UNIT 1 - KA3

Question 1

What is the function of the plasma membrane

Answer 1

The plasma membrane surrounds cells and controls entry and exit of materials

Question 2

What is the fluid mosaic model

Answer 2

The fluid mosaic model describes the structure of the plasma membrane

Question 3

What is the plasma membrane composed of

Answer 3

• phospholipids
• proteins

Question 4

Phospholipid head

Answer 4

The head region of a phospholipid molecule is charged therefore hydrophilic (attracted to water)

Question 5

Phospholipid tail

Answer 5

The tail region is uncharged and non polar therefore hydrophobic (repelled by water)

Question 6

What gives the membrane its fluid quality

Answer 6

The phospholipids are constantly changing position this gives the membrane its fluid quality.

Question 7

How are phospholipids arranged in the plasma membrane

Answer 7

The phospholipids are arranged into a bilayer in the plasma membrane

Question 8

What does the hydrophobic centre of the phospholipid bilayer allow

Answer 8

The hydrophobic centre of the phospholipid bilayer allows oxygen and carbon dioxide to pass through directly by simple diffusion because they are small non polar molecules

Question 9

How must many molecules pass through

Answer 9

Many molecules therefore must pass across the membrane with the help of proteins

Question 10

What is the cell membrane embedded with

Answer 10

The cell membrane is embedded with protein which form a patchy mosaic

Question 11

What are some functions of membrane proteins (5)

Answer 11

• active transport proteins
• Chanel forming proteins
• enzymes
• receptors
• proteins for the cell cytoskeleton

Question 12

What are the two types of protein in the plasma membrane

Answer 12

1- integral protein
2- peripheral protein

Question 13

Where are integral proteins found

Answer 13

These are proteins found within the membrane

Question 14

What are transmembrane integral proteins

Answer 14

Some integral proteins are transmembrane, this means that they span the entire width of the membrane

Question 15

What are examples of transmembranes

Answer 15

• channels
• transporters
• many receptors

Question 16

What are phospholipid bilayer integral proteins held in place by

Answer 16

They are held in place by strong hydrophobic interactions with the lipid tails

Question 17

What do regions of strong hydrophobic R groups allow

Answer 17

Regions of hydrophobic R groups allow strong hydrophobic interactions that hold integral proteins within the phospholipid bilayer

Question 18

Where are peripheral proteins found

Answer 18

These proteins are found on the surface of the membrane

Question 19

What kind of R groups predominate on the surface of peripheral membrane proteins

Answer 19

Hydrophilic R groups on their surface and are bound to the surface of membranes

Question 20

What kind of interactions bind peripheral membrane proteins to the surface of the membrane / integral proteins

Answer 20

Mainly by weak ionic and hydrogen bond interactions

Question 21

Summary of integral and peripheral

Answer 21

Integral - within membrane - hydrophobic - hydrophobic interactions
Peripheral - surface of membrane - hydrophilic - weak ionic and hydrogen bonds

Question 22

What is the phospholipid bilayer a barrier to

Answer 22

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

Question 23

What is facilitated diffusion

Answer 23

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

Question 24

What do different cells have to perform specialised functions

Answer 24

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

Question 25

What are the types of proteins involved in transporting substances

Answer 25

1) Channel - a) ligand gated b) voltage gated 2) transporter proteins 3) protein pumps

Question 26

What are most channel proteins in animal and plant cells

Answer 26

Most channel proteins in animal and plant cells are highly selective

Question 27

What are channels

Answer 27

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

Question 28

Why are some channel proteins gated and change conformation

Answer 28

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

Question 29

What are ligand gated channels controlled by

Answer 29

Ligand-gated channels are controlled by the binding of signal molecules

Question 30

What are voltage gated channels controlled by

Answer 30

voltage gated channels are controlled by changes in ion concentration

Question 31

What is a key point about gated channel proteins

Answer 31

Whilst gated-channel proteins undergo conformational change to open or close the channel. movement of molecules across the channel is dependant on the concentration gradient and the molecule is not transported across the membrane by the action of proteins

Question 32

Transporter proteins

Answer 32

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

Question 33

What do transporters alternate between

Answer 33

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 34

How does transporter protein differ from channel proteins

Answer 34

It differs from transport through channel proteins in that it involves a conformational change in the protein. The proteins actually pass the ions or molecules across the membrane rather than just providing a route through

Question 35

What does active transport use

Answer 35

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

Question 36

What are pumps that mediate active transport

Answer 36

Pumps that mediate active transport are transporter proteins coupled to an energy source.

Question 37

A source of what is required for active transport

Answer 37

A source of metabolic energy is required for active transport

Question 38

What do some active transport proteins that hydrolyse atp do

Answer 38

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

Question 39

What do ATPases hydrolyse

Answer 39

ATPases hydrolyse ATP

Question 40

Describe what is meant by the term electrochemical gradient

Answer 40

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 41

What is a membrane potential (electrical potential difference)

Answer 41

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 42

How do ion pumps establish and maintain ion gradients

Answer 42

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

Question 43

What does the sodium-potassium pump transport

Answer 43

The sodium-potassium pump (also known as Na/K-ATPase) transports ions against a steep concentration gradient using energy directly from ATP hydrolysis

Question 44

Describe the action of the sodium - potassium pump include number of ions and directions

Answer 44

Three sodium ions are pumped out of the cell for every two potassium ions that are pumped into the cell

Question 45

2-K-IN

Answer 45

Two potassium ions pumped into the cell three sodium pumped out

Question 46

a

Answer 46

The pump has high affinity for sodium ions inside the cell therefore binding occurs

Question 47

b

Answer 47

The pump hydrolyses ATP and phosphate attaches to it. Phosphorylation by ATP causes the conformation of the protein to change

Question 48

c

Answer 48

The affinity for sodium ions decreases resulting in sodium being released outside the cell

Question 49

d

Answer 49

The pump has high affinity for potassium ions outside the cell therefore binding occurs

Question 50

f

Answer 50

Potassium ions are taken into the cell and the affinity returns to the start

Question 51

Where is the sodium-potassium found

Answer 51

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

Question 52

What drives the active transport of glucose in the small intestine

Answer 52

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

Question 53

What does the sodium potassium pump generate in intestinal epithelial cells

Answer 53

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

Question 54

What is the glucose transporter responsible for the active transport of glucose in the small intestine

Answer 54

The glucose transporter responsible for the active transport of glucose in the small intestine is a glucose symport protein

Question 55

What is a symporter protein

Answer 55

A symporter transports molecules across the plasma membrane at the same time and in the same direction

Question 56

Describe the action of the glucose symport protein

Answer 56

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