2.5 Biological Membranes

Question 1

What are the roles of a membrane?

Answer 1

Partially permeable barrier between the cell and the environment, within organelles and between organelles and the cytoplasm, site of chemical reactions, site of cell signalling.

Question 2

What is the fluid mosaic model comprised of?

Answer 2

Phospholipid bilayer and intrinsic and extrinsic proteins.

Question 3

What is the phospholipid bilayer comprised of?

Answer 3

Hydrophilic heads facing out, hydrophobic heads facing in, cholesterol.

Question 4

What are examples of intrinsic proteins?

Answer 4

Channel proteins and carrier proteins.

Question 5

What are examples of extrinsic proteins?

Answer 5

Glycolipids and glycoproteins.

Question 6

What is the role of cholesterol in the phospholipid bilayer?

Answer 6

To control the fluidity and stability of the plasma membrane.

Question 7

What is the order of components and bonds of a phospholipid from head to tail?

Answer 7

Phosphate group, phosphoester bond, glycerol, ester bond, fatty acid.

Question 8

What is a glycoprotein?

Answer 8

An extrinsic protein attached to a carbohydrate chain.

Question 9

What is a glycolipid?

Answer 9

A lipid attached to a carbohydrate chain.

Question 10

What are the functions of intrinsic proteins?

Answer 10

To act as channels and gates to let substances through the cell surface membrane.

Question 11

What are two features of the hydrophilic heads of the phospholipid bilayer?

Answer 11

They are polar and water soluble.

Question 12

What are two features of the hydrophobic tails of the phospholipid bilayer?

Answer 12

They are nonpolar and water insoluble.

Question 13

What is the role of the phospholipid bilayer?

Answer 13

To act as a barrier but let small molecules diffuse across.

Question 14

How fast do small polar and nonpolar molecules diffuse across the phospholipid bilayer?

Answer 14

Polar = rapidly, nonpolar = much more slowly.

Question 15

What substances are unlikely to diffuse across a membrane?

Answer 15

Large molecules and charged particles.

Question 16

What are the roles of glycoproteins?

Answer 16

Have antigens for cell recognition, cell signalling, receptors for hormones, cell adhesion.

Question 17

What are the four main types of proteins present in the cell surface membrane?

Answer 17

Channel proteins, carrier proteins, enzymes, receptors.

Question 18

What are the roles of glycolipids?

Answer 18

Stability and cell recognition.

Question 19

How does cholesterol perform its function?

Answer 19

It binds to hydrophobic tails of phospholipids, packing them more closely together.

Question 20

What is the definition of cell signalling?

Answer 20

Communication between cells, a molecule released by one cell attaches to another cell, cell recognition.

Question 21

What are the two ways of a signal molecule acting?

Answer 21

A signal molecule enters the cell or the binding of a signal molecule causes a change inside the cell.

Question 22

What are the three domains of membrane-bound receptors?

Answer 22

Extracellular domain, transmembrane domain and intracellular domain.

Question 23

How do hormones work?

Answer 23

They bind to receptors in the cell membranes and trigger a response in the target cell.

Question 24

What do lipid-based hormones do?

Answer 24

Diffuse through the plasma membrane.

Question 25

What do protein-based hormones do?

Answer 25

Bind to receptors and trigger secondary messengers.

Question 26

What is glucagon?

Answer 26

A hormone released to control blood sugar.

Question 27

Why are membrane receptors the target of many medicinal drugs?

Answer 27

They are involved in many diseases.

Question 28

What are agonists?

Answer 28

Drugs that bind to receptors and mimic the body’s normal messengers.

Question 29

What are antagonists?

Answer 29

Drugs that bind to receptors and block the body’s normal messengers.

Question 30

What is the definition of diffusion?

Answer 30

The net movement of particles down a concentration gradient, passive so now energy is involved.

Question 31

What is the rate of diffusion determined by?

Answer 31

Size of concentration gradient, thickness of exchange surface, distance between two areas, size of molecules, temperature.

Question 32

How do you calculate the surface area and volume of a sphere?

Answer 32

SA = 4πr², V = 4/3πr³.

Question 33

When does simple diffusion occur?

Answer 33

If the molecules involved can pass freely through a membrane, they have to be small and uncharged, if not, facilitated diffusion is required.

Question 34

What does facilitated diffusion transfer?

Answer 34

Water soluble molecules, charged particles and large molecules (e.g. amino acids or glucose).

Question 35

How do substances diffuse using facilitated diffusion?

Answer 35

They move down a concentration gradient through carrier proteins or channel proteins (passive like simple diffusion).

Question 36

How do carrier proteins work?

Answer 36

Molecules attach, carrier changes shape, releases molecules on other side.

Question 37

How do channel proteins work?

Answer 37

Form pores in the membrane, charged particles move down a concentration gradient, only open in response to presence of a molecule.

Question 38

What is the definition of osmosis?

Answer 38

The net movement of water across a partially permeable membrane down a water potential gradient (less negative to more negative.

Question 39

What is the unit of water potential?

Answer 39

kPa (kilopascals).

Question 40

What is the definition of water potential?

Answer 40

The tendency of water molecules in a system to move.

Question 41

What is the water potential of pure water?

Answer 41

0 kPa (the highest possible water potential).

Question 42

What happens to a cell in a hypertonic environment in plants?

Answer 42

More water moves outside the cell than into the cell so it will become plasmolyzed.

Question 43

What happens to a cell in an isotonic environment in plants?

Answer 43

The same volume of water outside the cell is the same as in the cell so it is flaccid.

Question 44

What happens to a cell in a hypotonic environment in plants?

Answer 44

Less water moves outside the cell than into the cell so it will become turgid.

Question 45

What happens to a cell in a hypertonic environment in animals?

Answer 45

Cells have higher water potential than solution, net movement of water out, shrivelled cells (crenation).

Question 46

What happens to a cell in an isotonic environment in animals?

Answer 46

Water potential equal between cells and solution, no net movement water, normal cells.

Question 47

What happens to a cell in a hypotonic environment in animals?

Answer 47

Cells have lower water potential than solution, net movement of water in, cells swell, may burst (lysis).

Question 48

What is the definition of active transport?

Answer 48

Carrier proteins moving molecules across a membrane against the concentration gradient, which requires energy (not passive).

Question 49

What are examples of active transport?

Answer 49

Uptake of glucose and amino acids in the small intestine, the absorption of mineral ions by root hair cells, hydrogen ions uptake by companion cells, exchange of sodium and potassium ions in neurons and muscle cells.

Question 50

What is the process pf active transport?

Answer 50

Molecule attaches to carrier protein, ATP molecule provides energy to go against gradient, carrier changes shape and molecule is released on the other side.

Question 51

What do cells carrying out active transport need?

Answer 51

Lots of mitochondria to produce enough ATP.

Question 52

What is bulk transport?

Answer 52

Used to move extremely large substances across a cell membrane, the two types are exocytosis and endocytosis.

Question 53

What is the definition of endocytosis?

Answer 53

The bulk transport of material into the cell.

Question 54

What is the definition of exocytosis?

Answer 54

The bulk transport of material out of the cell.