Cell membranes and transport 1.3

Question 1

What is the structure of cell membranes?

Answer 1

-Appears under the electron microscope as a double line
-Barrier is 7-8nm across
-Made of phospholipids, proteins & other macromolecules

Question 2

What is the function of cell membrane?

Answer 2

-Separates living cell from non-living surroundings
-Takes up nutrients, secretes chemicals, allows cell recognition
-Selectively permeable to water and some solutes

Question 3

What are Phospholipids?

Answer 3

-Hydrophilic Phosphate head
-Hydrophobic Phosphate tail
-Arranged as a Bilayer

Question 4

What theory did Singer and Nicolson propose?

Answer 4

Membrane proteins are inserted into the Phospholipid bilayer (The ‘fluid mosaic’ model)

Question 5

Why is the word ‘fluid used’ in the Singer and Nicolson theory?

Answer 5

Lipids and membrane proteins can move laterally or sideways through the membrane

Question 6

Why is the word ‘mosaic’ used in the Singer and Nicolson theory?

Answer 6

It is made up of many different parts such as proteins, glycoproteins, phospholipids, glycolipids, and in some cases cholesterol & lipoproteins

Question 7

What is the glycocalyx?

Answer 7

A carbohydrate coating that covers the outside of many cells, particularly bacteria

Question 8

What is the function of extrinsic proteins?

Answer 8

-Eukaryotic: recognition of cell
-Bacterial: protective coat from host factors
-Can be glycosylated to make glycocalyx
-Cell surface identity marker (antigen)

Question 9

What is the function of intrinsic proteins?

Answer 9

-Penetrate lipid bilayer, usually across the whole membrane
-Transport proteins
-Channel proteins and carrier proteins (transmembrane)

Question 10

How does temperature affect permeability?

Answer 10

-Low temperature=low kinetic energy, the membrane is rigid
-High temperature=high kinetic energy, forms gaps
-Above 45 degrees C membrane denatures

Question 11

How does ethanol affect permeability?

Answer 11

Ethanol can dissolve non-polar phospholipids. If ethanol concentration is high enough, membrane dissolves completely

Question 12

How does detergents affect permeability?

Answer 12

Reduces surface tension and disperses the phospholipids in membrane, permeability increases

Question 13

How does NaCl affect permeability?

Answer 13

Na+ ions will bond to Oxygen atoms in phosphate heads, increasing rigidity

Question 14

What can the rate of diffusion be affected by?

Answer 14

-Temperature
-Thickness of membrane
-Size of a molecule
-Lipid solubility
-Concentration gradient

Question 15

What molecules can diffuse directly?

Answer 15

-Lipid soluble
-Non charged
-Vitamine A,D, & E

Question 16

What molecules use protein channels?

Answer 16

-Not lipid soluble
-Charged
-Large

Question 17

What are the three methods of facilitated diffusion?

Answer 17

-Channel protein
-Carrier protein
-Co-transport

Question 18

What is exocytosis?

Answer 18

Substances leaving the cell after being transported through the cytoplasm in a vesicle (needs ATP)

Question 19

What is endocytosis?

Answer 19

Substance being engulfed by infolding membrane

Question 20

What is pinocytosis?

Answer 20

endocytosis of liquid materials (smaller vesicles)

Question 21

What is phagocytosis?

Answer 21

endocytosis of solids
destroys bacteria
digests cell debris
Amoeba use this method to feed

Question 22

Describe co-transport

Answer 22

1) Sodium and glucose is deposited into cell via a carrier protein
2)Sodium is pumped out of cell by active transport. Potassium is pumped in
3) Glucose leaves cell via facilitated diffusion

Question 23

What molecules use carrier proteins?

Answer 23

large sugars and amino acids

Question 24

What molecules use channel proteins?

Answer 24

Charged substances

Question 25

How does temperature affect membrane permeanility?

Answer 25

-Low temperature, Low KE, membrane is rigid
-Temperature increase, KE increases, gaps form
-Above 45c, proteins denature, fully permeable

Question 26

How does ethanol affect permeability?

Answer 26

Dissolves non polar substances like the phospholipids, increasing permeability

Question 27

How does detergent affect permability?

Answer 27

reduces surface tension, creating gaps, increasing permeability

Question 28

How does NaCl affect permeability?

Answer 28

Na+ ions bond to oxygen in the phospholipid heads, making membranes rigid, decreasing permeability