Ch 6 - transport of ions across membranes

Question 1

diffusion

Answer 1

random molecular motion of solutes down a chemical or electrochemical gradient

Question 2

osmosis

Answer 2

diffusion of water across a semipermeable membrane

Question 3

protein-mediated transport

Answer 3

• more rapid than simple diffusion
• saturation kinetics (the rate of transport increases until it reaches a point at which it stabilizes
• chemical specificity and stereospecificity (only molecules of a particular shape and chemical structure are transported
• competitive inhibition (structurally related molecules can block transport)
• transport can be inhibited by compounds that bind to or structurally alter the transport protein

Question 4

types of protein-mediated transport

Answer 4

• facilitated transport

- active transport

Question 5

facilitated transport

Answer 5

• cannot move ions against an electrical potential difference
• cant move uncharged particles against a concentration gradient
• the transported molecule may alter transport by producing a conformational change in the transport protein

Question 6

active transport

Answer 6

• ATP required
• metabolic inhibitors can block
• substances can move against concentration

Question 7

types of transport proteins

Answer 7

carrier proteins and channel proteins

Question 8

carrier proteins

Answer 8

molecules bind to these proteins and are moved across the membrane by a conformational change in the carrier

Question 9

uniport

Answer 9

one type of molecule is transported across a membrane without help from a carrier

Question 10

symport

Answer 10

two different molecules transported in the same direction

Question 11

antiport

Answer 11

two different molecules transported in different directions

Question 12

channel proteins

Answer 12

form pores that open and close to transmit certain molecules across the membrane

Question 13

Na, K, ATPase

Answer 13

• maintains low Na and high K inside the cell by active transport
• 3 Na: 2 K: 1 ATP
• chemical potential energy created is used to drive other systems like amino acid transport

Question 14

Ca ATPases

Answer 14

• maintain very low Ca in cytoplasm ( hi Ca will activate cells)
• phosphorylation and dephosphorylation fuels pumping
• activity of these ATPases may be regulated by the protein calmodulin

Question 15

Na-Ca antiporter

Answer 15

• the energy of the Na gradient is used to transport Ca from the cell
• cause rapid and transient decreases in intracellular Ca
• activity stimulated by calmodulin

Question 16

Na-H antiport

Answer 16

prevents acidification of cytoplasm

Question 17

chloride-bicarbonate antiporter

Answer 17

• prevents cytosolic pH from becoming too basic

- this protein is important in red blood cells for CO2 transport and renal tubular cells for bicarbonate reabsorption.

Question 18

Na-K-Cl symporter

Answer 18

• transports 1 Na: 1K: 2Cl into the cell
• can regulate cell volume, cell shrinkage acivates this symporter and the resultant ionic influx pulls in water osmotically
• in the kidney, this transporter is heavily involve dn the reabsorption of sodium. inhibition of the action of this symporter by furosemide (Lasix) increased sodium and water excretion (diuresis).

Question 19

structure and function of ion transport channels

Answer 19

• one or more sets of transmembrane alpha-helices
• ion selectivity arises from the arrangement of charged amino acids spanning helices that line the pore
• the beta subunit of hte channel molecule forms a physical gate on the outside of the cell

Question 20

two types of ion transport channels

Answer 20

1. voltage gated

2. ligand gated

Question 21

voltage gated

Answer 21

activated by changes in membrane potential

• voltage sensor in one of transmembrane helices and contains a row of 7 positively charged amino acids
• they are for Na, K, and Ca

Question 22

ligand gated

Answer 22

activated by the binding of a ligand to the receptor portion of the channel molecule, which then opens the gate

Question 23

what type of channel does ketamine work on? and what is its name?

Answer 23

• acts to block a ligand-gated ion channel for Na and Ca.
• this channel is called the NMDA channel and is normally activated by glutamate
• ketamine blocks depolarization of hte cell and thus the generation of action potentials which normally activate the NMDA channel.

Question 24

protein-mediated transport of small molecules

Answer 24

• is faster than simple diffusion
• can be subject to competitive inhibition
• can be saturated
• displays chemical specificity