Download In the previous lecture we talked about DNA replication in bacteria

# In the previous lecture we talked about DNA replication in bacteria, and we said that there is
no prophase, no metaphase, no anaphase and no telophase.
# if bacterial cell is located in a good environmental condition it will replicate and produce
thousands of cells after just 24 hours!!
All of those cells are descended from a single parent cell so they are genetically identical. By
this huge replication they make what we called “colony” or “clone”.
generation time for bacteria is very short.
# generation time: is the time which bacteria spent to give new generation.
generation time for bacteria ranges between 1-3 hours. In e-coly for example, if there is
optimal condition, it gives new generation every 20 minutes, and because of its short
generation time ( 20 minutes ) we use it in research and laboratory.
# scientists estimate that if bacteria replicate during 2 days it will produce cells that weight
more than the weight of the earth. But this is impossible to occur because we limits their
replication.
Since all food will be absorbed! like in soil if they replicate in high rates they will start
combating for space and food, also some bacteria start to produce antibiotic to kill other
bacteria.
DNA replication:
# ribosomes in bacteria consist of two subunits that have the same function as in Eukaryotes
but RNA and protein in prokaryotic ribosome differ from those in eukaryotic ribosome.
# the target for some antibiotic is the ribosome, the antibiotic inhibits bacterial ribosomes, and
this will allow to the death of the cell.
There’s no effect for antibiotic in our ribosomes cause of the differ in chemical composition
from bacterial ribosomes.
# bacteria have ability to produce endospores, when bacteria is exposed to harsh
environmental condition they will make a cope at their DNA and surrounds it with a tough
multi-layered forming the endospore. Then water is removed from the endospore and this will
lead to slow metabolic rate in the cell, then the original cell degenerate. If the optimal
condition become available, endospore will dehydrate and start germinating.
# we can kill endospores just by:
1) heating above 121 C.
2) high pressure.
Rapid reproduction and mutation:
although prokaryotes don’t reproduce sexually, but the genetic variation may occur.
the source of genetic variation:
1) Mutation: If errors occur during DNA replication, this lead to producing new cells with
mutation. If the mutation is useful all new cells will carry this mutation and survive.
2) Bacterial transformation.
3) Viral transduction.
4) conjugation.
Bacterial transformation:
# the genotype and possibly phenotype at a prokaryotic cell are altered by uptake of foreign
DNA from its surrounding.
# allele: different forms of the same genes.
# they discovered that many bacteria have at their surface, specific protein responsible for
recognize and transport DNA foreign, as long as this DNA is from related species, when DNA
foreign enters the cell it can be inter corporate into genome by homologous DNA.
# recombined DNA: the new gene which results from transformation.
Viral transduction:
# refer to figure 27.11 page 608.
# transport of gene to bacteria via virus ( bacteriophages ).
# bacteriophages: phages that infect bacteria to replicate because they loses ribosome.
1) It injects its DNA, DNA use ribosome to make many copies of its genome and capsid.
2) sometimes an error may occur and it leads to cutting a part in the bacteria, DNA enter
capsid and phage.
3) lysis will occur and the cell degenerates.
4) phages which carry parts of the bacterial DNA infect other bacterial cell and injection occur.
the donor: the cell which its DNA package and transform to other cell via phages.
the recipient: the cell which receive the new DNA.
5) the recipient cell replicate and produce new copy of recombinant gene.
Conjugation:
# keep in mind that the purpose of all these mechanisms is genetic vatiation.
# refer to figure 27.13 and notice the steps of mechanism for conjugation ( just part (a)).
# some bacterial cells have an extra circular DNA ( small rings ) we call them “plasmids”. Those
plasmids carry genes not responsible for everyday activity, they are responsible about special
features.
#plasmids replicate independently from the main DNA.
# there are two types of plasmids:
1) R-plasmids.
2) F-plasmids.
1) R-plasmids ( R: resistance for antibiotic ).
the genes which help bacteria to resist antibiotic exist in plasmids.
2) F-plasmids ( F: fertility ).
carrying about 25 genes responsible for production of apili and help cell to make conjugation.
F+ cells: cells which have the F-plasmids.
F- cells: cells which don’t have the F-plasmids.
#study the mechanism from the book page 609 part ( a ).
we call this case ( contagious ) F+ cell convert F- cell to F+ cell has F-plasmids gene, then this new
cell can convert other cell.
# in those three mechanism there is unidirectional transfer of various amount of DNA.
Horizontal gene transfer:
# unidirectional transform of genes from one cell. Usually we use this term ( horizontal gene
transfer ) if they two cells are from different spices.
# we talk about structure of cells, and its shape, structure of cell walls, reproduction and
motility.
Nutrition:
# there are two types of nutrition: autotropic and heterotopic.
# we classify bacteria according to nutrition depending:
1) source of energy.
2) source of carbon.
# bacteria are the most diverse concerning nutrition.
inorganic
autotrophs
# carbon source
organic
heterotrophs
light
Photoheterotrophs.
light
Photoautotrophs.
source of energy
inorganic chemicals
Chemoautotrophs.
organic
Chemoheterotophs.
The role of oxygen in metabolism:
# according to the requirement of O2 for bacteria we classify them in 3 groups:
1) obligate aerobs: must use O2 for cellular respiration and connate grow without it.
2) obligate anaerobs: are poisoned by O2 and can’t live if O2 is present. They carry out
fermentation of anaerobic respiration.
3) facultative anaerobs: use O2 if it is present, but can also carry out fermentation or anaerobic
respiration in absence of O2.
#anaerobic respiration: extract chemical energy in which substance other than O 2 such as ( SO4
, NO3 ) accept electrons in downhill end of electron transport chain.