Cell-surface Membrane

Question 1

What is the basic structure of cell membranes?

Answer 1

• Phospholipid bilayer
• Proteins

The structure enables control of the passage of substances across exchange surfaces by passive or active transport.

Question 2

The fluid-mosaic model describes the structure of the cell membrane as consisting of:

Answer 2

• Constantly moving phospholipid molecules
• Unevenly distributed protein molecules

This model illustrates the dynamic nature of the cell membrane.

Question 3

What are the orientations of the hydrophilic heads and hydrophobic tails in the phospholipid bilayer?

Answer 3

• Hydrophilic heads: inward toward cytoplasm or outward toward extracellular fluid
• Hydrophobic tails: toward each other

This orientation acts as a barrier to certain substances.

Question 4

Which small molecules can diffuse through the gaps between phospholipids?

Answer 4

• Carbon dioxide
• Oxygen

These molecules can pass freely due to their size and non-polar nature.

Question 5

Water passes through the cell membrane via ________ by osmosis.

Answer 5

aquaporins

Aquaporins are specialized protein channels that facilitate water movement.

Question 6

What type of molecules can pass quickly through the phospholipid bilayer?

Answer 6

• Lipid soluble molecules

The bilayer restricts the passage of water-soluble ions and polar molecules.

Question 7

Which types of molecules cannot cross the phospholipid bilayer by simple diffusion?

Answer 7

• Charged substances
• Large polar molecules

These molecules require transport proteins to cross the membrane.

Question 8

What is the role of transport proteins in the cell membrane?

Answer 8

• Facilitate the crossing of charged substances
• Assist large polar molecules

Transport proteins are essential for moving substances that cannot diffuse freely.

Question 9

Examples of lipid-soluble molecules that can pass through the cell membrane include:

Answer 9

• Benzene
• Ethanol

These molecules have little or no charge and are small enough to pass between phospholipids.

Question 10

What type of molecules are restricted from passing through the phospholipid bilayer?

Answer 10

• Water-soluble ions
• Polar molecules

Their charge and polarity prevent them from diffusing freely across the membrane.

Question 11

What role does cholesterol play in the cell membrane?

Answer 11

Provides strength and restricts movement of phospholipids, making the membrane less fluid

This helps to reduce the loss of ions from the cell.

Question 12

What are carrier proteins responsible for?

Answer 12

Transporting polar molecules such as glucose or amino acids by facilitated diffusion and active transport

They possess a specific tertiary structure complementary to the molecules they transport.

Question 13

What determines which molecules can be transported by channel proteins?

Answer 13

The specific tertiary structure, charge, and size of the protein

This structure allows for facilitated diffusion of certain molecules across the membrane.

Question 14

What is the function of receptor proteins in the cell membrane?

Answer 14

Act as specific receptors for hormones, allowing the cell to respond

They have a specific tertiary structure that allows hormones to attach to their binding sites.

Question 15

What are glycolipids and glycoproteins?

Answer 15

Glycolipids are lipids with carbohydrate chains; glycoproteins are proteins with carbohydrate chains

Both can act as receptors and are involved in cell-cell recognition.

Question 16

What do branched carbohydrate chains on membranes do?

Answer 16

Act as receptors and can be involved in cell-cell recognition

They can also act as antigens, helping the immune system recognize foreign invaders.

Question 17

Fill in the blank: Non-polar molecules diffuse _______ and easiest across the membrane.

Answer 17

fastest

This includes small molecules like oxygen and carbon dioxide.

Question 18

What type of molecules use facilitated diffusion?

Answer 18

Large or charged molecules

They require channel or carrier proteins to cross the membrane.

Question 19

What is the effect of saturated fatty acids on membrane permeability?

Answer 19

Lower permeability

Unsaturated fatty acids increase permeability.

Question 20

What is the role of glycoproteins in the immune system?

Answer 20

Act as antigens, allowing the immune system to recognize and attack foreign invaders

This is crucial for identifying bacteria and other pathogens.