Mol Lecture #34

Question 1

Active Transport p.1

(overview)

Answer 1

• Process for moving entities against a gradient. (Going from an area of low concentration into an area of high concentration)
  Important for:
• uptake of essential nutrients
• Removal of waste products from the cell
• Maintenance of constant internal concentration of certain key ions H+, Ca 2+, Na+, K+.

Question 2

Active Transport p.2

Answer 2

• Think about charge differences across the membrane (We’re also taking into account the build up of charge gradient across the membrane)
• Energy source: Because active transport requires energy
  Primary active transport: driven by ATP hydrolysis, and works for both passive and active
  Secondary Active Transport

Question 3

Ca2+ Pump (Primary)

Answer 3

• Pumps things against their gradient
• Carrier (one ion at a time)
• Energized by the direct use of hydrolysis of ATP
• Ca2+ Pump helps to maintain low Ca2+ concentration in the cytoplasm by pumping into ER (endoplasmic reticulum)

Question 4

The Na+/K+ Pump (primary)

Answer 4

• Push 3 Na+ out (against its gradient) and 2 K+ in with each cycle, to maintain gradients of these two ions and set up a charge difference.
• Setting up a charge gradient because we send 3+ out and only 2+ in, thus creating a charger difference across the membrane.
• Low K+ outside the cell, and high Na+ outside the cell

Question 5

Membrane Potential

Answer 5

• Chemical gradient: difference in concentration of a specific molecule or ion
• Electrical gradient: difference in overall charge across a membrane
• Membrane potential: is (also) the difference between the overall charge across the membrane
• In cells is usually maintained so that cells are slightly more negative inside.
  (Can do both a chemical/electrical gradient at the same time)

Question 6

Secondary Active Transport

Answer 6

• Energy from the concentration gradient of one solute (Driver solute) is used to transport another solute (cargo) against a gradient
• Driver is going to go down its gradient, in doing so it is going to push cargo up its gradient
• Mediated by co-transporters

Question 7

Active Transport: Symport & Antiport

Answer 7

• In symport, both entities move in the same directions. (The energy from the driver pushes the other molecule against its concentration gradient.)
• In antiport, the entities move in opposite directions. (Instead of the cargo ion moving in with the driver, it is being pushed out by the driver going down its concentration gradient.)

Question 8

Glucose Transporter

Active Transport

Answer 8

• use Na+ ions (high on the outside- because of the Na+/K+ pump) to drive glucose entry (high on the inside) → symporter. Important for the glucose uptake in the small intestine and glucose reabsorption by the kidney

Question 9

Na+/H+ exchanger

Answer 9

• antiporter- that transports Na+ in, while removing H+ from the cell. How do we setup the gradient? ATP hydrolysis (ex.) → energy somewhere was expended in order to use secondary active transport

Question 10

Exocytosis and Endocytosis

Answer 10

• Passive and Active Transport can only transport entities up to a certain size. (about the same size as glucose)
• Use a system of membrane budding and fusion to move larger entities into the cell. Ends up in the endomembrane system.
• Functioning all the time, cell is constantly performing the two.

Question 11

Exocytosis

Answer 11

• Move out
  Ex. proteins being released from the cell
• They are moved up to the plasma membrane (in a vesicle)
• Fuse the vesicle with the membrane, and exocytose the proteins
• Membrane-bound vesicle originating from the endomembrane system (possibly from the Golgi) fuse with the PM to release contents outside of the cell.

Question 12

Endocytosis

Answer 12

• Membrane-bound vesicles containing extracellular contents bud from the PM into the cell. Fusion of this vesicle w/ internal membrane-bound organelle releases contents into the cell (inside endomembrane system).

Question 13

Two types of endocytosis

Answer 13

• Pinocytosis: used to non-specifically capture extracellular fluid cargo (bulk-phase endocytosis)
• Receptor-mediated endocytosis: use receptors on the cell surface to capture specific cargo.
  →The receptors are included in the vesicle that eventually buds off into the cell.
  → Clathrin helps facilitate budding of the membrane in association with the receptor.

Question 14

Cytoskeleton

(Overview)

Answer 14

• Set of protein complexes that perform many jobs in the cell. Including maintaining cell shape and organization.
  → involved in cell division, cell attachment, cell movement, internal processes such as vesicular transport.
• All cytoskeletal types: can form stable structures but are highly dynamic. Those stable structures are probably still transient and evolving.

Question 15

Cytoskeleton, 3 Types:

Answer 15

-Microtubules
- Intermediate filaments
- Microfilaments (actin filaments)