Unit 1 Part 3a (Movement Of Molecules Across Membranes)

Question 1

What do regions of hydrophobic R groups allow?

Answer 1

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

Question 2

Describe integral membrane proteins

Answer 2

Interact exclusively with the hydrophobic region of membrane phospholipids
Some are transmembrane proteins

Question 3

Describe peripheral membrane proteins

Answer 3

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.

Question 4

What is the phospholipid bilayer?

Answer 4

A barrier to ions and most uncharged polar molecules

Question 5

Describe facilitated diffusion

Answer 5

Some small molecules (such as oxygen and CO2) can pass through the bilayer by simple diffusion.
However, facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins.

Question 6

Describe channel proteins

Answer 6

Most are highly selective
Some are gated and change conformation to allow/prevent diffusion
Ligand-gated: controlled by the binding of signal molecules
Voltage-gated: controlled by changes in ion concentration

Question 7

Describe transporter proteins

Answer 7

Bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane
Transporters alternate between two conform so that the binding site for a solute is sequentially exposed on one side of the bilayer, then the other.

Question 8

How does active transport work?

Answer 8

Uses pump proteins (transporter proteins coupled to an energy source) that transfer substances across the membrane against their concentration gradient

Question 9

What do ATPases do?

Answer 9

Hydrolyse ATP directly to provide energy for the conformational change required to move substances across the membrane.