1.5 lipids and the membrane

Question 1

phospholipid bilayer arrangements

Answer 1

smaller head and double tails
flat

Question 2

liposome phospholipid arrangement

Answer 2

often MIXED lipids
some double tails, some single tails
its like a ball but there’s a circle in the middle

Question 3

Micelle phospholipid arrangement

Answer 3

bulkier heads and single tails
its a ball

Question 4

molecular self-assembly

Answer 4

process where by molecules or complexes of molecules form a particular and characteristic 3D conformation/structure

result of:
- interaction with surrounding WATER molecules
- INTERmolecular interaction (non covalent)
- INTRAmolecular interaction (covalent, ionic)

Question 5

thermodynamics

Answer 5

study of system stability
field of them that dead with the LIKELIHOOD (not speed) of reactions occurring in a system

Question 6

spontaneous

Answer 6

energetically favourable process
likely to happen in this direction
reaction moves from LESS STABLE to MORE STABLE

Question 7

not spontaneous

Answer 7

energetically unfavourable process
requires energy input to happen in this direction
reaction moves from MORE STABLE to LESS STABLE

Question 8

what does system stability depend on

Answer 8

enthalpy and entropy

Question 9

enthalpy

Answer 9

measures how strongly bonded a system is

Question 10

entropy

Answer 10

measures the freedom to move of components of a system

Question 11

largest contributor to system stability in bilayer formation

Answer 11

entropy of the WATER
i.e. increase in motional freedom of the water molecules

Question 12

hydrophobic effect

Answer 12

allows for building and stabilizing lipid bilayers AND 3D structure of protein sand DNA

burying non polar groups away from water, leaving the water molecules emotionally free

the water molecules near the head groups have restricted motion

buuuuut there’s more that are chill and free to move so is good

Question 13

how do phospholipids interact in a bilayer?

Answer 13

non-covalent interactions

Question 14

why is membrane formation spontaneous

Answer 14

thermodynamics principles and hydrophobic effect

Question 15

lipid bilayer

Answer 15

• is a selective bilayer
• semi-permeable
• helps maintain homeostasis – a characteristic of what defines life and cells!!

Question 16

when molecules move through the lipid bilayer, they:

Answer 16

move by diffusion!! meaning they:
- move with/along the concentration gradient
- move in both directions
- they do not stop moving at equilibrium

Question 17

osmosis

Answer 17

movement of water through semipermeable membrane

Question 18

diffusion

Answer 18

movement of everything OTHER than water

Question 19

what are membranes made out of

Answer 19

lipids (main component)
also made of:
- proteins (important functions such as transporting molecules)
- carbohydrates (usually attached to lipids and proteins)

Question 20

phospholipids

Answer 20

major type of lipid found in cell membrane

○ Made up of a glycerol backbone attached to a phosphate group and two fatty acids

Question 21

Phosophate head group

Answer 21

hydrophilic
○ Water loving
○ Polar
Forms hydrogen bonds with water

Question 22

fatty acid tails

Answer 22

hydrophobic
○ Water fearing
○ Non polar
○ No hydrogen bonds

Question 23

AMPHIPATHIC

Answer 23

molecules with both hydrophilic and hydrophobic regions

Question 24

why do lipids freely associate with each other

Answer 24

because of the extensive van der Waals forces between their fatty acid tails!!
○ Easily broken and reformed so lipid molecules are able to move within the plane of the membrane sometimes rapidly
§ As a result, membrane is said to be fluid

Question 25

saturated vs unsaturated lipids in membrane mobility

Answer 25

○ The longer the fatty acid tails, the more surface is available to participate in van der Waals interactions
§ Tighter packing!! -> reduces lipid mobility
○ Saturated -> straight and tightly packed, reducing mobility
○ Unsaturated has kinks in fatty acid tails, enhancing lipid mobility

Question 26

different functions of proteins

Answer 26

○ Transporters – move ions/other molecules across the cell membrane
○ Receptors – allow the cell to receive signals from the environment
○ Enzymes – catalyze chemical reactions
○ Anchors – attach to other proteins and help to maintain cell structure and shape

Question 27

Integral membrane proteins

Answer 27

permanently associated with cell membranes, cannot be separed without destroying the membrane

Question 28

Peripheral membrane proteins

Answer 28

temporarily associated with the lipid bilayer or with integral membrane proteins through weak noncovalent interactions

Question 29

transmembrane proteins

Answer 29

• Most integral membrane proteins (IMP) are transmembrane proteins that Span entire lipid bilayer
  ○ Three regions:
  § Two hydrophilic regions, one from each face of the membrane
  § Connecting hydrophobic region that spans the membrane
  Allows for separate functions and capabilities of each end of the protein!!

Question 30

Fluid mosaic model

Answer 30

○ Lipid bilayer is a fluid structure within which molesules move laterally
○ Is a mosiac (mixture) of two types of molecules: lipids and proteins