1.3

Question 1

Describe the structure of the phospholipid bilayer of the plasma membrane

Answer 1

The cell membrane consists of two adjacent layers of phospholipids, which form a bilayer.

The fatty acid tails of phospholipids are exposed to the interior of the membrane and the phosphate heads are exposed to the exterior aqueous side.

Question 2

What hold integral membrane proteins in the phospholipid bilayer

Answer 2

Regions of hydrophobic R groups allow strong, hydrophobic interactions that holds integral membrane proteins within the phospholipid bilayer.

The integral membrane proteins interact extensively with the hydrophobic region of membrane phospholipids.

Question 3

Link between integral and transmembrane proteins

Answer 3

Some integral membrane proteins are transmembrane proteins

Question 4

Describe peripheral membrane proteins

Answer 4

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

(Not embedded)

Question 5

What do many peripheral membrane proteins interact with?

Answer 5

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

Question 6

Functions of peripheral membrane proteins

Answer 6

Peripheral/extrinsic proteins have fewer hydrophobic R-groups interacting with the phospholipids and are responsible for cell-cell interactions

Question 7

What does the phospholipid bilayer act as?

Answer 7

The phospholipid bilayer acts as a barrier to ions, and most uncharged polar structures.

Question 8

What transports large, charged and hydrophilic molecules across the cell membranes?

Answer 8

Transmembrane proteins - This process is called facilitated diffusion

Question 9

What can transmembrane proteins act as

Answer 9

Transmembrane proteins can act as channels or transporters

Question 10

How do you small molecules such as oxygen and carbon dioxide passed through the phospholipid bilayer

Answer 10

Diffusion

Question 11

Describe, facilitated diffusion

Answer 11

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

Question 12

What do different cells have to perform specialised functions

Answer 12

To perform, specialised functions, different cell types have different channel and transporter proteins

Question 13

Describe channels

Answer 13

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

Question 14

Describe how transport occurs across channels

Answer 14

Transport across the channels is always passive and specific to one type of ion or molecule (facilitated diffusion). Solute passage can be gated or ungated.

Question 15

Describe Passage through an ungated channel protein

Answer 15

Passage through an ungated channel protein does not require a change to the conformation of the protein.

Movement of molecules as passive, and is specific to the ions or molecules that are being allowed to pass across.

Question 16

Describe passage through a gated protein channel

Answer 16

Gated protein channels, change confirmation to allow or prevent diffusion.

Gated channels respond to a stimulus which causes them to open or close. The stimulus may be chemical (ligand gated) or electrical (voltage gated).

Question 17

Describe how ligand gated channels and voltage gated channels are controlled

Answer 17

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

Question 18

Describe how transporter proteins work

Answer 18

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

Question 19

What are the types of transport?

Answer 19

Facilitated diffusion or active

Question 20

What does the conformational change an active transport require?

Answer 20

Energy from the hydrolysis of ATP by ATPases

Question 21

Describe how active transport works

Answer 21

Active transport uses pump proteins that transfer substances across the membrane against a concentration gradient.

Question 22

Explain pumps involved in active transport

Answer 22

Pumps that mediate active transport transport of protein coupled to an energy source

Question 23

What is required for active transport?

Answer 23

A source of metabolic energy is required for active transport

Question 24

How is an electrochemical gradient formed

Answer 24

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.

Question 25

How is a membrane potential created?

Answer 25

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 26

What is the sodium potassium pump?

Answer 26

Na/K-ATPase (sodium potassium pump) it’s an enzyme found in the plasma membrane of all animal cells.

Question 27

How do ion pumps establish and maintain ion gradients?

Answer 27

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

Question 28

Describe how the sodium potassium pump works

Answer 28

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 (against their concentration gradient).

Question 29

Describe the process of the sodium potassium pump

Answer 29

1. The pump has high affinity for Na+ ions inside the cell and 3 Na+ ions bind to the binding sites.
2. Transporter proteins hydrolyses ATP to ADP + Pi
3. Protein attaches to Pi (phosphorylation) causing a confirmational change to the protein. Protein new has low affinity for Na+ ions which are released outside of the cell.
4. New confirmation has a high affinity for K+ ions, and 2 K+ ions bind to the surface of the protein outside of the cell.
5. This triggers dephosphorylation (release of phosphate group) of protein; protein revert to original confirmation with binding sites exposed to the interior of the cell.
6. Protein now has low affinity for K+ ions inside the cell and are released into the cell. Protein has high affinity for Na+ ions which bind to the protein. The cycle begins again.

Question 30

How is a concentration gradient and electrical gradient established in sodium potassium pumps?

Answer 30

For each ATP hydrolysed, 3 Na+ ions are transported out of the cell and 2 K+ ions are transported into the cell. This establishes both concentration gradient and an electrical gradient.

Question 31

Where is the sodium potassium pump found?

Answer 31

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

Question 32

What drives active transport of glucose in the small intestine?

Answer 32

In the small intestine, the sodium gradient created by the sodium potassium pump, drives the active transport of glucose.

Question 33

What does the sodium potassium pump generate in intestinal epithelial cells

Answer 33

In intestinal epithelial cells the sodium potassium pump generates a sodium ion gradient across the plasma membrane

Question 34

The transport of sodium ions and glucose in the small intestine

Answer 34

The glucose transporter responsible for this glucose symport transports sodium ions and glucose at the same time, and in the same direction

Question 35

How does sodium ions enter the intestinal epithelial cells?

Answer 35

Sodium ions enter the cell down its concentration gradient; the simultaneous transport of glucose pumps glucose into the cell against its concentration gradient