4.1) Structure of the cell surface membrane

Question 1

What is the primary structure of the cell-surface membrane?

Answer 1

Phospholipid bilayer

The phospholipid bilayer consists of hydrophilic phosphate heads and hydrophobic hydrocarbon tails.

Question 2

What is the function of the cell-surface membrane?

Answer 2

Controls movement of substances in and out of the cell

It establishes different conditions inside and outside the cell.

Question 3

Describe the fluid-mosaic model of cell membrane structure.

Answer 3

A model that describes the cell membrane as a mosaic of diverse protein molecules floating in or on the fluid lipid bilayer.

Question 4

What are the characteristics of phospholipids in the cell-surface membrane?

Answer 4

• Hydrophilic heads point outward
• Hydrophobic tails point inward
• Form a bilayer structure

Question 5

What role do phospholipids play in the cell membrane?

Answer 5

• Allow lipid-soluble substances to enter and leave the cell
• Prevent water-soluble substances from entering and leaving the cell
• Make the membrane flexible and self-sealing

Question 6

How are proteins embedded in the cell-surface membrane?

Answer 6

• Some proteins are on the surface of the bilayer
• Others span the bilayer completely

Question 7

What are the functions of proteins in the cell membrane?

Answer 7

• Provide structural support
• Act as channels for water-soluble substances
• Allow active transport through carrier proteins
• Serve as surface receptors
• Help cells adhere together

Question 8

What is the function of cholesterol in the cell-surface membrane?

Answer 8

• Adds strength to the membrane
• Prevents loss of water and dissolved ions
• Reduces lateral movement of phospholipids

Question 9

What are glycolipids and their function in the membrane?

Answer 9

• Made of carbohydrate and lipid
• Act as recognition sites
• Help maintain membrane stability
• Assist in cell attachment

Question 10

What are glycoproteins and their role in the cell membrane?

Answer 10

• Carbohydrate chains attached to extrinsic proteins
• Act as cell-surface receptors for hormones and neurotransmitters
• Help cells to recognize one another

Question 11

True or False: All plasma membranes have the same phospholipid bilayer structure.

Answer 11

True

The differences in properties arise from the various substances contained within.

Question 12

Fill in the blank: The hydrophilic heads of phospholipids are attracted to _______.

Answer 12

[water]

Question 13

Fill in the blank: Cholesterol molecules in the membrane help to _______ the movement of phospholipids.

Answer 13

[reduce]

Question 14

What is the significance of the carbohydrate portion of glycolipids?

Answer 14

Acts as a cell-surface receptor for specific chemicals

Example: The human ABO blood system operates through glycolipids.

Question 15

What do carrier proteins do in the cell membrane?

Answer 15

Bind to ions or molecules and change shape to transport them across the membrane.

Question 16

What is the role of surface receptors in the cell membrane?

Answer 16

Identify cells and react to specific molecules, such as hormones.

Question 17

What is the overall function of the cell-surface membrane?

Answer 17

Controls the movement of substances in and out of the cell.

Question 18

Which end of the phospholipid molecule lies towards the inside of the cell-surface membrane?

Answer 18

Hydrophobic tails.

Question 19

What type of molecule is likely to pass through the cell-surface membrane if it is soluble in lipids?

Answer 19

Lipid-soluble molecules.

Question 20

What type of molecule is likely to pass through the cell-surface membrane if it is a mineral ion?

Answer 20

Channel proteins.

Question 21

Suggest two properties that a drug should possess to enter a cell rapidly.

Answer 21

• Lipid-soluble
• Small size.

Question 22

True or False: Most molecules can freely diffuse across the cell-surface membrane.

Answer 22

False.

Question 23

List three reasons why many molecules do not freely diffuse across the cell-surface membrane.

Answer 23

• Too large to pass through channels
• Charged and repelled by protein channels
• Polar and have difficulty passing through non-polar hydrophobic tails.

Question 24

What does the fluid-mosaic model describe?

Answer 24

The arrangement and structure of the cell-surface membrane.

Question 25

Why is the cell-surface membrane described as ‘fluid’?

Answer 25

Phospholipid molecules can move relative to one another.

Question 26

Why is the cell-surface membrane described as ‘mosaic’?

Answer 26

Proteins embedded in the phospholipid bilayer vary in shape, size, and pattern.

Question 27

What role does cholesterol play in the cell-surface membrane?

Answer 27

Adds strength.

Question 28

What is the function of glycoproteins in the cell-surface membrane?

Answer 28

Acts as recognition sites for chemicals like hormones.

Question 29

Fill in the blank: The cell-surface membrane provides an internal transport system, such as the _______.

Answer 29

[endoplasmic reticulum].

Question 30

What is the function of lysosomes in the cell?

Answer 30

Isolate enzymes that might damage the cell.

Question 31

What is the significance of ribosomes on the rough endoplasmic reticulum?

Answer 31

Protein synthesis.

Question 32

What are the hydrophilic heads of phospholipids?

Answer 32

The part of the phospholipid that interacts with water.