ECM, Membranes (Lecture 6) Flashcards
What are the functions of Extracellular Matrix (ECM) and cell walls?
Support, adhesion, protection, gateway for in/out and intercellular communication
Secreted from cells
About extracellular matrix in animals?
- mostly proteins/glycoproteins
- widely variable composition depending on cell type
Cell walls in plants, fungi, and bacteria?
Plants - mostly cellulose
Fungi - mostly chitin
Bacteria - mostly peptidoglycans
What are the roles of the animal ECM?
- adhesion
- support
- shape/migration
- cell division
Most abundant protein in ECM is collagen
What are the 3 animal cell junctions?
- Anchoring junction
- Tight junction
- Gap junction
What are anchoring junctions?
Adjoining cells adhere at mass of proteins (a plaque) anchored beneath their plasma membrane by many intermediate filaments (desmosomes) or microfilaments (adherens junctions) of the cytoskeleton)
What are tight junctions?
Tight connections form between adjacent cells by fusion of plasma membrane proteins on their outer surfaces. A complex network of junction proteins makes a seal tight enough to prevent leaks of ions or molecules between cells
What are gap junctions?
Cylindrical arrays of proteins form direct channels that allow small molecules and ions to flow between the cytoplasm of adjacent cells
What cells does turgor pressure affect?
Bacteria, plants, fungi
What are plant cell wall functions?
- support
- adhesion
- protection
- intercellular communication
What is the composition of plant cell walls?
- cellulose + other polysaccharides + proteins
-
primary walls-
-> in a cell
-> relatively flexible -
secondary walls-
-> impregnated with lignin, which makes them very rigid
-> found in cells involved in support, protection, or nutrient transport
What is the structure of a primary cell wall?
- a pectin-rich middle lamella joins adjacent cells
- perforations called plasmodesmata allow intercellular transport and communication
About primary and secondary cell walls?
- both are screamed from the cell
- 2 wall is secreated after 1, so it is internal to the 1, but still outside the plasma membrane
What is the bacterial cell wall and surface structure?
- mostly peptidoglycans
- cell wall typically surrounded by a glycocalyx:
->composed of polysaccharides
->when firmly attached, it is a capsule
->when loosely, it is a slime layer
What is the structure of a phospholipid?
Amphipathic (one end hydrophilic, other end hydrophobic)
How does self-assembly of phospholipids in aqueous environment work?
- happens spontaneously because they are the lowest energy states
- depends on lipid concentration
About membrane asymmetry?
- outer and inner leaflets (monolayers) differ in composition (lipids, proteins, and carbohydrates)
- first evidence: the freeze-fracture method
What are the major factors influencing membrane fluidity?
- Temperature (higher increases fluidity
- Structure of phospholipid tails
- Cholesterol levels
How does phospholipid composition influence membrane fluidity?
- Length of fatty acid tail (longer = more viscous)
- Degree of unsaturation (double bonds) in tail (more = more fluid)
Which double bonds cause liquid tails to kink? Saturated fatty acids or unsaturated fatty acids?
Unsaturated fatty acids, due to desaturase enzyme
Cholesterol is in the membrane of animal cells, how does cholesterol counter the effects of temperature extremes?
At high temps, it reduces membrane fluidity by restraining movement of lipids
At low temps, it increases membrane fluidity by preventing lipids from ordering
Summary of the factors that affect membrane fluidity
(High) phospholipid tail length - (Low) membrane fluidity
(High temperature - (High) membrane fluidity
At (High) temperatures, cholesterol (Lowers) membrane fluidity
At (Low) temperatures, cholesterol (raises) membrane fluidity
(High) saturated fatty acid content (Lowers) membrane fluidity
What are the two membrane protein locations?
- Integral membrane proteins (contain hydrophobic domains that cross the bilayer)
- Peripheral proteins (sit on the surface and form non-covalent bonds with lipids and membrane proteins)
What are the major functions of membrane proteins?
- Transporters
- Enzymes
- Signal transduction
- Cell surface attachment/recognition
How can transmembrane proteins be identified based on their amino acid sequences?
Stretches of non-polar amino acids indicate transmembrane domains
(Polar and charged amino acids are hydrophilic)
(Non-polar amino acids are hydrophobic)
What are the three movement across membranes (membrane transport) types?
- Passive
- diffusion
-facilitated diffusion - Active transport
- primary
- secondary - Exo/endocytosis
What does diffusion mean?
Things move from high to low concentration
- things move “down their concentration gradient”
Passive transport
From high to low concentration is driven by increase in entropy
Active transport
Against the concentration gradient (from low to high concentration) requires energy
Osmosis
Movement of a solvent from high to low concentrations
