Unit 1: Key Area 3

Question 1

Describe the structure of the membrane

Answer 1

Membranes contain 2 molecules: proteins and phospholipids
Phospholipids have a hydrophilic head and hydrophobic tail
There are two types of membrane proteins:
Integral and peripheral

Question 2

Describe the structure of integral proteins

Answer 2

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

Question 3

Describe peripheral proteins

Answer 3

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

Question 4

What do many peripheral membrane proteins interact with

Answer 4

Many peripheral membrane proteins interact with the surfaces of integral membrane proteins

Question 5

What do integral membrane proteins interact with

Answer 5

Integral membrane proteins interact excessively with the hydrophobic region of membrane phospholipids

Question 6

What is the phosphate bilayer

Answer 6

The phosphate bilayer is a barrier to ions and most uncharged polar molecules

Question 7

What passed through the bilayer by simple diffusion

Answer 7

Some small molecules such as oxygen and carbon dioxide, pass through the bilayer by simple diffusion

Question 8

What is facilitated diffusion

Answer 8

Facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins

Question 9

To preform specialized functions, different cell types have different _______ and _________ _________.
Most channel proteins in plant and animal cells are _____ ________

Answer 9

To preform specialized functions, different cell types have different channel and transporter proteins
Most channel proteins in plant and animal cells are highly selective.

Question 10

What are channels

Answer 10

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

Question 11

Some channel proteins are _____ and change ______ to allow or prevent ______.

Answer 11

Some channel proteins are gated and change conformation to allow or prevent diffusion

Question 12

What are ligand gated channels and voltage gated channels controlled by

Answer 12

Ligand gated channels are controlled by the binding of signal molecules, and voltage gated channels are controlled by changes in ion concentration

Question 13

What do transporter proteins bind to

Answer 13

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

Question 14

Describe active transport

Answer 14

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.

A source of metabolic energy is required for active transport

Some active transport proteins hydrolyse ATP directly to provide the energy for the conformational change required to move substances across the membrane
ATPases hydrolyse ATP.

Question 15

What is a membrane potential and how is it created

Answer 15

A membrane potential (an electrical potential difference) is created when there is a difference in electrical charge on the two sides of the membrane

Question 16

How do Ion pumps determine the ion gradient

Answer 16

Ion pumps, such as the sodium-potassium pump, use energy from the hydrolysis of ATP to establish and maintain ion gradients

Question 17

Describe ion pumps and give an example

Answer 17

The sodium-potassium pump transports ions
against a steep concentration gradient using
energy directly from ATP hydrolysis

Question 18

Describe the sodium potassium pump and what it does

Answer 18

The sodium-potassium pump transports ions against a steep concentration gradient using energy directly from ATP hydrolysis
It actively transports sodium ions out of the cell and potassium ions into the cell
The pump has high affinity for sodium ions inside the cell; binding occurs; phosphorylation by ATP; conformation changes; affinity for sodium ions decreases; sodium ions released outside of the cell; potassium ions bind outside the cell; dephosphorylation; conformation changes; potassium ions taken into cell; affinity returns to start
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.

Question 19

In what cell type are sodium potassium pumps found and what does it account for in organisms

Answer 19

The sodium-potassium pump is found in most animal cells, accounting for a high proportion of the basal metabolic rate in many organisms

Question 20

Describe the role of sodium potassium pumps in the small intestine

Answer 20

In the small intestine, the sodium gradient
created by the sodium-potassium pump
drives the active transport of glucose
In intestinal epithelial cells the sodiumpotassium 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.