Lecture #7: Prokaryotes II Flashcards
Eukaryotes are the Masters of the Membrane
Membranes regulate what goes into and out of the cell, an organelle.
Membranes shuttle substances around in vesicles in the cell, and take-in as well as secrete larger substances. Endo-, exocytosis.
Membranes control mass flow, modification, and fate within the cell (ER, Golgi = UPS of the cell).
Membranes Within Chloroplasts, Mitochondria Order Steps in Conversion Reactions
Allow for efficiency. Products of the conversion series ordered along internal membrane systems feed into reactions in the adjacent liquid phase (between the inner and outer mitochondrial membranes, in the stroma of the chloroplast).
So the Larger Cells of Eukaryotes
Need more support.
Move and mix the cytoplasm, facilitating enzyme-substrate interaction.
Require a spindle to efficiently separate the chromosomes.
Use membranes to compartmentalize and concentrate enzymes so processes are efficient.
Use endo- and exocytosis to get larger things in and out.
Are longer lived and more is invested into their development and maintenance.
Can be specialized.
Are set up for intercellular communication within a tissue.
Prokaryotes Have an Entirely Different Strategy
Short-lived, and live to divide.
Small volumes where diffusion is immensely important.
Cytoplasm is uncluttered, lacking organelles.
Do not endo-, exocytose but do ‘drool.’ Akin to fungi.
Divide without using a spindle (Binary Fission).
Use microtubules sparingly vs. the elaborate cytoskeleton of a eukaryote.
Collectively show an range of metabolic specialization that dwarfs that of eukaryotes—individually each microbe has its own metabolic specialty.
They are the Masters of Metabolism, Masters of Multiplication.
Procaryotes Have a Nucleoid Region
No nucleus.
Long loop of double stranded DNA. Twisted, condensed ‘nucleoid’ region. Genes accessible 24/7. In Escherichia coli the length of DNA is 210 times the length of the cell.
The chromosome lacks histone proteins and does not coil as tightly or precisely as in a eukaryote where genes are locked away during cell division, and inaccessible.
The DNA in Eukaryotes is
Splayed out as chromatin during Interphase, supercoiled during cell division.
Metabolism between cell divisions, and temporary shutdown while DNA is condensed. Energy diverted to cell division only.
Prokaryotes are Structurally Simple
Uncluttered cytoplasm that lacks membrane-bound organelles.
Efficient for a limited existence.
Primitive? No, just have a wholly different plan. Don’t invest in cells same way eukaryotes do—quick and direct. Super8 Motel vs. the Ambassador.
Prokaryotes Have Rapid Turnover
One cell to 2 to 4 to 8 to16 to 32… Each cycle takes 20 minutes or so.
Single cell at 8 a.m. yields over a million by 4 p.m.
Long Evolutionary History
An amazing range of metabolic types. Specialized for various niches over the long anaerobic geologic history of the earth. Then strong selection with oxygenation and further diversification.
Archaea named for their antiquity; Archaean Eon.
Some Species Are Characteristically Pleiomorphic
Cell shape is variable.
Rigidity & Flagellation Differ
Cocci are not flagellated. They are not motile.
Rods and spirilli may have flagella. Numbers and distributions differ.
Spirochaetes are more flexible and have internal or sheathed flagella.
Polysaccharide Coverings – A Matter of Degree
Is a ‘sheath’ that is called a glycocalyx if soft and gooey, loose mucilage if it is just slime, and a capsule if it is rigid. Capsules allow attachment, and survival under stressful conditions (protective).
Projections – Tubular or Hairlike
Pili are tubular extensions, used in ‘sexual’ reproduction.
Fimbriae are fine and hairlike. Aid in attachment.
Flagella
Bacterial flagella are hollow tubes. Built of a single protein (flagellin). Assembled outside the cell.
Eucaryotic Flagellum
Surrounded by a membrane sheath (extension from the cell membrane).
The tubules are constructed of alpha and beta tubulin.
Bacterial Cell Walls
Made of peptidoglycan (murein).
Like a sac as the cell wall is a long, growing chain or backbone (glycan part) with crosslinks (peptido part, or protein). Network. Crosslinks are routinely broken as material is added in for growth.
Preferable to refer to the outer coverings as the cell envelope.
Both Envelopes are Reinforced
Gram + Cell Wall is reinforced with long strings of sugar derivatives called teichoic acids. Woven perpendicular to the long backbone of the wall. Some anchor in cell membrane (lipoteichoic acids). Depart a negative charge to the cell wall.
Outside layer of tile-like proteins, S layer. Resistance, host defenses or adhesion to host tissues.
Proteins Bound to Wall May Have a Role in Virulence
M Protein in Streptococci, Staphylococci. (Skin, nasal passages). Rebecca Lancefield.
Bound to the proteins which crosslink the backbone of cell wall.
M Protein & Typing of Streptococci
M Protein is a virulence factor in Streptococcus and other Gram + forms.
Lancefield Series. Sorted antigenic types based on version of the M protein.
Gram - Envelope
Inner and outer membranes are different in structure and function.
Cell wall and o.m. linked by bridging molecule (Braun’s Lipoprotein).
LPS System in O.M.
Molecules with an outer part, a neck and an anchoring structure. Lipids allow link to membrane. O antigen streams out, triggers an immune response. Lipid A has FA tails – toxin.
Important Portions – Inner & Outer
Lipid A is an endotoxin. Released when cells die. FA tails and is heat stable. Toxic in nanogram amounts. General systemic effects and bacteremia—fever, shock, weakness. Possible complication of food poisoning.
O antigen is what antibodies recognize and bind to in an immune response. Escherichia coli O157:H7 is the nasty servovar (immune type) that causes internal bleeding with food poisoning. It taints undercooked meat, spinach. Source???
Alpha Glucose Chains
Starch - Food storage in plants.
Glycogen - Food storage in animals. Basic chain with alpha 1, 4 linkages and side chains as alpha 1, 6.
Β Glucose Chains
β bonds resist attack by enzymes. Used to build resistant structures. Cell walls, exoskeletons.
Plant cell walls are cellulose, a beta glucose polymer. A.K.A. fiber.
Chitin
Chitin is a long chain of modified glucose molecules.
Tough, resilient, long-lasting.
Cell Walls - Peptidoglycan
Peptido- Protein. Peptide bonds link the amino acids into a protein.
Here, protein side chains stabilize the sugar backbone.
Glycan- Sugar. Backbone of the wall is a long sugar polymer.
Peptidoglycan is an enormous polymer of sugars. NAM & NAG alternate in long chain. NAM makes connections.
Cells Grow by Lysing Connections
Cells secrete autolysins that break protein side chains so more material can be added in.
Enzymes in the periplasm break the glycan backbone. Activated NAM-NAG units added in (carry along their own energy source for forging the new bonds).
Glycan backbone is extended, and protein side chains interconnect the chains.
Side Chains
Composition varies Gram Positive vs. Gram Negative
Composition varies between species. Characteristic.
D-amino acids (see AI.8) in peptide side chains; harder to attack linkages. Normal version is L.
Some molecules that connect to outer membrane or project beyond the wall link to the side chains.
Penicillin affects cell wall synthesis by blocking the linking of proteins in side chains. Thus, prevents growth of the cell and also cell division. Why does it prevent cell division?
Proteins Link the Glycan Strands
The side chains are proteins, which are polymers of amino acids.
Protein
Proteins are chains of amino acids.
The Crosslinks are Peptides
Shorter, direct links for tighter wall.
Longer connections for a more flexible wall (pentaglycine bridges).
Synthesis & Activation within the Cell, Assembly & Cross-linking outside it.
Passed to a carrier molecule in the membrane, and inserted into the backbone outside the cell.
Assembly takes place outside the cell. So does cross-linking.
