Title: Lipids
1Lipids
- Highly diverse structures
- Unifying property
- Hydrophobic little to no affinity to water
- Contains hydrocarbons, which form nonpolar
covalent bonds - Do not form polymers
- Most important in biological context
- Fats
- Phospholipids
- Steroids
2Fats
- Structure
- Composed of two different molecules bonded by
ester linkage - glycerol and fatty acids
- Glycerol
- Three-carbon alcohol
- Each carbon attached to hydroxyl group
- - Fatty acid
- Hydrocarbon chain with a carboxyl group at
one end
Try to Draw
3LE 5-11a
Fatty acid (palmitic acid)
Glycerol
Dehydration reaction in the synthesis of a fat
4LE 5-11b
Ester linkage
Fat molecule (triacylglycerol)
5Properties of Fats
- Hydrophobic
- H2O molecules form hydrogen bonds with each other
and EXCLUDE fatty acid chains--gt - Fats separate from H2O
Fatty acids variable chain length (often 16-18
carbons)
6Saturated fats - refer to saturated fatty acid
chains -contain maximum number of hydrogens -
result in 100 single bonds - more
linear, pack tightly to form solid Tend to be
from animals
7LE 5-12a
Stearic acid
Saturated fat and fatty acid.
8Unsaturated fats -contain unsaturated fatty
acids -carbon-carbon double bonds
(gt1) -irregular hydrocarbon conformation - poor
packing - form liquids (oils) at room
temperature Tend to be from plants and fish
9LE 5-12b
Oleic acid
cis double bond causes bending
Unsaturated fat and fatty acid.
10Phospholipids
- Structure
- two fatty acids bonded glycerol through ester
linkage - Phosphate bonded to third hydroxyl group
-
- Fatty acids Hydrophobic tail
- Phosphate and other groups hydrophilic head
Draw schematic
11LE 5-13
Choline
Hydrophilic head
Phosphate
Glycerol
Hydrophobic tails
Fatty acids
Hydrophilic head
Hydrophobic tails
Structural formula
Space-filling model
Phospholipid symbol
12If many phospholipids were mixed in H2O into
what structures would they self-assemble?
- Micelle (draw)
- - Detergents
- Bilayer (draw)
- -Cell membranes
13LE 5-14
WATER
Hydrophilic head
Hydrophobic tails
WATER
14Steroids
- Structure
- - Hydrophobic molecules made of 4 fused rings
- Examples and Diverse Functions
- Cholesterol, an important steroid, is a component
in animal cell membranes - High levels--gt contribute to heart disease
- Building block for steroid sex hormones such as
- Estrogen, testosterone, progesterone
15Cholesterol
16estradiol
testosterone
17Pardon me. I think I missed something
18- Ch 7 Membrane Structure and Function
19Cellular membrane -overall functions
- - Boundary between intracellular compartments,
living cells, and abiotic environment - Selectively permeable
- Some molecules cross membranes easier than others
20(No Transcript)
21Membrane Structure
- Predominant constituent phospholipids
- Amphipathic molecules hydrophobic AND
hydrophilic properties
Dispersed protein components
Membrane organization and properties described
by Fluid Mosaic Model
Singer and Nicolson 1972
22LE 7-2
Organization of membrane phospholipids
WATER
Hydrophilic head
Hydrophobic tail
WATER
23Mosaic something made of small pieces
24LE 7-3
Mosaic Proteins dispersed among phospholipids in
membrane
Hydrophilic region of protein
Phospholipid bilayer
Hydrophobic region of protein
25- Freeze-fracture studies of the plasma membrane
-
- Splits a frozen membrane along the middle of the
phospholipid bilayer using a knife - Imaged by EM
- Supports mosaic part of model
26LE 7-4
Extracellular layer
Proteins
Knife
Cytoplasmic layer
Plasma membrane
Cytoplasmic layer
Extracellular layer
27The Fluidity of Membranes
- Phospholipids move within the bilayer
- Most of the lipids, and some proteins, drift
laterally - Rarely does a molecule flip-flop transversely
across the membrane
28LE 7-5a
Lateral movement (107 times per second)
Flip-flop ( once per month)
Movement of phospholipids
29Effects of Temperature on membranes
- Cool temp membranes switch from fluid to solid
state - Solidifications depends on the types of lipids
- What propertyof lipids would favor solid versus
liquid state?
30LE 7-5b
Degree of saturation of fatty acid tails
Viscous
Fluid
Unsaturated hydrocarbon tails with kinks
Saturated hydro- carbon tails
Membrane fluidity
31Steroid cholesterol also component of membranes
- Tends to moderate effects of temp on membrane
state - At warm temperatures (such as 37C), restrains
movement of phospholipids - At cool temperatures, maintains fluidity by
preventing tight packing
32LE 7-5c
Cholesterol
Cholesterol within the animal cell membrane
33Movement of membrane proteins
- Can drift within the bilayer
- Proteins much larger than lipids--gt move more
slowly - Cell fusion studies done to test fluidity of
membrane proteins
34LE 7-6
Membrane proteins
Mouse cell
Mixed proteins after 1 hour
Human cell
Hybrid cell
35Membrane Proteins and Their Functions
- Proteins determine most of the membranes
specific functions - Peripheral membrane proteins
- not embedded
- Integral membrane proteins
- penetrate the hydrophobic core of bilayer
- often span the membrane
36LE 7-7
Fibers of extracellular matrix (ECM)
Glycoprotein
Carbohydrate
Glycolipid
EXTRACELLULAR SIDE OF MEMBRANE
Cholesterol
Peripheral proteins
Microfilaments of cytoskeleton
Integral protein
CYTOPLASMIC SIDE OF MEMBRANE