Cell Structure - Cell Membrane

Question 1

How thick is the plasma membrane that separates living cells from surroundings?

Answer 1

8nm thick

Question 2

What are the P. Membranes 3 main functions?

Answer 2

1.It has selective permeability
2.Maintenance of cell integrity
3.Transport and cell signalling

Question 3

4 components of the cell membrane

Answer 3

1.Phospholipid bilayer
2.Cholesterol
3.Carbohydrates
4.Proteins

Question 4

Describe the polarity and structure of a phospholipid

Answer 4

The negatively charged phosphate head makes it hydrophilic, whereas the non polar fatty acid chains are hydrophobic, making it an amphipathic

Question 5

Name 4 prominent phospholipids found in animals

Answer 5

1.phosphatydlcholine (PC)
2.Phosphatydlethanolamine (PE)
3.Phosphatydlserine (PS)
4.Sphingomyelin

Question 6

What are michelles like

Answer 6

Michelles in water face hydrophobic heads outside and form a sphere interior can be aqueous

Question 7

What phospholipids does the outer leaflet of bilayers usually contain?

Answer 7

Phosphotydlcholine
Sphingomyelin

Question 8

What phospholipids does the inner bilayer contain?

Answer 8

Phosphatydlethanolamine
Phosphatydlserine

Question 9

How is fluidity of the phospholipid bilayer affected by temperature?

Answer 9

Governed by adjacent hydrocarbon chain interacting

High temp: interactions are overcome and fluidity (double bonds lower Mt)
Low temp: high degree of interaction, membrane is more solid

Question 10

How is fluidity affected by the saturation of fatty acids?

Answer 10

saturated FAs only = Less fluidity
Saturated and mono saturated mixed= more fluidity

Question 11

What is the major sterol of mammalian membranes?

Answer 11

Cholesterol (ampipathic) like PL molecules

Question 12

What does cholesterol do to fluidity of the bilayer?

Answer 12

1.Makes lipid bilayer less deformable
2.Decreease it’s penalty to small water soluble molecules
3.prevents phase shifts

Low temp:stops tight packing of PL in bilayer
High temp:Holds PL together

Question 13

What does cholesterol do to the movement of PLs?

Answer 13

Limits movements of PLs and keeps membrane stabilised

Question 14

Describe the movements of phospholipids and how often they occur

Answer 14

Lateral movements occur 10^7 times/sec
Flip flop movement occurs once a month

Question 15

Describe membrane carbohydrates

Answer 15

Usually <15 units, short and branched
Covalent bound to lipids and proteins to form glycolipids/proteins and vary amongst species, and cell types

Question 16

Name 3 functions of membrane carbohydrates

Answer 16

They are involved in cell-cell recognition
Cell sorting to form tissues and organs
Detection of foreign cells (P-selectin)

Also can tell us certain blood types so used as identification markers

Question 17

Describe a membrane protein

Answer 17

Collage of proteins embedded into bilayer and determines a cells specific functions

Integral proteins : transmembrane and partially embedded proteins

Peripheral proteins: usually attached to PL head or other integral proteins

Question 18

What are 4 types of functions membrane proteins can have?

Answer 18

1.Transporters
2.Anchors
3.Receptors
4.Enzymes

Question 19

Membranes proteins are very mobile, what bonds hold membrane molecules in place?

Answer 19

Membrane molecules are held in place by weak hydrophobic interactions

Question 20

What is FRAP?

Answer 20

A technique developed by Axelrod used to study protein mobility in living cells using intense laser

Question 21

Describe plasma membrane permeability?

Answer 21

P. Membranes are selectively permeable

free movement of a molecule through membrane depends on interaction of a molecule with the hydrophobic core of the membrane

Question 22

What type of molecules can diffuse through the lipid bilayer?

Answer 22

Hydrophobic molecules such as CO2, O2, hydrocarbons can diffuse through bilayer

Question 23

What type of molecules require the aid of membrane proteins to cross the membrane?

Answer 23

Ions, polar molecules (water), and large molecules (glucose) require membrane proteins to cross the membrane

Question 24

What does molecule movement through the membrane depend on (what gradients)?

Answer 24

Internal vs external concentration /electricochemical gradients

Question 25

What is a uniporter,symporter and an anti porter?

Answer 25

Uniporters move one molecule at a time and are passive

Symporter moves two molecules at the same time requires ATP

Antiporter move one molecule in and one out at the same time like calcium potassium channel requires ATP

Question 26

How many ions does passive move and how many does active transport move?

Answer 26

Passive - 10^7 ions per sec

Active Transport - 450 ions per second

Question 27

Two examples of uniporters and what they move

Answer 27

Aquaporin - moves water

Gated sodium ion channel - moves Sodium

Question 28

What do antiporters and symporters move?

Answer 28

Antiporters - sodium/potassium channel (muscles)

Symporter - sodium/glucose channel