Chapter 4 - Transport across cell membranes

Question 1

What is a carrier protein?

Answer 1

A protein completely covering the phospholipid bilayer which bind to ions or minerals to move molecules across the membrane

Question 2

What is a protein channel?

Answer 2

A protein completely spanning the phospholipid bilayer which form water-filled tubes to allow water-soluble ions to diffuse across the membrane

Question 3

How permeable are plasma membranes?

Answer 3

Partially permeable to allow molecules in and out of the cell

Question 4

What are 5 functions of membranes within cells?

Answer 4

• seperates organelles from cytoplasm
• controls entry and exit of materials
• isolates enzymes that might damage
• provide surface for reactions
• provides internal support system

Question 5

Why are mitochondria and nuclei surrounded by a double membrane?

Answer 5

They are the superior organelles and have evolved form a single membrane for extra support

Question 6

When was the fluid-mosaic model invented?

Answer 6

1972

Question 7

What is the fluid-mosaic model?

Answer 7

The model of a cell membrane - phospholipids are constantly moving, and proteins are scattered through the bilayer

Question 8

What is a phospholipid bilayer?

Answer 8

A membrane with 2 phospholipid layers with the hydrophilic heads in the outside and the hydrophobic tails on the inside

Question 9

Why are the fatty acid tails on the inside?

Answer 9

They are hydrophobic and protect polar, larger molecules from being exchanged

Question 10

What types of molecules can be transported freely through the bilayer?

Answer 10

They need to be soluble, small and non-polar

Question 11

How does water move around a cell membrane?

Answer 11

As it is polar, water is diffuse through the membrane by osmosis

Question 12

What are the functions of intrinsic proteins?

Answer 12

Channel proteins and carrier proteins allow large, polar molecules and ions to pass through the membrane actively or passively

Question 13

What is the function of peripheral proteins?

Answer 13

Proteins that act as receptors and allow the cell to detect chemicals released form other cells so they can respond (hormones)

Question 14

What are glycoproteins?

Answer 14

Protein with a carbohydrate attached

Question 15

What are glycolipids?

Answer 15

Lipid with a carbohydrate attached

Question 16

What are the roles of glycolipids and glycoproteins?

Answer 16

• Act as antigens for cellular recognition, which is crucial for the immune system
• Cell signalling and communication
• Help with cell adhesion

Question 17

What is the role of cholesterol?

Answer 17

• Restricts movement of other molecules in the membrane to provide stability. This is done by binding to the tails of phospholipids so they pack more closely together
• Makes the membrane less fluid at high temperatures
• Prevents the leakage of water and ions from the cell

Question 18

Why is there a lot of cholesterol found in red blood cells?

Answer 18

They are not supported by other cells and need rigidity to move around blood vessels

Question 19

What are the roles of phospholipids in the membrane?

Answer 19

• allow lipid-soluble molecules to be exchanged
• prevent exchange of water-soluble molecules
• make the membrane flexible and self-healing

Question 20

What are 3 functions of plasma membranes?

Answer 20

• isolates cytoplasm from extracellular environment
• selectively permeable to regular transport of substances
• involved in cell signalling/cell recognition