chap 4- transport (b1- foundation)

Question 1

what types of transport require energy from ATP?

Answer 1

• primary
• secondary active transport (co-transport & counter transport)
• endocytosis
• exocytosis
• phagocytosis

Question 2

active transport definition

Answer 2

movement of substances against the electrochemical gradient

• requires energy which is obtained mainly by breakdown of high energy compounds like ATP

Question 3

diffusion vs active transport

Answer 3

diffusion: random molecular movement of substances molecule by molecule
- energy that causes diffusion is energy of normal kinetic motion of matter

active transport: movement of ions or other substances across membrane w/ carrier protein such that substances move AGAINST their concentration gradient
- requires additional source of energy

Question 4

an important difference b/w simple diffusion & facilitated diffusion

Answer 4

simple diffusion: no carrier
- as conc. of diffusing substrate increases, rate of diffusion just keeps increasing proportionately

facilitated diffusion: carrier- mediated
- as conc. of diffusing substrate increases, rate of diffusion cannot rise higher than the Vmax
- bc carrier proteins just cant open and close fast enough to allow it to keep increasing

Question 5

what is simple diffusion & what factors does it depend on?

Answer 5

simple diffusion no carrier proteins needed, movement of molecules/ions occurs through membrane openings of intermolecular spaces

rate of diffusion depends on:
- amount of substance available
- velocity of kinetic motion
- # & size of openings in membrane through which molecules/ions can move

Question 6

simple diffusion: lipid soluble substances through the lipid bilayer

Answer 6

rate of diffusion of lipid soluble substances is directly proportional to its lipid solubility (how non polar it is, the more nonpolar = faster it will go through)

highly lipid soluble substances: O2, CO2, fatty acids, steroids

(how O2 gets in so easily - its so needed too)

Question 7

2 ways that simple diffusion occurs

Answer 7

1. Lipid solubility of substance through lipid bilayer (just goes in depending on whether or not its nonpolar- mostly for O2/CO2)
   - for nonpolar things

aquaporins are simple

2. Protein channels - extend throughout membrane and allow water to come in rapidly
   - aquaporins, K+/Na+ channels
   - for polar things

Question 8

how do water soluble (polar) substances get through the cell membrane?

Answer 8

through protein channels

• such as Na+, K+, & Ca2+

Question 9

what are aquaporins/what do they do?

Answer 9

selectively permit rapid passage of water through the membrane

• very selective, however; can sometimes also let molecules like urea & glycerol pass through (but at a MUCH smaller rate)

Question 10

2 distinguishing characteristics of protein channels

Answer 10

1. selectively permeable to certain substances
   - based on: diameter, shape, electrical charges, chemical bonds (inside surface)
2. opened/closed by gates/chemical (voltage-gated or ligand-gated channels)

Question 11

structure of potassium channels

Answer 11

1. tetrameric structure (4 identical proteins subunits; purple coils that make like a V, 2 of these helixes are transmembrane)
2. 4 subunits surround a central pore that has pore loops at the top
3. Pore loops form a selectivity filter that has carbonyl oxygens lining it - carbonyl oxygens dehydrate potassium (pull the water) to allow potassium to pass
4. This makes it selective and only lets K+ through even though Na+ is smaller

Question 12

potassium channels vs potassium gates (for own knowledge)

Answer 12

K+ channel: full protein structure that allows K⁺ to move
- always includes the selectivity filter

K+ gate: the movable part of the channel that opens or closes
- found in voltage-gated or ligand-gated channels

Question 13

how is the sodium channel highly selective for passage of sodium ions?

Answer 13

selectivity filter on these channels are lined with strongly negatively charged amino acid residues

• the charge pulls small Na+ molecules away from their water, dehydrates them, and lets them pass (they don’t get fully dehydrated though)

Question 14

opening/closing of the gates of protein channels are controlled by what 2 factors?

Answer 14

1. voltage gating: responds to electrical potential across cell membrane
   - ex. strong (-) charge on inside of cell membrane causes outside sodium gates to remain closed, but when gains (+) charge, gates suddenly open
2. chemical (ligand) gating: opened by binding of chemical substance (ligand) with protein = causes conformational change in protein molecule that opens/closes gate
   - ex. acetylcholine ligand-gated ion channel that’s gates only open when ACh binds to receptors

Question 15

what is facilitated diffusion? and what are the 3 important characteristics of it?

Answer 15

facilitated diffusion: requires carrier protein to aid passage of molecules/ions by binding with them chemically

1. specificity: each carrier only transports 1 specific substance (or very similar ones)
2. saturation: if all carriers are full, rate of transport reaches maximum (the Vmax thing)
3. competition: similar substances may compete for the same carrier

molecules can be transported in either direction

Question 16

important example of facilitated diffusion

Answer 16

GLUT-4: glucose transporter that is activated by insulin which can increase the rate of facilitated diffusion of glucose by 10-20x
(how insulin regulates glucose levels in the body)

mainly through facilitated diffusion: glucose & amino acids

Question 17

how is osmosis different from aquaporins? (for own knowledge)

Answer 17

water can short of cross through the membrane but really really slowly so aquaporins exist to speed up this process

“While osmosis is the underlying process of water movement, aquaporins act as specialized protein channels to speed up and regulate this process.”

Question 18

what is osmosis?

Answer 18

type of passive transport- doesn’t require energy (ATP)

net movement of water across a semipermeable membrane caused by conc. difference
- membrane allows water to pass through, but not solutes (like salt or sugar)
- usually net water conc. doesnt exist, its sort of just at 0, maintained, but sometimes can happen and then osmosis starts

water moves from area of low conc. to higher conc.

Question 19

what is osmotic pressure?

Answer 19

amount of pressure required to stop osmosis (prevent net movement of water across membrane)

“osmotic pressure pulls water in”

Question 20

osmolarity vs osmolality + normal osmolarity of ECF (blood plasma)

Answer 20

both measure how concentrated a solution is

osmolarity: # of solute particles in 1 liter of total solution (which includes both solute + solvent)

osmolality: measures # of solute particles in 1 kilogram of JUST SOLVENT (water)

normals osmolality of blood plasma - 300 milliosmoles/kg water (which is basically 300 solute particles/kg water)

Question 21

net diffusion rate across a membrane is proportional to what? whats the equation?

Answer 21

proportional to concentration difference across membrane

rate of net diffusion into cell is proportional to conc on outside minus conc on inside

Question 22

what is Nersnt potential? what is the equation?

Answer 22

nersnt potential: electrical voltage/potential that will balance a given concentration difference
- at this voltage, ion is in equilibrium meaning no net movement of that ion across membrane

equation: EMF (in mV) = +_61log(C1/C2)
C1= conc. on side 1, C2= conc. on side 2

balance point b/w chemical force & electrical force is the Nernst potential- when ions no longer wanna move

Question 23

The principal mechanism by which Insulin controls glucose transport across the cell membrane is:

Answer 23

facilitated diffusion

Question 24

what type of channels are Acetylcholine receptors?

Answer 24

ligand gated channels

Question 24

2 types of active transport

Answer 24

**primary active transport**: energy is directly derived from breakdown of ATP **secondary active transport**: energy is derived secondarily from energy from ionic concentration differences - difference was created originally by primary active transport *both depend on carrier proteins that penetrate through the cell membrane*

Question 25

structure of sodium-potassium pump (Na+-K+ pump)

Answer 25

protein complex of 2 separate globular proteins- *1 is α and 1 is β (smaller)* the smaller one's function is unknown but the bigger one (α) has 3 specific features: 1. has **3 binding sites for sodium** on inside portion of cell 2. has **2 binding sites for K+** on outside 3. inside portion near sodium binding sites has **ATP-ase activity**

Question 25

how does the sodium-potassium pump work?

Answer 25

1. when **2 K+ ions bind on the outside** and **3 Na+ ions bind on the inside**, ATPase function of protein gets activated 2. activation leads to **cleavage of 1 molecule of ATP** creating liberated energy 3. that energy causes a **chemical & conformational gradient** in molecule, pushing **3 Na+ to outside & 2 K+ to inside**

Question 26

what are the functions of the sodium-potassium pump?

Answer 26

most important function is that it **controls cell volume** (b/c if gets too hypertonic or hypotonic, cell can shrivel or burst) also **electrogenic in nature** which creates an action potential across the cell membrane - *this action potential is basic requirement in nerve & muscle fibers for transmitting nerve & muscle signals*

Question 27

calcium pump (Ca2+-ATPase)

Answer 27

example of *primary active transporters* - normally, *calcium levels inside cell are very low* & much higher outside cell two types: 1. In **cell membrane**: pumps **Ca2+ out of cell** 2. Pumps Ca2+ into **sarcoplasmic reticulum of muscle cells & mitochondria of all cells** this carrier protein has the same ability to cleave ATP like in sodium channels

Question 27

hydrogen pump (H+ ATPase) + where its found

Answer 27

*another ex. of primary active transporters*- more or less same role as the calcium one except with just H+ ions important in 2 parts of the body: - **parietal cells of stomach (gastric glands)**: to secrete HCl into stomach - **intercalated cells of kidneys (renal tubules)**: to control blood pH by regulating H+ levels

Question 28

2 types of secondary active transport

Answer 28

**co-transport**: diffusion energy of Na+ can *pull other substances w it* to inside of membrane - *ex. co-transport of glucose & amino acids w/ Na+* **counter-transport**: diffusion energy of Na+ used to transport another substance *outside* while Na+ goes *inside* - *ex. sodium-calcium counter transport, sodium-hydrogen counter transport* *both use coupling mechanism- both Na+ & substance have to bind in order for carrier protein to work*

Question 28

co-tranport of glucose & amino acids along w/ sodium (*secondary active transport*)

Answer 28

2 binding sites on transport protein- 1 for Na+ & 1 for glucose - **only starts to work when both of them bind** energy for movement is **generated from the concentration gradient** of Na+ b/c Na+ just constantly trying to go in - *esp important across renal & epithelial cells* to promote absorption of these substances into the blood

Question 29

counter-transport of calcium & hydrogen ions with sodium (*secondary active transport*)

Answer 29

this is in addition to the already existing calcium/hydrogen active pumps (counter transport is not nearly as powerful but still helpful) **Na+ moves in, Ca2+ moves out** and are bound to the same transport protein (*has 2 sides- 1 on outside & 1 on inside*)

Question 30

active transport through cellular sheets

Answer 30

**cellular sheet**: layer of closely packed cells- connected tightly & have 2 sides: one that faces the inside space & 1 that faces the blood *active transport through cellular sheets is movement across the whole layer of cells* occurs through: **epithelium of intestine, renal tubules, exocrine glands, & gallbladder** happens by: 1. **active transport** through membrane on 1 side of transporting cells 2. **simple or facilitated diffusion** on opposite side of cell

Question 31

what is transcytosis?

Answer 31

- **receptor-mediated uptake** of a ligand on one side of the cell - then **vesicular transport across** the cell - lastly, **exocytosis of the vesicle contents** on the opposite side

Question 32

uniport vs. symport vs. antiport

Answer 32

**uniport**: carries only *one substance* in a *single direction* **symport**: transports *2 different substances* in the *same direction* **antiport**: transports *2 different substances* in the *opposite direction*

Question 33

which disease is caused by defective Cl- channel?

Answer 33

cystic fibrosis - body produces abnormally thick mucus