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1. Bacteria has how many chromosomes
2. Humans have how many chromosomes
makes proteins for cellular needs
Regulation of Gene Expression
Prevents synthesis of enzymes not needed
Bacteria regulates gene expression at the level of transcription
Method of regulation: Operon Model
lac operon summary
Repressor prevents gene expression (polymerase to transcript). when glucose is scarce...the inducer molecule allolactose appears in the cell then binds to repressor molecule and inactivates it. RNA polymerase can now transcribe the operon. three of the lac operon genes get transcribed into Mrna. Ribosomes then bind to Mrna and the three proteins are translated. Beta galactosidase, lactose permease and galactoside transacetylase. The induction of the lac operon enables the bacterium to efficiently transport lactose into the cell and metabolize it.
first protein from lac operon. it breaks down lactose into two simple sugars
a membrane bound protein (it goes and stays at the cell membrane)
it embeds into cell membrane. it functions as a direct route for the lactose outside of the cell to come in through
- regulatory proteins that block the ability of RNA polymerase to initiate transcription from
- repressed genes
Repression occurs as response to
- overabundance of metabolic end-products & results in decrease of synthesis of enzymes of
- that product.
Default position of gene: on
induction of transcription of gene or genes
-An inducer induces transcription of a gene.
Default position of gene: off
The Lac Operon
Contains genes needed to catabolize lactose
–3 genes coordinately regulated
- Only expressed when (1) glucose levels
- are low and (2) lactose is present
Operon is controlled by
–Repressor & inducer for the repressor (allolactose)
–Activator (CAP) & inducer for the activator (cAMP)
•Change in base sequence of DNA. Can result in change of end product.
Environmental agents that bring about mutations
Typical form of an organism as it occurs in nature
One base change within a codon
makes the individual have a different amino acid
Changes the amino acid into a stop codon.
the rest of the amino acids after the stop codon will not be translated. This will result in a nonfunctional protein product
Still codes for the same amino acid
does not affect the product
Addition or deletion of a base.
Changes the amino acid sequence that follows. It may or may not become a functional protein.
–X-rays and Gamma rays
–Cause breaks in DNA molecule
–Causes thymine dimers
Exposure to ultraviolet light causes adjacent thymines to become cross-linked disrupting their normal base pairing
Repair of DNA Damage
•DNA polymerase “proof-reading”
•Thymine Dimer Repair
1. Light repair using photolyases
2. Nucleotide excision repair (dark repair)
An enzyme requiring visible light for activity breaks the two bonds joining the two thymines. It goes back to its original shape
An endonuclease cuts the DNA, and an exonuclease removes the damaged DNA. DNA polymerase fills the gap. DNA ligase seals the gap
The Ames Test
•Uses Salmonella His- auxotroph
A test developed for identifying possible carcinogens by studying their mutagenic effect on bacteria
What is a positive result? (look for answser later)
Vertical gene transfer
Transmission of genes from parent to offspring
Horizontal gene transfer
Exchange of genes between 2 DNA molecules to form new combinations of genes
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