4. Lipids and membranes

Question 1

What are the three types of lipids?

Answer 1

Sterols
Fats, oils and waxes
Phospholipids

Question 2

What are lipids?

Answer 2

Hydrocarbons that are insoluble in water because of their many non polar covalent bonds

Question 3

What do fats and oils do?

Answer 3

Energy storage and insulation

Question 4

What do waxes do?

Answer 4

Waxes are for protective coatings which repel water and prevent excessive evaporation of water

Question 5

List the overall functions of lipids?

Answer 5

• Fats and oils for energy storage and insulation
• Waxes for protective coatings
• Chemical messengers
• Structural components of membranes

Question 6

What is the difference between fats and oils?

Answer 6

Triglycerides that are solid at room temperature are called fats and those that are liquid at room temperature are called oils

Question 7

What are the two building blocks of triglycerides?

Answer 7

Fatty acids and glycerol

Question 8

What is the difference between saturated and unsaturated fatty acids?

Answer 8

A saturated fatty acid has a hydrocarbon chain with no double bonds. These molecules can pack together tightly. The hydrocar- bon chain of an unsaturated fatty acid has one or more double bonds that bend the chain, preventing close packing.

Question 9

Explain the structure of a phospholipid

Answer 9

A phospholipid has a hydrophobic hydrocarbon “tail” and a hydrophilic phosphate “head”; that is, it is amphipathic. In water, the interactions of the tails and heads of phospholipids generate a phospholipid bilayer.

Question 10

How are the phospholipid molecule arranged in the cell?

Answer 10

The heads are directed outward where they interact with the surrounding water. TH details are packed together in the interior of the bilayer, away from water

Question 11

What are peripheral membrane proteins?

Answer 11

These lack exposed hydrophobic groups and are not embedded in the bilayer. Instead they have polar regions that interact with exposed parts of integral membrane proteins or with polar heads of phospholipid molecules

Question 12

What are integral membrane proteins?

Answer 12

They are embedded in the phospholipid bilayer and have both hydrophilic and hydrophobic regions

Question 13

What is a transmembrane protein?

Answer 13

An integral protein that extends all the way through the phospholipid bilayer and protrudes on both sides

Question 14

What is a glycolipid?

Answer 14

A carbohydrate covalently bonded to a lipid. The carb may serve as a recognition signal for interactions between cells.

Question 15

What is a glycoprotein?

Answer 15

One or more short carbohydrate chains covalently bonded to a protein.Function in cell recognition and adhesion.

Question 16

What are all the ways in which molecules enter cells?

Answer 16

Diffusion, facilitated diffusion, active transport, pinocytosis and phagocytosis

Question 17

What is the definition of osmosis?

Answer 17

The movement of water through a differentially permeable membrane for a region of high water concentration to a region of low water concentration

Question 18

Where does the energy for passive transport of a substance come from?

Answer 18

The difference between its concentration one one side of the membrane and its concentration on the other

Question 19

What is osmotic potential?

Answer 19

The pressure required to prevent the movement of water in to a solution if the solution is separated from that water by a selectively permeable membrane.

Question 20

What is the osmotic potential like if there is a greater solute concentration?

Answer 20

A more negative potential, so water moves from higher to lower (more negative) potential

Question 21

Hypertonic solution

Answer 21

Hypertonic refers to a solution with a higher concentration of solutes compared to the solute concentration inside a cell. There will be a net movement of water out of the cell into surrounding solution

Question 22

Hypotonic solution

Answer 22

Hypotonic refers to a solution with a lower concentration of solutes compared to the solute concentration inside a cell. There will be a net movement of water into the cell from surrounding cells

Question 23

Isotonic solution

Answer 23

When the surrounding fluid is of equal concentration to the solution inside the cell it is said to be isotonic. There will be no net movements of water (water will diffuse equally in both directions).

Question 24

What happens to plant cells in a hypotonic solution?

Answer 24

Plant cells contain a freely permeable cell wall and a large vacuole which contain sap rich in solutes a solution of high concentration.
If the external concentration of solute molecules is hypotonic than inside the vacuole water will move freely into the vacuole via osmosis from adjacent cells. The vacuole swells and pushes the cell membrane against the cell wall making the cell turgid through osmotic pressure.

Question 25

What happens to plant cells in a hypertonic solution?

Answer 25

The the concentration of solutes in the external environment is greater than the vacuole water will move out via osmosis.
This reduces the size of the vacuole the plasma membrane moves away from the cell wall and the cell becomes flaccid through plasmolysis.

Question 26

What happens to animal cells place in hypotonic solution?

Answer 26

Animal cells such as red blood cells placed in a hypotonic solution will burst. Called haemolysis.

Question 27

What happens to animal cells placed in a hypertonic solution?

Answer 27

In a hypertonic solution, red blood cells will shrink and crinkle. This is called crenation.

Question 28

Channel proteins

Answer 28

integral membrane proteins that form channels across the membrane through which certain sub- stances can pass.

Question 29

Carrier proteins

Answer 29

bind substances and speed up their diffu- sion through the phospholipid bilayer

Question 30

What is a gated channel

Answer 30

A channel protein that opens when the stimulus causes a change in the 3D shape of the channel.

Question 31

What is a uniporter

Answer 31

A membrane protein that moves a single substance in one direction

Question 32

What is a symporter?

Answer 32

A membrane protein moves two substances in the same direction.

Question 33

What is an anti porter?

Answer 33

A membrane proteins that moves two substances in opposite direction, one in the cell (or organelle) and the other out of the cell (or organelle)

Question 34

What are the two difference types of active transport?

Answer 34

Primary active transport involves the direct hydrolysis of ATP which provides the energy required for transport.
Secondary active transport does not use ATP directly. Instead an ion concentration graded established by primary (ATP driven) active transport supplies the energy.

Question 35

What are the steps in the sodium potassium pump?

Answer 35

1. 3 sodium and 1 ATP bind to the protein pump.
2. Hydrolysis of ATP phosphorylates the pump protein and changes its shape.
3. The shape change releases Na= outside the cell and enables potassium to bind to the pump
4. Release of Pi returns the pump to its original shape, releasing potassium to the cell’s interior and once again exposing sodium binding sites. The cycle repeats.

Question 36

What is the process of endocytosis?

Answer 36

The plasma membrane surrounds a part of the exterior environment and buds off as a vesicle.

Question 37

What is the process of exocytosis?

Answer 37

A vesicle fuses with the plasma membrane. The contents of the vesicle are released, and its membrane becomes part of the plasma membrane.