Membrane Transport

Materials must do what

Move across membranes to supply cells with materials

Purpose of raw materials

Remove waste products

Movement across membranes is also important to maintain what

Proper composition of body fluids

Movement of substances through cell membrane depends on what 4 things

Lipid solubility

Molecular size

Charge

Presence of channels and transporters

Passive vs active transport

Passive: no energy required to move things down concentration gradient

Active: energy required to move things against concentration gradient

Passive diffusion

Spontaneous movement of particles down gradient that does not require energy or protein

What stops when equilibrium is reached

Net diffusion(molecules can still move, but net concentration doesn't change)

Diffusion is required for what to occur

Respiration

Osmotic pressure

Pressure that would have to be applied to a pure solvent to prevent it from passing into a solution

Osmolarity is often used to

Express concentration of solution

Isotonic vs. Hypotonic vs. Hypertonic environments

Isotonic: same concentration as cytoplasm(no movement)

Hypotonic: environment has lower concentration than cytoplasm(water moves in cell)

Hypertonic: environment has higher concentration than cytoplasm(water moves out of cell)

Water can cross cell membrane via what 2 routes

Diffusion through lipid bilayer

Mass flow through aquaporins

Aquaporins

water channel proteins

Facilitated diffusion

Movement of molecules through membrane transportes down their concentration gradient(cannot pass through bilayer on their own, large polar, charged compounds)

Two types of membrane proteins for transport

Channel proteins

Carrier proteins

Many transport proteins are

Gated(they require specific ligand or voltage to work)

Electrochemical gradient

The diffusion gradient of an ion, representing a type of potential energy that accounts for both the concentration difference of the ion across a membrane and its tendency to move relative to the membrane potential

Direction of electrochemical gradient of sodium

Inwards

Electric and chemical gradients of potassium

Chemical: outwards

Electrical: inwards(inside of cell is negative)

Nernst equilibrium voltage

Applying electrical potential to prevent ion from moving down its concentration gradient

Nernst equilibrium potentials for K+, Na+, and Cl-

K+: -88mV

Na+: +60mV

Cl-: -61mV

Our cells are more permeable to

Potassium(more potassium leakage channels, why resting potential is closer to -88mV)

If the membrane potential is not equal to the equilibrium(nernst) potential what will happen

Ion will move across membrane to force membrane potential towards equilibrium

Active transport is mediated by

Proteins/pumps

Each type of carrier protein has one or more

Specific binding sites for its solute/ligand

What is required for active transport

Energy(carrier must be linked to energy source)

Na/K ATPase

pumps three sodium ions out of the cell for every two potassium ions pumped in(uses atp, large amount of atp produced is used for these pumps)

Tight coupling between transport of two solutes allows carriers to do what

Harvest energy stored in one electrochemical gradient to power another(secondary active transport)

This type of transport can work in which direction

Either direction

uniport vs symport vs antiport

Uniport: Single molecule moved in one direction across membrane

Symport: two molecules move simultaneously in same direction across membrane

Antiport: two molecules move simultaneously in opposite directions across membrane

In mammalian cells the movement of sodium down its concentration gradient produces what

Energy to power an active form of transport

To function, cells in the small intestine must do what

Load sugars across their cell membrane

Epithelium in the intestine contain what transporters

Sodium glucose cotransporter

In intestinal epithelium, sodium binds inducing what

Conformational change that opens the glucose binding pocket

Glucose binds to pocket and the transporter does what

Reorients so pockets holding Na and glucose are moved inside the cell

Freshwater fish have large differences in in concentration of ions across

Their gills

In fish, their blood is higher in

Na+ and Cl- than surrounding water

Fish must expend energy to combat what

Gain of water and loss of ions

In freshwater fish, antiport proteins do what

Exchange waste for Na+ and Cl-(waste moves down gradient out of fish, to power ions back into fish against gradient)

Cells must have mechanisms for signal reception to do what

Detect stimuli

The detection of stimuli does what

Modifies intracellular activity to respond to stimuli

What binds to receptors

Ligands(only occurs at specific receptor site)

Ligands which are large and polar bind to what receptors

Cell surface receptors(signal transduction pathway)

small hydrophobic ligands bind to receptors in what location

Intracellular receptors(steroid hormones)

Ligand gated receptor

Acts as receptor and channel

Ionotropic

Quick opening of channel when ligand binds to ligand gated channel

G protein receptors

Mediates intracellular effects by activating G protein

In G coupled receptors, do chemicals pass the membrane

No

G coupled protein pathway is

Slower

Metabotropic

Indirect action using G protein, in which ion regulation or complex action occurs elsewhere and can be more complex

enzyme/enzyme-linked receptors

intracellular domain of such receptors is an enzyme whose catalytic activity is regulated by the binding of an extracellular signal

Intracellular receptor

Ligand binds to receptor inside cell

Chemoreceptors

Osmoreceptors

Thermoreceptors

Baroreceptors

Mechanoreceptors

Photoreceptors

Nociceptors

Chemoreceptors: detect changes in chemicals

Osmoreceptors: detect changes in osmotic pressure

Thermoreceptors: detect changes in temp

Baroreceptors: detect changes in blood pressure(type of mechanoreceptor)

Mechanoreceptors: detect mechanical forces(touch)

Photoreceptors: detect light

Nociceptors: detect pain

Ion channels permit passive transport of ions when opened by

Specific stimuli

3 types of ion channels

Ligand gated

Stretch gated

Voltage gated