BC 6 Membrane Transport

Question 1

Active and Passive Trans

Answer 1

Down Concentration gradient: Passive
Up concentration gradient: Active-requires energy

Uncharged molecules cross by concentration gradient only (sugars, glycerol) membrane voltage gradient not a factor

ELECTROCHEMICAL: concentration gradient & electrostatic environment

inside cell: NEG
outside cell: POS
positive pass through from out to in most favorable

Question 2

Channel Protiens

Answer 2

do NOT bind to solutes
hydrophilic tunnel down CG (AlWAYS Passive)
can be GATED

Acetylcholine Gated. ACH binds to alpha subunit causing conf change to allow sodium into cell (down CG)

Question 3

Transporter Proteins

Answer 3

DO bind to solutes
PASSIVE OR ACTIVE
1. Uniport
2. SymPort
3. Antiport

Passive: GLUT(1-4) uniporter for Glucose
varying affinity for glucose depending which cells need it most
1. Brain, blood, placenta, fetal (constant)(HIGH)
2. Liver Kidney, intestive, Bcells (LOW)
3. Brain VERY HIGH, used in hypoglycemia
4. Muscle/adipose (medium) insulin regulated, recruits flut4 transporters from intracellular stores (on demand)

ACTIVE:
Primary: energy of ATP
Secondary: maintenance of ion gradient provides energy (Na+, inside cell Na is low and charge is negative)

Question 4

Glucose in Intestinal Lumen

Answer 4

1. Paracellular (between cells) can loosen
2. Transcellular- through apical to basolateral
   primarily #2

Requires passive, active primary and secondary
1. From Lumen through Apical
Na driven Glucose trans 1 glucose 2 Na
2. out basolateral: 3Na+ 2K+ in -ATP
Na Binds on inside, atp binds, conf change, expelled
K+ binds, Dephosphorylation back to original conf
3. Basolateral Glut2 passive transport out of cell to CT and Blood supply

Na+ leaks back through tight junction back to intestinal lumen

Outside cell in lumen: High Na+ low Glucose
inside cell: low Na+ high glucose
outside cell (basal): high Na+ low glucose