Prokaryotic Cell Structure Flashcards
Prokaryote
Cells with no true nucleus and no internal membrane. Also no cytoskeleton. There are exceptions to each of these.
Eukaryote
Cells that contain a true nucleus as well as significant amounts of internal membrane. Has a cytoskeleton.
Spherical Bacterial Cells
Cocci
Rod-Shaped Bacterial Cells
Bacilli
Spiral-Shaped Bacterial Cells
Spirilla
Comma-Shaped Bacterial Cells
Vibrios
Bacterial Cells with No Defined Shape
Pleomorphic
S-Layer
“Surface Layer” Outermost layer. Varying thickness. Made of protein. Function not well understood. May protect against osmotic problems and/or ions
Gram Positive Cell Wall
Stains blue/purple. Made of peptidoglycan and teichoic acids.
Peptidoglycan
Made of polysaccharides (sugars) and amino acids. 2 6-C sugars: NAM and NAG. Alternate. There are 4 amino acids from every NAM. (L-D-L-D). One of the few places in nature where D amino acids exist. A.A. in 4 position of one chain binds to A.A. in 3 position of another chain. Uses interbridge to bind (usually Gly5) (5 glycines in a chain).
NAM
N-Acetyl Muramic Acid
NAG
N-Acetyl Glucosamine
Teichoic Acid
Polymers of either glycerol (3C) or ribitol (5C). Pokes through peptidoglycan matrix to increase rigidity.
Lipoteichoic Acid
Teichoic acid that pokes through bottom of peptidoglycan matrix and binds to cell membrane.
Gram Negative Cell Wall
Thin layer of peptidoglycan. No teichoic acid. Does not use interbridges, uses direct bonds instead. Strands of polysaccharides must be closer together. Has outer membrane bound to peptidoglycan with lipoprotein (LP). Outermembrane has LPS.
Lipopolysaccharide
LPS. Endotoxin (toxic structural component of cell) released when cell is destroyed. Newer than Gram + in evolutionary terms.
What phylum has Gram - cell walls?
Proteobacteria
Purpose of a Cell Wall
- Protection (to some degree - very porous)
- Provides structure/maintains shape
- Protects against osmotic shock
Flagella
- Optional outer structure
- Used for motility
- Requires ATP
- Made of protein called flagellin
- Cells may have 1, many, or no flagella
Axial Filament
- Found in spirochaetes
- Made of flagellin
- Used for motility
- Winds around cell
Pili
(a. k.a fimbriae)
- Small “hairs” covering cell
- Made of protein called pilin
- No motility function
- Variety of functions
Glycocalyx
2 types: Capsule and slime layer
- Generally made of polysaccharides
- Protective structure
- Makes cell or cells “sticky” - increases pathogenicity
- Helps cells resist being washed away
Capsule
- Completely surrounds a single cell
- Allows bacteria to escape immune system of host
Slime Layer
-Contains many cells
Griffith
Looked at 2 strains of Pneumococcus (Streptococcus pneumoniae). S-strain (wild-type): smooth colonies and R-strain (mutant): rought colonies. R strain was non-pathogenic (had no capsule). S strain had a capsule and was pathogenic.
Biofilms
- Layer of material that contains a community of bacteria.
- Resists being washed away
- Similar to a slime layer
- Plaque is a biofilm
3 Functions of Cell Membrane (bacteria)
- Maintains integrity of the cell (accomplished by phospholipids)
- Allows for transportation of materials into and out of cell (accomplished by proteins)
- Serves as site for electron transport chain
Diffusion
The movement of molecules from an area of high concentration to an area of low concentration.
- Fat soluble molecules diffuse through membrane
- Water diffuses through porins
Facilitated Diffusion
Diffusion facilitated by a protein. (Material being transported actually binds to protein)
Active Transport
Requires cellular energy. Moves materials against a concentration gradient.
Hopanoids
Similar to sterols, but not as rigid. Four 6 membered rings and one 5 membered ring. Used to “toughen” cell membrane. Eukaryotes and mycoplasmas use sterols because they have to cell wall and need more rigidity.
Bacterial Cytoplasm
Liquid salt/sugar solution with small amount of cytoskeleton. Contains salts, sugars, enzymes, other proteins, organelles.
Nucleoid
Double-stranded DNA molecule. This is the single chromosome present in bacterial cells. Folds in cytoplasm. Usually not membrane bound.
Plasmid
Small, double stranded DNA molecule in addition to Nucleoid. Optional. Can spread from cell to cell. Confers new traits on cell. Some are resistance plasmids - makes cell resistant to drugs
Bacteriocins
Proteins released by cell that are toxic to other types of bacteria. Some plasmids encode for these proteins.
Ribosomes
- Made of protein and RNA
- Synthesize proteins
- 2 subunits: large and small
- ALL cells have ribosomes
mRNA
“Blueprint” for a protein. Ribosome binds mRNA and uses it to make new proteins.
Prokaryotic Ribosomes
70S (small: 30S; large: 50S)
Eukaryotic Ribosomes
80S (small: 40S; large 60S)
Mitochondrial Ribosomes
70S
Lynn Margulies
Developed endosymbiotic theory. Mitochondria originated as invading bacteria. Made cells better at making ATP. Mitochondria are considered by many to be a phylum of bacteria. Chloroplasts in plant cells are also thought to have originated as invading bacteria.
Evidence for Endosymbiotic Theory
Bacteria and mitochondria both have circular DNA, have 70S ribosomes, and replicated by binary fission. This is also true of chloroplasts.
Thylacoid
- Optional internal structure
- Found in cyanobacteria
- Membrane bound
- Contains chlorophyll
- Gives bacteria power of photosynthesis
Nitrifying organelles
- Optional internal structure
- Membrane bound
- Found in bacteria in nodules on roots of legumes
- Converts N2 to NH3 and NO3- (ammonia and nitrate)
Microcompartments
- Optional internal structures
- Protein-bound
- Various functions
Gas vessicles
- Optional internal structure
- Made of protein
- Hold gas allowing bacteria to float
- Important for photosynthetic organisms
