Membrane Structure & Function

Question 1

How thin are membranes?

Answer 1

8nm.

Question 2

What are membranes made of?

Answer 2

Lipids, proteins and sometimes carbohydrates.

Question 3

What do plasma membranes do?

Answer 3

Separate cells from the environment and allow them to respond to the environment.

Question 4

What do internal membranes do?

Answer 4

Segregate functional compartments within cells and create organelles.

Question 5

What to membranes allow for?

Answer 5

Controlled transport of materials across permeability barriers.

Question 6

What are the most abundant membrane lipids?

Answer 6

Phospholipids.

Question 7

What are the two characteristics of phospholipids?

Answer 7

They have both hydrophilic and hydrophobic regions.

Question 8

What does amphipathic mean?

Answer 8

Its both hydrophobic and hydrophilic.

Question 9

What do phospholipids for together?

Answer 9

A fluid mosaic lipid bilayer.

Question 10

How often do phospholipids form membranes?

Answer 10

Spontaneously.

Question 11

What do the amphipathic properties of phospholipids lead to?

Answer 11

The spontaneous formation of bilayers.

Question 12

Hydrophobic tails contact…

Answer 12

Each other.

Question 13

Hydrophilic heads point in…

Answer 13

Opposite directions.

Question 14

What do the phospholipids contact on each side of the membrane?

Answer 14

Aqueous Solutions.

Question 15

Are the components of the fluid mosaic model static?

Answer 15

No, everything moves about and is capable of lateral diffusion.

Question 16

Where can proteins be found within the mosaic?

Answer 16

Spanning the whole membrane or just on either of the sides.

Question 17

What is freeze-thaw?

Answer 17

An EM technique that rapidly freezes cells and then they are slip along the middle.

Question 18

Lateral movement of phospholipids is…

Answer 18

Very frequent.

Question 19

Flip-flop movement of phospholipids is…

Answer 19

Exceedingly rare.

Question 20

When do phospholipids flip-flop?

Answer 20

When carried by a protein.

Question 21

What influences phospholipid movement?

Answer 21

The composition of bilayers.

Question 22

What prevents tight molecular packing?

Answer 22

High levels of fatty acid tails.

Question 23

What increases phospholipid movement and membrane fluidity?

Answer 23

The lack of tight molecular packing due to the high level of fatty acid tails.

Question 24

What will make a membrane more solid?

Answer 24

Cholesterol at physiological temperatures.

Question 25

Where are phospholipids made?

Answer 25

Smooth ER.

Question 26

What are the name of the proteins that flip-flop phospholipids?

Answer 26

Flippases.

Question 27

What targets ribosomes to ER membrane?

Answer 27

The signal sequences of membrane proteins.

Question 28

What is the protein pore that ribosomes dock on during membrane synthesis called?

Answer 28

Translocon.

Question 29

During membrane synthesis, what happens after the ribosome has docked?

Answer 29

Protein synthesis continues and the protein is extruded into the ER lumen or a membrane.

Question 30

What determines the specific functions of phospholipids?

Answer 30

Proteins.

Question 31

Which proteins span the membrane?

Answer 31

Integral membrane proteins.

Question 32

Which proteins can form pores?

Answer 32

Ones with amphipathic alpha-helices.

Question 33

What can protein functions be categorised into?

Answer 33

Transport, enzymatic activity, signal transduction, cell-cell/cell-solute recognition, intercellular connections and attachments to the cytoskeleton or ECM.

Question 34

In channels, materials can only pass which way with out energy?

Answer 34

Down the concentration gradient.

Question 35

To move a solute up a concentration gradient requires?

Answer 35

Energy in the for of ATP.

Question 36

What does a pore allow for?

Answer 36

Movement of material from one side to the other.

Question 37

Related enzymes can often be associated?

Answer 37

Together.

Question 38

In some cases, enzymes can be linked to proteins that...

Answer 38

Are involved in signal transduction.

Question 39

Binding of molecules activates what?

Answer 39

Signal transduction pathways.

Question 40

What happens when a signalling molecule binds to a receptor?

Answer 40

It changes its shape.

Question 41

What doe glycosylated molecules act as?

Answer 41

Cellular identity tags.

Question 42

Some viruses can entre cells by binding to?

Answer 42

Surface glycoproteins.

Question 43

How do viruses initially infect cells?

Answer 43

By binding to the plasma membrane.

Question 44

HIV invade CD4+T cells by?

Answer 44

Binding to CD4 and CCR5 proteins.

Question 45

What can prevent HIV and how to anti-HIV drugs use this?

Answer 45

A lack of CCR5 proteins prevents infection and anti-HIV drugs try to block these proteins.

Question 46

How do tight junctions work?

Answer 46

They prevent the movement of substances through gaps between the cells.

Question 47

Which type of junctions bind cells together?

Answer 47

Desmosomes.

Question 48

What do gap junctions permit?

Answer 48

Intercellular cytoplasmic continuity.

Question 49

What interaction is important in giving cells shape?

Answer 49

Interactions of cytoskeleton with membrane proteins.

Question 50

What do integrins do?

Answer 50

Integrate extracellular and intracellular environments.

Question 51

The orientation of proteins is determined by?

Answer 51

Amino acid sequences.

Question 52

Biological membranes are important barriers between what?

Answer 52

Different environments.

Question 53

Part of the membrane's barrier function is to do with what?

Answer 53

The hydrophobic nature of the inner membrane.

Question 54

How can hydrophilic substances such as sugars or ions cross the membrane?

Answer 54

They need to be carried by something.

Question 55

What is passive transport?

Answer 55

Movement of solutes across a membrane with no energy input.

Question 56

How is passive transport driven?

Answer 56

Using concentration gradients.

Question 57

What is active transport?

Answer 57

Transport that moves solutes against their concentration gradients with energy from ATP.

Question 58

What is diffusion?

Answer 58

Passive transport aided by specific proteins to move solutes down their concentration gradients.

Question 59

If a membrane does not allow the movement of a solute, the solute can still?

Answer 59

Influence solution behaviour.

Question 60

Tonicity is defined as what?

Answer 60

As the ability of a solution to make a cell gain or lose water.

Question 61

What is a channel?

Answer 61

A protein that passes through the membrane which has a hole in it to allow the passage of materials.

Question 62

How to gated channels open and close?

Answer 62

In response to changes in membrane potential.

Question 63

How to gated channels open and close in the nervous system?

Answer 63

In response to neurotransmitters.

Question 64

Many molecules are transported across membrane by what?

Answer 64

Carriers.

Question 65

When the solute binds on one side of the channel, what is created?

Answer 65

A conformational change.

Question 66

What does the conformational change allow the solute to do?

Answer 66

Be taken across the membrane and released.

Question 67

All proteins in active transports are?

Answer 67

Carriers and not channels.

Question 68

In animal cells, sodium is...

Answer 68

High outside and low inside.

Question 69

In animal cells, potassium is...

Answer 69

Low inside and high outside.

Question 70

In cystic fibrosis thick mucus clogs up in certain areas due to what?

Answer 70

A defective Cl pump.

Question 71

What makes up an electrochemical gradient?

Answer 71

The combination of concentration and electrical gradients.

Question 72

What are the main generators of membrane potentials in plants, fungi and bacteria?

Answer 72

Proton pumps.

Question 73

What is used to import sucrose in plants?

Answer 73

H+ pumps.

Question 74

What is transported packed into membrane vesicles?

Answer 74

Most large molecules such as proteins or polysaccharides,.

Question 75

What happens in exocytosis?

Answer 75

Material is realised from the cell.

Question 76

What happens in endocytosis?

Answer 76

Material is taken up into cells.

Question 77

How many types of endocytosis are there?

Answer 77

3.

Question 78

What is familial hypercholesterolemia?

Answer 78

A defect of receptor-mediated endocytosis.