Lecture 2: Cell Structure and Function Part 2 Flashcards
Describe the cell walls Of Archaea and bacteria
• Outside the cell membrane
• Rigid
- Helps determine cell shape
- Not a major permeability barrier (as long as its small it can come thru)
- Porous to most small molecules
- Protects the cell from osmotic changes
Describe how the cell wall functions when cell is hypertonic
cell= hypertonic
environment= hypotonic
so water rushes in
the plasma membrane swells when water rushes in the cell wall pushes back and exerts a counter pressure so cell won’t burst
*CELL WALL WILL ONLY PROVIDE INDEFINITE PROTECTION- CELL WILL EVENTUALLY BURT IF TO MUCH WATER
How does penicillin impact the cell wall?
When we take penicillin it actively interferes with formation of peptidoglycan so the peptidoglycan on an organism that’s growing doesn’t have cross links so it’s not strong
-> bacterium that’s trying to grow in presence of penicillin will have holes in PM bc cell burst bc it didn’t have strong cell wall to protect against osmotic rupture
Describe the function of the cell wall
- Cell wall prevents cell expansion – protects against osmotic lysis
- Protects against toxic substances – large hydrophobic molecules
- Ex) detergents, antibiotics
- Pathogenicity
- Helps evade host immune system
- Helps bacterium stick to surfaces
• Partly responsible for cell shape.
-> rigid but some also have cytoskeleton to help with shape
Isotonic
water will come and go but there’s no net movement of water
- cell shape is constant
- ideal
Hypotonic solution
water moves into the cell and may cause the cell to burst if the wall is weak or damaged (osmotic lysis0
- cell components come out and cell is no longer living- DEAD
Hypertonic
water rushes out causing PM to shrink
- > plasmolysis
- > found in salty environments
- > PM shrinks cell wall stays the same
- > not dead just dehydrated (shriveled) asleep (metabolically inactive) as soon as its hydrated it will become active (resume metabolism)
Explain why honey doesn’t need to be refrigerated?
bc its so hypertonic
-> the bacteria are dehydrated so they don’t have enough water to metabolize sugar to grow and increase in number
same reason why salty meats don’t get spoiled
What is the name of bacteria that is an exception being neither gram positive or negative?
mycoplasma
Gram-negative cell wall
Two layers:LPS and
peptidoglycan
Gram-positive cell wall
One layer:peptidoglycan
Peptidoglycan
Rigid layer that provides strength to cell wall (imp bc they are unicellular so have cell wall offers even more protection)
• Polysaccharide composed of: • N-acetylglucosamine and N- acetylmuramic acid • Amino acids • Lysine or diaminopimelic acid (DAP) • Cross-linked differently in gram- negative bacteria and gram- positive bacteria • Form glycan tetrapeptide
- perpendicular cross links create lattice structure to make structure strong
What isomer do prokaryotes recognize?
D
us- L
What does penicillin target?
the enzymes used to form the cross links
Is penicillin more effective on gram positive or gram negative organisms why?
Gram positive bc theres more peptidoglycan
Describe the NAG and NAM
disaccharide
- beta 1- 4 linkages
Lysozyme
destroys NAM and NAG
targets the beta 1-4 bond
- when it breaks that bond, the linear chains are fragmented (disassembling the cell wall of the organism)
- in doing so it protects our eyes, skin, mouth against bacterial infection
- but has to have peptidoglycan & will have more of an impact on organisms that are gram + b/c they have thick layers of PD
Interbridge
No interbridge is present in gram-negative Bacteria (e.g. E. coli) bc they have a single layer of peptidoglycan
The interbridge in Staphylococcus aureus (gram positive) is made up of 5 glycine residues
Describe the composition of Gram-positive cell walls
• Contain up to 90% peptidoglycan
• Common to have teichoic acids (acidic substances) embedded in their cell wall
• Lipoteichoicacids: teichoic acids covalently bound to membrane lipids
- embedded within lipid layer of PM
Model of Peptidoglycan Surrounding cell wall
- Backbone formed of NAM and NAG connected by glycosidic bonds
- Crosslinks formed by peptides
- Peptidoglycan strand is helical
- Allows 3-dimensional cross linking
- E. coli has one layer
- Some cell walls can be 50 - 100 layers thick, e.g. Bacillus species (gram positive)
Name Prokaryotes that lack cell walls
- Mycoplasmas
- Group Of Pathogenic Bacteria
- Have sterols(cholesterol/ other sterols which adds hot/ cold stability, we also use cholestrol) in cytoplasmic membrane–adds strength and rigidity to
- Thermoplasma
- Species of Archaea
- Contain lipoglycans in membrane that have strengthening effect
LPS: The Outer Membrane
- Total cell wall contains ~10% peptidoglycan
- Most of cell wall composed of outer membrane, aka lipopolysaccharide (LPS) layer
- LPS consists of core polysaccharide and O-polysaccharide
- LPS replaces most phospholipids in outer half of outer membrane
- Endotoxin(lipidA):the toxic component of LPS
Endotoxin(lipidA)
:the toxic component of LPS
- only toxic when released from dead cell not toxic when attached to the cell
Describe the outer leaflet of the outer membrane
contains the LPS and some phospholipids
inner leaflet contains phospholipids
What is gram negative sepsis?
Organism is everywhere
- endotoxin dramatically activates the immune system
- > causes blood vessels to dilate (inflammation)
- > when systemic it causes all the blood vessels to dilate lowering bp you don’t have enough pressure to deliver nutrients and oxygen and your tissues start to die
What happens if a person with gram negative sepsis is given antibiotics?
ENDOTOXIN gets RELEASED when you aggressively kill bacteria in really high [ ] in the cell structure
- can kill them
What should a person with gram negative sepsis be given?
bacteriostatic drug that interferes with growth
-> prevent from increase in number so it doesn’t kill bacteria
Periplasm:
space located between cytoplasmic and outer membranes
• ~15 nm wide
• Contents have gel-like consistency
• Houses many proteins
Porins
channels for movement of hydrophilic low-molecular-weight
substances
- beta pleated sheet as secondary structure
Describe Archaeal Cell Walls
- No peptidoglycan
* Typically no outer membrane
• Pseudomurein
- Polysaccharide similar to peptidoglycan
- Composed of N-acetylglucosamine and N-acetyltalosaminuronic acid
- Found in cell walls of certain methanogenic Archaea (make methane c4)
- Cell walls of some Archaea lack pseudomurein
S-Layers
• Most common cell wall type among
Archaea
• Consist of protein or glycoprotein
• Paracrystalline structure
• Some Archaea have only S-layer (no other cell wall components)
• Most have additional cell wall elements
Cytoplasm
material bounded by plasma membrane (PM)
cytosol= fluid and all components within
ex- ribosomes
Protoplast
- Macromolecules – amino acids, nucleotides, etc
- Soluble proteins
- DNA and RNA (nucleoid)
Proteins
Serve many functions:
• Enzymes – Catalyze chemical reactions (usually made out of proteins but can be out of rnA)
• Transport proteins – Move other molecules across membranes (ex; porin, ABC transporters)
• Structural proteins – Help determine shape of the cell
• Involved in cell division
• Proteins are made of polypeptides
• Polypeptide – a long polymer of amino acids joined by peptide bonds
The Nucleoid
- Region that contains the genome
- The typical bacterial genome:
- Single circular double stranded (ds) DNA chromosome
- May have one or more plasmids
- Smaller circular dsDNA
- Self-replicating
- Carry non-essential genes
- Selective advantage
- Ex) Genes for antibiotic resistance
- DNA
- Carries genetic info of all living cells
- Polymer of deoxyribonucleotides
no fence around it
70S ribosome
- 2 parts
- 30S subunit (Small subunit)
- Protein
- 16S rRNA
- 50S subunit (large subunit)
- Protein
- 23S and 5S rRNA
• Cytoplasmic ribosomes
• Cytoplasmic proteins
PM associated ribosomes
• Membrane proteins
• Proteins to be exported from the cell
70S (50S + 30S)
& also could have 70S bound to PM - NOT all prok’s have but if there, they make protein that get exported (like rough ER) to outside of cell - could be toxin, signalling molecule that communicate with buddies nearby etc.
Are Cell Surface Structures present on all bacteria or just some? Where are they?
Present on SOME bacteria
OUTSIDE of CELL WALL (1st thing you’ll see)
List the possible Cell Surface Structures that can be present on SOME bacteria:
- Capsules and slime layers
- Fimbriae
- Pili
What is the difference b/t Capsules and slime layers?
Capsules - VERY ORGANIZED
- & TIGHT to surface - provides a lot of contour dets to cell underneath
think: TIGHT sweatpants
- can see shape of person underneath
Slime layers - LOOSE
- think: BAGGY sweatpants
- still covering but DISORGANIZED & hanging off person - so you can’t see any of the shape dets underneath
Capsules and slime layers characteristics
- Polysaccharide / protein layers
- May be thick or thin, rigid or flexible
- Assist in attachment to surfaces
- Protect against phagocytosis
- Resist desiccation
Describe how Capsules and slime layers, “Assist in attachment to surface.”
your body produces alot of fluids so if bacteria has any chance of staying they need to be able to stick otherwise bacteria will get ejected
Describe how Capsules and slime layers, “Protect against phagocytosis” & what a phagocyte is
Phagocyte- immune cell used to bind to bacterium in order to get it to leave
needs to have some attachment spot and if doesnt bc bug is covered by capsule it wont get bound and killed so phagocytosis process is destroyed bc of capsule
Describe how Capsules and slime layers, “Resist desiccation”
organism can better maintain water in the cell
If you have 2 bacteria both from the same strain but one has a capsule one doesn’t which one is more dangerous?
The one with the capsule bc it can cause disease while the other will get flushed out
Fimbriae
Filamentous protein structures
• Enable organisms to stick to surfaces or form pellicles
- made out of pilin proteins
*TYPICALLY ONLY IN GRAM NEGATIVE
Pili
- Filamentous protein structures (made out of pilin protein)
- Typically longer than fimbriae
- Assist in surface attachment
- Facilitate genetic exchange between cells (conjugation)
- Type IV pili involved in twitching motility
Describe how pili assist in attachment
they can polymerize or depolymerize and become closer or further away from the surface
Describe twitching motility
- type 4 pili
- more closer to the surface so more control
Describe the conjugation
the pili is like a tunnel it can be used a mode of exchange between the same species of different species
-> ex; you have a F+ plasmid which has a fertility plasmid it replicates autonomously and the F plasmid is sent to a F- so the F- becomes F+ bc it receives the fertility plasmid
horizontal gene transfer bc not from mother to daughter but from buddy cell to buddy cell
Cell Inclusion Bodies
• Visible aggregates in cytoplasm
• Carbon storage polymers
• Poly-β-hydroxybutyric acid (PHB): lipid
• Glycogen: glucose polymer
• Polyphosphates: accumulations of inorganic phosphate
• Sulfur globules: composed of elemental sulfur (energy and also needed to build cysteine and methionine AA’s
• Magnetosomes: magnetic storage inclusions
-> give the cell magnetic properties so it can align itself in magnetic field to be able to move back and fourth
• Carbon storage polymers
- Poly-b-hydroxybutyrate (PHB)
- Lipid storage (anabolic material, catabolized releases energy but also lets you build things
- Glycogen granules hydrolyzed to release free glc)
- Polymer of glucose
What can happen to carbon containing molecules
they can get catabolized
Inorganic inclusions
Polyphosphate granules – volutin
• Storage of phosphate and energy
-> required to make ATP nucleotides and lipids
- Sulfur globules
- Storage of sulfur used in energy generation
Magnetosomes
Magnetic inclusions
• Intracellular granules of Fe3O4 or Fe3S4
• Gives the cell magnetic properties
• Allows it to orient itself in a magnetic field
• Bacteria migrate along Earth’s magnetic field – magnetotaxis
Gas Vesicles
• Confer buoyancy in planktonic cells • Spindle-shaped, gas-filled structures made of protein • Function by decreasing cell density • Impermeable to water-. bc if filled with water they would sink
will sink to the bottom but bc cyanobacteria it does photosynthesis and needs sun so they need to be close to the surface
gas vesicles decrease density so they dont sink
Autotrophic
carbon soure
phototrophic
sunligth
Describe Cyanobacteria form “blooms”
usually nitrogen and phosphorous limit growth but they end up in runoff so theres nothing that limits cyanobacterias growth so they form these blooms that parasite and produce neurotoxins
Endospores
- Highly differentiated cells resistant to heat, harsh chemicals, and radiation
- Dormant stage of bacterial life cycle
- Ideal for dispersal via wind, water, or animal gut
Which organisms produce endospores
Produced only by some Gram positives
• Ex) Bacillus sp. – aerobic Gram + rods
• Clostridium sp. – anaerobic Gram + rods
Vegetative cell
capable of normal growth
• Metabolically active mother cell
where is endospore formed and when
dormant cell, formed inside of a mother cell • Metabolically inactive • Triggered by lack of nutrients • Takes about 8 - 10 hours • •
