Membrane transport

Welcome

Welcome! Lets have a revision system on membrane transport.

This is lecture number 4 for General Module.

This is just an overview

Remember that plasma membrane consists of lipid bilayer. Between the layer, we have proteins that intervene between it.

They are 2 main type of proteins.

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Integral proteins

• Extend into or through the lipid bilayer

• Not firmly embedded in the membrane

• Most are transmembrane proteins

• Attached to the polar heads of the membrane lipids

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Peripheral proteins

• Extend into or through the lipid bilayer

• Not firmly embedded in the membrane

• Most are transmembrane proteins

• Attached to the polar heads of the membrane lipids

This slide just to recap again the 5 major functions of membrane protein.

Multiple Choice

Receptor proteins

• breaks down chemical mesengger

• open and close to allow passage of ions

• is a protein that binds to chemical mesengger such as hormone

• glycoprotein that acts as cell-identity marker

Multiple Choice

Gated ion channels

• breaks down chemical mesengger

• open and close to allow passage of ions

• is a protein that binds to chemical mesengger such as hormone

• glycoprotein that acts as cell-identity marker

The plasma membrane has a property called as selective permeability

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Cell membrane is freely permeable to

• oxygen

• glucose

• sodium ions

• ethanol

Let us now revise on passive transport

There are 3 type of passive transport. Simple diffusion, carrier-mediated and channel mediated facilitated diffusion and osmosis.

These are the criteria of simple diffusion.

Facilitated diffusion involves transmembrane integral protein. One major example is glucose transporter.

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Regarding simple diffusion:

• It is saturable.

• Molecules across by diffusion

• ATP required

• It involves transmembrane protein.

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Regarding facilitated diffusion:

• It is saturable

• Molecules across by diffusion

• ATP required

• It involves transmembrane integral protein

Remember the location of the main type of glucose transporter.

Multiple Choice

The first step in glucose uptake by the cell is

• Conformational change of transport protein

• Glucose binds to binding site

• Protein returns to its original form

• Glucose release inside

Multiple Choice

The second step in glucose uptake by the cell is

• Conformational change of transport protein

• Glucose binds to binding site

• Protein returns to its original form

• Glucose release inside

Multiple Choice

The final step in glucose uptake by the cell is

• Conformational change of transport protein

• Glucose binds to binding site

• Protein returns to its original form

• Glucose release inside

Remember that insulin must present as such the Glucose transporter 4 can be exocytose to the cell surface.

Open Ended

List the five main properties of facilitated diffusion.

Remember the characteristics of osmosis.

There are 7 main types of Aquoporins.

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Osmosis involves

• hydrolysis of ATP.

• diffusion of a solvent.

• specific channel protein.

• binding of water to the receptor.

Let us now revise the active transport.

The two major type of active transport is primary and secondary active transport.

These are the main criteria of primary active transport. The example is sodium potasium A.T.P ase

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Regarding active transport:

• It involves transmembrane protein.

• ATP required

• Molecules are pumped across

• It involves movement of molecules down its concentration gradient.

Multiple Choice

Between the listed steps below, the first step that occur during the pumping of sodium potassium ATPase is

• Phosphorylation by ATP

• Binding of cytoplasmic Na+

• Pump changing shape

Multiple Choice

Between the listed steps below, the final step that occur during the pumping of sodium potassium ATPase is

• Binding of cytoplasmic Na+, leading to phosphorylation by ATP

• Pump changing shape

• Expel Na+ to extracellular fluid. Extracellular K+ binds to ATPase.

• Restores pump original shape. K+ releases

• Release phosphate group

Remember the three main classes of A.T.P.ase

The major classes of A.T.P. ase with their descriptions. Remember the description for each class!

Multiple Choice

Which type of ATPase that fulfill the criteria below?

•Intracellular organelles: lysosomes, endosomes, secretory vesicles

•Actively accumulate H+ in the vesicle lumen of lysosomes

• P-type

• V-type

• F-type

• E-type

Multiple Choice

Which type of ATPase that fulfill the criteria below?

•Transporter gets phosphorylated

•Membrane cells

•Example is Na+-K+ ATPase

• P-type

• V-type

• F-type

• E-type

Multiple Choice

Which type of ATPase that fulfill the criteria below?

ATPases with enzyme hydrolyzing site on the outside of the membrane

• P-type

• V-type

• F-type

• E-type

These are the criteria of secondary active transport.

SGLT is an example of secondary active transport.

Remember the 7 main steps involve in secodary active transport.

These are the steps. Starting from the binding of sodium ions to SGLT1 until the sodium is actively transport out by sodium postassium ions A.T.P ase.

Multiple Choice

What is step 1?

• Binding of glucose to SGLT1

• SGLT1 then rotates facing the inside of the cell.

• Na+ binds to SGLT1

Multiple Choice

What is step 4?

• Decreases the affinity of SGLT for glucose, hence, glucose is also released.

• Glucose is transported across the basolateral membrane by the Glucose transporter

• Concentration of Na+ is low inside. Hence Na+ comes off

Multiple Choice

What is step 7?

• Sodium actively transported by the sodium-potassium ATPase

• Glucose is transported across the basolateral membrane by the glucose transporter.

• Decreases the affinity of SGLT for glucose, hence, glucose is also released.

Dont forget the main characteristics for SGLT1 and SGLT2.

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The following are the criteria for SGLT1:

• Late proximal tubule and the intestine

• Has high affinity for glucose but relatively low transport capacity.

• Stoichiometry of 1:1

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The following are the criteria for SGLT 2:

• Early proximal tubule

• Has high affinity for glucose but relatively low transport capacity.

• Transports 1 Na+ and 1 glucose (1:1).

Let us know revise the transportation of large size molecule.

There are two main type which are endocytosis and exocytosis.

The three main type of endocytosis.

Phagocytosis involves the engulfing of large particles by the cell by projecting pseudopods.

Pinocytosis involves the gulping of extracellular fluids by the cell.

Remember the characterictics of endocytosis.

Multiple Select

Regarding phagocytosis:

• Engulf large particles

• Consists of projecting pseudopods (false feet)

• Cell ‘gulps’ drops of extracellular fluid

• Ligands binds to specific receptor protein in coated pits

Multiple Select

Regarding pinocytosis:

• Engulf large particles

• Consists of projecting pseudopods (false feet)

• Cell ‘gulps’ drops of extracellular fluid

• Ligands binds to specific receptor protein in coated pits

This is the summary slide.

Thank you!