Unit 1--Lecture 2 (Microbial Cell Structure) Flashcards
Refraction
Passage through lens material bends light
Resolution
The ability to distinguish two adjacent objects or points form one another
AKA Resolving Power
RP = (wavelength of light in nm) / (2 X Numerical Aperture)
Numerical Aperture describes the relative efficiency of a lens in bending light rays
Bacterial Cell Shapes
Coccus/Cocci: balls
Bacillus/Bacilli: rods
Spirochetes/Spirillum: spiral rods
Diplo: 2
Tetrad: 4
Sarcina: 8
Strepto: chain
Staphylo: grape-like cluster
Advantages to being small
more surface area relative to cell volume (higher S/V ratio)
grow faster than larger cells
Cell Membrane
The structure that defines the existence of a cell
Membrane Constituents
Membranes are approximately equal parts phospholipids and proteins
Phospholipid
Glycerol with ester links to 2 fatty acids and a phosphoric head group
Membrane Protein Functions
structural support
secretion of virulence factors
transmission of communication signals
ion transport and energy storage
Transport across Cell Membrane
The cell membrane acts as a semi-permeable barrier
Selective transport is essential for survival
Small uncharged molecules (O2 & CO2) easily permeate the membrane by diffusion
Water diffuses across the membrane by osmosis
Diffusion of Weak Acids
Weak acids and bases can diffuse across the membrane and change the pH of the cell
Transport
Polar and charged molecules require transport through specific protein transporters
Passive Transport
Molecules move along their concentration gradient
Active Transport
Molecules move against their concentration gradient
Requires energy
Membrane Fluidity
In eukaryotic membranes, the reinforcing agents are sterols (cholesterol & ergosterol)
In bacteria, the same function is filled by hopanoids, or hopanes
Nucleoid
Contains the genetic material
No nuclear membrane
Singel circular chromosome
Haploid
Prokaryote Ribosome
Two subunits (30S & 50S)
Total size is 70S
Thylakoids (Phototroph Structures)
Extensively folded intracellular membranes
Carboxysomes (Phototroph Structures)
Polyhedral bodies packed with the enzyme rubisco for CO2 fixation
Gas Vesicles (Phototroph Structures)
To increase buoyancy
Other Inclusion Bodies
Storage granules
Glycogen, PHB, PHA
Sulfur
Volutin
Magnetosomes
Bacterial Cytoskeleton (Shape-determining proteins)
FtsZ– forms a “Z ring” for septum placement
MreB– forms a coil inside rod-shaped cells
CreS– “cresentin”- forms a polymer along the inner side of crescent-shaped bacteria
The Cell Wall
Confers shape and rigidity to the cell and helps it withstand turgor pressure
Bacterial Cell Walls
Most bacterial cell walls are made up of peptidoglycan (or murein)
The molecule consists of:
NAG and NAM bound to a peptide of 4-6 amino acids
The peptides can form cross-bridges connecting the parallel glycan strands
Bacterial Envelopes
Provide structural support and protection
Envelope composition defines:
Gram-positive bacteria– thick cell wall (Firmicutes)
Gram-negative bacteria– thin cell wall (Proteobacteria)
