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Z gene

B-galactosidase
Y gene

permease
A gene

transacetylase
Allows lactose to enter the cell

Y gene. permease.
breaks down lactose into glucose and galactose

Z gene. b-galactosidase.
lactose operon gene that has unknown function

A Gene. Transacetylase
Function of lac repressor when lactose is absent

Binds to the operator, preventing transcription from occuring.
Function of repressor when lactose is present.

Lactose molecules bind to repressor proteins and prevent them form binding to the operator. RNA Polymerase cand translate the Lac genes
always contain active enzymes for glucose metabolism even when glucose is not present.

constitutive enzymes
sythesized by genes that are sometimes active and sometimes inactive, depending on the presense of absence of substrate

inducible enzymes
regulator i gene

works in conjunction with the operon but may be located some distance from it.
What is Catabolite Repression in Lac Operon

Regulates expression of the operon when another carbohydrate (other than lactose) is also available.
Explain the glucose effect on Lac Operon

Glucose metabolic enzymes are constitutive. saves energy.
What are the two types of Mutations?

Point Mutation & Frameshift Mutations
What is a Point Mutation?
- when one nucleotide has been exchanged for another.
- Includes: Base substitution
- Missense mutation
- Nonsense mutation
What is base substitution

Point mutation that may have no effect
What is Missense mutation?

Point mutation that changes in codon such that a different amino acid is substituted
What is Nonsense Mutation?

a Point mutation that base change results in a stop codon.
What are the types of Frameshift mutations?

Deletion and Insertion
What are Deletion mutations?
- a type of frameshift mutation.
- bases are deleted from DNA Sequence
What are Insertion Mutations?
- A type of frameshift mutation.
- Bases are inserted into DNA sequence.
How does radiation act as a mutagen?

High energy rays strike DNA causing Thymine to bond with adjacent Thymine causing dimers
What are the two types of Mutagens

Chemical mutagens & radiation mutagens
What are the Four types of Chemical Mutagens?
- Base analogs.
- Alkylating agents.
- Deaminating agents (nitrates and nitrites).
- Acridine Orange.
What do base analogs do?

Base analogs cause errors in base pairing and increase the occurence of a mutation.
What is AZT?

A base analog that acts as an analog of thymine: acts as a chain terminator.
What is 5-Bromouracil?
- A base analog that is similart to thymine in structure.
- It does not complementary base pair with adenine.
What do dimers do?

Dimers prevent RNA Polymerase transcription activity.
What is excision (dark) repair?
- A distortion of dimers recognized.
- Dimer is cut out.
- DNA polymerase I fills gap.
- DNA ligase seals the final nick in DNA
What is Photoreactivation?
- Light repair occurs in bacteria.
- Activation of photolyase that repairs thymine dimer.

Author

Fontana02

505

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Description

Chapter 7

Updated

2009-10-27T08:24:45Z