1. Lipids Highly diverse structures Unifying property
Hydrophobic: little to no affinity to water
Contains hydrocarbons, which form nonpolar covalent bonds
Do not form polymers
Biologically important lipids containing molecules:
Fats
Phospholipids
Steroids

2. Fats Structure - Fatty acid
Composed of two different molecules bonded by ester linkage
fatty acid & glycerol
- Fatty acid
Hydrocarbon chain with a carboxyl group at one end
Glycerol
Three-carbon alcohol
Each carbon attached to hydroxyl group
Try to Draw

3. Dehydration reaction in the synthesis of a fat
LE 5-11a
Fatty acid
(palmitic acid)
Glycerol
Dehydration reaction in the synthesis of a fat

4. Fat molecule (triacylglycerol)
LE 5-11b
Ester linkage
Fat molecule (triacylglycerol)

5. Properties of Fats Hydrophobic Fatty acids
H2O molecules form hydrogen bonds with each other and EXCLUDE fatty acid chains-->
Fats separate from H2O (like oil & vinegar)
Fatty acids
variable chain length (often carbons)

6. Saturated fat - refers to saturated fatty acid chains
- carbons contains maximum number of hydrogens
- results in 100% single bonds (no double bonds)
- more linear, packs tightly to form solid
Tend to be from animals

7. Saturated or unsaturated?
LE 5-11b
Saturated or unsaturated?
Ester linkage
Fat molecule (triacylglycerol)

8. LE 5-12a
Butter
Stearic acid
Saturated fat and fatty acid.

9. Unsaturated fat -contains unsaturated fatty acids
-carbon-carbon double bonds (>1)
-irregular hydrocarbon conformation
-poor packing
-forms liquids (oils) at room temperature
Tend to be from plants and fish

10. Other liquid fats (unsaturated)?
LE 5-12b
Olive oil
Other liquid fats (unsaturated)?
Oleic acid
cis double bond
causes bending
Unsaturated fat and fatty acid.

11. Phospholipids Structure Fatty acids= Hydrophobic tail
two fatty acids bonded to glycerol through ester linkage
Phosphate bonded to third hydroxyl group of glycerol
Fatty acids= Hydrophobic tail
Phosphate and other groups= hydrophilic head
Draw schematic

12. Choline Hydrophilic head Phosphate Glycerol Hydrophobic tails
LE 5-13
Choline
Hydrophilic head
Phosphate
Glycerol
Hydrophobic tails
Fatty acids
Hydrophilic
head
Hydrophobic
tails
Structural formula
Space-filling model
Phospholipid symbol

13. If many phospholipids were mixed in H2O
into what structures would they self-assemble?
Micelle (draw)
- Detergents
Bilayer (draw)
-Cell membranes

14. Cellular membrane: Phospholipid Bilayer
LE 5-14
Cellular membrane: Phospholipid Bilayer
WATER
Hydrophilic
head
Hydrophobic
tails
WATER

15. Steroids Structure Examples and Diverse Functions
- Hydrophobic molecules made of 4 fused hydrocarbon rings
Examples and Diverse Functions
Cholesterol
Component of animal cell membranes
Building block for steroid sex hormones such as
Estrogen, testosterone, progesterone
High levels--> contribute to heart disease

16. Cholesterol

17. estradiol
testosterone

18. Pardon me. Did you miss
anything?

19. Ch 7 Membrane Structure and Function

20. Cellular membrane -overall functions
- Boundary between intracellular compartments, living cells, and abiotic environment
Selectively permeable
Some molecules cross membranes more readily than others

22. Membrane Structure Predominant constituent: phospholipids
Amphipathic molecules: hydrophobic AND hydrophilic
Dispersed protein components
Membrane organization and properties described by:
Fluid Mosaic Model
Singer and Nicolson 1972

23. Organization of membrane phospholipids
LE 7-2
Organization of membrane phospholipids
WATER
Hydrophilic
head
Hydrophobic
tail
WATER

24. Mosaic: something made of small pieces

25. Mosaic: Proteins dispersed among phospholipids in membrane:
LE 7-3
Mosaic: Proteins dispersed among phospholipids in membrane:
Hydrophilic region
of protein
Phospholipid
bilayer
Hydrophobic region of protein

26. Imaged by EM Freeze-fracture studies of the plasma membrane
Frozen membrane split along the middle of the phospholipid bilayer using a knife
Imaged by EM
Supports mosaic part of model

27. Extracellular layer Proteins Knife Plasma membrane Cytoplasmic layer
LE 7-4
Extracellular
layer
Proteins
Knife
Plasma
membrane
Cytoplasmic
layer
Extracellular layer
Cytoplasmic layer

28. The Fluidity of Membranes
Phospholipids move laterally within the bilayer
Some membrane proteins also drift laterally
Rarely does a phospholipid flip-flop transversely across the membrane

29. Movement of phospholipids
LE 7-5a
Lateral movement
(~107 times per second)
Flip-flop
(~ once per month)
Movement of phospholipids

30. Cool temp: membranes switch from fluid to more solid state
Effects of Temperature on membranes
Cool temp: membranes switch from fluid to more solid state
Solidification depends on type of lipid
What property of lipids would favor liquid versus solid state?

31. Degree of saturation of fatty acid tails
LE 7-5b
Degree of saturation of fatty acid tails
Fluid
Viscous
Unsaturated hydrocarbon
tails with kinks
Saturated hydro-
carbon tails
Membrane fluidity

32. Tends to moderate effects of temp. on membrane state
Steroid cholesterol
also component of membranes
Tends to moderate effects of temp. on membrane state
At warm temperatures (such as 37°C), restrains movement of phospholipids
At cool temperatures, maintains fluidity by preventing tight packing

33. Cholesterol within the animal cell membrane
LE 7-5c
Cholesterol
Cholesterol within the animal cell membrane

34. Movement of membrane proteins
Can drift within the bilayer
Proteins much larger than lipids--> move more slowly
Cell fusion studies support fluidity of membrane proteins

35. Membrane proteins Mouse cell Mixed proteins after 1 hour Human cell
LE 7-6
Membrane proteins
Mouse cell
Mixed
proteins
after
1 hour
Human cell
Hybrid cell

36. Membrane Proteins and Their Functions
Proteins determine most of the membrane’s specific functions
Peripheral membrane proteins
not embedded
attached to extracellular or cytoplasmic surface
Integral membrane proteins
penetrate the hydrophobic core of bilayer
often span the membrane

37. LE 7-7 Fibers of extracellular matrix (ECM) Glycoprotein Carbohydrate
Glycolipid
EXTRACELLULAR
SIDE OF
MEMBRANE
Cholesterol
Microfilaments
of cytoskeleton
Peripheral
proteins
Integral
protein
CYTOPLASMIC SIDE
OF MEMBRANE