Unit 1 : Cells and Proteins Key Area 3

Question 1

How is the plasma membrane often descibed?

Answer 1

As a fluid mosaic model, they are not static and include a variety of proteins

Question 2

what does molecules of cholesterol help to maintain?

Answer 2

the fluidity of the membrane, and the addition of carbohydrate groups to some proteins to form glycoproteins

Question 3

What is the primary membrane primarily comprised of?

Answer 3

phospholipids, which have hydrophilic phosphate heads and hydrophobic lipid tails

Question 4

How many layers of phospholipids form the phospholipid bilayer

Answer 4

two

Question 5

Proteins that are associated with the membrane can have various functions such as:

Answer 5

Receptors, channels, transporters, pumps and enzymes

Question 6

Where are integral membrane proteins found?

Answer 6

within the phospholipid bilayer

Question 7

some integral membrane proteins are what type of proteins? how far do these span?

Answer 7

transmembrane proteins, they span the entire width of the membrane

Question 8

examples of integral proteins include…

Answer 8

receptors, transporters and channels.

Question 9

Where on the protein are hydrophobic R-groups situated?

Answer 9

on the surface of the protein area within the membrane

Question 10

What do hydrophobic R-groups on the protein allow to happen?

Answer 10

Allows strong hydrophobic interactions to hold the protein in place

Question 11

Where on the protein are hydrophilic R-groups situated?

Answer 11

on the surface of the protein that is exposed to the intracellular or extracellular enviroment

Question 12

what do the hydrophilic R-groups on the protein do?

Answer 12

Interact with peripheral proteins

Question 13

Where are peripheral membrane proteins found?

Answer 13

on the surface of the membrane - can be on the intracellular side or extracellular

Question 14

what do many peripheral membrane proteins interact with?

Answer 14

the surfaces of integral membrane proteins

Question 15

Where do peripheral membrane proteins have Hydrophilic R-groups?

Answer 15

on the surface and are bound to the surface of the membranes

Question 16

How are the hydrophilic R-groups bound to the surface of membranes

Answer 16

by mainly ionic and hydrogren bond interactions

Question 17

Where on a peripheral membrane protein are hydrophobic R-groups?

Answer 17

Hydrophobic r-groups cluster to the inside of the protein

Question 18

Where are integral proteins located?

Answer 18

embedded into the membrane - some can be transmembrane + span the entire width of the membrane

Question 19

How do integral membrane proteins interact with the membrane?

Answer 19

are held in place by strong hydrophobic interactions between the R-groups of the protein and the hydrophilic region of the membrane

Question 20

Where are peripheral proteins located?

Answer 20

located on the surface of the membrane - can be intracellular or extracellular

Question 21

how do peripheral membrane proteins interact with the membrane?

Answer 21

have hydrophobic groups on the surface of the protein and often interact with the surfaces of integral proteins bound to the membrane surface by hydrogen and ionic bonds.

Question 22

What does the phospholipid bilayer act as due to its hydrophobic and hydrophilic regions?

Answer 22

Acts as a barrier to ions, non-charged, polar and hydrophilic molecules - these molecules cannot pass through the membrane without help from membrane proteins

Question 23

What molecules can freely move through the membrane, and by what process?

Answer 23

Simple molecules - such as carbon dioxide and oxygen. These move through the membrane by diffusion.

Question 24

Describe the process of facilitated diffusion?

Answer 24

Facilitated diffusion is the passive transport of substances across the membrane through specific transmembrane proteins such as channels or transporters.

Question 25

Describe facilitated diffusion in terms of energy and concentration gradients?

Answer 25

This process doesn’t require energy, and still moves substances down their concentration gradient.

Question 26

What are channels?

Answer 26

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

Question 27

What are most channel proteins in animals and plant cells?

Answer 27

Highly selective

Question 28

Different cell types might have what type of channels?

Answer 28

Different

Question 29

Channel proteins may be gated and change conformation to allow or prevent what? how do they do this?

Answer 29

To allow/prevent diffusion, they respond to a stimulus which causes them to open or close.

Question 30

How do ligand gated channels change conformation?

Answer 30

In response to the binding of a ligand to the protein channel

Question 31

What does the binding of the ligand to the protein channel allow to happen?

Answer 31

it allows the channel to open and molecules to pass through it.

Question 32

What do voltage gated channels change conformation in response to?

Answer 32

changes in concentration - as ions are charged molecules the voltage changes

Question 33

What does the change in concentration allow the voltage gated channel to do?

Answer 33

To open and molecules to pass through the channel.

Question 34

What do transporter proteins do?

Answer 34

Bind to the specific substance to be transported and undergo a conformational change to transfer the solute across the membrane.

Question 35

What to transporter proteins alternate between? why do they do this?

Answer 35

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 36

How are some molecules and ions transported across the membrane?

Answer 36

by proteins that require and energy source

Question 37

What are these transport proteins that require an energy source called?

Answer 37

Protein pumps - during active transport proteins are moved against their concentration gradient

Question 37

What are ATPases

Answer 37

Pumps coupled with an energy source that hydrolyse (breaks down using water) ATP directly + these catalyse the conversion of ATP into ADP + Pi

Question 37

Name the molecules transported during simple diffusion and how they are transported?

Answer 37

Oxygen and carbon dioxide - they move down a concentration gradient and through the bilayer

Question 37

Whats an example of ATPase?

Answer 37

The sodium potassium pump

Question 38

What molecules are transported during active transport? and how are they transported?

Answer 38

Ions such as sodium and potassium, glucose - against the concentration gradient by transporter pumps or ATPase pumps. Requires a source of energy.

Question 38

Name the molecules transported during facilitated diffusion and how they’re transported?

Answer 38

Glucose and water - down concentration gradient with the help of transporter or channel proteins

Question 38

What do these two gradients combine to form?

Answer 38

the electrochemical gradient

Question 38

Membranes are influenced by two gradients - name them?

Answer 38

Concentration gradient and electrical potential difference (membrane potential)

Question 39

what does the electrochemical gradient determine?

Answer 39

How a charged molecule will be transported and in which direction

Question 40

What is concentration gradient?

Answer 40

Difference in concentration of a solute across the plasma membrane

Question 41

When is membrane potential / electrical potential difference created?

Answer 41

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

Question 42

What does the sodium-potassium pump do?

Answer 42

Transports sodium and potassium ions against a steep concentration gradient using energy directly from ATP hydrolysis

Question 43

The maintenance of the Na/K gradient accounts for what?

Answer 43

a signifigant part of the basal metabolic rate

Question 44

What happens during the sodium potassium pump? what does this establish?

Answer 44

3 sodium ions are pumped out of the cell and 2 potassium ions are pumped into the cell. This establishes and maintains both a concentration and electrical gradient across the membrane - also resulting in an overall negative charge within the cell, increasing polarity.

Question 45

The high concentration of sodium ions outside the cell is of particular importance to what process?

Answer 45

the movement of glucose into the cells of the small intestine.

Question 46

What do symports do?

Answer 46

cotransport two substances at the same time, in the same direction, across a membrane.

Question 47

The glucose symport is an example of what type of transport? why?

Answer 47

Active transport - it’s dependent on the Na+ ion gradient established by the sodium potassium pump.

Question 48

List the steps involved in the cotransport of sodium ions and glucose in the small intestine?

Answer 48

1. gradient of sodium ions is established by the sodium-potassium pump.
2. sodium ions move into the intestinal epithelial cells down their concentration gradient through the glucose symport which transports glucose into the cell at the same time.
3. glucose is transported against the concentration gradient.