Lecture 15: Cellular membrane processes

Question 1

How thick is the cell membrane?

Answer 1

8 nm

Question 2

What is the model for the cell membrane called?

Answer 2

Fluid mosaic model

Question 3

What is the composition of the cell membrane?

Answer 3

50% lipid and 50% protein held together by hydrogen bonds

Question 4

What are the 3 types of lipid molecules found in cellular membrane?

Answer 4

Glycolipid
Phospholipid
Cholesterol

Question 5

What is a phospholipid?

Answer 5

A phosphate head and two fatty acid tails 0 amphipathic

Makes up 75% of lipids

Question 6

What does amphipathic mean?

Answer 6

Contains both a polar and non-polar region

Question 7

What does membrane fluidity mean?

Answer 7

The lipids and proteins are able to move around within the plane of the membrane leaflet - on a side of phospholipids however cannot move between phospholipid layers

Question 8

What are the determinants of fluidity?

Answer 8

Lipid tail length
Cholesterol
Double bonds in fatty acid tails

Question 9

How does lipid tail length affect fluidity?

Answer 9

Longer lipid tail lengths decrease fluidity

Question 10

How does cholesterol level affect fluidity?

Answer 10

More cholesterol molecules within the cell membrane make it less fluid

Question 11

How does number of double bonds affect fluidity?

Answer 11

More double bonds in the fatty acids of the phospholipids increase fluidity

Question 12

What are integral proteins?

Answer 12

Proteins in the cell membrane which extend completely across the membrane

Question 13

What are peripheral proteins?

Answer 13

Attached to either inner or outer surface of cell membrane and are easily removed

Example is proteins that bind to the cytoskeleton of the cell determining the shape of the membrane

Question 14

What are features of integral membrane proteins?

Answer 14

Amphipathic - have hydrophobic and hydrophilic regions

The hydrophobic regions usually coil up into helices making up the inner part of the protein

Question 15

What are the functions of membrane proteins?

Answer 15

Receptor proteins
Cell signaling
Linkers
Enzymes
Ion channels
Transporter proteins

Question 16

What is a channel protein?

Answer 16

A transport protein which allows specific substsances to move through a water-filled pore.

Question 17

What is a transporter protein?

Answer 17

A transport protein which moves specific substances across membrane by changing shape

Question 18

What does selective permeability mean?

Answer 18

Allows some substances to pass and blocks other substances

Question 19

What molecules can pass the phospholipid bilayer (with no proteins involved)?

Answer 19

• Non-polar uncharged molecules (oxygen, nitrogen)
• Lipid soluble molecules (steroids, fatty acids)
• Small uncharged polar molecules (water, urea, CO2)

Question 20

What molecules cannot pass the phospholipid bilayer without transport proteins?

Answer 20

• Large uncharged polar molecules (glucose, amino acids)

- Ions (sodium, potassium, chlorine, calcium)

Question 21

What is diffusion?

Answer 21

Movement of substances across a selectively permeable membrane down a concentration gradient

Question 22

What is equilibrium?

Answer 22

The state in which there is no diffusion occurring as the concentration is equal to each other

Question 23

Why does diffusion occur?

Answer 23

Due to particle’s having kinetic energy - more molecules move away from an area of high concentration to an area of low concentration

Question 24

What are the factors that affect the rate of diffusion?

Answer 24

Surface area
Distance of diffusion
Size of molecule
Temperature
Steepness of concentration gradient

Question 25

How does the properties of diffusion limit the size of a cell? - what is the limit?

Answer 25

Longer diffusion distances mean slower rates of diffusion. Hence, if a cell is too large, normal cellular processes cannot occur therefore cells are capped at 20 micrometers

Question 26

What are the two types of gradients that exist across a membrane?

Answer 26

Concentration gradient

Electrical gradient

Question 27

What is an electrical gradient?

Answer 27

The difference in charge across the membrane due to the presence of ions

Question 28

How is an electrochemical gradient across a membrane maintained?

Answer 28

Due to the selective permeable nature of membranes some molecules cannot pass through maintaining the electrical gradient

Question 29

What is osmosis?

Answer 29

Net movement of water through a selectively permeable membrane from an area of high water potential to an area of lower water potential

Question 30

What determines the permeability of a membrane to water?

Answer 30

The permeability of lipid bilayer + presence of aquaporins (family of proteins that allow osmosis of water)

Pw= Pd + Pf

Question 31

Can the permeability of a membrane to water be affected by temperature?

Answer 31

Yes

Question 32

What is osmotic pressure?

Answer 32

The pressure applied to a solution to prevent the inward flow of water across a semi-permeable membrane

Question 33

What are the ion gradients across the membrane? Describe the charges between the cytoplasm and extracellular fluid

Answer 33

HIgh Na+ and Cl- outside
High K+ inside

Cells use 30% of resting energy to maintain this gradient