Bacteria Flashcards
what feature surrounds a prokaryotic cell
nearly all prokaryotes have a cell wall
most prokaryotes - cell wall surrounded by a sticky layer of polysaccharides called the capsule or slime layer
what are the functions of a cell wall in prokaryotic cells
maintains shape
prevents it from bursting in a hypotonic environment
(in a hypotonic environment plasmolyse)
how are the cell walls of bacterial cells different from those of eukaryotes that have cell walls (plants and fungi)
prokaryotic cell walls are made of peptidoglycan (sugars and polypeptides)
eukaryotic cells made of cellulose or chitin
what are the cell walls of archaea made from
polysaccharides and proteins but lack peptidoglycan
what is a gram stain
enables biologists to categorise bacteria by the composition of the cell wall
Gram positive bacteria have simple cell walls composed of a thick layer of peptidoglycan on top of the plasma membrane
Gram negative bacteria have wall that have less peptidoglycan and include lipopolysaccharides
peptidoglycan layer between two plasma membranes
why is gram staining important
in medicine enables doctors to match medications to the cell wall structure
capsule
capsule
sticky layer of polysaccharides or protein surrounds the cell wall of many prokaryotes
enable prokaryotes to adhere to their substrate or to other individuals in a colony
what surrounds the cell wall of many prokaryotes
Glycocalyx - outer coating consisting of capsule or slime layer
surrounded by a sticky layer of polysaccharides or protein called the capsule if it is dense and well defined or the slime layer of it is less well organised.
Enables prokaryotes to stick to substrate or each other
what is the function of the capsule or slime layer that surrounds the cell wall of many prokaryotes
allows it to stick to substrate or each other
some protect against dehydration
some shield pathogenic prokaryotes from attacks by their host’s immune system
endospore
in harsh conditions bacteria develop an endospore - produce a copy of their DNA and surround it with a multilayered structure called an endospore
water is removed and metabolism halts
cell lyses and releases the endospore - remain dormant
e.g. anthrax
fimbriae
hairlike appendages that enable some prokaryotes to stick to their substrate or each other
pilli
appendages that pull two cells together prior to DNA transfer from one cell to another
taxis in prokaryotes
movement in prokaryotes - directed towards or away from stimulus
e.g. chemotaxis - change in movement pattern in response to chemicals
how do more prokaryotes move?
flagella - may be scattered all over or at one or both ends
the flagella of prokaryotes and eukaryotes are considered examples of analogous evolution. Why?
while they look and behave similarly they are composed of different and unrelated proteins and are structurally different
analogous - perform similar functions but not related by common descent
how is the genome of a prokaryote different to that of a eukaryote
prokaryote has less DNA
prokaryotes have circular chromosomes whereas eukaryotes have linear chromosomes
prokaryote chromosomes have many fewer proteins than in the chromosomes of eukaryotes
prokaryotes lack a nucleus - chromosome is located in a nucleoid
nucleoid
prokaryotes lack a nucleus
chromosome is located in a nucleoid - a region of the cytoplasm that is not enclosed in a membrane
plasmids
in prokaryotic cells - small rings of independently replicating DNA molecules carrying only a few genes
how are prokaryotic ribosomes different to those in eukaryotes
prokaryotic ribosomes are slightly smaller than eukaryotic ribosomes
prokaryotic ribosomes differ in their protein and RNA content
how do prokaryotes reproduce
binary fission
asexually
offspring are genetically identical
what adaptations enable prokaryotes to survive in harsh conditions
capsule
ability to form endospores
biochemical adaptations e.g. enable them to survive in hot or salty environments
while they have no membrane bound organelles some prokaryotes have membranes. Describe
some prokaryotes have specialised membranes that perform metabolic functions - usually infoldings of the plasma membrane
cyanbacteria have thylakoid membranes much like those in chloroplasts
some prokaryotes have small compartments
do prokaryotes have a plasma membrane
a plasma membrane encloses the cytoplasm
structure of a prokaryotic cell
nucleioid - region for DNA ribosomes - protein synthesis plasma membrane cell wall glycocalyx - capsule or slime layer flagella fimbriae
Prokaryotes exhibit extensive genetic variation. How does variation occur in prokaryotic cells
rapid reproduction and short generation times and therefore a greater probability of mutation
genetic recombination
what is genetic recombination
the combining of DNA from two sources
three mechanisms - transformation, transduction, conjugation bring together prokaryotic DNA from different individuals
when those individuals are from different species this is called horizontal gene transfer
transformation
genotype of a prokaryotic cell altered by the uptake of foreign DNA from its surroundings e.g. harmless bacteria becomes pathogenic when exposed to a pathogenic bacteria
many bacteria have cell surface proteins that recognise DNA from closely related species and transport it into the cell
once inside the cell the foreign DNA can be incorporated into the genome by homologous DNA exchange
transduction
phages (viruses that infect bacteria) carry genes from one host cell to another
conjugation
DNA is transferred between two prokaryotic cells (usually the same species) that are temporarily joined.
in bacteria DNA transfer is always one way - one cell donates and the other receives e.g. e coli
pilli pull together - formation of a mating bridge
reliant on F factor (fertility) in genome
F factor can exist as a plasmid or segment of DNA
R plasmids
plasmids (small pieces of DNA in the cytoplasm) carry antibiotic resistant genes
problem is compounded by the fact that many R plasmids have genes that encode for pili and enable DNA transfer by conjugation
some R plasmids carry genes for resistance to as manu as 10 antibiotics
phototrophs
organisms that obtain energy from light
chemotrophs
obtain energy from chemicals
autotrophs
need only carbon dioxide or related compounds as a carbon source
heterotrophs
require at lease one organic unit such a glucose to make organic compounds
photoautotroph
use light as an energy source
use carbon dioxide as a carbon source
photosynthetic organisms - photosynthetic prokaryotes e.g. cyanobacteria / plants / some protists
chemoautotroph
energy source - inorganic chemicals
carbon source - carbons dioxide or related
e.g. certain prokaryotes
photoheterotroph
energy source - light
carbon source - organic compounds
example - certain aquatic and salt loving prokaryotes
chemoheterotroph
energy source - organic compounds
carbon source - organic compounds
e.g. many prokaryotes, protists, animals, fungi, some plants
obligate aerobes
must use oxygen for cellular respiration and cannot grow without it
obligate anaerobes
poisoned by oxygen
use anaerobic respiration - substances other than oxygen drive electron transport chains in cellular respiration (nitrate ions or sulphate ions)
may use fermentation
facultative anaerobes
in cellular respiration - use oxygen if available but can also carry out fermentation in an anaerobic environment
how many prokaryotic species are there
10,600 have been named
how many prokaryotes in a handful of soil
book says - 10,000 prokaryotic species
lecture - 100 million and a billion in a teaspoon of soil
major groups of bacteria
proteobacteria chlamydias spirochetes cyanobacteria gram positive bacteria
proteobacteria
five groups - alpha, beta, gamma, delta, epsilon
there are differences between gene expression in bacteria and archaea/ eukaryotes (who are similar)
bacteria - only one RNA polymerase
initiator amino acid for protein synthesis is formyl methionine (A and Es have methionine)
no introns in genes
no histones associated with genes
extremophiles
archaea - lovers of extreme conditions
extreme halophiles
archaea that live in highly saline environments
extreme thermophiles
archaea that thrive in very hot environments
e.g. sulfolobus
methanogens
archaea
anaerobes - poisoned by oxygen
use carbon dioxide to oxidise hydrogen - produces energy and methane (marsh gas)
decomposers / live in gut of cattle, termites, herbivores
CRISPR-Cas system
helps bacteria and archaea defend against attack by viruses
has been developed into a tool for altering genes in any organisms
Cas proteins can cut DNA
how is the cell wall of archaea different from bacterial
bacteria - unbranched hydrocarbons
archaea - some branched hydrocarbons / no peptidoglycan present
thermoacidophiles
archaea that survive in extreme acidity and temperature
endosymbiosis
eukaryotic cells originated by endosymbiosis when a prokaryotic cell engulfed a small cell that would evolve into the mitochondrion
serial endosymbiosis hypothesis
ancestral prokaryote - bacteria - developed infoldings of plasma membranes that developed into a nucleus and ER
Engulfed an aerobic bacterium - the bacterium became the mitochondria
Secondary symbiosis - engulfed a photosynthetic bacterium to form plastids
evidence for endosymbiosis
inner membranes of mitochondrion and plastids is homologous to inner membranes of bacteria
mitochondria and plastids replicate by a process like binary fission
mitochondria and plastids have circular DNA / no histones
mitochondria and plastids have ribosomes / these ribosomes are more similar to bacterial ribosomes than to the cytoplasmic ribosomes of eukaryotic cells
protists
very small eukaryotes just 0.5 - 2 um in diameter
eukaryotes that are not plants, animals or fungi
most protists are unicellular
most common of eukaryotes
why was the kingdom of protista abandoned
genetic studies revealed that some protists are most closely related to plants, fungi or animals than to other protists
most biologists
what are the three domains of life
eukaryotes, bacteria and archaea
what types of eukaryotes are there
animals plants fungi protists
how are eukaryotes different from prokaryotes
nucleus and other membrane bound organelles
cytoskeleton - prokaryotic cells lack a well developed cytoskeleton
