Chapter 12 - Transport Across Cell Membranes

why do water-soluble molecules and ions have difficulty crossing the lipid bilayer?

it is due to them being hydrophilic or having a charge

what is simple diffusion?

when diffusion occurs across channels that does not require ATP
(slow)

what is facilitated transport

when diffusion goes against the gradient so it requires ATP and a pump
(fast)

what are the properties that govern the rate at which a given solute can cross a protein-free lipid bilayer

1. small nonpolar solutes can cross easily

2. small uncharged polar solutes can cross but at a reduce rate

3. large, uncharged polar solutes have difficulty crossing

4. ions can not cross.

what is resting membrane potential?

when an unstimulated cell is in a stesady state condtion
typically betwwen -20 and -200v

how do transporters discriminate among solutes/moving only a select subset across the membrane?

they only transfer molecules or ions that fit into specific binding sites on the protein

how do channels discriminate among solutes/moving only a select subset across the membrane?

they discriminate mainly on the basis of size and charge
-When the channel is open, any ion or molecule that is small enough and carries the appropriate charge can pass through

what is active transport and what type of membrane transport protein carries it out?

takes place in pumps and requires ATP use travelling across the gradient in a backwards manner

what is passive transport and what type of membrane transport protein carries it out?

takes place in channels and requires no energy that moves solution from an area of high concentration to low concentration

what forces govern the passive transport of charged solutes across a cell membrane?

depends on voltage, membrane potential tends to pull positively charged solutes into the cell and drive negatively charged ones out.

what forces govern the passive transport of uncharged solutes across a cell membrane?

direction of passive transport is determined solely by its concentration gradient

compare the electrocehmical gradeint for sodium and potassium ions

Na+ abundant outside of cell and will flow into cell w/ net force being great since voltage and conc. gradient work in same direction
K+ abundant in cell less outside but outside cell is pos. so voltage and conc. gradient work in diff direction so net force weak

what are the three sources of energy used by transmembrane pumps to actively transport a solute against its concentration gradient?

1.gradients
2.ATP
3.Light

how do plant cells maintain their osmoatic equilibrium?

by the cell wall and vacuole storage

how do animal cells maintain their osmotic equilibrium?

by channels and pumps that move the ions out

how do protozoa maintain their osmotic equilibrium?

by contractile vacuole

how do proton pumps provide the energy for transport of solutes in

h+ pumps release h+ into the cell environment, causing an increase in acidic medium around the cell. Lysosomes in the cell break down the materials in order to keep the acidity levels and produce ATP

why—and how—cells keep the cytosolic concentration of calcium ions low.

1) iron is kept low to cause more sensitivity in order to increase ca2+
2)is done by ca2+ pumps (Used via ATP Hydropysis) which pumps Calcium from cytoplasm to return to orignal conformation without a 2nd ion

uniport glucose transport

ferries only 1 type of solute across the membrane

Symport Glucose Transport

moves (couples) solutes in the same direction across the membrane

Antiport coupled transport

moves (couples) solutes in the opposite direction across the membrane

Compare the uniport glucose transporter and the glucose-sodium symport in terms of their activities and roles in glucose transport in intestinal epithelial cells.

uniport: release glucose after fasting and after feast (area from high to low conc)

glucose na symport: conc of glucose can be high but still transported usin this, does it by using steep electrochem gradient of na+ which allows glucose to come in as well

cell uses both of these symport on apical domain (gut lumen) which takes in glucose and na and keeps them in plasma membrane then released passively using uniport on basal domain

Explain how the structure of ion channels leads to their ion selectivity.

selectivity depends on the diameter and shape of the ion channel and on the distribution of the charged amino acids that line it

ion channel narrow which forces ion to contact channel so that only those with proper size/charge pass

how do potassium leak channels participate in establishing the cell's resting membrane potential?

when leak channel open, k leaves and causes unbalanced neg charges

Review how the Nernst equation can be used to calculate the resting membrane potential across a membrane.

V=62log(Co/Ci)

can be used if ion concentration on both sides of membrane are known

how can patch-clamp recordings be used to study the activity of ion channels?

glass tube used as microelectrode and makes contact with channel can vary each side ion concentration.

voltage across the membrane patch—that is, the membrane potential—can also be set and held "clamped" at any chosen value

what is gating?

the conditions that influence their opening and closing

voltage gated: controlled by membrane potential

ligand gated: controlled by binding of some molecule to channel

mech gated: physical force opens it

what is resting membrane potential?

the flow of positive and negative ions across the plasma membrane is precisely balanced so that no further difference in charge accumulates across the membrane

how does ion channels in auditory hair cells allow the detection of sound?

Sound vibrations pull the channels open causing ions to flow into the hair cells; which causes an electrical signal that is transmitted from the hair cell to the auditory nerve, which conveys the signal to the brain

how does electrical signals travel from one neuron to another?

dendrites receive signals and flows to axon to nerve terminals

how does membrane depolarization triggers an action potential?

membrane potential shifts to less neg. if this is large enough will cause opening na channels, influx causes more channels to open causing explosive amplifying entry continues till 40 mV

how does action potential spreads along the membrane?

Na+ flowing in through open Na+ channels begins to depolarize the neighboring region of the membrane, which then goes through the same self-amplifying cycle. In this way, an action potential spreads outward as a traveling wave from the initial site of depolarization, eventually reaching the axon terminals

How did studying the giant axon of a squid revealed the different roles of potassium and sodium ions in establishing the resting membrane potential and propagating an action potential

In varying Na concentration affect action potential peaks while potassium concentrations revert to the negative voltage
As the membrane lost its permeability to Na+, it became even more permeable to K+ than before, presumably because additional K+ channels opened, accelerating the resetting of the membrane potential to the resting state, and readying the membrane for the next action potential.

what conformations does Na-gated ion channels cycle through as an action potential travels along the axonal membrane

Na-gated ion channels are comform via closed open inactivations
(Im still working on this card hold on)

what is the role of Na-gated ion channels in action potential

Na+ induces action potential (working in progress card)

what is the role of K-gated ion channels in action potential

K+ saves action potential (working in progress card)