1. Gene Expression and Regulation

2. I. Gene Regulation in Eukaryotes
Transcriptional Controls
1. Gene amplification
2. Chemical Modification
Post-transcriptional Controls
Translational Controls

3. A. Transcriptional Control
1. Gene Amplification: A gene sequence can be repeated many times on a DNA sequence…resulting in multiple mRNA transcripts, therefore more gene expression.

4. Different gene regions of a DNA molecule
TRANSCRIPTION
Different gene regions of a DNA molecule
mRNA
rRNA
tRNA
Transcript processing
proteins
mature mRNA
subunits for ribosomes
mature tRNA
convergence of RNAs
TRANSLATION
Pools of amino acids, tRNAs, and ribosomal subunits in the cytoplasm
synthesis of polypeptide chain on the platform of an intact ribosome
FINAL PROTEIN
Fig. 15.5, p. 245
for use in cell or for export

5. A. Transcriptional Control
2. Chemical Modification: A DNA segment may be wrapped tightly with histones, preventing gene expression.
In mammalian females, the
extra “X” is tightly bound,
resulting in the presence
of a Barr Body in the
nucleus.

6. Mosiac Effect and X inactivation

7. B. Post Transcription
Splicesomes: Enzymes that rearrange segements of introns, creating new combinations of proteins.

8. C. Translational Controls
mRNA transcript will be digested when it reaches the cytoplasm (a good thing, or once a gene were turned on it would be forever expressed). A transcript has a cap added to the 5’ end and a poly-A tail added to the 3’ end. If these tails/caps are long, it will take the enzymes in the cytoplasm a greater amount of time to digest the coding region of the transcript.

9. unit of transcription in a DNA strand
exon
intron
exon
intron
exon 3’ 5’
transcription into pre-mRNA
poly-A
tail
cap 5’ 3’
(snipped out)
(snipped out) 5’ 3’
mature mRNA transcript
Fig. 14.9, p. 229

10. II. Gene Regulation in Prokaryotes
Prokaryotes have only one DNA molecule (circular and not protected by nuclear envelope) and this DNA molecule is not bound up with histones. Thus, gene regulation in prokaryotes is unique. One of the best known pathways of gene recognition is the lac Operon, a regulatory pathway by which bacteria are able to produce the enzyme to digest lactose only when necessary (when lactose is present in the environment).

11. A. Operon and DNA
Operon is a regulatory system that controls DNA transcription in prokaryotes.
Operon contains a promoter (the specific nucleotide sequence that tells a cell to begin or start transcription), an operator (a segment of DNA that can be used to turn gene expression on or off) and more than one gene.

12. B. Actors in Lac Operon
Regulatory or Repressor Protein – Binds with operator (segment of DNA) to prevent a gene from being transcribed.
Substrate/Inducer – Interacts with protein to prevent it from adhering to DNA.
Operator – Section of DNA
Promoter – Section of DNA.
Operon – The entire system.

13. (codes for trans-acetylase)
regulator gene
gene 1
(codes for
b-galactosidase)
gene 2
(codes for premease)
gene 3
(codes for trans-acetylase)
transcription,
translation
promoter (binding site for RNA polymerase)
operator (binding site for repressor)
repressor protein
lactose operon
Fig. 15.4a, p. 243

14. translation into three polypeptide chains for three different enzymes
RNA polymerase
mRNA transcript
translation into three polypeptide chains for three different enzymes
lactose
b-galactosidase
permease
trans-acetylase
Fig. 15.4b, p. 243

15. Without Lactose:
Describe the chain of events that occurs in a bacterial colony when no lactose is present.

16. With Lactose:
Describe the chain of events that occur when lactose is present in a bacterial culture:

17. Positive Control: Glucose Digestion
Bacterial cells digest glucose before lactose.
If glucose is present, cAMP is converted to ATP.
cAMP, when present, bonds to promoter region and helps RNA polymerase begin transcription of lactose digestion genes.