Lecture 8-9

Question 1

tight junctions

Answer 1

• act as seals to limit the loss of fluid and ions
• contain membrane proteins
• b/w adjacent cells

Question 2

Desmosomes

Answer 2

• function as anchor points between cells. -
• Intermediate filaments of the cytoskeleton are important components of desmosomes

Question 3

Gap Junctions

Answer 3

• linkage between the cytoplasmic compartments of two cells.
• Formed from proteins called connexons that form a ‘tube’ between cells.
• allows groups of cells to communicate

Question 4

Plant Cell Structure

Answer 4

• mainly made of cellulose
• a thin primary cell wall.
• a middle lamella, which is sticky and made up of polysaccharides called pectins.
• as the plant matures, a thicker and less flexible set of secondary cell walls is layered. (is less flexible and can be quite rigid)
• cells linked by plasodesmata

Question 5

for cells to function efficiently the cell surfaces and membranes must do 2 things

Answer 5

• MUST control what goes in and what comes out
  1. control internal environment
  2. control it’s interactions with extracellular environment

Question 6

lipid bilayer

Answer 6

• are AMPHIPATHIC = have both hydrophobic and hydrophilic parts
• selectively permeable barrier that lets in nonpolar molecules because of nonpolar hydrophobic tails
• allows cell to maintain internal environment as well as separate and distinct chemical and structural environments

Question 7

influences on membrane fluidity

Answer 7

1. Structure:
   - unsaturated = double bonds (liquid)
   - saturated fatty acids = single bonds so tightly packed (solid)
2. amount of cholesterol (amphipathic) in membrane
   - reduce fluidity
3. Temperature
   - Cholesterol reduces membrane fluidity at 37C by reducing the movement of phospholipids.
   - But at lower temperatures stops membrane from becoming too viscous by preventing the tight packing of the phospholipids

Question 8

Transmembrane Proteins

Answer 8

• amphoteric = hydrophilic/phobic parts
• straddle across membrane

Question 9

6 Functions of Membrane Proteins

Answer 9

1. transport
2. enzymatic activity
3. signal transduction
4. cell to cell recognition
5. intercellular joining
6. Attachment to cytoskeleton and extracellular matrix (EXM)

Question 10

Isotonic, Hypotonic and hypertonic solutions

Answer 10

When comparing two solutions, the one with a higher concentration is hypertonic, the lower one hypotonic.
If they are the same concentration, they are isotonic.

Question 11

Passive Transport

Answer 11

Diffusion: solution goes down a concentration gradient till reaches equilibrium

Question 12

Osmosis

Answer 12

the movement of water along a concentration gradient and through a membrane that has limited permeability (a semi or selectively-permeable membrane) to one or more solutes.

Question 13

Active Transport

Answer 13

• needs energy
• ATP is derived directly or indirectly by hydrolysis
• goes against conc. gradient
• is direction with 3 types: symport, antiport, and uniport

Question 14

facilitated diffusion

Answer 14

is passive and needs a pathway

Question 15

simple diffusion

Answer 15

can go straight through lipid bilayer
- High permeability = small non polar molecules
ex: O2, CO2, N2
- less permeable but still goes through = H2O and glycerol

Question 16

channel proteins

Answer 16

• facilitated diffusion
• needs a channel to flow through
• are lined with polar (hydrophilic) amino acids. Nonpolar (hydrophobic) amino acids face the outside of the channel, toward the fatty acid tails of the lipid molecules

Question 17

Carrier/Transport Proteins

Answer 17

• facilitated diffusion
• they specifically bind to the transported substance which allows selective transport
  ex: glucose transport

Question 18

ion channels

Answer 18

• channel proteins for diffusion
• gated and are open or closed

Question 19

uniport transport

Answer 19

move 1 molecule against conc. gradient

Question 20

symport transport

Answer 20

move 2 molecules but only one is going against conc. gradient
- coupled transport

Question 21

antiport transport

Answer 21

move 2 molecules in opposite direction and both are against their conc. gradient
- coupled transport
ex: sodium potassium pump (Na+ out & K+ in)

Question 22

Sodium Potassium Pump

Answer 22

• first part is the ion gated channel to bring in sodium
• second is antiport
• Na+ out & K+ in
• for each molecule of ATP used 3 Na+ pump out and 2 K+ in

Question 23

Electrogenic Pump

Answer 23

• active transport
• Electrogenic pumps move ions against an ionic gradient and generate a voltage (potential) difference across the membrane

Question 24

Cotransport

Answer 24

example of proton/sucrose cotransport
- movement of one ion/molecule that helps move another across the membrane

Question 25

proton/sucrose transporter

Answer 25

• cotransport
• Electrogenic pumps can be used to help drive symporters such as the sucrose transporter by maintaining an ionic gradient

Question 26

sodium/potassium pump

Answer 26

1. symport of sodium and glucose from outside to inside cell
2. sodium binds to Na/K pump
3. when Na+ binds it stimulates phosphorylation of protein by ATP
4. phosphorylation changes shape of protein to release Na+
5. K+ binds to protein which releases the Ph group (dephosphorylates)
6. by losing the Ph the protein returns to original shape
7. K+ is released inside cell and cycle continues

Question 27

Phagocytosis

Answer 27

allows food particles to enter cells using endocytosis

Question 28

pinocytosis

Answer 28

uptake of extracellular fluid and solutes

Question 29

receptor mediated endocytosis

Answer 29

A coated pit and a coated vesicle formed
during receptor-mediated endocytosis
(TEMs)