Prokaryotes form & function Flashcards
What size range are prokaryotes? What size is E.coli?
Size range: 0.2 -750 um
Typically: 0.5-5 um
E. coli 1-2 um
Why are prokaryotes so small?
Fick’s law of diffusion
Larger cells reach a point where they can’t diffuse nutrients through the cell quick enough to compete with smaller cells
Smaller cells can also grow faster, out competing larger cells.
The lower limit in size is set by the size of DNA and proteins required to be viable
What is the function of the cell/cytoplasmic membrane?
Permeability barrier – stops solutes moving in and out of cell and separates cell from its environment.
Protein anchor - participate in transport, bioenergetics and chemotaxis
Energy conservation - allows generation of energy by maintaining proton gradient so protons/hydrogen ions are positively charged, allowing cell to maintain a gradient between inside of the cell and the environment.
What is the structure of a cell membrane?
Lipid bilayer - hydrophobic and hydrophilic
Transport proteins act as pores and channels for solute allowing the controlled movement of solute across the membrane (selectivity)
Proteins stabilise the structure of the fluid lipids
Features of lipid bilayer
A great permeability barrier
Fluid and flexible (but not very strong).
What is a monolayer?
Two tails with a head at each end.
Some archaea have this instead of bilayer
What is the cell wall in Gram +ve bacteria made up of?
Simple wall
Multiple sheets of peptidoglycan (protein and sugar polymer).
Up to 90% of wall is peptidoglycan.
Is permeable to small molecules.
Features of cell wall in Gram -ve bacteria and what is it made up of?
Inner membrane
Periplasmic space containing peptidoglycan and proteins/enzymes
Only around 10% peptidoglycan
Second layer of lipids and sugars, the ‘Lipopolysaccharide layer’
Outer layer is more permeable to smaller molecules (not proteins) due to porins.
What is Gram stain?
1884
Uses crystal violet that is trapped in the walls and stains the violet when under a microscope.
Gram negative bacteria stain pink as they have two membranes.
What are archaea cell walls made up of?
Pseudomurein (a polysaccharide), or S-layers: interlocking protein and glycoprotein molecules.
(S-layers are also found in some bacteria, but don’t make up the bulk of the cell wall).
What are capsules?
Surround cell
Made up of Polysaccharide (sugar polymer)
Gives cell protection and may help evade immune systems
Also allows some cells to ‘stick together’ forming biofilms
What are Fimbriae & Pili?
Fimbriae - Protein filaments, allows attachment to tissues (pathogenic bacteria)
Pili - longer, 1 or a few per cell, Help the cell attach to tissue (in pathogenic bacteria)
Can be used to transfer genetic material in a process called conjugation
What are flagella?
Protein filaments that rotate and propel cell through water.
Prokaryotic flagella can be ATP-driven (Archaea) or proton-driven (Bacteria).
What are the main characteristics of a prokaryotic cell?
Cell wall
Cytoplasmic membrane
Nucleoid
Cytoplasm
Plasmic
Ribosomes
What is a nucleoid?
Contains main genetic information - double stranded DNA
What is a Plasmid?
Circular loop of double stranded DNA - contains genes
What are ribosomes?
Translate mRNA to proteins in the cytoplasm
What is binary fission?
DNA copied
Cell divides
Each daughter cell has copy of original double stranded DNA and half the cytoplasm, cell membrane and cell wall.
Relies on enzymes helicase and primase, RNA primer so DNA polymerase can add nucleotides to one of the strands of DNA to make double stranded DNA.
What is horizontal gene transfer?
Transfer of genetic information between cells
What is transformation?
Process of horizontal gene transfer by which somebacteriatake up foreign genetic material (naked DNA) from the environment.
When experiencing a new environment they can add genes to their genome that would benefit them
What is conjugation?
Plasmid is passed and copied from
one prokaryotic cell to another, through pili
A single stranded piece of plasmid
DNA is passed to the recipient.
The recipient cell synthesises a new
DNA strand (complimentary DNA strand).
Both cells end up with a double stranded copy of the plasmid DNA (genes).
What is transduction?
Accidental
When Bacteriophages (dominant virus) replicate their DNA they can sometimes pick up DNA from their host cells.
Very rarely this can result in a stable transformation transduction event where DNA is incorporated into host.
Core genome vs pan genome
core genome: shared by all strains of the species
pan genome: includes core plus genes present in some but not all strains of the species
What are cell inclusions?
Inclusions function as
energy stores of stores
of functional building
blocks.
What storage vesicles do prokaryotic cells have?
Carbon stores – poly-hydrocarbons, glycogen
Polyphosphate – required for DNA and lipid synthesis
Sulphur – Oxidised as energy source in some forms of metabolism
What are magnetosomes?
Exact purpose not know but could allow bacteria to orientate themselves to earths magnetic field
What are gas vesicles and their purpose?
Found in bacteria and archaea
Made of proteins impermeable to water and solutes but permeable to gases.
Make cell less dense and therefore allow changes in buoyancy.
What are endospores?
Some prokaryotes can form endospores.
Extremely resistant to heat, harsh chemicals and radiation.
Normally occurs when nutrients become limiting.
Can survive for many years before ‘germinating’.
