Gene Expression

Question 1

How is gene expression controlled in bacteria?

Answer 1

Genes are turned on and off by starting or stopping transcription.

Question 2

What are operons?

Answer 2

a unit of genetic function which consists of a promoter, operator, and genes that are grouped together based on their job

Question 3

What are the two types of negative gene regulation (feedback)?

Answer 3

repressible and inducible operons

Question 4

Explain repressible operons.

Answer 4

• transcription is usually on but can be turned off
• function in anabolic pathways (building large molecules)
• regulatory gene codes for a repressor upstream from the operon and makes it when there is enough of a protein, a corepressor (the protein) then binds to a repressor which activates it and causes it to bind to the operator which inhibits RNA polymerase from binding to the operon

Question 5

Explain inducible operons.

Answer 5

• transcription is usually off but can be turned on
• function in catabolic pathways (break down molecules)
• when a repressor is made, it is immediately activated and attaches to the operator, preventing the binding of RNA polymerase. The presence of a substance (the inducer) then attaches to the repressor and deactivates it. RNA polymerase is then free to bind and transcribe.

Question 6

How is positive gene regulation controlled?

Answer 6

an activator (protein) binds to the promoter and stimulates transcription of a gene by attracting RNA polymerase

Question 7

Give an example for a repressible operon, an inducible operon, and positive gene regulation.

Answer 7

1. tryptophan synthesis
2. Lac operon- makes enzyme (B-galactosidase) that breaks down lactose (inducer)
3. CAP (catabolite activator protein) which is activated by cAMP

Question 8

What are the 7 places gene expression can be controlled in humans?

Answer 8

Chromatin modification, DNA methylation, Regulation of transcription initiation, Alternative RNA splicing, mRNA Degradation, Regulatory proteins, Protein Degradation

Question 9

Chromatin modification

Answer 9

Loosens the chromatin (loosens the DNA from the proteins) in a nucleosome, structure of 8 histone proteins with DNA coiled around twice. This is done by histone modification - that addition of acetyl groups
-encourages gene expression

Question 10

DNA methylation

Answer 10

Inactivates the DNA

• addition of methyl groups
• how x inactivation happens

Question 11

Epigenetic inheritance

Answer 11

The inheritance of traits not directly involved DNA

• the way genes expressed are affected by chemicals so they are different
• even identical twins look different this way
• different genes are expressed at different times

Question 12

Regulation of transcription initiation

Answer 12

Transcription factors called activators attach to control elements called enhancers upstream from the genes both of which are specific to each gene. Control elements are non-coding segments of DNA. The activators are attracted to other transcription factors on the promoter with mediator proteins with the help of a DNA-bending protein. The combination of these proteins allows RNA polymerase to transcribe.

Question 13

How is the regulation of transcription initiation an example of cell type-specific transcription?

Answer 13

Gene expression varies from cell to cell because different activators are available in different cells so liver proteins may be expressed in one cell but eye proteins may be expressed in another.

Question 14

Alternative RNA splicing

Answer 14

Different mRNA molecules can be made from the same portion of DNA depending on which introns are spliced out

Question 15

mRNA degradation

Answer 15

mRNA can last days or weeks. This controls how many proteins are made from that strand.

Question 16

Regulatory proteins

Answer 16

Can block the attachment of mRNA to ribosomes thus preventing translation, enzymes controlling a feedback mechanism

Question 17

Protein degradation

Answer 17

By proteasome, broken into pieces

Question 18

What are noncoding RNAs and what are the two types?

Answer 18

ncRNA's
Do not help protein synthesis
MicroRNAs - miRNA
 -break down mRNA
 -block translation
Small interfering RNA's - siRNAs
 -block translation

Question 19

Why is regulated gene expression especially important in an embryo?

Answer 19

Differentiation

Morphogenesis by homeotic genes and cytoplasmic determinants

Question 20

Differential gene expression

Answer 20

Expression of different genes by different types of cells that all have the same genome

Question 21

Differentiation

Answer 21

The process by which your cells become specialized in structure and function

Question 22

Morphogenesis

Answer 22

Creation of form - to change shape

The physical process that gives and organism it’s shape

Question 23

Cytoplasmic determinants

Answer 23

Substances in cytoplasm of mom’s egg cell that influence early gene expression in an embryo

Question 24

Homeotic genes

Answer 24

Pattern formation in late embryo and larvae (head, bone, tissue, etc.) and (head, thorax, abdomen)

Question 25

What is cancer?

Answer 25

Changes in cell division/cell cycle

Question 26

Oncogenes

Answer 26

Abnormal mutated cancer-causing genes

Question 27

Mutagens and carcinogens

Answer 27

Anything that leads to a mutation

Cancer-causing substances

Question 28

Proto-oncogenes

Answer 28

Code for proteins that stimulate normal cell growth and division (normal)

Question 29

Tumor-suppressor genes

Answer 29

Code for proteins that inhibit cell division (normal)

Question 30

How is cell division controlled by these genes?

Answer 30

Signal pathways

Question 31

The discovery of viruses

Answer 31

TMV- tobacco mosaic virus

Question 32

Why aren’t viruses living things?

Answer 32

1. Cannot reproduce on their own
2. Cannot perform protein synthesis so can’t grow

Obligate Intracellular Parasites- requires a host for survival

Question 33

Restriction enzymes

Answer 33

Enzymes that cut apart viral DNA, restrict virus’ ability to infect bacteria

Question 34

Lytic Cycle

Answer 34

1. Attachment- tail fibers connect with receptors
2. Entry- nucleic acid through capsid, degrades host’s DNA
3. Synthesis- uses host’s contents and enzymes to copy genome and make proteins
4. Assembly- create heads, tails, etc. packs genome into capsid
5. Release- enzyme damages walls, allows fluid into cell which cause cell to burst

Question 35

Lysogenic cycle

Answer 35

1. Entry- factors decide whether lytic or lysogenic cycle
2. Combination- viral DNA with host’s DNA, creating a prophage
3. Cell division- creates large population of cells with prophages
4. Result- daughter cells with prophages
   Triggers- an environmental/chemical signal that causes a change from the lysogenic cycle to the lytic cycle

Question 36

What phases can be replicated by both the lysogenic and the lytic cycles?

Answer 36

Temperate phages (phage lambda)

Question 37

Retroviruses - RNA virus

Answer 37

Reverse transcriptase - an enzyme which transcribes mRNA into DNA

Question 38

What is an example of this?

Answer 38

HIV- human immuno deficiency that attacks white blood cells, destroying immune system, this can be inactive in your body for long time but then replicates, is activated, and turns into AIDS (acquired immuno deficiency syndrome)

Question 39

How do viruses make you sick?

Answer 39

Cell/tissue destruction

Release toxins

Question 40

How are viruses treated?

Answer 40

Vaccination programs and antiviral drugs

Question 41

How do viruses spread?

Answer 41

Indirect- coughing, sneezing

Direct- touch