3A: Introduction to the plasma membrane

Question 1

The plasma membranes of cells do what?

Answer 1

• control the movement of substances/toxins in and out of the cells
• protects cell

Question 2

Phospholipids have a ______ phosphate head that orientates towards the watery extracellular and intracellular fluid. They are also made up of two ______ fatty acid tails that comprise the interior of the plasma membrane.

Answer 2

polar/hydrophilic; nonpolar/hydrophobic

Question 3

What is a glycolipid, where is it found, and what does it do?

Answer 3

Glycolipids are lipids with a carbohydrate attached.
(RS)
- maintain stability of the cell membrane
- facilitate cellular recognition

Question 4

What is cholesterol, where is it found, and what does it do?

Answer 4

Lipid-based molecule.
To regulate and modulate the fluidity and stability of membrane.

Question 5

What is a glycoprotein, and function?

Answer 5

Molecules made of protein and carbohydrate chains
- facilitate cellular recognition + cell adhesion

Question 6

What is a carbohydrate, function, and where is it found?

Answer 6

• signaling and adhesion.
• part of glycolipids or glycoproteins
• immediate source of energy

Question 7

What is an integral protein, and where is it found?

Answer 7

Proteins that are a permanent part of the membrane, and deeply imbedded into the fatty acid tails (even halfway).

Question 8

What is a channel protein, and where is it found?

Answer 8

A channel protein forms a pore in the hydrophobic interior where ions and small polar molecules can pass through (chloride).

Question 9

What is a peripheral protein, and where is it found?

Answer 9

Temporary proteins that attach on the surface of the membrane

Question 10

What is a phospholipid bilayer, and what is the function?

Answer 10

• stable barrier
• choose what can enter and exit the cell (toxins)
• protects cell

Question 11

The plasma membrane is said to be fluid in structure because

Answer 11

The phospholipids within the bilayer move laterally, transversely, and rotationally within the structure.

Question 12

The plasma membranes of animal cells have a ____ region?

Answer 12

have a hydrophobic region similar to the plant plasma membrane.

Question 13

Explain why scientists describe the plasma membrane as a ‘fluid mosaic’.

Answer 13

The plasma membrane is fluid because the phospholipids and other molecules can move around – they are not stiff or held in one place. The plasma membrane is mosaic because many different molecules are embedded in the membrane

Question 14

Which organelle is not membrane bound?

Ribosome, Golgi body, Mitochondria, Smooth endoplasmic reticulum

Answer 14

Ribosome

Question 15

True or false?
Cells with a high plasma membrane surface area compared to cytosol volume are more effective at exchanging materials
with their environment.

Answer 15

True

Question 16

When calculating how many lipids in a cell, why is a red blood cell a good option?

Answer 16

Red blood cell does not include internal organelles or a nucleus, and they are all membrane-bound organelles. With these extra organelles, all of these lipids would have been counted as well, giving an inaccurate result.

Question 17

What is a carrier protein?

Answer 17

Molecules enter the carrier protein and bind themselves inside, which signals for the carrier protein to change shape to let the molecule out (glucose, amino acids).

Question 18

What is a cytoskeleton?

Answer 18

The cytoskeleton gives shape and support to the cell and transports molecules around the cell.

Question 19

How do phospholipids naturally form bilayers?

Answer 19

They are made up of a hydrophilic head region and a hydrophobic tail region, making them amphipathic. Non-polar is attracted to non-polar, so that is why the tails always face inwards. They are hydrophobic, meaning they are afraid of the water in the extracellular and intracellular environment. The phosphate heads are hydrophilic, meaning they attract water, which is why they are facing the extracellular and intracellular environments.

Question 20

What causes unsaturated fatty acid tails?

Answer 20

Double C=C bonds causes a kink in the chain. The greater the number of double bonds in the hydrophobic tails, the greater the fluidity of the membrane.

Question 21

What do unsaturated fatty acid tails do to the phospholipid bilayer of the plasma membrane?

Answer 21

The phospholipids do not stack neatly together, which produces a more fluid membrane. At lower temperatures, this will also happen, and the phospholipids will slop around and become unstable.

Question 22

Which molecules can diffuse through the plasma membrane on their own?

Answer 22

Lipid soluble molecules and water molecules (small, uncharged, non-polar molecules)
GASES and STEROIDS

Question 23

Which molecules can diffuse through the plasma membrane via channel proteins?

Answer 23

Water and ions (water soluble)
Sugars, amino acids

Question 24

Which molecules must be transported across the membrane by carrier proteins?

Answer 24

Larger, charged, hydrophilic or polar molecules such as glucose, amino acids, ions, nucleosides

Question 25

Why do the phosphate heads face outwards?

Answer 25

heads are hydrophilic, they face outward and are attracted to the intracellular and extracellular fluid.