Chapter 3 Flashcards
cytoplasm
gel-like network made of proteins and other macromolecules
cell membrane
encloses the cytoplasm. The structure that defines the existence of the cell.
cell wall
covers the cell membrane, b/w inner and outer membrane.
nucleoid
non-membrane bound area of cytoplasm w/ chromosome in the form of looped coils
cell membrane made up of
•Double layer of phospholipids • Proteins embedded in membrane -Anchor membranes to envelope -Sense the outside world -Transport materials into cell
cell membrane functions
• Mechanical boundary • transport nutrients/waste • Site for electron transport chain -Respiration -Photosynthesis • Contain (“sensing”) receptor proteins • Most membrane proteins (~80%) are integral, the rest are peripheral
most membrane lipids are
phospholipids. Phospholipids are amphipathic = have a polar and non-polar end.
proteins float in
2-dimensional “sea” of phospholipids. membrane fluidity is required.
increase membrane fluidity
• Use lipid molecules with shorter chain lengths and that have more double bonds (unsaturation)– adds “kinks”
• Decrease membrane fluidity (increase rigidity)
• Use longer chain lengths (Van der Waals)
• Use fewer double bonds
• Use molecules that hinder movement of phospholipids
-Stiff planar rings
-Reinforcing agents
-Sterols (e.g.) cholesterol
-Eukaryotes
-Hopanoids
-Structurally similar to steroids
-ProkaryotesBacteria would adapt to increasing
temperature by?
Increase # of long chain lipids, decrease # of double bonds.
proteins form about
half the mass of the membrane
Transport across the cell membrane
- The cell membrane acts as a semipermeable barrier
- Selective transport is needed for survival
- weak acids/bases can cross membrane
diffusion
Small uncharged molecules, like O2 and CO2, permeate the membrane
transporters
pass material into and out of cell
• Polar/charged molecules need transport
concentration gradient
always going from high to low.
passive transport
molecules move along their concentration gradient
active transport
molecules move against their concentration gradient
• Requires energy
How do prokaryotes protect their cell membrane?
cell envelope includes structural support (cell wall.)
-some have S-layer
• prokaryotes like mycoplasmas have cell membrane w/ no outer layers
sacculus
bacterial cell wall w/ single interlinked molecule that covers cell.
• cage-like structure (flexible)
• has shape and withstands intracellular turgor pressure
Most bacterial cell walls are composed of
peptidoglycan (murein)
glycan chains
Long polymers of two disaccharides:
• N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
Peptidoglycan
polymer of peptide-linked chains of amino sugars. unique to bacteria. good for antibiotics.
Gram-positive-
gram negative-
Mycobacteria-
– thick cell wall (e.g. firmicutes)
– thin cell wall (e.g. proteobacteria)
– multilayered envelope w/ defensive structures like mycolic acids (e.g. Mycobacterium tuberculosis)
gram positive cell envelope
• S-layer -Made of protein (contains large pores) • Thick cell wall (3-20 layers of peptidoglycan) • teichoic acids for strength • Cell membrane
gram negative cell envelope
• Outer membrane (OM)
-Covers peptidoglycan layer
-has defensive abilities and toxigenic properties
• Thin peptidoglycan layer (1-2 sheets)
• Periplasm – area b/w membranes(cell wall)
• Inward facing leaflet of OM (gram neg.)
has lipoproteins that connect OM to peptide bridges of cell wall
• Outward facing leaflet of OM (gram neg)
has lipopolysaccharide (LPS) (endotoxin)
Mycobacterial cell envelope
-has features of both gram-positive and gram negative
• Unusual sugars -arabinogalactans
in e coli, the cell membrane is called the
inner membrane. contains phospholipids, transporter proteins, and more molecules.
nucleoid is not
enclosed by membrane.
essential ions
potassium, magnesium, chloride ions
nucleic acid content of bacteria
8% for e coli
leaflets
two layers of phospholipids in the bilayer
cardiolipin
double phospholipid linked by glycerol
hopanoids
cyclopentane
membrane lipids of archaea differ from bacteria and eukaryotes bc
instead of ester link, there is ether link (C-O-C)
The E. coli nucleoid
appears as clear regions that exclude the ribosome and has DNA strands
domains
nucleoid forms about 50 loops
within each domain
DNA is supercoiled and compacted by gyrases and DNA-binding proteins
the ribosome is a target for
antibiotics
Protein synthesis and secretion
• In prokaryotes, membrane/secreted proteins are synthesized together w/ cell membrane
-signal recognition particle (SRP), which binds to the growing peptide
replisome includes
leading strand and lagging strand
septum
-DNA termination site. divides envelope. seals off the two daughter cells
- If septation occurs in:
- Parallel planes-
- Random orientations-
- Right angles to the previous division-
- cells form chains (Streptococcus)
- cells form compact hexagonal arrays (Staphylococcus)
- cells form tetrads and cubical octads (sarcinae)
Thylakoids
folded intracellular membrane
• has layers of folded sheets (lamellae) or tubes of
membranes packed w/ chlorophyls and electron carriers
Carboxysomes
polyhedral bodies packed w/ enzyme Rubisco for CO2 fixation
Gas vesicles
increase buoyancy
Storage granules
- Glycogen, PHB, and PHA for energy
* Sulfur, for oxidation
Magnetosomes
- Membrane-embedded crystals of magnetite, Fe3O4
* Orient the swimming of magnetotactic bacteria
Pili or fimbriae
– straight filaments of pilin protein
• Used in attachment
stalks
extensions of cytoplasm
• Tips secrete adhesion factors called holdfasts
nanotubes
intercellular connections that pass material from one cell to the next
Peritrichous cells
(ex E. coli, Salmonella) have flagella randomly distributed around the cell
• Flagella rotate together in a bundle behind swimming cell
Lophotrichous cells
(ex Rhodospirillum rubrum) have flagella attached at
one or both ends
Monotrichous cells
(ex Caulobacter swarmer) have a single flagellum on
one end
Chemotaxis
movement of a bacterium in response to a chemical
gradient
• Attractants cause CCW rotation
- Flagella bundle together
- Push cell forward
- “Run”
• Repellants cause CW rotation
- Flagella bundle falls apart
- “Tumble”
- Bacterium pauses, then changes direction
“random walk”
The alternating runs and tumbles causes this
bacteria do not undergo
mitosis or meiosis
origin of replication
at the midpoint on dna. Attached to the cell envelope at a point on the cell’s equator
