1. Chapter 18
Gene Expression

2. I) What are Genes? A) Sequences of nucleotides that determine
the sequence of amino acids in proteins
B) Two Types of Genes
Regulatory Genes
Structural Genes

3. I) What are Genes? A) Sequences of nucleotides that determine
the sequence of amino acids in proteins
B) Two Types of Genes
Regulatory Genes
Structural Genes
Control transcription and expression of other genes

4. I) What are Genes? A) Sequences of nucleotides that determine
the sequence of amino acids in proteins
B) Two Types of Genes
Regulatory Genes
Structural Genes
Control transcription and expression of other genes
Function as “on/off” switches

5. I) What are Genes? A) Sequences of nucleotides that determine
the sequence of amino acids in proteins
B) Two Types of Genes
Regulatory Genes
Structural Genes
Control transcription and expression of other genes
Function as “on/off” switches
Some code for RNA

6. I) What are Genes? A) Sequences of nucleotides that determine
the sequence of amino acids in proteins
B) Two Types of Genes
Regulatory Genes
Structural Genes
Control transcription and expression of other genes
Function as “on/off” switches
Some code for RNA
Determine the structure of a protein

7. I) What are Genes? A) Sequences of nucleotides that determine
the sequence of amino acids in proteins
B) Two Types of Genes
Regulatory Genes
Structural Genes
Control transcription and expression of other genes
Function as “on/off” switches
Some code for RNA
Determine the structure of a protein
Control amino acid sequences

8. I) Differentiation
The process in which cells become specialized as specific genes are activated
Function of a cell is dictated by DNA
Not all genes are activated in every cell
Some genes are only active at specific points in the life cycle of a cell

9. III) Prokaryotic Gene Regulation
OPERONS - Specific genes within DNA that control the transcription of RNA and control protein synthesis
Operons contain four components
Regulatory Gene – codes for either a repressor protein or an activator protein
Repressor protein prevents RNA transcription (turns genes off)
Activator protein starts RNA transcription (turns genes on)
Promoter – region of DNA where RNA polymerase binds and begins transcription (the Start Codon)
Operator – region of DNA to which a repressor or activator protein binds – this is the “ON/OFF SWITCH”
Structural Gene – DNA sequences that determine the amino acid sequence for a specific protein or proteins

10. Inducible Genes
Repressible Genes
Genes that are usually off and need to be activated for short periods of time

11. Inducible Genes
Repressible Genes
Genes that are usually off and need to be activated for short periods of time
Require an activator to remove a repressor protein

12. Inducible Genes
Repressible Genes
Genes that are usually off and need to be activated for short periods of time
Require an activator to remove a repressor protein
lac operon

13. Inducible Genes
Repressible Genes
Genes that are usually off and need to be activated for short periods of time
Require an activator to remove a repressor protein
lac operon
Genes that are usually on all the time and need to be inactivated for brief periods

14. Inducible Genes
Repressible Genes
Genes that are usually off and need to be activated for short periods of time
Require an activator to remove a repressor protein
lac operon
Genes that are usually on all the time and need to be inactivated for brief periods
Require a repressor to block transcription

15. Inducible Genes
Repressible Genes
Genes that are usually off and need to be activated for short periods of time
Require an activator to remove a repressor protein
lac operon
Genes that are usually on all the time and need to be inactivated for brief periods
Require a repressor to block transcription
trp operon

16. IV) Eukaryotic Gene Regulation
A) Control of Transcription
1) Transcription Activation
Transcription Factors
Proteins that bind to promoters and affect RNA polymerase activity
Coactivator proteins then bind to the transcription factors (the activators) and helps initiate RNA transcription
These enhance or promote transcription
Inhibition of Transcription
Methylation
Methyl groups (-CH3) attach themselves to the cytosines that reside in CG (cytosine-guanine) doublets on DNA.
Methylation near a gene promoter on DNA will generally prevent transcription of that gene.

17. Factor Promoter Transcription
Estrogen receptors normally reside in the cell’s nucleus, along with DNA molecules.
In the absence of estrogen molecules, these estrogen receptors are inactive and have no influence on DNA (which contains the cell’s genes). But when an estrogen molecule enters a cell and passes into the nucleus, the estrogen binds to its receptor, thereby causing the shape of the receptor to change. This estrogen-receptor complex then binds to specific DNA sites, called estrogen response elements, which are located near genes that are controlled by estrogen.
After it has become attached to estrogen response elements in DNA, this estrogen-receptor complex binds to coactivator proteins and more nearby genes become active. The active genes produce molecules of messenger RNA, which guide the synthesis of specific proteins. These proteins can then influence cell behavior in different ways, depending on the cell type involved.

18. Regulatory Switches and Gene Regulation

19. Small RNAs such as miRNAs and siRNAs block RNA translation a) miRNA:
B) Post-transcriptional Control in Eukaryotes 1) Gene regulation after RNA transcription 2) RNA interference (RNAi)
Small RNAs such as miRNAs and siRNAs
block RNA translation
a) miRNA:
microRNAs (miRNAs) are a class of naturally
occurring, small non-coding RNA molecules, about 21–25 nucleotides in length.
miRNAs are partially complementary to one or more messenger RNA (mRNA) molecules, and their main function is to down-regulate (supress) gene expression
miRNA forms double stranded RNA to prevent translation into protein
miRNA base pairing is not exact – results in many more possible points of interference

21. siRNA (small interfering RNA)
Double Stranded (dsRNA) is cleaved by an enzyme, Dicer, into double stranded small interfering RNAs (siRNA)
the siRNAs become integrated into a multi-subunit protein complex, commonly known as the RNAi induced silencing complex (RISC), which guides the siRNAs to the target RNA sequence
At some point the siRNA and RISC directs degradation of the complementary mRNA sequence
Many genes are thought to be regulated this way
Prevents RNA translation into protein
siRNA has exact base pairing

22. EPIGENETICS Gene expression regulated by environmental factors.
Changes do not involve nucleotide sequence changes.
Changes can be passed to future generations.
Diet, stress, and other factors play a role.
Epigenetics is regulated by DNA methylation
Methylation inhibits gene expression while demethylation induces gene expression

24. Effects of Bis-Phenol A (BPA)
BPA causes demethylation which activates genes known to induce obesity in GENETICALLY IDENTICAL MICE
BPA is linked to diabetes, obesity, and developmental problems in children
BPA is an estrogen-like substance that affects cell growth and differentiation.
Effects of BPA can be seen in fourth generation offspring

26. When pregnant yellow agouti mothers were fed BPA, more yellow, unhealthy babies were born than normal. Exposure to BPA during early development had caused decreased methylation of the agouti gene. However, when BPA-exposed, pregnant yellow mice were fed methyl-rich foods, the offspring were predominantly brown. The maternal nutrient supplementation had counteracted the negative effects of exposure

27. Lick Your Rats!
The nurturing behavior of a mother rat during the first week of life shapes her pups' epigenomes. The epigenetic pattern that mom establishes tends to stay put, even after the pups become adults. These patterns can be reversed through the introduction of methyl in the diet or a removal of methyl using chemical compounds

30. BARR BODIES
A Barr body (named after discoverer Murray Barr) is the inactive X chromosome in a female somatic cell. A normal human female has only one barr body per somatic cell, while a normal human male has none.