BIOL 107 - Topic 8: Structures External to the Plasma Membrane

Cell Wall

A wall of protection against mechanical, chemical, and osmotic damage

• shape, support, cell-cell interactions

• all bacteria, archaea, and many eukaryotes

• NOT in animals

Bacterial Cell Wall

A cell wall in bacteria made of peptidoglycan (PG)

• polysaccharide chains cross-linked by short polypeptides to produce a network

• NAG = N-acetylglucosamine

• NAM = N-acetylmuramic acid

• gram-positive or gram-negative

Gram-Positive Bacteria

Bacteria with a thick peptidoglycan layer in the cell wall

• more susceptible to antibiotics

• retains purple crystal violet stain during gram staining

Gram-Negative Bacteria

Bacteria with a thin peptidoglycan layer and a thick outer membrane that offers more protection

• has a carbohydrate portion of lipopolysaccharides evolved to protect the cell

  • tends to put immune systems to overdrive, toxic shock, septic shock

Plant Cell Wall

A cell wall in plants made of cellulose for protection, cell shape, and to hold up against gravity

• glucose polymer (with β-1,4-glycosidic bonds)

• parallel cellulose molecules are held together by H-bonds into microfibrils

• microfibrils are embedded in a matrix of proteins and other polysaccharides

Plasmodesmata

Channels through the plasma membrane and cell wall of adjacent plant cells

• physically connects cytoplasms (the cytoplasm of one plant is directly linked with another cytoplasm)

• allows passage of ion, water, and other materials

Extracellular Matrix (ECM)

A network of carbohydrates and proteins outside of the cell membrane

• physical support, adhesion, communication

• found in animals

Collagen (ECM)

A protein in the ECM that forms strong fibres

• provides structure

• most abundant protein in ECM

Proteoglycan (ECM)

Branched sugar molecules with small core proteins

• forms network

• interacts with collagen

• hydration/lubrication/swelling, cartilage, skin

Fibronectin (ECM)

Proteins that connects the ECM to the cell membrane

• interacts with collagen and integrin proteins

Integrin (ECM)

Integral membrane proteins that attach to fibronectins on the outside and cytoskeleton proteins inside the cytoplasm

• allows communication between ECM and inside of the cell

• in the plasma membrane

Capsule

A sticky layer of polysaccharide outside of the cell wall found in some bacteria

• protection against dehydration

• shield from immune system and WBC

• adhesion

• biofilm formation (layers of bacterial cells embedded in shared capsule material)

Bacterial Flagella

A filament in bacteria made of flagellin proteins used for cell movement

• external (outside plasma membrane)

• motor is anchored in cell membrane and cell wall

• motor is powered by proton gradient

• motor causes movement (not the protein itself)

• rotates

Eukaryotic Flagella

A filament in bacteria made of microtubules used for cell movement

• internal (inside plasma membrane)

• powered by ATP Hydrolysis

• bends back and forth