene is not expressed; the ___ gene is expressed.

Answer 36

Hypermethylated; hypomethylated

Question 37

Imprinting is ___-dependent.

Answer 37

Sex; the gene retains methylation in the sperm or the egg (not both)

Question 38

What does imprinting lead to?

Answer 38

Sex-dependent non-Mendelian genetic expression of the imprinted gene; a functionally haploid cell.

Question 39

Imprint “on” = ___. Imprint “off” = ___.

Answer 39

Normal copy; not expressed (methylated)

Question 40

When are imprints erased?

Answer 40

During germ-cell formation, but before meiosis

Question 41

When are imprints reimposed?

Answer 41

In a sex-specific pattern later in germ-cell development