Chapter 2: Cell structure and function Flashcards
Cell envelope
It is a series of layered structures surrounding cytoplasm and governing interactions with the environment.
It includes:
Cytoplasmic membrane
Cell Wall
Outer membrane
S-layers (capsules and slime layers)
Cytoplasmic membrane
Also called plasma membrane
Surrounds cytoplasm
its main function is selective permeabilty so nutrients enter and wastes leave and membrane proetins facillitate these reactions and functions in energy metabolism
Plasm membrane structure
8-10nm wide
It is a phospholipid bilayer containing embedded proteins
It contains both hydrophobic fatty acid tails and hydrophilic glycerol and phosphate and other functional groups
The fatty acids associate inwards to form hyrdrophobic environment and the hydrophilic head groups remain exposed to external environment and cytoplasm
membrane proteins
Embedded proteins: Integral membrane proteins
Transmembrane proteins: extend completely across membrane
Peripheral membrane proteins; Loosely attached
Domains
Bacteria
Archae
Eukarya
Archael cytoplasmic membranes
-Ether linkages
-Archael lipids have isoprenes instead of fatty acids
-Major lipids are phosphoglycerol diethers with phytanyl C20 side chains and diphosphoglycerol tetra
-Many different isoprenoid chains including ring structures
Cytoplasmic membrane function
-Permeability barrier
* Polar and charged molecules must be transported
* Transport proteins accumulate solutes against concentration gradient
-Protein anchor
*Holds proteins in place
_energy conservation and consumption
* Generation of proton motive force
Eukaryotic plasma membrane
-Eu and Bac have ester linkages
-Contain Carbohydrates that function as attachment and receptor sites
-Contains Glycoproteins
-Contains sterols
*HUmans contain cholestral while fungal cells contain ergosterol
NB antifungal target
Ergosterol in membrane
Active transport mechanisms
-Simple transport
-Group translocation
-ABC system
Simple transport
-Driven by proton motor force
-Either symport: solute and H+ cotransported in one direction
-Or antiport: Solute and H+ transported in different directions
Group translocation
-Substance transport is chemically modified
-Energy-rich organic compound (not proton motive force) drives transport
-Best studied
E.Translocation
Phosphotransferase system in E.coli
-glucose, fructose and mannose
-5 proteins required
-energy from phosphoenolpyruvate
ABC transporter system
ABC= ATP binding cassette
-200 different systems for organic and inorgnic
-Substrate binding proteins outside of cell have high substrate affinity
-ATP drives uptake
-Binding protein binds to target and brngs it to transporter. Transporter breaks down ATP to transport target across
What type of organisms prefer ABC transporters
EXtremophiles as they are under stress with limited resources and ABC allow them to find specific substances in small concentrations
Cell Wall
-Needs to withstand osmotic/turgor pressure to prevent cell lysis
-Maintains cell shape and rigidity
-Bacteria seperated into two groups based off gram stain
Gram positive
envelope contains cytoplasmic membrane and thick cell wall with many layers of peptidoglycan
stains purple
Gram negative
Envelope consistes of membrane, thin cell wall with very little peptidoglycan, outermembrane and periplasm
stains pink
Bacterial cell wall component
It contains glycan tetrapeptide which is made up of:
-Sugar backbone (alternating modiefed glucose made of NAG and NAM joined by B1-4 linkages
-The linkage is what is targeted
-Short peptides are joined to NAM like L-alanine, D-alanine, D-glutamic acid, L-lysine or DAP
NAG
N-acetylglucosamine
NAM
N-acetylmuramic acid
DAP
diaminoplimelic acid
Go over diagram of gram positive
DIagram of Gram negative
Acid fast cell walls
Cells contain a high percentage of mycolic acid
-Hydrophobic waxy lipid
Forms a layer outside of the tin peptidoglycan layer
-Causes cells to stick together
-Is detected by acid fast stains
Archael cell walls
-Lack peptidoglycan and outer membrane
-Most lack polusaccharide wall and instead of S-layer (protein shell)
Archael cell wall makeup
-pseudomurein cell wall
-similar to peptidoglycan
-Alternating NAg and NAT
-B1-3 glycosidic bonds instead of B1-4
-Amino acids all L-stereoisomer
NAT
N-acetyltalosaminuronic acid
Arachael sensitivity to lysosmes
Enzymes are specific to B1-4 bonds instead of B1-3
Eu cell walls
Plants contain cellulose
Fungi contain chitin which is a polymer of NAG units and is an important antifungal drug target
Yeast cell walls contain glucan and mannan
Outer membrane structure of gram negative
second bilayer external to cell wall
-Outer membrane contains polysaccharides covalently bound to lipids: lipopolysaccharide layer (LPS)
-Facilitates surface recognition, important virulence factors and add strength
-Contains porins
LPS
lipopolysaccharide layer
-Contains core polysaccharide and O-polysaccharide
-Lipid bond sto divalent cations (Mg2+) and adds strength
-Lipid A portion
-LPS replaces most of phospholipids in outer half of membrane
Braun lipoprotein
ANchors outer membrane to peptidoglycan
Endotoxin
Lipid A, toxic component of LPS when cell dies
responsible for symptoms associated with infection
core polysaccharide
Attached to lipid A and provides structural stability
O polysaccharide
Functions as antigen and is useful for distinguishing between different strains
antibodis bind here
S-layer
paracrystalline structure consisting of protein or glycoprotein
-Always outermost layer
-functions: strenght, protection from lysis, conferring shape, creating periplasmic-like space, facilitting cell surface interactions, promoting adhesion, protecting cell from host defences
Mycoplasms
tough cell membrane in Bac without cell wall
Thermoplasm
Tough cell membrane in Archae that lack cell walls
Capsule and slime layer component
sticky polysaccaride coat outside cell envelope
Capsule
If tightly attached, tight matrix; visible if treated with INdia ink
Slime layer
Loosely attached, eaily deformed and is easier to wash off than capsuleC
Capsule and Slime functions
Assist in attachment to surfaces
Roles in development and maintanence of biofilms
Contribute to infectivity ( capsule pieces kill macrophages)( prevents antibiotic from reaching target)
Prevent dehydration/desiccation
Surface structures
Hair like appendages shorter than flagella
made of pillin
include fimbriae and Pili
Fimbria
Can occur all over the cell
Numbers in 100s
involved in biofilm formation and colonisation
Pilus
Longer than fimbriae
only few per cell
Functions:
-Motility by twitching and glidng
-DNA transfer (conjugation)
Hamus/Hami
Archael grappling hooks that assist in surface attachment and forming biofilms
-structurally resemble type IV pili except for barbed termini, which attaches cells to surfaces or each other
Cell inclusions
Function as energy reserves, carbon or phosphorus reservoirs and or have special fucntions
-enclosed by thin protein membrane
-reduce osmotic stress
Carbon storgae polmers
-synthesised when carbon in excess
-broken down as carbon or energy sources if needed
-glycogen is a glucose polymer
Phosphate granules
Inorganic phosphate
elemental sulfur accumulates in periplasmic granules and oxidised to sulfate (SO4)
Sulfur granules not found in Gram positive
Thick layer prevents periplasmic layer from expanding as much which reduces storage space
Magnetosomes
Allow bacteria to orient within magnetic field
-Biomineralised magnetic iron oxides
-Allow cell to undergo magnetotaxis: migration along magnetic field lines
Gas vesicles
Conical-shaped, gas filled structures made of two proteins
Endospores
Dormant, tough and non-reproductive structure produced by certain bacteria (usually gram positive)
-Formation triggered by lack of nutrients
-Able to survive for millions of years through hasrh conditions and structures are not metabolically active
exosporium
Outer layer
-interacts with environment or host organism and may contain spore antigens which trigger an immune response
Spore coat
Resistant to many toxic molecules and may also contain enzymes involved in germination
Cortex
Beneath the spore coat and consists of peptidoglycan and makes the endospore resistant to temperature
core wall
provides endospore resistance to UV light and harsh chemicals
Core
Contains spore chromosomal DNA
-Encased in chromatin -like proteins known as SASPs
-SASPs protect spore DNA from UV radiation and heat
-DPA further stabilises protein and DNA
-Also contains normal cell structure such as ribisomes and other enzymes
SASP
small acid-soluble spore proteins
DPA
Dipicolinic acid
Endosprulation
Insert
Endospore germination
INsert
how to kill endospores
-destroyed by burning or autoclaving (takes several hours)
-Prolonged exposure to ionising radiation
-A 10% sodium hypochlorite solution where contact time exceeds 10 minutes
-Hospitals use ethylene oxide which is a low-temp sterilant
Flagella
-assists in swimming in Bac and Archae
-Long thin appendages (15-20nm wide) anchored in cell
-Different arrangements
-Increase or decrease rotational speed relative to strenght of proton motive force
Polar/monotrichous
single flagellum at 1 pole
Lophotrichous
Tuft of flagella at one pole
Amphitrichous
Flagella at both poles
Peritrichous
Flagella all over
Amphilophotrichous
Tuft of flagella at both ends
Flagella structure
Filament composed of flagelin protein
-hook
-basal body
* G-Neg have 2 sets of rings (one to cell wall and one to plasma membrane)
*G-Pos only have inner set of rings
Flagella synthesis
Several genes
MS ring made first
Anchoring proteins, hook, cap are made next
Filament forms with flagellin exported through export apparatus
Movement with bundeled flagella
MOvement with single flagella
Archaella
proteins unrelated to flagella, more closely related to type IV pili
-smaller than bacterial flagella
-Move by rotation driven by ATP hydrolysis (move slower)
Twitching motility
Requires Type IV pili
extend from one cell pole, attach to surface, retract to pull cell forward
-Energy from ATP hydrolysis
Gliding motility
smooth, continuous motion along long axis without external structures
-Only bacteria
-helical intracellular protein track, gliding motors and adhesion proteins
Taxis
Directed movement in response to chemicl or physical stimuli
enhances access to resources and allows avoidance of death
Chemotaxis
Chemicals
Phototaxis
Light
Run and tumble behaviour
Run: smooth motin, flagellar motion rotates counterclockwise
Tumble: stops and jiggles because flagellar motor rotates clockwise, flagellar bundle comes apart
-after tumble another run beings in a random direction
Biased random walk
Bacterial respond to temporal and not spatial differnce in chem concentration
increaed chem gradient results in longer lenght of run
Osmotaxis
ionic strength
Hydrotaxis
water
Aerotaxis
Oxygen
Magnetotaxis
Magnetic current
It is used to wim toward or away from O2
Scotophobotaxis
Response to absence of light
enetering darkness causes cells to tumble and head back to light
Mitochondria
respiration and oxidative phosphorylation for aerobic Eu
number varies
surrounded by 2 membranes
-Cristae:folded internal membranes
-contain enzymes needed for respiration and ATP production
-Matrix: inermost area and contains citric acid enzymes
Chloroplasts
Contains chlorophyll
site of photsynthesis
double membrane
innermemrane surrounds stroma and contains large amounts of RuBisCO for Calvin cycle
Thylakoids are flattened membrane discs containing chlorophyll and ATP synthetic components and form proton motive force
Cytoskeleton
Microtubules
-Hollow tube that have 25nm diamters and are composed of alpha and beta tubulin
-Maintain cell shape, motility, move chromosomes and organelles
Microfilaments
-7nm in diamter and are polymers of actin protein
-Maintain and change cell shape; involved in amoeboid motility and cell division
Intermediate filaments
-8-12nm in diameter; fibrous keratin proteins
-Maintain cell shape and position organelles
Endoplasmic reticulum
Rough contains ribisomes while smooth does not
Smooth participates in synthesis of lipis and carb metabolism
Rough produces glycoproteins and new membrane material
Golgi Complex
Stacks of membrane-bound sacs modifying ER products
Lysosmes
Membrane enclosed compartments containing digestive enzymes and recycling cell components
Flagella and Cili
Cilia are shorter than Flagella and beat in synchrony
Eu flagella are long and propel through whiplike motion
protein called dynein found in them
