Advanced Higher Biology

Membrane proteins

What can some integral membrane proteins be?

Transmembrane proteins

What can some transmembrane proteins be?

Channel or transporter proteins

What can some channel proteins be?

Ligand or voltage gated

What is an example of a transporter protein?

The sodium potassium pump

What do regions of hydrophobic R groups allow?

Strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer

What do integral membrane proteins interact with extensively?

The hydrophobic region of membrane phospholipids

What do peripheral membrane proteins have? And what are they bound to?

Hydrophobic R groups on their surface and are bound to the surface of membranes mainly by ionic and hydrogen bond interactions

What do many peripheral proteins do?

Interact with the surface of integral membrane proteins

What is the phospholipid bilayer?

A barrier to ions and most uncharged polar molecules

How do small molecules (such as carbon dioxide and water) pass through the bilayer?

Through simple diffusion

What is facilitated diffusion?

The passive transport of substances across the membrane through specific transmembrane proteins

How do different cell types perform specialised functions?

They have different channel and transport proteins

What are most channel proteins in animal and plant cells?

Highly selective

What are channels?

Multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane

How do channel proteins allow/ prevent diffusion?

They are gated and change conformation

How are ligand gated channels controlled?

By the binding of signal molecules

How are voltage gated channels controlled?

By changes in ion concentration

How do transporter proteins transfer the solute across the membrane?

They bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane

How do transporter proteins work?

They alternate between 2 conformations so that the binding site for a solute is sequentially exposed on one side of the bilayer then the other

What does active transport use?

Pump proteins that transfer substances across the membrane against their concentration gradient

What are pumps that mediate active transport?

Transporter proteins coupled to an energy source

What is required for active transport?

A source of metabolic energy

What do ATPases do?

Hydrolyse ATP

Why do some active transport proteins hydrolyse ATP directly?

To provide the energy for the conformational change required to move substances across the membrane

What determines the transport of the solute?

The electrochemical gradient

What combines to form he electrochemical gradient?

For a solute carrying a net charge, the concentration gradientv

and the electrical potential difference combine

What is a membrane potential?

An electrical potential difference

How is a membrane potential created?

When there is a difference in electrical charge on the two sides of the membrane

How do ion pumps establish and maintain ion gradients?

They use the energy from the hydrolysis of ATP

What is an example of an ion pump?

The sodium-potassium pump

What does the sodium potassium pump do?

Transports ions against a steep concentration gradient using energy directly from ATP hydrolysis

Where are the sodium and potassium ions transported?

The sodium-potassium pump transports sodium ions OUT of the cell and potassium ions INTO the cell

What is the mechanism for the sodium-potassium pump?

1. The pump has a high affinity for sodium ions inside the cell

2. Binding occurs

3. Phosphorylation by ATP

4. Conformation changes

5. Affinity for sodium ions decreases

6. Sodium ions are released outside of the cell

7. Potassium ions bind outside the cell

8. Dephosphorylation

9. Conformation changes

10. Potassium ions taken into cell

11. Affinity returns to start

What is true for each ATP hydrolysed? And what does this establish?

3 sodium ions are transported out of the cell and 2 potassium ions are transported into the cell. This establishes both concentration gradients and electrical gradients

Where is the sodium-potassium pump found and what does this account for?

It is found in most animal cells, accounting for a high proportion of the basal metabolic rate in many organisms

What drives the active transport of glucose in the small intestine?

The sodium gradient created by the sodium-potassium pump

What does the sodium-potassium pump in intestinal epithelial cells?

It generates a sodium ion gradient across the plasma membrane

What does the glucose transport do?

Transport sodium ions and glucose at the same time and in the same direction

Do sodium ions enter the cell up or down the concentration gradient?

Down

What does the simultaneous transport of glucose do?

Pump glucose into the cell against it concentration gradient