Genetics 7
HC 18
7.1
Bacteria possess allelic differences between strains affecting cellular traits. In addition, they
are normally haploid, which makes it easier to identify loss-of-function mutations, since
there is no dominant allele masking a recessive one. They reproduce asexually, so crosses
cannot be used in genetic analysis. Research thus relies on genetic transfer; one bacterium
transfers genetic material to another, adding to the genetic diversity. It takes place via:
- Conjugation: direct physical contact between two cells, where one donates and the
other receives.
- Transduction: a virus infects a bacterium and then transfers that genetic material to
another.
- Transformation: genetic material is released upon death to the environment, which
other cells take up.
7.2
The minimal medium contains the essential nutrients for a wild-type bacterium to grow;
when it is unable to do so and needs an extra nutrient in the medium which it does not
synthesize itself, it is auxotroph. If it would make this nutrient itself, it is prototroph. Often,
different strains have different nutritional growth requirements; heterotrophs. In some
cases, each heterotroph alone could not survive on minimal medium, but they could
exchange genetic material enabling them to get a genotype possible to live on it. For this to
happen, they must have physical contact though.
Certain strains of E. coli in addition to their circular chromosomes, have a fertility factor F
and some do not; it is needed for proper conjugation between cells. Contact between donor
and recipient is initiated by sex pili, encoded for genes in the F factor. Long pili eject from
the donor, contact the recipient, then shorten, pulling the cells together, where after a
conjugation bridge is formed that is the passageway for DNA transfer. The transfer is
concretely made up of plasmids, extra-chromosomal DNA, that contains the F factor with
the genes necessary for conjugation. The relaxosome is produced, a protein complex
encoded by F factor recognizes origin of transfer within F factor cuts one DNA strand,
the T DNA relaxosome disassociates from T DNA, aside from relaxase (together with T
DNA = nucleoprotein) nucleoprotein recognized by coupling factor promotes entry of
the exporter to the conjugation bridge, out of the donor cell and into the recipient cell
relaxase promoter circularity of T DNA both in the donor cell and the recipient cell, single
stranded DNA is made double stranded; the recipient now also has the F factor.
There are more plasmids aside from the F factor, but those that can integrate into a
chromosome are termed episomes. There are five types:
- Fertility plasmids: allow conjugation, like F factor
- Resistance plasmids: allow resistance against viruses and antibiotics
- Degradative plasmids: allow digestion of unusual substances
- Col-plasmids: encode proteins that kill other bacteria
- Virulence plasmids: turn bacterium into pathogenic state.
HC 18
7.1
Bacteria possess allelic differences between strains affecting cellular traits. In addition, they
are normally haploid, which makes it easier to identify loss-of-function mutations, since
there is no dominant allele masking a recessive one. They reproduce asexually, so crosses
cannot be used in genetic analysis. Research thus relies on genetic transfer; one bacterium
transfers genetic material to another, adding to the genetic diversity. It takes place via:
- Conjugation: direct physical contact between two cells, where one donates and the
other receives.
- Transduction: a virus infects a bacterium and then transfers that genetic material to
another.
- Transformation: genetic material is released upon death to the environment, which
other cells take up.
7.2
The minimal medium contains the essential nutrients for a wild-type bacterium to grow;
when it is unable to do so and needs an extra nutrient in the medium which it does not
synthesize itself, it is auxotroph. If it would make this nutrient itself, it is prototroph. Often,
different strains have different nutritional growth requirements; heterotrophs. In some
cases, each heterotroph alone could not survive on minimal medium, but they could
exchange genetic material enabling them to get a genotype possible to live on it. For this to
happen, they must have physical contact though.
Certain strains of E. coli in addition to their circular chromosomes, have a fertility factor F
and some do not; it is needed for proper conjugation between cells. Contact between donor
and recipient is initiated by sex pili, encoded for genes in the F factor. Long pili eject from
the donor, contact the recipient, then shorten, pulling the cells together, where after a
conjugation bridge is formed that is the passageway for DNA transfer. The transfer is
concretely made up of plasmids, extra-chromosomal DNA, that contains the F factor with
the genes necessary for conjugation. The relaxosome is produced, a protein complex
encoded by F factor recognizes origin of transfer within F factor cuts one DNA strand,
the T DNA relaxosome disassociates from T DNA, aside from relaxase (together with T
DNA = nucleoprotein) nucleoprotein recognized by coupling factor promotes entry of
the exporter to the conjugation bridge, out of the donor cell and into the recipient cell
relaxase promoter circularity of T DNA both in the donor cell and the recipient cell, single
stranded DNA is made double stranded; the recipient now also has the F factor.
There are more plasmids aside from the F factor, but those that can integrate into a
chromosome are termed episomes. There are five types:
- Fertility plasmids: allow conjugation, like F factor
- Resistance plasmids: allow resistance against viruses and antibiotics
- Degradative plasmids: allow digestion of unusual substances
- Col-plasmids: encode proteins that kill other bacteria
- Virulence plasmids: turn bacterium into pathogenic state.
