ECM, Membranes (Lecture 6)

Question 1

What are the functions of Extracellular Matrix (ECM) and cell walls?

Answer 1

Support, adhesion, protection, gateway for in/out and intercellular communication

Secreted from cells

Question 2

About extracellular matrix in animals?

Answer 2

• mostly proteins/glycoproteins
• widely variable composition depending on cell type

Question 3

Cell walls in plants, fungi, and bacteria?

Answer 3

Plants - mostly cellulose
Fungi - mostly chitin
Bacteria - mostly peptidoglycans

Question 4

What are the roles of the animal ECM?

Answer 4

• adhesion
• support
• shape/migration
• cell division

Most abundant protein in ECM is collagen

Question 5

What are the 3 animal cell junctions?

Answer 5

1. Anchoring junction
2. Tight junction
3. Gap junction

Question 6

What are anchoring junctions?

Answer 6

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)

Question 7

What are tight junctions?

Answer 7

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

Question 8

What are gap junctions?

Answer 8

Cylindrical arrays of proteins form direct channels that allow small molecules and ions to flow between the cytoplasm of adjacent cells

Question 9

What cells does turgor pressure affect?

Answer 9

Bacteria, plants, fungi

Question 10

What are plant cell wall functions?

Answer 10

• support
• adhesion
• protection
• intercellular communication

Question 11

What is the composition of plant cell walls?

Answer 11

• 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

Question 12

What is the structure of a primary cell wall?

Answer 12

• a pectin-rich middle lamella joins adjacent cells
• perforations called plasmodesmata allow intercellular transport and communication

Question 13

About primary and secondary cell walls?

Answer 13

• 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

Question 14

What is the bacterial cell wall and surface structure?

Answer 14

• 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

Question 15

What is the structure of a phospholipid?

Answer 15

Amphipathic (one end hydrophilic, other end hydrophobic)

Question 16

How does self-assembly of phospholipids in aqueous environment work?

Answer 16

• happens spontaneously because they are the lowest energy states
• depends on lipid concentration

Question 17

About membrane asymmetry?

Answer 17

• outer and inner leaflets (monolayers) differ in composition (lipids, proteins, and carbohydrates)
• first evidence: the freeze-fracture method

Question 18

What are the major factors influencing membrane fluidity?

Answer 18

1. Temperature (higher increases fluidity
2. Structure of phospholipid tails
3. Cholesterol levels

Question 19

How does phospholipid composition influence membrane fluidity?

Answer 19

1. Length of fatty acid tail (longer = more viscous)
2. Degree of unsaturation (double bonds) in tail (more = more fluid)

Question 20

Which double bonds cause liquid tails to kink? Saturated fatty acids or unsaturated fatty acids?

Answer 20

Unsaturated fatty acids, due to desaturase enzyme

Question 21

Cholesterol is in the membrane of animal cells, how does cholesterol counter the effects of temperature extremes?

Answer 21

At high temps, it reduces membrane fluidity by restraining movement of lipids
At low temps, it increases membrane fluidity by preventing lipids from ordering

Question 22

Summary of the factors that affect membrane fluidity

Answer 22

(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

Question 23

What are the two membrane protein locations?

Answer 23

1. Integral membrane proteins (contain hydrophobic domains that cross the bilayer)
2. Peripheral proteins (sit on the surface and form non-covalent bonds with lipids and membrane proteins)

Question 24

What are the major functions of membrane proteins?

Answer 24

1. Transporters
2. Enzymes
3. Signal transduction
4. Cell surface attachment/recognition

Question 25

How can transmembrane proteins be identified based on their amino acid sequences?

Answer 25

Stretches of non-polar amino acids indicate transmembrane domains
(Polar and charged amino acids are hydrophilic)
(Non-polar amino acids are hydrophobic)

Question 26

What are the three movement across membranes (membrane transport) types?

Answer 26

1. Passive
   - diffusion
   -facilitated diffusion
2. Active transport
   - primary
   - secondary
3. Exo/endocytosis

Question 27

What does diffusion mean?

Answer 27

Things move from high to low concentration
- things move “down their concentration gradient”

Question 28

Passive transport

Answer 28

From high to low concentration is driven by increase in entropy

Question 29

Active transport

Answer 29

Against the concentration gradient (from low to high concentration) requires energy

Question 30

Osmosis

Answer 30

Movement of a solvent from high to low concentrations