Exam 3 Study Guide BSC 315-001

Topic Sections Practice problems

14Bacterial genetics and gene expression

13.1-13.315.1-15.2

13:1015: 5-8, 11-13

15Eukaryotic gene expression 11.1-11.3 (omit 387-388, 391, 393-

394)16.1-16.4

16: 2-7,10-12, 14, 15, 17-19, 23-25

16Recombinant DNA 9.1-9.2

17.1-17.2, 17.49: 2, 3, 8-11, 13, 14

17 DNA sequencing 9.3-9.5 9: 1, 15-27

14 PROKARYOTIC GENE EXPRESSION Bacterial Phenotypes

Auxotrophic Mutantso Cannot make an essential compound. Defect in an anabolic (building up) pathway.o Wildtype strain: prototroph

Catabolic Mutantso Cannon break down or use particular compound as sole energy source. Defect in

catabolic (breaking down) pathways.

Gene Regulation (general aspects) Regulation of Transcription (most common)

o Trans-acting factors = regulatory proteins Trans = “away from.” Gene is being regulated by something coming from

somewhere else.o Cis-acting sequences = DNA sequences to which they bind

Cis = “close to.” Close to the gene being regulated. RNA processing (in eukaryotes only) Rate of translation or lack of translation Rate of RNA or protein turnover Positive vs. Negative Regulation

o Positive Regulation A bound regulatory protein is necessary for transcription. Positive regulatory proteins = activators

o Negative Regulation A bound regulatory protein prevents transcription

Lac Operon Positive Regulation

o A bound protein (CRP-cAMP complex) is required for the transcription of the lac operon.

CRP-cAMP complex binds to the lac promoter and recruits RNA polymerase. Negative Regulation

o A bound protein (lac repressor) represses the transcription of the lac operon. Lac repressor protein is a trans-acting factor The operator is a cis-acting regulatory element When lactose is present, lactose will bind to the repressor. The repressor-

lactose complex cannot bind to the operator, thus allowing for transcription in the presence of lactose.

E.g.: Lactose induces transcription by inactivating the repressor (2 negatives make a positive)

Lac Genes lacI

o Gene encodes: the lac repressor protein

Exam 3 Study Guide BSC 315-001

lac repressor protein acts in transo Transcribed independently, and at all timeso Mutations

lacI+ normal repressor protein Behavior: Phenotype:

lacI- mutant repressor protein cannot bing to operator Behavior: Phenotype:

lacIS mutant repressor protein that cannot bind lactose Behavior: binds to operator whether lactose is present or not. Phenotype: Represses expression when lactose is absent and when

it is present