LIPIDS Flashcards
These diverse compounds that make up
the lipid family are so grouped because
they are
insoluble in water
They are also ____ in other organic
solvents such as ether, acetone, and other
lipids.
soluble
serve a variety of important
functions in living organisms.
* They act as chemical messengers, serve as
valuable energy sources, provide
insulation, and are the main components
of membranes.
lipids
Major lipid groups
include
fats
, phospholipids
, steroids,
and waxes
The chemical term includes fats, oils,
and related compounds that are insoluble in
water and greasy to the touch.
* Some food lipids—butter, margarine, or
cooking oil—are easily recognized as fats.
* Other foods that appear to be
carbohydrates, such as bakery items or
potato chips, often contain significant
amounts of fat.
lipid
Lipids are ____compounds
consisting of a carbon chain with
hydrogen and oxygen atoms attached.
Particular lipids may have other
radicals or groups of elements
attached.
* Fatty acids and their related
compounds are the lipids important in
human nutrition.
organic
Lipids have something in common with
carbohydrates: the same chemical elements that
make up carbohydrates
the same chemical elements that make up
carbohydrates—
carbohydrates—carbon, hydrogen, and oxygen—also
make up fatty acids. However, carbohydrates and
lipids have two important structural differences:
Lipids are more ____, with more carbon (C)
and hydrogen (H) atoms and fewer oxygen (O)
atoms.
complex
The common structural units of lipids are fatty
acids, whereas the common structural units of
carbohydrates are .
simple sugars
The saturation or unsaturation of a lipid governs its physical characteristics:
- Saturated fats are hard
- Less-saturated fats are soft
- Unsaturated fats are liquid at room temperature
Lipids composed mostly of saturated fatty acids are called saturated fats.
Although saturated fatty acids are usually found in animal foods, the most saturated
food fats are two oils from plants: (1) coconut oil, which is 88% saturated, and (2)
palm kernel oil, which is 80% saturated. All other saturated fats are of animal origin
as found in meat; butter; whole, reduced-fat, and low-fat milk; and other dairy
products.
Saturated
Food lipids that have a high proportion of fatty acids with a pair of
hydrogen atoms missing, creating one double bond, are called monounsaturated fats.
These lipids are generally from plant sources. Canola oil (isolated from rapeseed) and
olive oil are primarily mono- unsaturated fats.
monosaturated
When fatty acids have four or more spaces unfilled with
hydrogen atoms, creating two or more double bonds, they are
polyunsaturated fats. Many of these fats are from plant sources and include
commonly used cooking oils such as corn oil and safflower oil.
Polyunsaturated fatty acids with two or more double bonds are also classified
according to the position in the carbon chain where the first double bond
appears. These are referred to as essential fatty acids because the body cannot
synthesize an n-3 or n-6 fatty acid. The n-3 fatty acids found in fatty fish have a
role in cardiovascular health.
Polyunsaturated:
Two different fatty acids—linoleic acid (an n-6 fatty
acid) and α-linolenic acid (an n-3 fatty acid) are
essential fatty acids for humans. Arachidonic acid,
another fatty acid important in human nutrition, can be
made from linoleic acid. Two n-3 fatty acids associated
with cardiovascular health—(1) eicosapentanoic acid
(EPA) and (2) docosahexaenoic acid (DHA)—can be
made from α-linolenic acid but these conversion rates
are extremely slow,13,14 and influenced by age, sex,
genetics, and overall dietary intake. Therefore,
individuals need to obtain these acids from regular
servings of fish.
Essential Fatty Acids
The essential fatty acids strengthen cell membranes and prevent a harmful
increase in skin permeability. Essential fatty acid deficiency causes breakdown in skin tissue,
with characteristic eczema and skin lesions. Essential fatty acid deficiency seldom occurs
with the exception of a patient receiving a parenteral nutrition formula that does not
include the essential fatty acids.
Skin integrity:
Polyunsaturated fatty acids can reduce blood lipid levels,
particularly if they are replacing saturated fat in the diet.
Regulation of lipid metabolism:
Normal growth requires an adequate supply of the essential fatty acids, and growth
is impaired in essential fatty acid deficiency; α-linolenic acid is especially important for the
development of brain tissue before and after birth.
Growth
The essential fatty acids regulate the production of enzymes needed for
synthesis of nonessential fatty acids.
Gene expression
Persons with essential fatty acid deficiency have an increased rate of
infection.
Immune Function
EPA and DHA prevent unwanted aggregation of blood platelets
that blocks the flow of blood in major arteries, causing heart attack or stroke.
Aggregation of blood platelets:
Essential fatty acids are metabolic precursors of a group of
physiologically and pharmacologically active compounds known as eicosanoids
- Synthesis of hormonelike agents:
Arachidonic acid and DHA play a critical role in
the brain and neural development of infants;
both are found in breast milk in liberal
amounts. Commercial infant formula sold in the
United States is fortified with arachidonic acid
and DHA to the levels found in human milk.
Based on the important role of DHA in both
prenatal and postnatal development, some
nutrition experts have proposed that both
pregnant and lactating women of DHA from
fish or supplements during pregnancy, the DHA
content of breast milk, and infant health
outcomes such as visual acuity and cognitive
development.
Special Needs of Infants
The best sources of the two essential fatty acids
are vegetable oils. Corn oil, safflower oil, soybean
oil, cottonseed oil, sun- flower oil, and peanut oil
are rich in linoleic acid (an n-6 acid), and α-
linolenic acid (an n-3 acid) is found in flaxseed,
soybean oil, and rapeseed oil (canola oil).
Food Sources of Essential Fatty Acids
which have received
increasing attention in the popular press
as an alternative to eating fish, should be
used only with the supervision of a health
care professional. Because EPA and DHA
can excessively prolong bleeding time,
persons taking anticoagulants including
warfarin and aspirin should use such
supplements with caution.
Use of Fish Oil Supplements
The body stores fatty acids in the form of
triglycerides made from three fatty acids attached
to a glycerol base. When glycerol is combined with
one fatty acid, it is called a monoglyceride; with two
fatty acids, it is a diglyceride; and with three fatty
acids it is termed a triglyceride. Glycerides are found
in food and also formed in the body. Most natural
lipids from animal or plant sources are triglycerides.
Triglycerides serve multiple functions throughout
the body. They appear in body cells as oily droplets
and circulate in the water-based blood plasma
encased in a covering of water-soluble protein.
These lipid-protein molecules are called lipoproteins.
Structure of Triglycerides
To meet the demand for solid fats for use as table fats or food ingredients the process of
________ was developed.
hydrogenation
have been implicated in the development of coronary artery disease. In addition, they
elevate the risk of type 2 diabetes and disrupt essential fatty acid functions in cells
Trans fatty acids have
Although _____ is not a fat or a triglyceride, it is often discussed in connection with dietary
lipids. Cholesterol belongs to a family of substances called steroids and travels in the blood
attached to long-chain fatty acids. People some- times confuse cholesterol with saturated fat
because both substances are believed to promote atherosclerosis.
cholesterol
is found in animal foods but not plant foods. Egg yolk; meat; whole, reduced-fat, and
low-fat milk; cheese; and organ meats supply cholesterol. Animal fats (but not plant fats) are rich
sources.
cholesterol
is required for normal body function and synthesized in the liver. If a
person obtained no cholesterol whatso- ever from food, the body would still have an
adequate supply. Cholesterol has broad roles as follows:
- Precursor to steroid hormones: A cholesterol compound in the skin,
7-dehydrocholesterol, is converted to vitamin D when the ultraviolet rays of the sun
pass into the skin; cholesterol is also a precursor of estrogen and testosterone.
*Formation of bile acids: Cholesterol is used to form bile acids, which emulsify fats and
facilitate their digestion; bile acids serve as carriers in fat absorption.
*Component of brain and nerve tissue: The brain and nerves include cholesterol in their
structure.
*Component of cell membranes: Cell membranes contain cholesterol.
Cholesterol
The liver is the body clearinghouse for fatty acids and cholesterol, whether supplied in
food or produced in body tissues. When received by the liver, fatty acids and
cholesterol are packaged into lipoproteins and released into the circulation for
transport to cells.
Lipoproteins
Lipids are insoluble in water, which poses a problem when they need to be carried in a
water-based circulatory system. The body solves this problem by producing
lipoproteins, a complex of lipids and lipid like substances surrounded by water-soluble
protein.
* Special compounds called phospholipids are important in the structure of lipoproteins.
Phospholipids are molecules in which one of the three fatty acids attached to a glycerol
base is replaced with a phosphate (PO4−3) group that is water soluble and assists in the
transport of lipoproteins.
* Phospholipids in cell membranes help lipid molecules move from the circulatory system
into the cell.
* Lipoproteins contain fatty acids, triglycerides, cholesterol, phospholipids, and traces of
fat-soluble vitamins and steroid hormones.
Lipid Transport
are classified according to their density, as determined by their
relative content of lipid and protein. The more protein present, the greater
the density. The amount of each lipoprotein in the blood is influenced by the
time since the last meal and the quantity and type of fat that a person
consumes on a regular basis. The five lipoprotein classes are as follows:
Lipoproteins
These relatively large particles are formed in the intestinal wall after a meal and carry the
digested and absorbed fat to the liver for conversion to other lipoproteins.
Chylomicrons:
The VLDLs are formed in the liver during the fasting interval
between meals. When there is no food in the digestive tract and chylomicrons are not entering the
circulatory system, VLDLs transport endogenous triglycerides from the liver to tissue cells.
Very low-density lipoproteins (VLDLs):
IDLs are formed from VLDLs and continue the delivery of
endogenous triglycerides to the cells.
Intermediate-density lipoproteins (IDLs):
LDLs are formed from VLDLs and IDLs and carry mainly cholesterol, as
most of the triglyceride has already been moved into cells.
Low-density lipoproteins (LDLs):
HDLs return cholesterol from the cells to the liver for breakdown and
excretion.
High-density lipoproteins (HDLs):
short chain faty acids contain
4 to 6 carbon atoms
medium-chain fatty acids have
8, 10, or 12 carbon atoms
long-chain fatty acids haves
14, 16, 18, or more carbon atoms
Highly saturated fat (solid at room temp)
stick margarine
butter
beef fat
less-saturated fat (very soft at room temp)
tub margarine
squeeze margarine
unsaturated fat (lipid at room temp.)
salad oil
