Week 2 cp 5 & 12 Flashcards
what does the cell membrane do?
- separates the cytoplasm from the outside environment
- prevents cytoplasmic proteins from leaking out, and it maintains concentration gradients of ions and nutrients
- also the site of oxidative phosphorylation (or respiration) process in which electrons pulled from food molecules yield energy to pump hydrogen ions (H+) across the membrane
- cell membranes is covered by a cell wall
- mediates exchange w/ the environment such as toxin secretions and communications w/ fellow pathogens
what is a cell wall?
-is a single interlinked molecule that encloses the entire cell
outside the cell membrane is the cell wall
-a rigid mesh-like structure called peptidoglycan. it is a single molecule that surrounds the cell like a cage
-peptidoglycan consists of sugar chains linked covalently by peptides
-highly porous to ions and small organic molecules
what constitutes the cell envelope?
the cell membrane, the cell wall, and outer membrane (for gram-negative species)
- it protects the cell from environmental stress and predators
- envelope protects pathogens from macrophage phagocytosis
what is a nucleoid?
not an enclosed membrane, so could of DNA can extend throughout the cytoplasm
- loops of DNA from the nucleoid are transcribed by the enzyme RNA polymerase to form MRNA
- MRNA transcribe and bind to ribosomes to start synthesizing polypeptide chains (proteins)
- protein synthesis occur
what is passive transport?
- no energy required
- moves nutrients with the concentration gradient from (high to low) across the membrane
what is active transport?
- energy required to move against the concentration gradient from low to high
ex. antiport pump- sodium and potassium pump
what is coupled transport?
the use of energy from one gradient to drive transport up another gradient
what are the two types of coupled transport systems?
symport and antiport
what is symport?
- two molecules travel in the same direction
1. energy is released as one substrate (red) moves down the concentration gradient
2. this energy moves a second substrate (blue) against its gradient and into the cell
what is antiport?
- actively tranported molecule moves in the direction opposite to the driving ion
1. antiporter binds substrate A (red) on the cytoplasmic side of the membrane
2. antiporter opens to the outside of the cell, where the concentration of A is lower
3. substrate A leaves its binding site and substrate B (blue) then binds to its site
4. antiporter opens to the inside of the cell. substrate B is released in exchange for substrate A.
what is ABC transported?
- uses the energy from ATP hydrolysis to move solutes “uphill” against their concentration gradient
1. solute binds to the substrate-binding protein and the complex then binds to the membrane transporter (green)
2. the ATPase activity of one component (yellow) powers the opening of the channel (green) and movement of the solute into the cell
what are siderophores?
-tightly bind whatever ferric iron is available in the environment
-these iron scavenger molecules are produced and sent forth by cells when the intracellular iron concentration is low
-the siderophores binds iron in the environment and the siderophore-iron-complex then attaches to specific receptors in the bacterial out membrane
-the complex may then be transported across the cell membrane by an ABC transporter
=iron is transported into the cell
what is peptidoglycan?
consists of parallel polymers of discarcchardies called glycan chains
- glycan chains are cross-linked w/ short peptides
- they are unique to only bacteria- never human cells
- spaces between links are open, porous to large molecules
gram positive bacteria
have a thick cell wall w/ multiple layers of peptidoglycan
-outside the cell wall, has an outer membrane
gram-negative bacteria
has a thin cell wall (single layer of peptidoglycan) enclosed by an outer membrane
gram-negative- what is murein lipoprotein?
inner leaflet of the outer membrane that forms a peptide bond with peptidoglycan
gram-negative- what is lipopolysaccharide (LPS)?
- crucial medical important b/c its lipid A component acts as an endotoxin
- endotoxin is harmless as long as the pathogen remains intact, but when released by a lysed cell, the endotoxin (lipid A) overstimulates host defenses, including potentially lethal endotoxic shock (dangerously low B/P and high fever)
- lipid A acts as an endotoxin in lysed cell, so antibiotics treatment can kill cells but can also cause endotoxic shock in patients
what are the 3 parts of LPS?
- lipid A (anchored in the outer membrane)
- a core polysaccharide
- O antigen (O polysaccharide)
what is mycobacteria?
- contains a unique envelope
- mycobacterial envelope excludes most antibiotics and prevents phagocytosis
- mycobacteria slow nutrients enter= leading to slow growth
- has a complex cell wall with peptidoglycan and mycolic acid - it provides the basis for acid-fasting staining an important diagnostic test for mycobacteria and actinomycetes
what is the s-layer?
composed of proteins, is highly porous but can prevent phagocytosis
-in archaea, the s-layer serves the structural function of a cell wall
what happens in bacterial cell division?
- DNA replication- once replicated completely to form two daughter genomes, the cell may divide to form two daughter cells
- protein synthesis occurs
- replication of the DNA termination site triggers growth of the dividing partition of the envelope, called the septum. The septum grows inward from the sides of the cell, at last constricting and sealing off the two daughter cells in the process of septation.
what is pili?
- most common structures that bacteria use to attach to a substrate are pili
- are straight filaments of protein monomers made up of piling protein
what is fimbriae?
short attachment pili that attach cells to surfaces
what is conjugation (sex) pilus
- different kind of pili that facilitates transfer of DNA between cells
- serves to attach a “male” donor cell to a “female” recipient cell before transferring DNA in a process called conjugation
what are stalks?
are membranous extension of cytoplasm that secrete adhesion factors
what are flagella/flagellum?
- bacteria and archaea that are mollie generally swim using rotary flagella
- are helical propellers that drive the cell forward like the motor of a boat
- flagella enhance virulence
- most flagellated cells have an elaborate sensory system known as chemotaxis that enables them to swim towards favourable environments and away from inferior environments
what is chemotaxis?
involves rotation of the flagella that properly the cell in response to stimuli
-positive vs negative chemotaxis
what is positive chemotaxis?
- cell moves towards the attractants
- when a cell is swimming toward an attractant chemical, the flagella rotate counterclockwise (CCW) and form a rotating helical bundle
what is negative chemotaxis?
cell moves away from repellents
- cells veers away from the attractant, receptors send a signal that allows one or more flagella to switch rotation clockwise against the twist of the helix
- CW rotation stops forward, so cell tumbles and changes direction -bacteria is moving backwards
what is thylakoids?
photosynthetic bacteria (phototrophs) need to collect as much light as possible to drive photosynthesis. To do this, they grow extensively folded intracellular membranes called thylakoids
what is gas vesicles?
Aquatic phototrophs possess gas vesicles to increase buoyancy and keep themselves high in the water column, near the sunlight. The vesicles trap and collect gases such as hydrogen or carbon dioxide produced by the cell’s metabolism.
what is storage granules?
some bacteria store energy in storage granules composed of glycogen or other polymers called polyhydroxyalkanoates (PHA).
-PHA polymers are of interest as a biodegradable plastic, which bacteria are engineered to produce industrially.
what is sulfur granules?
sulfur-metabolizing bacteria deposit granules of solid sulfur within the cytoplasm or as “globules” attached outside the cell. The presence of toxic sulfur granules may help these cells avoid predation.
what is megnetosomes?
-Some anaerobic pond dwelling bacteria can swim along a magnetic field in a process called magnetotaxis, Magnetotactic species of bacteria
possess tiny magnets called magnetosomes.
-Magnetosomes are microscopic membrane-enclosed crystals of the magnetic mineral magnetite.
-Because Earth’s magnetic field lines
point downward in the northern latitudes, magnetotactic bacteria swim “downward” toward magnetic north. This drives magnetosome-equipped anaerobes toward the bottom of the pond, where oxygen concentration is low.
what is endoplasmic reticulum (ER)?
a complex membranous organelle of eukaryotic cells where protein and lipid synthesis occur
smooth vs rough ER
what is the golgi/golgi complex?
- the Golgi consists of sep- arate membrane stacks (cisternae) that each contain enzymes to “tag” proteins with carbohydrate chains that direct them to organelles such as lysosomes.
- proteins not targeted to lysosomes may be sent to the cell membrane
what is a lyosome?
a membranous organelle containing enzymes that kill bacteria and process organic material for nutrition
