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