Genetics Chapter 16

Exam 3

What are structural genes?

Encoding all proteins in a cell

What are regulatory genes?

encoding products that interact with other sequences and affect the transcription and translation of these sequences

What are regulatory elements?

DNA sequences that are not transcribed but play a role in regulating other nucleotide sequences

What does gene regulation do in bacteria?

Maintains internal flexibility, turning genes on and off in response to environmental changes

What does gene regulation do in multicellular eukaryotic organisms

Gene regulation also brings about cell differentiation

What is constitutive expression?

Continuously expressed under normal cellular conditions

What is positive control?

Stimulates gene expression

What is negative control?

Inhibits gene expression

What are examples of gene control?

Chromatid condensation, histone modification

What is the domain of DNA-Binding Proteins?

~60-90 amino acids, responsible for binding to DNA, forming hydrogen bonds with DNA

What is the motif of DNA-Binding Proteins?

Within the binding domain, a simple structure that fits into the major groove of the DNA

What are the types of motifs of DNA-Binding Proteins?

Helix-turn-Helix, Zinc Fingers, Leucine Zipper

What is an operon?

A single transcriptional unit that includes a promoter, an operator, and a series of structural genes

What is a regulator gene?

DNA sequence-encoding products that affect the operon function but are not part of the operon

What are inducible operons?

Operons where transcription is usually off and needs to be turned on

What are repressible operons?

Operons where transcription is normally on and needs to be turned off

What is a negative inducible operon? (REVIEW)

The control at the operator site is negative. Molecule binding is to the operator, inhibiting transcription. Such operons are usually off and need to be turned on, so the transcription is inducible

What is an inducer?

Small molecule that turns on the transcription

What is a negative repressible operon?

The control at the operator site is negative. But such transcription is usually on and needs to be turned off, so the transcription is repressible

What is a corepressor?

A small molecule that binds to the repressor and makes it capable of binding to the operator to turn off transcription

What is positive control?

In positive transcriptional control, the regulatory protein involved is an activator. It binds to DNA (usually at a site other than the operator) and stimulates transcription

What is the structural gene associated with lacZ?

β-galactosidase

What is the structural gene associated with lacY?

Permease

What is the structural gene associated with lacA?

Transacetylase

What is lacO?

Operon operator

What is the lac Operon of E. coli?

A negative inducible operon involved with lactose metabolism

What is the inducer of the lac Operon?

Allolactose

What is lacI?

Repressor encoding gene

What is lacP?

Operon promoter

Does the repression of the lac operon completely shut down transcription?

No; even if there is no lactose, there is still a basal level of transcription

What is the structure of lactose and where is it found?

Consists of two 6-carbon sugars linked together; major carbohydrate found in milk

What is the position of the operator in the lac operon?

The operator overlaps the promoter and the 5’ end of the first structural gene

What is a partial diploid?

Full bacterial chromosome and an extra piece of DNA on F plasmid

What are structural gene mutations?

Mutations that affect the structure of the enzymes but not the regulations of their synthesis

What produces fully functional β-galactosidase and permease?

lacZ⁺lacY^-/lacZ^-lacY⁺

What configuration are mutations with the lac promoter and lac operator?

cis-acting mutations

What configuration are mutations with the lacI (repressor)?

trans-acting mutation

What are regulator-gene mutations?

lacI^- leads to constitutive transcription of three structural genes

How does lacI⁺ compare to lacI^-?

lacI⁺ is dominant over lacI^- and is trans acting. A single copy of lacI⁺ brings about normal regulation of lac operon

What produces fully functional β-galactosidase? REVIEW

lacI⁺lacZ^-/lacI^-lacZ⁺

How does the partial diploid lacI⁺lacZ^-/lacI^-lacZ⁺ produce β-galactosidase?

It produces β-galactosidase only in the presence of lactose because the lacI gene is trans dominant