Download Lecture 7

What Are Lipids?
Lecture 7:
Lipids, Part 1
• Made up of carbon, oxygen, hydrogen
• Do not dissolve in water
• Three types of lipids are found in
foods:
– Triglycerides
Nutrition 150
Shallin Busch, Ph.D.
– Phospholipids
– Sterols
Fatty Acids
Triglycerides
Composed of
– Three fatty acid molecules
• Fatty acids are long chains of carbon atoms
surrounded by hydrogen atoms
– One glycerol molecule
• Glycerol is a 3-carbon alcohol that is the
backbone of a triglyceride
Length of their carbon chain
- Short-, medium-, or long-chain
Level of saturation
- Saturation refers to how many
hydrogen atoms surround each
carbon
Shape
Fatty Acid
Fatty Acids
•Saturated fatty acids have hydrogen atoms
surrounding every carbon in the chain.
•Monounsaturated fatty acids lack hydrogen
atoms in only one region.
•Polyunsaturated fatty acids lack hydrogen
atoms in multiple locations.
Fatty Acids - Shape
Linolenic acid, an omega-3 fatty acid
Omega carbon
Acid end
Methyl end
• Determined by the saturation of the
carbon chains.
• Saturated fatty acids can pack tightly
together and are solid at room
temperature.
Linoleic acid, an omega-6 fatty acid
– For example animal fats, butter, and lard are
high in saturated fatty acids.
Omega carbon
Acid end
Methyl end
• Unsaturated fatty acids do not stack
together well and are liquid at room
temperature.
– Plant oils have unsaturated fatty acids.
Fatty Acids
Trans Fatty Acids
The hydrogen atoms at an unsaturated
region can be arranged in different
positions:
– Cis – hydrogens on same side of the
carbon chain
– Trans – hydrogens on opposite sides of
the chain
Cis- and Trans-Fatty Acids
Fatty Acids
cis-fatty acid
Hydrogenation: The addition of hydrogen
atoms to unsaturated fatty acids.
– Coverts liquid fats (oils) into a more solid
form
– Used to create margarine from plant oil
– Often creates trans fatty acids
trans-fatty acid
Hydrogenation
Triglycerides
Composed of
– Three fatty acid molecules
Polyunsaturated fatty acid
Hydrogenated (saturated) fatty acid
• Fatty acids are long chains of carbon atoms
surrounded by hydrogen atoms
– One glycerol molecule
• Glycerol is a 3-carbon alcohol that is the
backbone of a triglyceride
Glycerol
Figure 5-3
Page 145
Glycerol and 3 Fatty Acids Form a Triglyceride
To make a triglyceride, three fatty acids attach to glycerol in condensation reactions:
Glycerol + 3 fatty acids
Triglyceride + 3 water molecules
When glycerol is free, an OH group is attached to each carbon. When
glycerol is part of a triglyceride, each carbon is attached to a fatty acid
by a carbon-oxygen bond.
A Mixed Triglyceride
Phospholipids
Are composed of
• Glycerol backbone
• 2 fatty acids
• Phosphate
Are soluble in water
Are manufactured in our bodies so they
are not required in our diet
This mixed triglyceride includes a saturated fatty acid, a monounsaturated fatty acid, and a polyunsaturated fatty acid.
Phospholipid
Phospholipids
From 2
fatty acids
From glycerol
From phosphate
Sterols
Sterols
Sterols: Lipids containing multiple rings
of carbon atoms.
– Are crucial components of cell
membranes and many hormones
– Are manufactured in our bodies and
therefore are not essential components
of our diet
Sterols
(Carbohydrate are also made of rings, but the rings
are not combined directly.)
A Bile Acid
Bile acid made from cholesterol
Cholesterol
Vitamin D3
Bound to an amino
acid from protein
Lipases Digest Fats
Digestion of a Triglyceride
Lipase: Enzyme that facilitates breakdown of
triglycerides. Triglycerides are broken into 2 fatty
acids and a monoglyceride.
Bonds break
Mouth: Lingual lipase from salivary glands
Stomach: Mixing breaks fat into droplets; gastric
lipase
Bonds break
Triglyceride
Pancreas: Pancreatic lipase
Monoglyceride + 2 fatty acids
Small Intestine: Intestinal lipase
Bile
• Made by liver, stored in gall bladder,
released into small intestine
In-text Figure
Page 149
Oil
• Bile disperses fat into smaller fat
droplets
• An Emulsifier: “Substance that has
both water-soluble and fat-soluble
portions that promotes the mixing of
oils and fats in watery solutions.”
Whitney and Rolfes
Water
Without help from emulsifiers, fats and water don’t mix.
A Bile Acid
Emulsification of Fat by Bile
Fat
Fat
Watery
GI juices
Bile acid made from cholesterol
Enzyme
Bound to an amino
acid from protein
Bile
Emulsified
fat
Emulsified
fat
Emulsified
fat
Enzymes
Absorption of Fat
Small intestine
Stomach
Lipid Absorption
Monoglyceride
Short-chain
fatty acids
Medium-chain
fatty acids
• Lipids enter cells by diffusion
Glycerol
• Glycerol, small and medium-chain fatty
acids are absorbed directly into the blood
• Micelles: Molecules of bile surrounded by
monoglycerides and fatty acids. Brought to
intestinal cells where contents are
absorbed.
Chylomicrons
Micelle
Protein
Triglyceride
Lacteal
(lymph)
Capillary network
Chylomicron
Blood vessels
To blood
To liver
Longchain
fatty
acids
Transportation of Lipids
Structure of a Lipoprotein
• Fatty acids are arranged as
lipoproteins (clusters of lipid and
protein)
– Chylomicron
– Very-low-density lipoprotein
– Low-density lipoprotein
– High-density lipoprotein
Chylomicron
A lipoprotein produced by cells lining
the small intestine.
Transportation
• Chylomicrons are made by cells of the small
intestine
• Travel through the lymphatic system
– Composed of fatty acid and cholesterol
surrounded by phospholipids and
proteins
Protein
Phospholipid
• Transferred to the bloodstream
– Soluble in water
• Triglycerides in the chylomicrons must be
disassembled by lipoprotein lipase before
they can enter body cells.
Cholesterol
Triglyceride
• Components (mostly triglycerides) taken up
by cells in the body
Absorption of Fat
Small intestine
Blood Lipids
Stomach
Monoglyceride
Short-chain
fatty acids
Medium-chain
fatty acids
Glycerol
Chylomicrons
2. VLDLs – very low-density lipoproteins
Triglyceride
3. LDLs – low-density lipoproteins
Lacteal
(lymph)
Capillary network
1. Chylomicrons
Micelle
Protein
Chylomicron
Blood vessels
Longchain
fatty
acids
4. HDLs – high-density lipoproteins
All made of triglyceride, phospholipid,
cholesterol, and protein
To blood
To liver
Very-low-density
Lipoproteins
Low-Density Lipoprotein
• Made by the liver
• Is VLDL minus triglycerides
• Composed of lipids from blood stream
and lipids made by the liver
• Delivers triglycerides, cholesterol,
and phospholipids to cells
• Leaves the liver for transportation to
other parts of the body
• Cleared from the blood by liver
(special receptors on liver collect it)
• Loses triglycerides to cells and
becomes LDL
• “Bad cholesterol”
Relative Size of Lipid Transport Molecules
High-Density Lipoprotein
• Made by the liver
• Carries cholesterol from the cells to
the liver for recycling and disposal
Chylomicron
• “Good cholesterol”
LDL
VLDL
HDL
Composition of Lipid Transport Molecules
100
Percent
80
Protein
60
40
Cholesterol
20
0
Phospholipid
Triglyceride
Chylomicron
VLDL
LDL
HDL
Triglycerides in the Body
After entering body cells, triglycerides
can be
– Used immediately for energy
– Used to make lipid-containing compounds
– Stored in liver, muscle, and adipose (fat)
cells
An Adipose Cell
Newly imported triglycerides first form
small droplets at the periphery of the
cell, then merge with the large, central
globule.
Cell nucleus
Large central globule
of (pure) fat
Cytoplasm
As the central globule enlarges, the fat
cell membrane expands to accommodate
its swollen contents.