Bacteria basics Flashcards
What are bacteria?
Very small and morphologically simple organisms lacking a nuclear membrane, multicellularity or complexity.
A group of organisms which are capable of degrading almost anything and living almost anywhere.
Capable of exponential growth and have sophisticated methods of growth regulation.
Contain most of the evolutionary diversity on Earth, and store half of the world’s carbon.
What do bacteria possess?
Cytoplasmic membrane
Cell wall
Flagellum
Magnetosome
What is Brownian motion?
Constant movement due to collisions with water molecules meaning that they hardly coast if they stop powering their movement, due to the relative viscosity of water.
Consequences of their shape?
Only soluble material can enter the cell, and only by diffusion.
Maintain small structures in order to limit internal gradients, so the whole of a small cell therefore has the same chemical makeup.
Small cell can actually exceed demand due to high SA:Vol ratio.
Link between mitochondria and bacteria?
Complex infolding on mitochondria to increase surface area for ATP production are seen in bacterial membranes as mitochondria originated from bacteria.
What is binary fission?
The cells elongate and then form a partition (septum) which eventually separates the cells into two daughter cells.
The septum is a result of the inward growth of the cytoplasmic membrane and cell wall from opposite directions until the daughter cells are pinched off.
Why are some bacteria classified as extremophiles?
Can live almost anywhere on Earth.
Min temp: -137 degrees Celcius
Can use iron as a food source when living in a stream bed.
Consequences of no nuclear membrane?
Ribosomes can attach to mRNA as it is being synthesised so simultaneous transcription and translation can occur.
Some key genetic features
No sexual reproduction. All mutations are immediately effective as they are haploid. Circular nucleoid. Supercoiled DNA. Sexually isolated (species issue).
Conjugation?
A pilus forms between the two organisms, transferring DNA in one direction. Source of variation in addition to mutations occurring.
The donor bacterium carries a DNA sequence called the fertility factor, or F-factor. The F-factor allows the donor to produce a thin, tubelike structure called a pilus, which the donor uses to contact the recipient. The pilus then draws the two bacteria together, at which time the donor bacterium transfers genetic material to the recipient bacterium. Typically, the genetic material is in the form of a plasmid, or a small, circular piece of DNA.
Main features of flagellum?
Energy efficient.
All of bacteria’s external features spontaneously assemble as there is no cytosis.
Helical twist to act as a propeller.
Cells cans sense chemotaxis and move away/towards a stimulus.
Functions of the cell membrane?
Solute transport and respiratory electron transport.
Two types of cell wall?
Gram positive and gram negative.
What are the main features of gram positive cell walls?
Very strong and determines cell shape.
Outside of the phospholipid bilayer is a thick sac of murein chains/sheets called peptidoglycan.
Show a big evolutionary divide.
What are the main features of gram negative cell walls?
Peptidoglycan is sandwiched between bilayer and the outer membrane.
The space between the membranes is called the periplasmic space.
How to test the difference between Gram positive and negative?
Gram positive will stain purple due to presence of more Peptidoglycan.
What is peptidoglycan?
Forms cell backbone layer for strength. Able to let sugars, amino acids and ions into the cell as needed.
What phenetic characters can be used for bacterial classification?
Morphological characters: gram stain & motility.
Biolog: different carbon source in each well and see which bacteria can use each substance.
Phenetic species concept?
A group of organisms that look similar to each other and distinct from other groups.
A form of artificial classification.
Biological species concept?
A reproductively isolated group, whose genes do not combine with those of outsiders, but are able to combine continually by sexual reproduction within the group.
A form of natural classification.
How is strain denoted?
An additional name is added to binomial name. Often related to pathogenicity as this can majorly affect humans.
Might relate to one single important gene product.
What is transformation?
Genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous genetic material from its surroundings through the cell membrane.
For example, dsDNA from environment can bind to the outside of the cell. Endonuclease digests ds to ss. The ssDNA associates with competence proteins so cell wall is altered to let DNA pass through more easily. The other strand gets replaced by donor DNA.
What is transduction?
Process by which foreign DNA is introduced into a cell by a virus or viral vector.
Consequences of horizontal gene transfer?
If very common and promiscuous – all bacteria would share a common gene pool and all belong to same species
If very uncommon and confined to intra-species exchange – very little gene pool mixing and the taxonomic unit could be individual clone
If common but confined to intra-species exchange – reproductive isolation and mixing of species gene pools would give equivalent of Biological Species Concept
What is ribosome sequence analysis?
Universal mechanism of protein translation so is a good molecule for comparison.
The ribosome is a mixture of ribosomal RNA and protein. Various parts of the structure is responsible for different functions.
Failure of ribosomal function is lethal so very strong purifying selection.
Ribosomal DNA can be assumed to be monophyletic as doesn’t undergo HGT - too large.
rRNA is a universal chronometer suitable for all organisms, a chronometer suitable for very long and very short evolutionary times, suitable for phylogeny of bacteria.
Why is it hard to describe bacteria?
Many bacteria cannot be cultured as the niche conditions cannot be reproduced. This is why bacteria were commonly described using phonetic characters.
Now use rRNA.
How to tell if a bacteria exists in a certain area?
Make a complementary strand, with radioactivity/fluorescence and can easily stain a kingdom.
Ecological species concept?
A species is a set of organisms adapted to a particular set of resources, called a niche, in the environment.
Where does most of the biodiversity come from?
The enormous metabolic flexibility, as all the prokaryotes are small and look simple
