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Lipids

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Contains hydrocarbons, which form nonpolar covalent bonds. Do not form polymers ... Oleic acid. cis double bond. causes bending. Phospholipids. Structure ... – PowerPoint PPT presentation

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Title: Lipids


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
  • Most important in biological context
  • Fats
  • Phospholipids
  • Steroids

2
Fats
  • 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
3
LE 5-11a
Fatty acid (palmitic acid)
Glycerol
Dehydration reaction in the synthesis of a fat
4
LE 5-11b
Ester linkage
Fat molecule (triacylglycerol)
5
Properties 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)
6
Saturated 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
7
LE 5-12a
Stearic acid
Saturated fat and fatty acid.
8
Unsaturated 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
9
LE 5-12b
Oleic acid
cis double bond causes bending
Unsaturated fat and fatty acid.
10
Phospholipids
  • 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
11
LE 5-13
Choline
Hydrophilic head
Phosphate
Glycerol
Hydrophobic tails
Fatty acids
Hydrophilic head
Hydrophobic tails
Structural formula
Space-filling model
Phospholipid symbol
12
If many phospholipids were mixed in H2O into
what structures would they self-assemble?
  • Micelle (draw)
  • - Detergents
  • Bilayer (draw)
  • -Cell membranes

13
LE 5-14
WATER
Hydrophilic head
Hydrophobic tails
WATER
14
Steroids
  • 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

15
Cholesterol
16
estradiol
testosterone
17
Pardon me. I think I missed something
18
  • Ch 7 Membrane Structure and Function

19
Cellular membrane -overall functions
  • - Boundary between intracellular compartments,
    living cells, and abiotic environment
  • Selectively permeable
  • Some molecules cross membranes easier than others

20
(No Transcript)
21
Membrane 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
22
LE 7-2
Organization of membrane phospholipids
WATER
Hydrophilic head
Hydrophobic tail
WATER
23
Mosaic something made of small pieces
24
LE 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

26
LE 7-4
Extracellular layer
Proteins
Knife
Cytoplasmic layer
Plasma membrane
Cytoplasmic layer
Extracellular layer
27
The 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

28
LE 7-5a
Lateral movement (107 times per second)
Flip-flop ( once per month)
Movement of phospholipids
29
Effects 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?

30
LE 7-5b
Degree of saturation of fatty acid tails
Viscous
Fluid
Unsaturated hydrocarbon tails with kinks
Saturated hydro- carbon tails
Membrane fluidity
31
Steroid 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

32
LE 7-5c
Cholesterol
Cholesterol within the animal cell membrane
33
Movement 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

34
LE 7-6
Membrane proteins
Mouse cell
Mixed proteins after 1 hour
Human cell
Hybrid cell
35
Membrane 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

36
LE 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
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