3.4 Plasma Membrane Structure and Function

Question 1

What is the function of the plasma membrane?

Answer 1

• separates the internal environment of the cell from the external environment
• regulates the entrance and exit of molecules from the cell
• helps the cell maintain homeostasis

Question 2

What is the plasma membrane made up of?

Answer 2

primarily of phospholipids

Question 3

What do the phospholipids of the membrane form?

Answer 3

a bilayer with the hydrophilic polar heads facing the outside and inside of the cell where water is present, and the hydrophobic nonpolar tails facing each other

Question 4

What is the fluid consistency of the phospholipid bilayer?

Answer 4

comparable to light oil

Question 5

What is the fluidity of the plasma membrane regulated by?

Answer 5

steroids such as cholesterol which serve to stiffen and strengthen the membrane

Question 6

What are peripheral proteins?

Answer 6

proteins that are associate with only one side of the plasma membrane

Question 7

What are peripheral proteins on the inside of the membrane often held in place by?

Answer 7

cytoskeletal filaments

Question 8

What are integral proteins?

Answer 8

proteins that span the membrane and can protrude from one or both sides

they are embedded in the membrane but can move laterally, changing their position in the membrane

Question 9

What do the proteins in the membrane form?

Answer 9

a mosaic pattern

Question 10

What is the fluid-mosaic model?

Answer 10

combination of proteins, steroids, and phospholipids of the membrane structure

Question 11

What are glycolipids?

Answer 11

phospholipids with attached carbohydrate chains

Question 12

What are glycoproteins?

Answer 12

proteins with attached carbohydrate chains

Question 13

What do glycolipids and glycoproteins play an important role in?

Answer 13

cellular identification

Question 14

Why are the two halves of the membrane not identical?

Answer 14

the carbohydrate chains occur only on the outside surface and peripheral proteins occur asymmetrically on one surface or the other

Question 15

Describe the fluid-mosaic model of the plasma membrane?

Answer 15

the membrane is composed of a phospholipid bilayer in which proteins are embedded (integral proteins) or associated with the cytoplasmic side (peripheral proteins)

steroids (cholesterol) help regulate the fluidity of the membrane

cytoskeleton filaments are attached to the inside surface by membrane proteins

Question 16

What are the functions of peripheral proteins?

Answer 16

• structural role: help stabilize and shape the membrane

- signal pathways

Question 17

What are the 5 types of integral proteins?

Answer 17

• channel
• carrier
• cell recognition
• receptor
• enzymatic

Question 18

What are channel proteins?

Answer 18

• involved in the passage of molecules through the membrane

- have a channel that allows a substance to simply move across the membrane

Question 19

Give an example of a channel protein function.

Answer 19

allows hydrogen ions to flow across the inner mitochondrial membrane

without this movement of hydrogen ions, ATP would never be produced

Question 20

How must a gate be opened in a channel protein?

Answer 20

by the binding of a specific molecule to the channel

Question 21

What is cystic fibrosis caused by?

Answer 21

a faulty chloride channel: chloride ion transport is reduced and so is the flow of sodium ions and water

researchers believe that the lack of water causes the mucus in the bronchial tubes and pancreatic ducts to be abnormally thick, therefore interfering with the function of the lungs and the pancreas

Question 22

What are carrier proteins?

Answer 22

• involved in the passage of molecules through the membrane

- combine with other specific Dsubstances and help it move across the membrane

Question 23

Give an example of a carrier protein function.

Answer 23

transports sodium and potassium ions across a nerve cell membrane, nerve conduction would be impossible without this carrier protein

Question 24

What are cell recognition proteins?

Answer 24

glycoproteins that, among other functions, help the body recognize when its being invaded by pathogens so that an immune reaction can occur

Question 25

Describe MHC (major histocompatibility complex) glycoproteins.

Answer 25

• different for each person, so organ transplants are difficult to achieve
• cells with foreign MHC glycoproteins are attacked by white blood cells responsible for immunity

Question 26

What are receptor proteins?

Answer 26

• have a shape that allows a specific molecule to bind to it

- the binding of this molecule causes the protein to change its shape and thereby bring about a cellular response

Question 27

Give an example of a receptor protein function.

Answer 27

the coordination of the body’s organs is totally dependent on receptor proteins

the liver stores glucose after it is signalled to do so by insulin

Question 28

Why does dwarfism occur?

Answer 28

some type occur not because the body doesn’t produce enough growth hormone, but because the plasma membrane growth hormone receptors are faulty and cannot interact with growth hormone

Question 29

What are enzymatic proteins?

Answer 29

• carry out metabolic reactions directly

- catalyzes a specific reaction

Question 30

What do the integral membrane proteins of the electron transport chain do?

Answer 30

carry out the final steps of aerobic respiration

Question 31

What are enzymes attached to?

Answer 31

some are attached to the various membranes of the cell

Question 32

What can’t a cell do without the presence of enzymes?

Answer 32

a cell would never be able to perform the metabolic reactions necessary to its proper function

Question 33

What membrane protein is involved in ATP metabolism?

Answer 33

adenylate cyclase

Question 34

What does cholera do?

Answer 34

releases a toxin that interferes with the proper functioning of adenylate cyclase which eventually leads to severe diarrhea