Cell Division Flashcards
What do microbes affect ?
Nearly everything !
- affect food availability - destroy crops /. Preserve food
- microbial diseases change history ( can shape how communities are formed )
Everywhere in life we are encountering microbes
N.B. Average adult has 1kg of microbes in gut
What are the 6 major groups studied by microbiologists?
- prokaryotes ( bacteria ) / ( archaea)
- eukaryotes ( algae )/ ( protests ) / ( fungi)
- viruses
What do you know about the discovery of microbes?
- light microscope invented in 1600s
- mid 1600s Hooke observes small eukaryotes
Who was anton van Leeuwenhoek ?
- Dutch scientist
- invented first compound microscope
First to observe living cells
He found prokaryotes
( took dental plaque from teeth to look at microbes )
What are microbes ?
Living organisms
- microbes arise from other microbes
- No spontaneous generation
- 1861- Pasteur shows that microbes do Not grow in liquid until introduced from outside
What is used to classify microbes?
- gram stains
- ability to metabolise different substrates
- use DNA sequence to classify - bacterial genomes are relatively small
What is the microbial family tree?
Microbial species are difficult to classify
- difficult to distinguish by shape
- often asexually reproduce
- pass DNA to each other without reproduction
They may have similar shapes but very different !
Archaea are not bacteria
Similar size, shape
Very different biochemistry
What are the differences between gram positive and gram negative ?
they react differently with gram staining - P= retain crystal violet dye and stain dark violet or purple N= can be decolourised to accept counterstain ( safranin ) - stain red
Peptidoglycan layer - P= thick ( multilayered) , N= thin ( single layered)
Teichoic acids - P= present in many , N= Absent
periplasmic space = P= Absent , N= present
outer membrane: P= Absent , N= Present
there are other factors to consider…
There were three basic shapes, arrangements and sizes for bacteria, what are they ?
- coccus - spherical
- bacillus - rod
- spirillium - helical, comma, twisted rod
What are some types of Bacillus ?
- coccobacillus - very short and plump (e.g. brucella abortus)
- streptobacilli ( bacillus subtilis)
- diplobacili
( there is also a type called Plemorphic - variable in shape ( corynebacterium)
What are some types of Spirillum ?
- spirochete - spring - like Flexible ( treponema pallidum )
- vibrio - gently curved ( vibrio cholera)
- spirilla - rigid ( Borella Species)
What are diplococci ?
- cocci that remain in pairs after dividing
what are streptococci?
- cocci that remain in chains after dividing
What are tetrads?
cocci that divide in two planes and remain in groups of four
What are sarcinae ?
cocci that divide in three planes and remain in groups cubes like groups of 8
What are staphylococci ?
- cocci that divide in multiple planes and form grape like clusters or sheets
What are bacilli?
- most bacilli appear as single rods
What are diplobacilli ?
- appears in pairs after division
What are streptobacilli?
appears in chains after division
What are coccobacillus ?
- some bacilli are so short and fat that they look like cocci
what is the size of bacterium?
- it would take approx 1000 bacteria placed end to end to span the 2mm semi - conductor
What does it mean to say ‘ growth of microbes’?
- increase in number of cells , not cell size
- one cell becomes colony of millions of cells
What are some direct methods ?
- dilution and plating
- microscopic counts
What are some indirect methods?
-estimating bacterial numbers by indirect methods -
e. g.
- Spectrophotometry - to measure turbidity , OD is function of cell number
- metabolic activity is another example
- dry weight
What are some environmental limits on microbial growth?
Nutrient source Temperature pH Osmolarity Oxygen Pressure
What are the stages of bacterial growth?
as the food depletes the bacterial growth increases, and as the food completely depletes , the bacterial growth then also decreases,
the stages are :
lag phase, log phase, declining growth phase, endogenous respiration phase.
What temperatures do different bacterium strive in ?
psychrophile - 0-20 degrees
mesophile - 10-45 degrees
thermophile - 40-80 degrees
extreme thermophile - 60-120 degrees
What is a barophile ?
- barophiles require high pressures to grow - though they die at still higher pressures.
What is a barotolerant?
- barotolerant organisms grow up to a certain pressure , but die at higher pressures.
What is Barosensitive ?
barosensitive organisms die as pressures increases
What is Psychrophiles?
they are cold loving microbes (e.g. polaromonas vacuolata)
What are hyperthermophiles ?
- heat loving microbes ( thermophiles and hyoperhermophiles )
(e. g. methanopyrus kandleri )
What are acidophiles ?
- acid loving microbes
sulfolobus acidocaldarius
what are halophiles?
- salt- loving microbes ( e.g. haloferax volvanii)
what is alkaliphiles?
- alkali- loving microbes (e.g. natronobacteri um gregoryi )
What is a common method of cell division?
Binary fission ( works at the FtsZ ring
What does it mean when you say generation time ?
DNA - DNA replication - Cell elongation - septum formation - cell separation
generation time is highly variable - from 20 mins to 24 hours ( or longer in natural environment)
e. coli - 20 mins
m. tuburculosis - 12 hours
What happens as cells grow and replicate?
- there is an increase in cell number
What are some alternatives to binary fission?
- sporulation
Why does sporulation occur?
- when nutrients are depleted , or the environment becomes adverse
What are the steps for endospore formation
- vegetative cell
- chromosome is duplicated and separated
- cell is separated into a sporandium and forespore
- sporangium engulfs forespore for further development
- sporangium begins to actively synthesize spore layers around forespore
- cortex and outer coat layers are deposited.
- Mature endspore
- Free spore is released with the loss of the sporangium
- Germination spore swells and releases the vegitative cell.
give an example of a solitary hunter?
bdellovibria bacteriovorus - that uses a single polar flagellum to seek other gram - negative bacteria
steps …
- elongation- elongation initiation , elongation completes
- synchronous septation - sptation initiation , septation propagation , filament fragmentation
- maturation - progeny maturation
- lysis - escape
example
the streptomyces coelicolor life cycle.
- gram positive
- prolific - antibiotic production
- morphological differentiation
The epulopiscium life cycle?
….
example of gemmata obscuriglobus cell budding cycle?
…
example of Stanieria life cycle?
- baeocyte production in the cyanobacterium stanieria
summary ?
Bacterial species are split into two main types -Gram-positive and Gram-negative.
• Bacteria come in a variety of shapes and cell division strategies have to cope.
• Microbial growth can be monitored directly or indirectly.
• The “Generation time” is time taken to generate progeny through asexual reproduction.
• Binary fission is the most understood method of cell division.
• There are many alternatives to binary fission.
What is binary fission?
- a continuum of processes that are interlinked
the process of binary fission?
- The bacterium before binary fission is when the DNA is tightly coiled.
- The DNA of the bacterium has replicated.
- The DNA is pulled to the separate poles of the bacterium as it increases size to prepare for splitting.
- The growth of a new cell wall begins to separate the bacterium.
- The new cell wall fully develops, resulting in the complete split of the bacterium.
- The new daughter cells have tightly coiled DNA, ribosomes, and plasmids
Where are the sites of cell wall elongation ?
….
what is the bacterial cell wall?
Sacculus made of peptidoglycan
Sugar chains wrapped in circles around cell
“glyco” = “sweet”
Sugar chains linked to each other by short polymers of amino acids
amino acid = “peptide”
What do you know about the peptidoglycan layer ?
Peptidoglycan: Rigid layer that provides strength
Polysaccharide composed of
N-acetylglucosamine (NAG or G) and N-acetylmuramic acid (NAM or M)
Amino acids
Lysine or diaminopimelic acid (DAP)
Cross-linked differently in gram-negative bacteria and gram-positive bacteria
What are NAG and NAMs?
…make up polysaccharide backbone
steps of DNA replication?
note:
ori - origin of replication
dif.- a unique site on the bacterial chromosome that is located in the replication termination region
steps: 1. initiation 2. elongation 3. termination 4 cell division
http://en.wikipedia.org/wiki/DNA_replication
what is initiation?
initiation of chromosome replication
requires:
Origin of replication.
DnaA boxes.
ATP-bound-DnaA
what is replication elongation?
…
What is termination of chromosome replication?
…
E.coli cell cycle ?
positions of origins (green circles)
Replication factories (blue ovoids)
Replication termini (red circles)
Black line (DNA)
Future site of septation (grey line)
What is cytokinesis and septation?
Cytokinesis is the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells. It occurs concurrently with two types of nuclear division called mitosis and meiosis, which occur in animal cells.
two main inhibitors of septation?
Two main inhibitors of FtsZ assembly:
MinC, MinD and MinE proteins and The nucleoid
locating the site of septation?
…
assembly and maturation of the Z-ring?
… constriction of the Z- ring
