1. Bacterial cell structure Flashcards
how is bacterial DNA structured
in two forms:
- nucleoid = region where chromosomes are found
- plasmids = small, circular closed DNA molecules, carry non essential genes
how many nucleoids per cell
1
what is the nucleoid responsible for
basic cell needs: reproduction, division, feeding
what are plasmids responsible for
carry non essential genes: e.g. antibiotic resistant genes
how are plasmids swapped between cells? what does this allow?
via a sex pili that facilitates conjugation
allows transfer of genes, e.g. antibiotic resistance
what are inclusions, what are they used for
granules of organic or inorganic material reserved for future use (e.g. when a bacterium exits a growth cycle and runs out of nutrients)
name 2 components of inclusions
glycogen, sulphur granules
true or false: bacteria have a phospholipid bilayer
true:
- permeable barrier containing integral proteins
what structure is used to classify bacteria
the cell wall
what colour Gram stain is a Gram-positive bacteria
purple
what colour Gram stain is a Gram-negative bacteria
pink
what does crystal violet bind to
peptidoglycan in the cell wall
what happens to the crystal violet in a Gram-negative species
binding is weak, following ethanol wash crystal violet dissociates
how can we identify the cells with no peptidoglycan
counter-staining with safranin
what two sugars is peptidoglycan composed of
G = NAG = n-acetylglucosamine M = NAM = n-acetylmuramic acid
what is the peptidoglycan structure
M-G polymer chains linked via peptide bridges holding the molecule together
what two acids are found in gram-positive cell walls
teichoic acid
lipoteichoic acid
what is teichoic acid used for
carbohydrate used by phagocyte for recognition of bacterial prey
what is the function of lipoteichoic acid
a adhesion molecule that can travel through the plasma membrane
Gram-negative bacteria has periplasm, what is this?
an inter-membrane space, prevents crystal violet binding
what is the role of porin? (Gram-neg)
allows soluble nutrients to be transported into the cell. the pore is filled with water and is mostly non-selective
Gram negative bacteria have lipopolysaccharide, what are its three components?
- lipid A = sits in the membrane anchoring the LPS
- Sugar chain = core polysaccharide
- O-polysaccharide = O antigen recognised by phagocytes (facilitating phagocytosis)
what does the capsule contain
thick layer of sugars and water
what is the function of the capsule
- protect host from phagocytosis: this thick layer is difficult to digest
- protect from harsh environment conditions
- overproduction - allows attachment to surfaces
S-layer:
- function?
- structure?
function = site for adhesion, anti-phagocytic structure = monolayer of identical proteins or glycoproteins
flagella:
- what protein is the motor for flagellum?
- use?
- arrangement?
- two types:
- dynein
- swimming, motility, attachment to surfaces
- 9 +2
- polar flagellum (at end of the cell), amphitrichous (one flagella at each end of the cell)
what are fimbrae
short hairs that cover the cell, used for recognition and attachment to surfaces
define population of bacteria
single species
define communities of bacteria
more than one species
why do we catalogue bacteria
- to bring a sense of order to the huge diversity
- enhance communication between scientists
how can we catalogue bacteria
by 16S rRNA comparison
describe the nature of the prokaryotic ribosome
two subunits:
50S = stable no subject to much variation
30S = variable, unconserved (we sequence this)
what does 16S rRNA sequencing allow
phylogenetic trees to be established - visualise evolutionary distance
what are the 3 domains of life
- bacteria
- archaea -> divides into Asgard archaea
- eukarya
