Advanced higher biology Unit 1 Key Area 3

fluid mosaic model

model that describes the arrangement and movement of the molecules that make up a cell membrane

Membrane phospholipids

are able to drift about in the plasma membrane

membrane proteins

Embedded proteins that perform specific functions for the cell membrane.

integral membrane proteins

proteins that are at least partially embedded in the plasma membrane

peripheral membrane proteins

proteins associated with but not embedded within the plasma membrane

phospholipid bilayer structure

has a hydrophilic head of the phospholipid to the outside of the bilayer and the hydrophobic tail to the inside of the bilayer.

Integral membrane proteins interact extensively with

the hydrophobic region of membrane phospholipids.

Regions of hydrophobic R groups allow

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

Some integral membrane proteins are

transmembrane proteins

Peripheral membrane proteins have

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

Many peripheral membrane proteins interact with

the surfaces of integral membrane proteins

The phospholipid bilayer is a barrier to

ions and most uncharged polar molecules

What can pass through the bilayer by simple diffusion?

Some small molecules, such as oxygen and carbon dioxide

What is facilitated diffusion?

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

Why do different cell types have different channel and transporter proteins?

To perform specialised functions

Most channel proteins in animal and plant cells are

highly selective

Channels are multi-subunit proteins with the

subunits arranged to form water-filled pores that extend across the membrane.

Some channel proteins are gated and change conformation to

allow or prevent diffusion

Ligand-gated channels are controlled by the

binding of signal molecules

Voltage gated channels are controlled by

changes in ion concentration

Transporter proteins bind to the specific substance to be transported and

undergo a conformational change to transfer the solute across the membrane

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.

Active transport uses

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

Pumps that mediate active transport are

transporter proteins coupled to an energy source.

What is required for active transport?

A source of metabolic energy

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

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

combine to form the electrochemical gradient that determines the transport of the solute

A membrane potential (an electrical potential difference) is

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

Ion pumps, such as the sodium-potassium pump, use energy from

the hydrolysis of ATP to establish and maintain ion gradients

The sodium-potassium pump transports ions

against a steep concentration gradient using energy directly from ATP hydrolysis

The Sodium Potassium pump ____________ transports sodium ions ________ of the cell and ________________________ ions into the cell

actively, out, potassium

The pump has high affinity for ____________ ions inside the cell; ________________occurs; ________________________ by ATP; ____________________ changes; affinity for sodium ions ______________________; sodium ions _________________________ outside of the cell; potassium ions _________ outside the cell; _________________________; conformation changes; _______________________________ ions taken into cell; affinity returns to start

sodium, binding, phosphorylation, conformation, decreases, released, bind, dephosphorylation, potassium

For each ATP hydrolysed, ______________ sodium ions are transported out of the cell and _____________potassium ions are transported into the cell.

3, 2

3 sodium ions out and 2 postassiunm ions in establishes

both concentration gradients and an electrical gradient.

Where is the sodium potassium pump found?

most animal cells

What does the sodium potassium pump account for in animal cells?

a high proportion of the basal metabolic rate in many organisms

In the small intestine, the sodium gradient created by the sodium-potassium pump

drives the active transport of glucose

In intestinal epithelial cells the sodium potassium pump generates

a sodium ion gradient across the plasma membrane.

The glucose transporter responsible for this glucose symport transports

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

Sodium ions enter the cell down their concentration gradient; the simultaneous transport of glucose pumps

glucose into the cell against its concentration gradient.