Lecture 8 - Transport

Question 1

Membrane transport (passive vs active)

Answer 1

Passive transport:
Substances move down concentration gradient (high to low)
Use no energy

Active transport:
Substances move against a concentration gradient (low to high)
Energy required

Question 2

Diffusion

Answer 2

Movement of molecules DOWN a concentration gradient

Influenced by:
Mass of molecule
Temp. of molecule
Steepness of gradient
Surface area
Distance to diffuse

Question 3

Simple diffusion

Answer 3

Diffusion through membrane without channel or carrier
Only done by lipids or very small molecules

Question 4

Facilitated diffusion

Answer 4

Sugars, amino acids or ions bind to protein carriers in membrane or move through channels

Question 5

Osmosis

Answer 5

Movement of water through a selectively permeable membrane
Solute molecules cannot cross

Question 6

Autophagy

Answer 6

“Self eating” cell digests its own structure

Question 7

Autolysis

Answer 7

Breakdown of cells during own enzymatic action

Question 8

Auqaporins

Answer 8

Integral membrane proteins that act as a water channel during osmosis

Question 9

Tonicity

Answer 9

Refers to the ability of a solution to change shape/tone depending on volume of water

Isotonic- same solute concentration
Hypertonic- high solute (crenate)
Hypotonic low solute (lyse)

Question 10

Active transport processes

Answer 10

Energy required because:
Solute too large for channels
Solute not lipid soluble
Solute not able to move down a gradient

Two major active membrane transport processes:
Active transport
Vesicular transport

Question 11

Carrier proteins

Answer 11

Bind specifically and reversibly with substance being moved

Anti-porters- Transport one substance into cell while transporting a different substance out of cell

Symporters- transport two different substances in the same direction

Question 12

Primary vs secondary active transport

Answer 12

Primary active transport:
Required energy comes directly from ATP hydrolysis
Shape change causes solutes to be pumped across the membrane

Secondary active transport:
Required energy comes indirectly from ionic gradients created by primary active

Question 13

Membrane Potential

Answer 13

A membrane is a voltage across the cell membrane that occurs due to separation of oppositely charged particles
Inside of the membrane is more negatively charged than the outside

Resting membrane potential:
Determined by concentration gradient of potassium ions that move freely out of cell down gradient, but also move into cell along electrical gradient

Question 14

Vesicular transport (endocytosis, exocytosis, transcytosis, vesicular trafficking)

Answer 14

Vesicular transport: Uses membrane is vesicles to transport large particles, macromolecules and fluids across the membrane or within cell, this requires energy

Endocytosis- is transport into the cell
Exocytosis- Is transport out of the cell
Transcytosis- Is transport into, across and out of the cell
Vesicular trafficking- is transport from one area for organelle in a cell to another

Question 15

Phagocytosis (cell eating)

Answer 15

Form of endocytosis in which large, solid materials are brought into cell


Question 16

Pinocytosis (cell drinking)

Answer 16

A form of Endocytosis that takes a small volume of extracellular fluids into the cell
No receptor used, process is non-specific

Question 17

Receptor mediated endocytosis

Answer 17

Allows cells to concentrate molecules found in small amounts in extracellular fluids
Because it uses receptors, it is HIGHLY SPECIFIC

many cells have receptors embedded in cathrin-coated pits
Enzymes,lipids, iron and insulin taken in this way
Some viruses- diphtheria and cholera toxins trick cells and enter this way

Caveolae are slightly different from clathrin, but still capture specific molecules (folic acid and tetanus toxin) and use transcytosis

Question 18

Exocytosis

Answer 18

Type of vesicular transport that moves molecules out of cell in a simple vesicle, often used for secretion or removal of waste from the cell

Protein of vesicle —> vSNARE fuses with tSNARE Proteins on membrane, triggers Exocytosis

Exocytosis can expel hormones,neurotransmitters, mucous etc.