Cell Structure and Functions

Spatial Orientation and Names of Cocci

• Parallel Planes: Streptococci (Strept=means chains)

• Random Planes: Staphylococci (Staphy=means groups/clusters)

• Perpendicular Planes: Tetrads (4 circles together) and Cubical Octads (8 circles together)

The Bacterial Cell

• Thick, Complex Outer Envelope

• Coordinate Cell Functions

• Do not contain a nucleus

• DNA is created in the center of the cell, nucleoid.

Subcellular Fractionation

Isolation of cell parts for further analysis. Use different chemicals to digest other things out.

Structural Analysis

Image of cell components through Electron microscopy, x-ray crystallography, etc..

Genetic Analysis

Determines function of cell component

Ultracentriguation

Rotation or spinning of cells at high speeds to separate cell parts from one another.

• The liquid and bacteria separate.

• Theodor Svedburg

• Sedimentation Rate: Rate at which particles of different size and shape travel to the bottom of the tube

Svedburg Coefficient

Contribution of particle mass and shape

• Bacterial Ribosomes= 70S, Eukaryotic Cells= 80S

• Smaller 30S+ Larger 50S= 70S (weight independently is more than together)

• Exception for Eukaryotic Cells: Mitochondria in human cells have 70S ribosomes bc of endosymbiosis.

Components of Bacterial Cells

• Cytoplasm: Consists of gel-like network

• Cell Membrane: Phospholipid bilayer-encloses cytoplasm

• Cell Wall: Covers the cell membrane

• Nucleoid: Non-membrane bound area of cytoplasm that contains genetic material

• Flagellum: External helical filament with a rotary motor use to propel the cell (not all bacteria are motile)

Cell Membrane

• Important in ATP making in bacteria

• The structure that defines the cell

• Composed of phospholipid bilayer with proteins embedded

• Phospholipids face one another to protect the hydrophobic side chains from water inside and outside the cell. (Polar Head= Hydrophilic, Polar Tails= Hydrophobic)

Bacteria vs Archaea Cell Membrane

Bacteria and Eukaryotic= Phospholipid Bilayer is linked through Ester bonds. Contains peptidoglycan. Lipid bilayer.

Archaea= Fatty Acids are connected to glycerol through Ether bonds (allow organisms to thrive in extreme enviroments) No peptidoglycan. Lipid bilayer or monolayer

Ester Bonds vs Ether Bond

• Ester Bonds= Oxygen atom is doubled bonded with Carbon, which bonds another Oxygen atom.

• Ether Bonds= Oxygen atom is singly bonded to two Carbon atoms

Membrane Proteins

• Structural Support

• Detection of environmental signals (toxins and nutrients)

• Secretion

• Ion Transport and Energy Storage (Polar and charged molecules which has to have energy to pass through)

• Have hydrophobic and hydrophilic regions that look the protein in the membrane

Ways of Transportation Across Cell Membrane

• Passive Transport: Molecules move along/with their concentration gradient

  • Diffusion: No extra energy needed (gradient) → Homeostasis: Equilibrium

• Active Transport: Molecules move against gradient. Requires energy. Usually in form of ATP Hydrolysis (break off of phosphate group)

Bacterial Cell Wall

• Protects the cell membrane

• Most contain Peptidoglycan (PTG) → Consists of NAG and NAM (Carbohydrates which are linked by gylcocidic bonds.) PTG layers are bound by peptide bonds with 4 to 6 amino acids.

• Gram Neg Walls and Gram Pos Walls

Gram Pos Wall vs Gram Neg Wall

• Gram Pos Wall: More Peptidoglycan. Very thick layer. Peptide Bridges, Lots Stronger. Teichoic Acid connected NAM to tetrapeptide.

• Gram Neg Wall: 2 Membranes (outer and inner). Less Peptidoglycan. Outer membrane has Lipopolysaccharide (LPS), O antigen, and Lipid A. Peptide bonds between amino acids.

Peptidoglycan

• Unique to bacteria.

• Excellent targets for antibiotics (wants to target prokaryotic cells).

• Penicillin (stops cross-bridge formations that cross-links the peptides → Blocks cell wall synthesis) and Vancomycin (prevents cross-bridge formation)

• Antibiotics Resistant Strains

  • MRSA

  • VRSA

Capsule

• Made of polyaccharide+ glycoprotein= glycocalyx

• Protects cells from phagocytosis

• Also found in some Gram Neg bacteria

S Layer

• Also known as slime layer

• Almost in all archaea and free-living bacteria

• Consisting of protein or glycoprotein

• Cell shape and protect cell from osmotic stress

Lipid A

Endotoxin. Triggers a strong inflammatory response.

Mycobacteria Cell Envelopes

• Contain complex cell walls

• Has Mycolic Acids (Unusual lipid that makes it difficult to stain)

• Arabinogalactans (Unusual sugar)

Cytoplasm

Material found in the interior portion of the cell

• Cytosol- liquid component of cytoplasm

Internal membranes have been observed in SOME bacterial cells.

Inclusions

• Formed by aggregation of substances that may be organic or inorganic

• Function: segregate certain cellular components so they do not free diffuse in cytoplasm (Acts as “storage” for enzymatic reaction or cell movements)

• Types of Inclusions:

  • Microcompartments

  • Gas Vacuole

  • Magnetosomes

Microcompartments

• Type of Inclusion

• Relatively large proteinaceous polyhedral

• Carboxysomes- present in many CO2-fixing bacteria (RUBISCO)

Gas Vacuole

• Type of Inclusion

• Buoyancy to aquatic microbes

• Important for organisms to be at depth to reach adequate light intensity, oxygen concentration, and nutrient levels

• Collapse vesicles to dive deeper in water, construct new vesicles to move upward

Magnetosomes

• Type of Inclusion

• Orient organism in Earth’s magnetic field

Ribsomes

• Site of Protein Synthesis

• Located in plasma membrane or can be transported out of cell

• Cytoplasmic Ribosomes synthesize proteins that will remain inside the cell

• 70S in prokaryotic

Nucleoid

• Ellipsoidal region containing cell’s chromosomes and many proteins (Coils DNA in the region).

• Distinct region observed through microscopy.

• Double strained DNA but some have linear chromosomes

• Monoploid: single copy of chromosome. Polyploid: more than 10 copies per cell.

Plasmids

• Double strained DNA molecules that exist independently of the chromosome (most of circular)

• Contain low number of genes (less than 30)

• Carry genes that offer an advantage to the bacterium.

• Replicate themselves

• Episomes: plasmids are integrated into the chromosome and are replicated as part of the chromosome.

Transcription

RNA synthesis is coupled, meaning occurring simultaneously, to protein synthesis

Cell Division

• DNA replication is coordinated with cell wall expansion (two daughter cells)

• Do not undergo Mitosis or Meiosis. Instead they undergo Binary Fission.

Septation

• Completes Cell Division; The septum grows inward, at last constricting and sealing off the two daughter cells

• Cell envelope elongation must occur before septation

• FtsZ: Genes that assembles the “Z Ring” that constricts around the equator of the cell. Found in Archaea and Bacteria.

Pilus

Straight filaments of pilin protein. Used in twitching motility.

• Sex Pilus: used for conjugation, exchange of genetic material when sex pilus is used. Projects from donor cell (F+) to recipient (F-).

Fimbriae

Used for attachment. Biofilms.

Flagellum

A spiral filament of protein monomers called flagellin.

• Filament is rotated by a proton motive force (Na+ ion potential)

• Helical ‘propellers’

• Very thin, cannot be viewed under BF microscope

• Can give the organism an advantage for host to give infection

Flagellar Arrangements

• Monotrichous cells have a single flagellum

• Amphitrichous cells have a single flagellum at both ends

• Lophotrichous cells have several flagellum (tuft) at one or both ends

• Peritrichous cells have flagella randomly distributed around cell

Structure of Bacterial Flagella

• Filament: long, thin, helical structure extending from cell

• Hook: connects filament to basal body aka the motor portion

• Basal Body: anchored in the plasma membrane and cell wall (rotary molecular motor)

Chemotaxis

The movement of a bacterium in response to chemical gradients.

• Attractants cause Counter Clock Wise (CCW) rotation. Flagella bundle together. Pushes cell forward “Run”

• Repellents cause Clockwise rotation. Flagellar bundle falls apart. “Tumble”= bacterium briefly stops, then changes direction.

• Protein receptors detect attractant concentrations (sugars, amino acids)

Twitching Motility

Short, intermittent, jerky movements. Type IV pili

Bacterial Gliding Motility

Creep along a solid surface

Corkscrew-like Motion

Periplasmic Flagella inside of the organism

Endospores

• Has DNA and Proteins

• Survive heat, radiation, and damaging chemical (must protect DNA and enzymes)

• Sporulation: Limit in nutrient availability leads to spore formation

• Germination: Returning to vegetative state