1.3 Membrane proteins

What is the cell membrane known as

Fluid mosaic model

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 extensively with

Hydrophobic region of membrane phospholipids

What are some integral membrane proteins known as

Transmembrane proteins

What do peripheral membrane proteins have on their surface

Hydrophilic R groups and are bound to the surface of membranes, mainly by ionic and hydrogen bond interactions

What do many peripheral membrane proteins interact with

the surfaces of integral membrane proteins

What is the phospholipid bilayer a barrier to

ions and most uncharged polar molecules

What molecules pass through the bilayer by simple diffusion

Small molecules such as oxygen and carbon dioxide

What is facilitated diffusion

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

How do cells perform specialised functions

different cell types have different channel and transporter 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

What are some channel proteins

Gates and change conformation to allow or prevent diffusion

What are ligand-gates channels controlled by

The binding of signal molecules

What are voltage-gates channels controlled by

changes in ion concentration

What do transporter proteins do

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

What does active transport use

pump proteins

What do pump proteins do

transfer substances across the membrane against their concentration gradient

Why do transporters alternate between two conformations

so that the binding site for a solute is sequentially exposed on one side of the bilayer, then the other

What are pumps that mediate transport

Transporter proteins coupled to an energy source

What is required for active transport

A source of metabolic energy

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 hydrolyses ATP

ATPases

what forms the electrochemical gradient

a solute carrying a net charge, the concentration gradient and the electrical potential difference forms it

What does the electrochemical gradient do

Determines the transport of the solute

What energy do ion pumps such as the sodium-potassium pump use

Energy from the hydrolysis of ATP

What do ion pumps such as sodium-potassium pump use energy for

To establish and maintain ion gradients

When is a membrane potential (an electrical potential difference) created

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

How does the sodium-potassium pump transport ions

against a steep concentration gradient using energy directly from ATP hydrolysis

Where are the sodium ions actively transported

Out of the cell

Where are the potassium ions actively transported

Into the cell

What affinity does the pump have for sodium ions inside the cell

High

What happens for each ATP hydrolysed

Three sodium ions are transported out of the cell and two potassium ions are transported into the cell. This establishes both concentration gradients and an electrical gradient

Where is the sodium-potassium pump 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 happens in intestinal epithelial cells

the sodium potassium pump generates a sodium ion gradient across the plasma membrane

What does the glucose transporter responsible for glucose symport transport

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

How do sodium ions enter the cell

down their concentration gradient

What does the simultaneous transport of glucose do

Pumps glucose into the cell against its concentration gradient