Chapter 8: Transport Across Membranes

Channel the transport of water

Aquaporin

Hydrophilic in nature so it can promote the transport of the polar water

Inner region

Hydrophobic because they are exposed to the hydrophobic interior of the plasma membrane

Outer region

How many aquaporins are there in one RBC?

200,000

Glucose is transported inward by a

glucose transporter (GLUT, GLUT1)

An integral membrane protein with 12 transmembrane segments (12 passes), which form a cavity with hydrophilic side chains

GLUT1

Involved in ETC. Establishing Electrochemical Gradient

Protein Complex of Electron Carriers

TRUE OR FALSE:

Sometimes we need to have an imbalance environment to push other cellular processes forward

True

TRUE OR FALSE:

Concentration of proton pumps (H+) will establish a gradient, which will push the synthesis of ADP

False

Ions have a difficulty in crossing the membrane because the cells have a lot of water, surrounding by the

sphere of hydration

Can go through, O2, CO2

Small, uncharged solutes

Glucose, sucrose. Can go through but to a lesser extend. Can use GLUT1 or tranpsorters

Large, uncharged solutes

Uses ATP. Needs energy. Movement is from the lower electrochemical gradient to higher concentration

Active Transport

Movement DOWN to the concentration movement (higher to lower)

Diffusion

Movement UP to the concentration movement (lower to higher)

Active transport

Diffusion where no membrane proteins needed to pass through like O2, CO2

Simple diffusion

Diffusion where it uses protein channels to pass through

Facilitated Diffusion

Diffusion where it is a movement up to the concentration gradient

Active transport

What would happen if O2 and CO2 diffusion will need membrane diffusion?

Difficulty in respiration

Change in conformation, Pushing the molecules inward

Carrier Membrane Proteins

Always open

Facilitated and Osmosis

How will the drug enter the plasma membrane? (Kinetics)

Transport mechanism

Small vesicles forming a closed, spherical lipid bilayer lacking proteins

Liposomes

Discovered that when lipids from cell membrane are dispersed in water, they form liposomes

Bangham

TRUE OR FALSE:

Solute molecules that are dissolved in water do not disrupt the interactions that normally occur between water molecules

False

TRUE OR FALSE

Water thus moves from regions of high to low solute concentration

False

Diffusion involving water

osmosis

Exposing the cell to very high concentration of solute outside the cell. Solute concentration is high outside the cell. Movement of water is from inside to outside of the cell. Animal cell will shrink

Hypertonic solution

Exposing the cell to so much solute outside. Solute will go inside

Hypotonic solution

FILL IN THE BLANKS:

The movement of an ion is determined by its ________________, the combined effect of its concentration gradient and the charged gradient across the membrane

electrochemical potential

FILL IN THE BLANKS:

The movement of an ion is determined by its electrochemical potential, the combined effect of its _________________ and the charged gradient across the membrane

concentration gradient

FILL IN THE BLANKS:

The movement of an ion is determined by its electrochemical potential, the combined effect of its concentration gradient and the _____________ across the membrane

charged gradient

Carry oxygen from the lungs to the body tissues, and to carry carbon dioxide (waste product) away from the tissues and back to the lungs

RBCs

An important protein in RBCs that carries oxygen from the lungs to all parts of our body

Hemoglobin (Hgb)

Oxygen, carbon dioxide, and water diffuse directly across the plasma membrane in response to their relative concentrations inside and outside the cell. No transport protein is required

Simple Diffusion

GLUT1 transports glucose into the erythrocyte, where the glucose concentration is lower. An anion exchange protein transports chloride (Cl-) and bicarbonate (HCO3) in opposite directions

Facilitated Diffusion

This channel proteins can facilitate the rapid inward or outward movement of water depending on the relative solute concentration on opposite sides of the membrane

Aquaporin

Push the transport from lower to higher concentration (movement up to the concentration gradient). Driven by the hydrolysis of ATP, the Na+/K+ pump moves sodium ions outward and potassium ions inward, establishing an electrochemical potential across the plasma membrane for both ions

Active Transport Using ATP-requiring Pumps

Oxygen gas traverses the lipid bilayer readily by

simple diffusion

TRUE OR FALSE:

Erythrocytes take up oxygen in the lungs where oxygen concentration is high and release it in the body tissues where oxygen concentration is low

True

When this happens, RBC through Hgb will deliver O2, collect metabolic waste through CO2, and CO2 will be converted to bicarbonate (HCO3-) ions

Depleted O2

Why is there a need to immediately convert CO2 to bicarbonate?

RBC can collect more CO2

Diffusion depends on these 3

Solute Size, Polarity, Charge

Lipid bilayers are more permeable to small molecules such as water, oxygen, CO2 than larger ones

Solute Size

Lipid bilayers are more permeable to nonpolar substances than to polar ones

Polarity

A simple measure of the polarity (or non- polarity) of a solute. Which is the ratio of its solubility in an organic solvent (such as vegetable oil or octanol) to its solubility in water

partition coefficient

The relative impermeability of polar substances, especially ions, is due to their associations with water molecules

Charge

The molecules of water form a this around polar substances. Ions will have a hard time to get inside the plasma membrane, repelled

sphere of hydration

TRUE OR FALSE:

The rate of simple diffusion is directly proportional to the concentration gradient

True

TRUE OR FALSE:

Facilitated diffusion is hypobolic because membrane proteins will help them to make the reaction faster

False

From hydrophobic channels through the membrane to provide a passage route for solutes

Channel Proteins

Transporters or permeases. Bind solute molecules on one side of a membrane, undergo a conformational change, and release the solute on the other side of the membrane

Carrier proteins

Sometimes are not selective. As long as the molecules are polar, the let them pass

Ion Channels

Provides a shield/protection against hydrophobic interior of the interior of the membrane to the solute passing through the membrane

Interior of the channel and carrier protein

Carrier protein. Proceeds with conformational change. Alternating conformational change

GLUT1

Membrane proteins behave like

enzymes

Involves binding a substrate on a specific solute binding site

Facilitated diffusion

When a carrier protein transports a single solute across the membrane, the process is called?

uniport

A carrier protein that transports a single solute is called a?

uniporter

When two solutes are transported simultaneously, and their transport is coupled, the process is called

coupled transport

Coupled transport in the same direction

Symport

Coupled transport in the opposite direction

Antiport

a uniport carrier for glucose

Glucose Transporter (GLUT1)

an antiport (coupled) anion carrier for Cl- and HCO3-

Anion exchange protein

Both the GLUT1 and Anion exchange protein can be found in the what of erythrocytes

plasma membranes

TRUE OR FALSE:

As the concentration of bicarbonate rises it moves out of the cell, coupled with uptake of CL- to prevent a net charge imbalance

True

By having this, bicarbonate will go out for balancing. Entry of Cl- ions will level of balance the ionic charges within the cells

Anion exchanger

Channel proteins from this that allow specific solutes to cross the membrane directly

hydrophilic transmembrane channels

Transmembrane channels that allow rapid passage of water. Movement of water across cell membranes in some tissues is faster than expected given the polarity of the water molecule

Aquaporins

Aquaporin was discovered when?

1992

TRUE OR FALSE:

Aquaporins allow rapid passage of water through membranes of erythrocytes and kidney cells in animals, and root cells and vacuolar membranes in plants

True

Transmembrane proteins that allow rapid passage of various solutes. The pores are formed by multipass transmembrane (as beta barrels) proteins called?

Porins

FILL IN THE BLANKS:

The beta barrel has a _________ pore at its center

water-filled

TRUE OR FALSE:

In porins, non-polar side chains line the inside of the pore, allowing passage of many hydrophilic solutes

False

TRUE OR FALSE:

In porins, the outside of the barrel contains many nonpolar side chains (amino acids) that interact with the hydrophobic interior of the membrane

True

FILL IN THE BLANKS:

All aquaporins are ___________ integral membrane proteins

tetrameric

TRUE OR FALSE:

The channels of aquaporin, lined with hydrophobic side chains (amino acids), are just large enough for water molecules to pass through one at a time

False

Transmembrane proteins that allow rapid passage of specific ions. Tiny pores lined with hydrophilic atoms are remarkably selective

Ion Channels

TRUE OR FALSE:

There are separate proteins needed to transport Na+, K+, Ca2+, and Cl-, etc

True

FILL IN THE BLANKS:

Most ion channels are ________, meaning that they open and close in response to some stimulus

gated

When Ca2+ enters the heart muscles, during heartbeat, it contributes to the electrical signal that coordinate the heart’s function

Calcium Ion Channels

They open and close in response to some stimulus

Gated Ion Channels

Ion channels that change their structure in response to voltage (changes in membrane potential) are called?

voltage-gated ion channels

The difference in total charge between the inside and outside of the cell is called the?

membrane potential

Regulate the relative concentrations of different ions inside and outside the cell. Opens and close in response to changes in membrane potential. Can regulate the relative concentration of ions

Voltage gated Ion channels

Triggered by the binding of certain substances to the channel protein

Ligand-gated channels

A molecule in the extracellular part of the cell (signalling molecule)

Ligand

Respond to mechanicals forces acting on the membrane

Mechanosensitive channels

Ranging from thermal molecular agitation to potentially destructive cell swelling caused by osmotic pressure gradients

Mechanical stimuli

TRUE OR FALSE:

Ion channels play roles in many types of cellular communication such as muscle contraction and electrical signaling of nerve cells

True

A chloride ion channel that helps maintain the proper Cl- concentration in the lungs. Defects in the protein cause cystic fibrosis.

cystic fibrosis transmembrane conductance regulator (CFTR)

If there’s irregularity in CFTR, there will be?

cystic fibrosis

Controls the flow of water and salts such as chloride ions into and outside the lung cells

CFTR

TRUE OR FALSE:

When Chloride is transported outside, promotes transport of water in the same direction. As a result, it will not have thickened mucus because it is diluted by water that is transported along with the Chloride

True

Muscle contraction starts with the release of neurotransmitter called what which will go in the cell via the ion channel receptors

acetylcholine

For the muscles contract, the acetylcholine neurotransmitters need to pass through the?

neurotransmitter receptors

To propagate nerve impulses across the neuromuscular junction between a nerve cell and muscle cell. Attaches to the receptors on the muscle cells and resulting to muscle contraction

Acetylcholine

Down the concentration Gradient

Passive

Up the concentration gradient, ATP requiring

Active

A type of active transport that is directly coupled with ATP to drive the transport forward

Direct