Week 2 cp 5 & 12

Question 1

what does the cell membrane do?

Answer 1

• 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

Question 2

what is a cell wall?

Answer 2

-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

Question 3

what constitutes the cell envelope?

Answer 3

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

Question 4

what is a nucleoid?

Answer 4

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

Question 5

what is passive transport?

Answer 5

• no energy required

- moves nutrients with the concentration gradient from (high to low) across the membrane

Question 6

what is active transport?

Answer 6

• energy required to move against the concentration gradient from low to high
  ex. antiport pump- sodium and potassium pump

Question 7

what is coupled transport?

Answer 7

the use of energy from one gradient to drive transport up another gradient

Question 8

what are the two types of coupled transport systems?

Answer 8

symport and antiport

Question 9

what is symport?

Answer 9

• 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

Question 10

what is antiport?

Answer 10

• 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.

Question 11

what is ABC transported?

Answer 11

• 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

Question 12

what are siderophores?

Answer 12

-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

Question 13

what is peptidoglycan?

Answer 13

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

Question 14

gram positive bacteria

Answer 14

have a thick cell wall w/ multiple layers of peptidoglycan

-outside the cell wall, has an outer membrane

Question 15

gram-negative bacteria

Answer 15

has a thin cell wall (single layer of peptidoglycan) enclosed by an outer membrane

Question 16

gram-negative- what is murein lipoprotein?

Answer 16

inner leaflet of the outer membrane that forms a peptide bond with peptidoglycan

Question 17

gram-negative- what is lipopolysaccharide (LPS)?

Answer 17

• 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

Question 18

what are the 3 parts of LPS?

Answer 18

• lipid A (anchored in the outer membrane)
• a core polysaccharide
• O antigen (O polysaccharide)

Question 19

what is mycobacteria?

Answer 19

• 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

Question 20

what is the s-layer?

Answer 20

composed of proteins, is highly porous but can prevent phagocytosis
-in archaea, the s-layer serves the structural function of a cell wall

Question 21

what happens in bacterial cell division?

Answer 21

• 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.

Question 22

what is pili?

Answer 22

• most common structures that bacteria use to attach to a substrate are pili
• are straight filaments of protein monomers made up of piling protein

Question 23

what is fimbriae?

Answer 23

short attachment pili that attach cells to surfaces

Question 24

what is conjugation (sex) pilus

Answer 24

• 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

Question 25

what are stalks?

Answer 25

are membranous extension of cytoplasm that secrete adhesion factors

Question 26

what are flagella/flagellum?

Answer 26

• 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

Question 27

what is chemotaxis?

Answer 27

involves rotation of the flagella that properly the cell in response to stimuli
-positive vs negative chemotaxis

Question 28

what is positive chemotaxis?

Answer 28

• 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

Question 29

what is negative chemotaxis?

Answer 29

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

Question 30

what is thylakoids?

Answer 30

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

Question 31

what is gas vesicles?

Answer 31

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.

Question 32

what is storage granules?

Answer 32

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.

Question 33

what is sulfur granules?

Answer 33

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.

Question 34

what is megnetosomes?

Answer 34

-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.

Question 35

what is endoplasmic reticulum (ER)?

Answer 35

a complex membranous organelle of eukaryotic cells where protein and lipid synthesis occur
smooth vs rough ER

Question 36

what is the golgi/golgi complex?

Answer 36

• 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

Question 37

what is a lyosome?

Answer 37

a membranous organelle containing enzymes that kill bacteria and process organic material for nutrition