Short overview on carbohydrates and
lipids
CARBOHYDRATES
Types of carbohydrates
Simplest – monosaccharides
Cannot be split or hydrolyzed into smaller compounds
Most common – glucose – C6H12O6
Disaccharide – has 2 monosaccharide units joined together
Can be split into smaller compounds
Table sugar – sucrose (C12H22O11) – disaccharide
By hydrolysis – glucose and fructose
A polysaccharide – contains many monosaccharide units
Polymer
Hydrolysed to yield many monosaccharide molecules
Monosaccharides
Chain of 3-8 C atoms, one in a carbonyl group and all others
attached to hydroxyl groups
Aldose – the carbonyl group is on the first C as an aldehyde
(-CHO)
Ketose – carbonyl group on the second carbon as a ketone
(C=O)
3 C atoms – triose
4 C atoms – tetrose
5 C atoms – pentose
6 C atoms – hexose
We can use both classification systems to indicate the type of
carbonyl group and the number of C atoms
Example: aldose
Only chiral carbon is the middle carbon
The –H and –OH groups can be drawn to the left of the chiral
atom – L stereoisomer
If it is drawn to the right – D stereoisomer
Fisher projections – also for compounds that have two or
more chiral carbons
Both C atoms at the intersections are chiral
To decide if L or D stereoisomer: by the position of the –
OH group attached to the chiral carbon farthest from the
carbonyl group
Important monosaccharides
Glucose, galactose and fructose
C6H12O6 – but are isomers of each other
D- stereoisomers are more commonly found in nature and
used in the cells of the body
Glucose
Also known as dextrose
and blood sugar
In fruits, vegetables, corn
syrup and honey
Building block of the
sucrose, lactose and
maltose
Also in polysaccharides
amylose, cellulose and
glycogen
Galactose
Aldohexose – obtained from the disaccharide lactose
Milk and milk products
Important in cellular membranes of the brain and nervous
system
Galactosemia – enzyme that converts galactose to glucose is
missing
Accumulation in the blood – cataracts, mental retardation
and liver disease
Treatment: removal of all galactose-containig foods (milk)
from the diet
Fructose
Ketohexose
The sweetest of the carbohydrates; twice as sweet as sucrose
Fruit sugar found in fruit juices and honey
Also obtained as one of hydrolysis products of sucrose
Chemistry Link to Health:
Hyperglycemia and Hypogycemia
Glucose tolerance test – evaluation of bodys ability to return
to normal glucose concentrations (70-90 mg/dL)
Fasting for 12 hours then taking a solution containing glucose
Blood samples are taken immediately followed by more
blood samples each ½ hour
Glucose exceeds 200 mg/dL and remains high –
hyperglycemia
Caused by diabetes mellitus
Person is hypogycemic – glucose levels rises and decreases
rapidly to levels low as 40 mg/dL
Caused by overproduction of insulin by the pancreas
Low blood sugar – dizziness, general weakness and muscle
tremors
Diet: several small meals high in protein and low in
carbohydrates
Chemical properties of monosaccharides
Contain functional groups – undergo chemical reactions
Aldose – aldehyde group oxidised to a carboxylic acid
Carbonyl group – reduced to give hydroxyl group
Can react with other compounds to form a variety of
derivatives – important in biological structures
Disaccharides
Composed of two monosaccharides linked together
Most common: maltose, lactose and sucrose
2 monosaccharides in dehydration reaction give disaccharide
Maltose Obtained from starch
Found in germinating grains
Used in cereals, candies or in brewing beverages
Glycosidic bond – ether bond that connects two
monosaccharides
Formation of Maltose
Lactose Milk sugar (milk and milk
products)
Makes 6-8% of human milk and 4-5% of cows milk
Lactase – enzyme that hydrolyses lactose
Unsufficient amount – lactose remains undigested
Colon bacteria digest it in fermentation process
Creates large amounts of gas (CO2 and methane)
Causes bloating and abdominal cramps
Sucrose
Cannot form an open chain
Cannot be oxidized
Is not reducing sugar
Sugar that we use to sweeten coffee or tea
20% from sugar cane or 15% from sugar beets
Sweeteners
Sugars and artificial
sweeteners
Differ in sweetness.
Are compared to
sucrose (table sugar),
which is assigned a value of
100.
Sweeteners
Extensive scientific research has studied the safety of the six low-calorie sweeteners currently approved for use in foods in the U.S. and Europe:
Stevia
Acesulfame-K
Aspartame
Neotame
Saccharin
Sucralose
Polysaccharides
Polymer consisting of many monosaccharides
Important: amylose, amylopectin, cellulose and glycogen
Polymers of D-glucose
Amylose
Makes up about 20% of starch
250-4000 D-glucose molecules
Straight-chain polymer
Coiled in helical fashion
Amylopectin Makes up around 80% of
starch
Branched-chain polysaccharide
Starches hydrolyze easily in water and acid – gives smaller saccharides dextrins
Those hydrolyze to maltose and finally to glucose
In the body – digested by amylase (saliva) and maltase (intestine)
Glycogen Animal starch
Polymer of glucose
Stored in liver and muscle of animals
Hydrolyzed in our cells at a rate that maintains the blood level of glucose
and provides energy between meals
Structure – similar to amylopectin, but more highly branched
Cellulose
Major structural material of wood and plants
Cotton – pure cellulose
Do not form coils like amylose
Aligned in parallel rows
Held in place by hydrogen bonds
Insoluble in water
Humans cannot digest cellulose
Summary
Types of carbohydrates
Important monosaccharides
Chemical properties of monosaccharides
Disaccharides
Polysaccharides
LIPIDS
Basic functions in the body
•Store and provide energy -Fats provide 9 kcal per gram
•Provide insulation
•Help manufacture steroids and bile salts
•Play a role in transporting fat-soluble nutrients in the blood
•Used to manufacture major sex hormones
•Key to the structure of cell membranes
Name: Greek word lipos (fat or lard)
Lipids
Lipid – a naturally occurring molecule from a plant or
animal; soluble in nonpolar organic solvents
Fatty acid – a long-chain carboxylic acid; in animal fats and
vegetable oils have between 12-22 C atoms
Waxes – carboxylic esters with long, straight hydrocarbon
chains in both R groups; secreted by glands in the skin and
perform external protective functions.
Fatty acids
Contains a long, unbranched carbon chain
Carboxylic acid group at one end – hydrophilic
Hydrophobic chain – makes them insoluble in water
Naturally occuring – even number of C atoms (12-20)
Example: lauric acid (12-C acid) from coconut oil
Saturated fatty acid – only C-C single bonds
Make the properties of a long-chain fatty acid aimilar to alkane
Unsaturated fatty acid – one or more C-C double bonds
Monounsaturated fatty acid – only one double bond
Polyunsaturated fatty acid – has at least two C-C double
bonds
Lipids of plants and animals – half of fatty acids are saturated and
half are unsaturated
Fatty Acids
Building blocks for triglycerides and phospholipids
A chain of carbon and hydrogen atoms with a carboxyl
group at the alpha end and a methyl group at the
omega end.
Cis and Trans Isomers of Unsaturated
FA Cis structure (example: oleic acid) is more prevalent isomer
found in naturally occuring unsaturated FA
In cis isomer – carbon chain has a “knick” at the double bond
site
The cis bond has a major impact on the physical properties
and uses
Humans – some fatty acids synthesized from carbohydrates
or other fatty acids
No sufficient amount of polyunsaturated fatty acids (linoleic
or linolenic acid)
Must be obtained from the diet – essential fatty acids
Deficiency in infants – skin dermatitits
Physical properties of FA Saturated – fit closely
together in regular pattern; allows many dispersion forces between C chains
Weak forces; significant when molecules of FA are close together
Significant amount of energy and high temperatures are required to separate and melt the FA
Saturated FA – solid at room temperature
Usaturated – cis double
bonds cause C chain to bend
or knick; irregular shape of
molecule
Result: cannot stack as closely
as saturated fatty acids
Have fewer interactions
between carbon chains
Less energy needed to
separate the molecules
Chemistry Link to Health:
Omega-3 Fatty Acids in Fish Oil
Unsaturated fats more beneficial than saturated
More of those fats included in diet because of atherosclerosis
and heart disease
Inuit people (Alaska) – diet with high levels of unsaturated
fats but also high levels of cholesterol
However, low occurrence of atherosclerosis and heart attacks
Fats primarily usaturated from fish rather than from land
animals
In vegetable oils – omega-6 acids
First double bond iccurs at carbon 6 counting from the methyl
end of the carbon chain
Linoleic acid (LA) and arachidonic acid (AA)
In fish are mostly omega-3 fatty acids
First double bond occurs at the third carbon counting from the
methyl group
Common: linolenic acid (ALA), eicosapentaenoic (EPA) and
docosahexaenoic acid (DHA)
Melting Points of Fats and Oils
A triacylglycerol that is a fat
Is solid at room temperature.
Is prevalent in meats, whole milk, butter, and cheese.
A triacylglycerol that is an oil
Is liquid at room temperature.
Is prevalent in plants such as olive and sunflower.
Waxes
Found in many plants and animals
Natural waxes – on the surface of fruits and on the leaves;
help prevent loss of water and pests damage
On the skin, fur and feather – waterproof coating
Wax – ester of a saturated fatty acid and a long-chain alcohol
Contains 14-30 C atoms
Triacylglycerols (TGAs)
In the body fatty acids are stored as triacylglycerols
(triglycerides)
Triesters of glycerol and fatty acids
TGAs – major form of energy storage for animals
Animals that hibernate eat large amounts of plants, seeds and
nuts (high in calories)
Gain up to 14 kg/week
External temperature drops – the animal goes into
hibernation
Body temperature drops, cellular activity, respiration and
heart rate are drastically reduced
4-7 months
Stored fat is only source of energy
Triglycerides
Most common lipid in both foods and the body
Make up about 95% of lipids found in foods
Functions
•Add texture
•Makes meats tender
•Preserves freshness
•Stores as adipose tissue for energy
Phospholipids
Family of lipids similar in structure to TAGs
Include:
glycerophospholipids and
sphingomyelins
Glycerophospholipids
Two FA form ester bonds with the first and second hydroxyl
groups of glycerol
Third hydroxyl group – forms an ester with phosphoric acid
which forms another phosphoester bond with an amino
alcohol
Glycerophospholipids – polar and nonpolar regions
Allows them to interact with both kinds of substances
Ionized amino alcohol and phosphate portion – polar; strongly
attached to water
Hydrocarbon chains – nonpolar, soluble in other nonpolar
substances (mostly lipids)
Phospholipids
Hydrophilic on one end; hydrophobic on the other
Make up the phospholipid bilayer in the cell membrane
•Lecithin (a.k.a. phosphatidylcholine)
-A major phospholipid in the cell membrane
-Used as an emulsifier in foods
Synthesized by the liver
Sphingomyelin
Sphingosine instead of glycerol
Steroids
Compounds containing steroid nucleus
Has 3 cyclohexane rings and one cyclopentane ring fused
together
The four rings are designated A, B, C and D
The carbon atoms are numbered beginning with the carbons
in ring A
Cholesterol
One of most abundant steroids in the body
Has OH group and oxygen at C3
Double bond between C5 and C6
Methyl group at C10 and C13
Carbon chain at C17
Compund of cellular membranes, myelin sheath, brain and nerve tissue
Also found in liver
Large quantities are in the skin – some of it become vitamin D when the skin is exposed to direct sunlight
In the adrenal gland – used to synthesize steroid hormones
Liver synthesizes it for the body from fats, carbohydrates and
proteins
Additional amount is obtained from meat, milk and eggs
No cholesterol in vegetable and plant products
Cholesterol in the Body
Saturated fats and cholesterol – associated with diseases: diabetes, cancer (breast, pancreas and colon) and atherosclerosis
Accumulation of protein-lipid complex (plaque) in the coronary blood vessels
Can lead to myocardial infarction (heart attack)
Other factors can increase the risk: family history, lack of exercise, smoking, obesity, diabetes, gender and age.
Bile Salts
Synthesized form the cholesterol in the liver
Stored in gallbladder
Secretion of bile in small intestine – bile salts mix with water-
insoluble fats and oils (from the diet)
Nonpolar and polar regions, act like soaps – breaking down large
globules of fat into smaller droplets
Smaller droplet – larger surface area to react with lipases
(enzmye that digest fats)
Salts also help with the absorption of cholesterol into the
intestinal mucosa
Accumulation of large cholesterol amounts in gallbladder –
cholesterol becomes solid (forms gallstones)
Stones – 100% cholesterol, with some Ca-salts, FA and
glycerophospholipids
Small stones – pass through the bile duct
Large stones – can get stuck; painful
If stones obstruct the duct – bile cannot be excreted
Bile pigments (bilirubin) go back up into liver and are excreted
via the blood
Causes hyperbilirubinemia – yellow color to the skin and the
whites of the eyes
Lipoproteins: Transporting lipids
Moving of the lipids through the body
Nonpolar lipids are insoluble in blood
Made more soluble by combining them with phospholipids
and proteins to form water-soluble complexes
Lipoproteins
Spherical particles
Outer surface – polar proteins and phospholipids
Surround hunderds of nonpolar molecules of TAGs and
cholesteryl esters (prevalent form of cholesterol in the
blood)
The good and the bad
Important lipoproteins are LDL and HDL
Transport cholesterol
LDL – carries to the tissues where it can be used for the
synthesis of cell membranes and steroid hormones
If exeeds the amount of choesterol – deposits it in the
artheries (plaque)
Bad cholesterol
HDL – carries cholesterol from the tissue to the liver
There it is converted to bile salts – eliminated from the body
Good cholesterol
Lipid panel – blood test that mesures serum lipid levels
(cholesterol, triglycerides, LDL and HDL)
The results – help for the treatment or evaluate a patients
risk of heart disease
Steroid hormones
Hormones – chemical messengers
Serve as communication system in the different parts of the body
Steroid hormones – sex hormones and adrenocortical hormones
Related in structure to cholesterol and depend on cholesterol for
their synthesis
Summary
Lipid types
Fatty acids
Waxes and triacylglycerols
Chemical properties of TAGs
Phospholipids
Steroids: Cholesterol, Bile Salts and Steroid hormones
Bile salts
LDL/HDL