The Cell Surface Membrane - Fluid Mosaic Model

Question 1

What is the function of the cell surface membrane?

Answer 1

• controls the the entry and exit of molecules, exchanges materials with surroundings
• it is selectively permeable
• only very small molecules can diffuse thru such as oxygen, glucose, amino acids + water
• it is a passive process

Question 2

What does the cell membrane consist of?

Answer 2

Proteins, glycoproteins, phospholipids and carbohydrates

Question 3

Why does the fluid mosaic model have its name?

Answer 3

• phospholipid molecules form a bilayer that is flexible + moves around like a fluid
• protein molecules are unevenly distributed forming a mosaic pattern
• structure is agreed on as chemical evidence

Question 4

What does the selective permeability of the cell membrane depend on?

Answer 4

The type and distribution of specific proteins and phospholipid molecules present in the membrane

Question 5

Define intrinsic proteins

Answer 5

Membrane proteins completely embedded thru phospholipid bilayer

Question 6

Define extrinsic proteins

Answer 6

Loosely bound proteins that are located outside of membrane

Question 7

Describe the functions of phospholipids

Answer 7

• hydrophobic tails attracted towards eachother + hydrophilic heads facing towards cytoplasm or extra - cellular fluid forming phosphlipid bilayer
• most common molecule found in all membranes
• allows lipid soluble molecules which are non polar, to simple diffuse thru
• prevents passage of small polar molecules e.g ions

Question 8

Describe functions of cholesterol

Answer 8

• decreases permeability + inc rigidity of membrane
• if theres more cholesterol = less fluidity
• diff types of cells have diff proportions of cholesterol

Question 9

Describe functions of channel proteins

Answer 9

• like gates within membrane
• only allows small molecules like ions to pass thru by facilitated diffusion
• intrinsic molecules
• proteins have specific tertiary structures so only transport molecules complementary to shape of channel protein

Question 10

Describe the functions of carrier proteins

Answer 10

• aid transport of ions, polar, and large molecules
• intrinsic proteins

Question 11

Describe the functions of receptor proteins

Answer 11

• specific cells have specific receptors
• only specific molecules can bind to specific receptor proteins
• as proteins have specific tertiary structures
• intrinsic proteins

Question 12

Describe the functions of enzymes

Answer 12

• intrinsic proteins
• shape of enzyme active site is specific + complementary to its substrate
• allowing them to bind + form enzyme substrate complexes

Question 13

Describe functions of glycoproteins

Answer 13

• composed of carbohyrate + protein
• all cells have them on outer cell surface membrane
• important in cell recognition
• often acting as antigens
• immune cells detect the specific shapes of glycoproteins to identify cells as foreign (non self) or not (self)
• produced in golgi body within cell

Question 14

Describe the functions of aquaporins

Answer 14

• special types of channel proteins specific to water
• more aquaporins = more permeable to water + carries out osmosis easier

Question 15

How does temp affect membrane permeability?

Answer 15

As temp increases, permeability increases

Question 16

How does alcohol affect membrane permeability?

Answer 16

Inc membrane permeability as it breaks down phospholipid bilayer so diffusion rate is faster