- The Bacterial
- Bacterium DNA:
- 1. singular and circular
- 2. found in the nucleoid region of the
- 3. contain a small double strand ring of
- Most bacteria reproduce by binary
fission. There is only one origin of
- 2 replication forks move in opposite
directions. Bacteria can completely divide in 20 minutes under
- Transfer and recombination of Bacterial
- There are three natural processes of gene
transfer in bacterium:
- 1. Transformation: Bacteria picks up
DNA from its environment. Avery's experiment.
- 2. Transduction: Gene transfer from
one bacterium to another using a bacteriophage.
- a). General
transduction: random pieces of host DNA
are packaged in within a phage capsid during the lytic
- b). Restricted
transduction: when a temperate phage
takes some of the host's DNA with it when it forms a new
Conjugation: transfer of
genetic material between 2 cells that are temporarily
- a). The cell donating the DNA extends an
external appendage called a sex
- b). This pili attaches to the cell
receiving the DNA.
- c). A cytoplasmic bridge forms which the
DNA is transferred.
- The ability for the sex pili to form is
conferred by genes in a plasmid called the F
factor. (fertility factor). Cells with the
F factor are designated F+ and cells without it are designated
F-. During conjugation between an F+ and an F- bacterium both
cells finish up as F+ forms. Sometime the the F factor inserts
into the circular chromosome. Integrated F factor is still
expressed. It is designated Hfr. (high frequency of
- Transfer of genetic material by
conjugation can help scientists map the chromosomes of
- 1. Specific strains of Hfr bacteria always
transfer genes in the same sequence.
- 2. The duration of conjugation determines
the number of genes transferred.
- Episomes: plasmids that can
integrate into the bacterial chromosome. (F factor). Can exist
independently of the circular chromosome or integrate and
replicate with it. Some carry up to 7 genes for resistance for
- Transposons: DNA sequences that can
move from one chromosomal site to another. Serve as natural
agents of genetic change. Occur in both prokaryotic and
- Control of gene expression in
- Cells have 2 ways of controlling
metabolism: Regulating enzyme activity and regulating enzyme
- 1. Regulating enzyme
activity: The end product of an
anabolic pathway may turn off its own production by inhibiting
activity of an enzyme at the beginning of the pathway.
- 2. Regulating enzyme
synthesis: Accumulation of products
triggers a mechanism that inhibits mRNA production by genes
that code for an enzyme at the beginning of the pathway. (gene
and their control:
- Francois Jacob and Jacques Mond proposed a
mechanism for gene regulation, the operon concept.
- Structural gene: gene that codes for
a regulated cluster of regulated structural genes with related
- a). common in bacteria and
- b). has a single promotor region, so an RNA
polymerase will transcribe all structural genes on an
- c). contains a single operator, a DNA
segment between the operon's promotor and structural genes. It
is a binding site for the operon's repressor protein. Acts as
the on /off switch for movement of RNA polymerase and
transcription of the structural genes.
- d). Repressor: specific protein that
binds to an operator and blocks transcription of the operon. It
blocks the attachment of RNA polymerase to the
- e). some operons are switched on by
activators. DNA-binding regulatory protein which activates
transcription of the operon.
- f). Regulatory genes: genes that
code for repressor and activator proteins.
- Repressible Operon:
- If there is no tryptophan in the cell, the
regulatory gene produces a repressor protein which remains
inactive,allowing the operator to proceed,by allowing the RNA
polymerase to complete the formation of the m-RNA and the
issuing polypeptides making tryptophan.
- If there is tryp in the cell, the repressor
protein binds to the promotor with trp as an allosteric
inhibitor. This stops the production of the
- An Inducible Operon:
- Lac operon: If lactose is absent
from a cell the enzymes will not be made. If the sugar enters
the cell, the operon will be switched on and produce the
enzymes needed to digest the lactose.
Lactose metabolism in E. coli is programmed by
the lac operon which has three structural genes. lac.Z codes
for B-glactosidase which hydrolyzes lactose.
lac. Y codes for permease, a membrane protein
that transports lactose into the cell, and lac A codes for
transacetylase, an enzyme that has no known action in lactose
metabolism. Lactose acts as an inducer to turn on the
- Repressible Enzymes Inducible
- 1. Their genes are switched on until 1.
There genes are switched off specific metabolite activates the
repressor until a specific metabolite inactivates the
- 2. Generally function in an anabolic
pathway. 2. Functions in catabolic pathways.
- 3. Pathway end product switches off its own
3. Enzyme synthesis is switched on production by repressing
enzyme synthesis. by the nutrient the pathway uses.
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