Transcript Carbohydrates

Carbohydrates
CHEM 2030
Carbohydrates – polyhydroxyaldehydes or
polyhydroxy-ketones of formula (CH2O)n, or
compounds that can be hydrolyzed to them. (aka
sugars or saccharides)
Monosaccharides – carbohydrates that cannot be
hydrolyzed to simpler carbohydrates; eg. Glucose
or fructose.
Disaccharides – carbohydrates that can be
hydrolyzed into two monosaccharide units; eg.
Sucrose, which is hydrolyzed into glucose and
fructose.
Oligosaccharides – carbohydrates that can be
hydrolyzed into a few monosaccharide units.
Polysaccharides – carbohydrates that are are
Aldose – polyhydroxyaldehyde, eg glucose
Ketose – polyhydroxyketone, eg fructose
Triose, tetrose, pentose, hexose, etc. –
carbohydrates that contain three, four, five, six,
etc. carbons per molecule (usually five or six); eg.
Aldohexose, ketopentose, etc.
Epimers – stereoisomers that differ only in
configuration about one chiral center.
H
HO
H
H
CHO
OH
H
OH
OH
CH2OH
D-glucose
HO
HO
H
H
CHO
H
H
OH
OH
CH2OH
D-mannose
epimers
glyceraldehyde
an aldotriose
CHO
H
OH
CH2OH
D-(+)-glyceraldehyde
*
CH2CHCH O
OH OH
CHO
HO
H
CH2OH
L-(-)-glyceraldehyde
D & L are used to relate configuration of the chiral center
most removed from the reducing group ( C=O ). If the -OH
is on the right in the Fischer projection, then it is D, if the -OH
is on the left, then it is L
23.2: Fischer Projections and the D, L Notation.
Representation of a three-dimensional molecule as a flat
structure (Ch. 7.7). Tetrahedral carbon represented by two
crossed lines:
horizontal line is coming
out of the plane of the
page (toward you)
substituent
(R)-(+)-glyceraldehyde
(S)-(-)-glyceraldehyde
vertical line is going back
behind the plane of the
paper (away from you)
carbon
6
before the R/S convention, stereochemistry was related to (+)-glyceraldehyde
7
D-glyceraldehyde
L-glyceraldehyde
R-(+)-glyceraldhyde
S-(-)-glyceraldhyde
(+)-rotation = dextrorotatory = d
(-)-rotation = levorotatory = l
D-carbohydrates have the -OH group of the highest numbered
chiral carbon pointing to the right in the Fischer projection as in
R-(+)-glyceraldhyde
For carbohydrates, the convention is to arrange the Fischer
projection with the carbonyl group at the top for aldoses and
closest to the top for ketoses. The carbons are numbered from
top to bottom.
Carbohydrates are designated as D- or L- according to the
stereochemistry of the highest numbered chiral carbon of the
Fischer projection. If the hydroxyl group of the highest numbered
chiral carbon is pointing to the right, the sugar is designated as
D (Dextro: Latin for on the right side). If the hydroxyl group is
pointing to the left, the sugar is designated as L (Levo: Latin for
on the left side). Most naturally occurring carbohydrates are of
the D-configuration.
8
23.3: The Aldotetroses. Glyceraldehyde is the simplest
carbohydrate (C3, aldotriose, 2,3-dihydroxypropanal). The next
carbohydrate are aldotetroses (C4, 2,3,4-trihydroxybutanal).
9
Manipulation of Fischer Projections
1. Fischer projections can be rotate by 180° (in the plane of the page)
10
only!
180°
180°
Valid
Fischer
projection
Valid
Fischer
projection
a 90° rotation inverts the stereochemistry and is illegal!
11
90°
This is not the correct convention
for Fischer projections
Should be projecting toward you
Should be projecting away you
This is the correct convention
for Fischer projections and is
the enantiomer
2. If one group of a Fischer projection is held steady, the other
three groups can be rotated clockwise or counterclockwise.
120°
hold
steady
hold
steady
120°
hold
steady
120°
hold
steady
120°
hold
steady
hold
steady
12
Symmetry
13
Monarch butterfly:
bilateral symmetry=
mirror symmetry
Whenever winds blow
butterflies find a new place
on the willow tree
-Basho (~1644 - 1694)
I anticipate
organic chemistry class
highlight of my day
- Rizzo
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aldotetroses
* *
CH2CHCHCH O
OH OHOH
CHO
H
OH
H
OH
CH2OH
CHO
HO
H
HO
H
CH2OH
D-erythrose
L-erythrose
CHO
H
OH
HO
H
CH2OH
CHO
HO
H
H
OH
CH2OH
L-threose
D-threose
(+)-glucose? An aldohexose
Emil Fischer (1902)
Four chiral centers, 24 = 16 stereoisomers
* * * *
CH2CHCHCHCHCH O
OH OHOHOHOH
CHO
OH?
CH2OH
Epimers – stereoisomers that differ only in
configuration about one chiral center.
H
HO
H
H
CHO
OH
H
OH
OH
CH2OH
D-glucose
HO
HO
H
H
CHO
H
H
OH
OH
CH2OH
D-mannose
epimers
H OH
H
HO
H
H
HO
HO
HO
H
H
H
OH
OH
CHO
OH
H
OH
OH
CH2OH
H OH
HO
HO
H
H
H
OH
OH
H
OH
H
beta-(+)-glucose
CH2OH
O
OH
H
H
alpha-(+)-glucose
H
HO
OH
CH2OH
O
OH
OH
H
H
OH
H
OH
OH
Addition of alcohols to aldehydes/ketones:
R
O
C
H
+ R'OH
OH
R C H
OR'
hemiacetal
geminal
ether/alcohol
reducing!
OR'
R C H
OR'
acetal
geminal
diether
non-reducing!
H OH
HO
HO
HO
H
H
OH
H
OH
H
HO
H
H
CHO
OH
H
OH
OH
CH2OH
H OH
HO
HO
HO
H
H
H
OH
OH
nucleophilic addition of -OH on carbon 5 to the aldehyde functional group
H OH
H
HO
H
H
CHO
OH
H
OH
OH
CH2OH
H
HO
H
HOH2C
CH O
OH
H
OH
H
OH
rotate C-5 OH to rear
HO
HO
HO
H
H
H
OH
OH

H OH
HO
HO
HO
H
H
OH
H
OH 
H OH
H OH
HO
HO
HO
H
H
alpha
O
4H-Pyran
H
OH
OH
HO
HO
HO
H
H
hemiacetal
OH
H
beta
D-glucopyranoses
OH
H
H
H
HOHO
O
HO
H
H
OH
OH
H
HOHO
O
HO
H
H
H
OH
H
alpha furanose form
beta furanose form
D-glucofuranoses
O
furan
OH
H OH
H OH
HO
HO
HO
H
H
H
OH
OH
HO
HO
HO
alpha
H
H
OH
H
OH
beta
anomers - epimers at C-1
chair conformations - alpha has one group axial
beta has all groups equatorial
mutarotation in solution to 63.6% beta/36.4% alpha
CH2OHO
H
H
OH
CH2OH
OH
H
OH
alpha-D-fructofuranose
CH2OH
O
HO
H
H
OH
H
OH
CH2OH
D-fructose
CH2OHO
H
H
OH
OH
OH
H
CH2OH
beta-D-fructofuranose
Disaccharides:
(+)-maltose
“malt sugar”
two glucose units (alpha)
(+)-cellobiose
two glucose units (beta)
(+)-lactose
“milk sugar”
galactose & glucose
(+)-sucrose
“table sugar”
glucose & fructose
H OH
HO
HO
HO
H
OH
H
H OH
HO
H
O
HO
HO
HO
HO
H
H
H
H
(+)-maltose
H OH
two glucose units
alpha C-1 to C-4
OH
H
OH
reducing sugar
H OH
O
OH HO
H
HO
H
H
(+)-cellobiose
OH
H
OH
two glucose units
beta C-1 to C-4
reducing sugar
HOOH
H OH
HO
H
HO
H
H
O
OH HO
H
galactose beta C-1
to C-4 glucose
HO
H
H
(+)-lactose
OH
H
OH
reducing sugar
HO
HO
HO
H
OH
H
acetal
non-reducing
H
CH2OH
H OH
OH
O
H OH
CH2OH
HO
H
(+)-sucrose
glucose alpha C-1
to beta C1 fructose
Polysaccharides
starch
cellulose
Starch
20% amylose (water soluble)
80% amylopectin (water insoluble)
amylose + H2O  (+)-maltose
(+)-maltose + H2O  (+)-glucose
starch is a poly glucose (alpha-glucoside to C-4)
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Amylopectin + H2O  (+)-maltose
(+)-maltose + H2O  (+)-glucose
Also a polyglucose, but branched every 20-25
units:
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
CH2
O
O
O
O
O
O
O
O
O
Cellulose is a polyglucose with a beta-linkage:
O O
O O
O O
O O
O O
O O
O O
O O
The Complex Carbohydrates

Fiber Sources
 Dietary
fibers are found in plant foods.
 Functional fibers are health-benefiting fibers that are
added to foods or supplements.
 Total fiber considers both dietary and functional fibers.


Resistant starches escape digestion and are found
in legumes, raw potatoes and unripe bananas.
Phytic acid or phytate has a close association with
fiber and binds some minerals.
Digestion and Absorption of
Carbohydrates

Carbohydrate Digestion

In the mouth, the salivary enzyme amylase begins to hydrolyze
starch into short polysaccharides and maltose.

In the stomach, acid continues to hydrolyze starch while fiber delays
gastric emptying and provides a feeling of fullness (satiety).
Digestion and Absorption of
Carbohydrates

Carbohydrate Digestion

In the small intestine, pancreatic amylase among other enzymes
(maltase, sucrase, and lactase) hydrolyzes starches to disaccharides
and monosaccharides.

In the large intestine, fibers remain and attract water, soften stools and
ferment.
Digestion and Absorption of
Carbohydrates

Carbohydrate Absorption

Primarily takes place in the small intestine

Glucose and galactose are absorbed by active transport.

Fructose is absorbed by facilitated diffusion.
Monosaccharides, the end products of carbohydrate
digestion, enter the capillaries of the intestinal villi.
In the liver,
galactose
and fructose
are
converted to
glucose.
Small intestine
Monosaccharides travel to
the liver via the portal vein.
Stepped Art
Fig. 4-11, p. 110
Digestion and Absorption of
Carbohydrates

Lactose Intolerance
 Symptoms
include bloating, abdominal discomfort,
and diarrhea.
 Causes
include lactase deficiency due to a natural
decrease that occurs with aging or damaged
intestinal villi.
 Prevalence
 Lowest
in Scandinavians and northern Europeans
 Highest
in Southeast Asians and native North Americans
Digestion and Absorption of
Carbohydrates

Lactose Intolerance - Dietary Changes
 Increase
consumption of milk products gradually.
 Mix dairy with other foods.
 Spread dairy intake throughout the day.
 Use of acidophilus milk, yogurt, and kefir (fermented
products)
 Use of enzymes
 Individualization of diets
 Must be careful that vitamin and mineral deficiencies
do not develop
Glucose in the Body

A Preview of Carbohydrate Metabolism
 The
body stores glucose as glycogen in liver and
muscle cells.
 The body uses glucose for energy if glycogen stores
are available.
 If glycogen stores are depleted, the body makes
glucose from protein.
 Gluconeogenesis
 Protein-sparing
is the conversion of protein to glucose.
action is having adequate carbohydrate in
the diet to prevent the breakdown of protein for energy.
Glucose in the Body

A Preview of Carbohydrate Metabolism
 Making
ketone bodies from fat fragments
 The
accumulation of ketone bodies in the blood is called
ketosis.
 Ketosis
 The
upsets the acid-base balance in the body.
body can use glucose to make body fat when
carbohydrates are consumed excessively.
Glucose in the Body

The Constancy of Blood Glucose

Maintaining Glucose Homeostasis

Low blood glucose may cause dizziness and weakness.

High blood glucose may cause fatigue.

Extreme fluctuations can be fatal.
Glucose in the Body

The Constancy of Blood Glucose

The Regulating Hormones
Insulin moves glucose into the cells and helps to lower blood
sugar levels.
 Glucagon brings glucose out of storage and raises blood sugar
levels.
 Epinephrine acts quickly to bring glucose out of storage during
times of stress.

Balance glucose within the normal range by eating
balanced meals regularly with adequate complex
carbohydrates.
 Blood glucose can fall outside the normal range with
hypoglycemia or diabetes.

Glucose in the Body

The Constancy of Blood Glucose
 Diabetes
 Type
1 diabetes is the less common type with no insulin
produced by the body.
 Type
2 diabetes is the more common type where fat cells
resist insulin.
 Prediabetes
is blood glucose that is higher than normal but
below the diagnosis of diabetes.
 Hypoglycemia
is low blood glucose and can often be
controlled by dietary changes.
Glucose in the Body

The Constancy of Blood Glucose
 Glycemic
response is how quickly the blood glucose
rises and elicits an insulin response.
 Glycemic
index classifies foods according to their potential
for raising blood glucose.
 Glycemic
load refers to a food’s glycemic index and the
amount of carbohydrate the food contains.
 The
benefit of the glycemic index is controversial.
Health Effects and Recommended Intakes of
Sugars

Sugar poses no major health problem except dental caries.

Excessive intakes may displace nutrients and contribute to obesity.

Consuming foods with added sugars should be limited.

Naturally occurring sugars from fruits, vegetables and milk are
acceptable sources.
Health Effects and Recommended Intakes of
Sugars

Health Effects of Sugars
 Foods
with added sugars have sugars listed as a first
ingredient.
 Nutrient
deficiencies may develop from the intake of
empty kcalories.
 Just
because a substance is natural does not mean it is
nutritious. (Example: honey)
 Dental
caries may be caused by bacteria residing in
dental plaque and the length of time sugars have
contact with the teeth.
Ename
l
Caries
Dentin
Gu
m
Pulp
(blood
vessels,
nerves)
Crown
Bone
Root
canal
Nerv
e
Blood vessel
Stepped Art
Fig. 4-14, p. 119
Health Effects and Recommended Intakes of
Sugars

Controversies Surrounding Sugars
 Excessive
sugar intake can contribute to the
development of body fat.
 Sugar may be able to alter blood lipid levels and
contribute to heart disease in some.
 There is no scientific evidence that sugar causes
misbehavior in children and criminal behavior in
adults.
 There is a theory that sugar increases serotonin levels,
which can lead to cravings and addictions.
Health Effects and Recommended Intakes of
Sugars

Recommended Intakes of Sugars

The USDA Food Guide states that added sugars can be included in the
diet as part of discretionary kcalories.

Dietary Guidelines state to limit intake of foods and beverages that are
high in added sugars.

DRI suggest added sugars should contribute no more than 25% of a
day’s total energy intake.
Health Effects and Recommended Intakes of
Starch and Fibers

Health Effects of Starch and Fibers

May be some protection from heart disease and stroke

Soluble fibers bind with bile and thereby lower blood cholesterol
levels.

Fiber may also displace fat in the diet.

Reduce the risk of type 2 diabetes by decreasing glucose
absorption

Enhance the health of the GI tract which can then block
the absorption of unwanted particles

May protect against colon cancer by removing potential
cancer-causing agents from the body
Health Effects and Recommended Intakes of
Starch and Fibers

Health Effects of Starch and Fibers

Promote weight control because complex carbohydrates provide less
fat and added sugar.

Harmful effects of excessive fiber intake

Displaces energy and nutrient-dense foods

Abdominal discomfort and distention

May interfere with nutrient absorption
Health Effects and Recommended Intakes of
Starch and Fibers

Recommended Intakes of Starch and Fibers
 RDA
for carbohydrate is 130 g per day, or 45-65% of
energy intake.
 Daily Value is 300 grams per day.
 Dietary Guidelines encourage a variety of whole
grains, vegetables, fruits and legumes daily.
 Healthy People 2010 recommends six servings of
grains and five servings of fruits and vegetables.
Health Effects and Recommended Intakes of
Starch and Fibers

Recommended Intakes of Fiber
 FDA
recommends 25 grams for a 2,000-kcalorie diet.
 DRI
at 14 g per 1000 kcalorie intake (28 grams for a
2,000 kcalorie diet)
 American
per day.
 World
Dietetic Association recommends 20-35 g
Health Organization suggests no more than 40
g per day.
Health Effects and Recommended Intakes of
Starch and Fibers

From Guidelines to Groceries
 Grains
– encourage whole grains
 Vegetables – starchy and nonstarchy vegetables
differ in carbohydrate content
 Fruits – vary in water, fiber and sugar content
 Milks and Milk Products – contain carbohydrate;
cheese is low
 Meat and Meat Alternates – meats are low but nuts
and legumes have some carbohydrate
 Food labels list grams of carbohydrate, fiber and
sugar; starch grams can be calculated.
Alternatives to Sugar
Artificial Sweeteners

Also called nonnutritive sweeteners

Saccharin

Used primarily in soft drinks and as a tabletop sweetener

Rapidly excreted in the urine

Does not accumulate in the body

Has been removed from list of cancer-causing substances
Artificial Sweeteners

Aspartame

General purpose sweetener

Warning about phenylalanine for those with PKU

Controversial finding that aspartame may have caused cancer in rats

Excessive intake should be avoided by those with epilepsy
Aspartic Phenylalanin
acid
e
Methyl
group
hydrolyze
d
Methano
l
Oxidize
d
Formaldehyd
e
Oxidize
d
Stepped Art
Carbon
Fig. H4-2, p. 134
Artificial Sweeteners

Acesulfame-K (acesulfame potassium)
 Research
confirms safety
Artificial Sweeteners


Sucralose

Made from sugar

Passes through digestive tract
Neotame

Most recent on the market

Very sweet

Phenylalanine not an issue
Artificial Sweeteners


Tagatose

Used for foods and beverages

Provides less kcalories than sugar

High doses can cause flatulence and loose stools.
Alitame and Cyclamate

Pending FDA approval

Approved in other countries
Artificial Sweeteners

Acceptable Daily Intake (ADI) is the level of
consumption, maintained every day and still safe by
a wide margin.
 Moderation

and variety are still recommended.
Artificial Sweeteners and Weight Control
 Much
 Using
research still being done
artificial sweeteners will not automatically
reduce energy intake.
Stevia – An Herbal Alternative

Lacks research

Classified as a dietary supplement

Not required to have testing and FDA approval
Sugar Replacers

Also called nutritive sweeteners, sugar alcohols, and polyols

Maltitol, mannitol, sorbitol, xylitol, isomalt, and lactitol

Absorbed more slowly and metabolized differently in the body

Low glycemic response

Side effects include GI discomfort
What Is Diabetes?
Learning Points

Know the difference between Type 1 and Type 2 diabetes

Know the job of glucose

Know the job of insulin

List some health factors related to getting Type 2 diabetes
Type 1 Diabetes

Body does not make insulin

Usually develops in children or young adults

Normal Weight

Must take insulin daily to live
Type 2 Diabetes

Cells do not use insulin properly

Not enough insulin being produced

Generally develops in adulthood

Becoming more common in children due to obesity

Common in persons who are overweight

Many different ways to treat, including diet and exercise, pills, or
insulin
Type 2 Diabetes, Key Concepts

Obesity

Insulin Resistance

Elevated Insulin Levels

Reduced ability to make insulin
Insulin Resistance

Common in persons who are overweight

Insulin not as effective, and does not allow glucose into cells
efficiently, causing blood sugar levels to rise

There is enough insulin activity to prevent diabetic coma
What Is Diabetes:
How Insulin Works
Insulin
Insulin Receptor
How Insulin Works

Insulin is a hormone made in your pancrease

It works like a key to unlock cells so that blood sugar (glucose) can
enter

Glucose is then used by the body as fuel
What Is Diabetes:
How Insulin Works
Insulin Fills
Receptor Sites
insulin
cell
cell
Receptor Site
insulin
glucose
Insulin Passageways
glucose
glucose
What Is Diabetes: Insulin Resistance
Due to Excess Weight
glucose
insulin
insulin
glucose
cell
glucose
glucose
What Is Diabetes: Normal Blood
Glucose & Insulin Levels
Normal Blood Glucose & Insulin
Levels
mg/dL
150
100
50
0
Early am Early pm Overnight
Blood
Glucose Level
Plasma
Insulin Level
Diabetes Pills:
Oral
Medications
Diabetes Pills:
Sulfonylureas
These
tell the pancreas to
make more insulin
Diabetes Pills:
Names of Sulfonyureas
Brand Name
Generic Name
Diabeta
Micronase
Glynase
glyburide
Glucotrol
Glucotrol XL
glipizide
Amaryl
glimepiride
Diabetes Pills:
Things to know about sulfonylureas

Main thing to watch out for is having too many
blood sugars.
low
If this happens, your doctor will
give you a lower dose.

Take the same way everyday

Glucotrol XL cannot be crushed or cut in half; might see its
empty shell in toilet
Diabetes Pills:
Metformin
Tells
the liver to stop sending out
sugar
Diabetes Pills:
Metformin

Comes as generic metformin or brand name Glucophage

Also comes in a long-acting form
Diabetes Pills:
Things to know about metformin

Can help people lose some weight

Main side effects are upset stomach and diarrhea


These usually get better after about 1 week

Taking with food can help
Does not cause blood sugar to go too low

Cannot be used in kidney disease or certain kinds of
heart failure. Talk with doctor if you have these.

Contact doctor if you notice new fatigue, nausea,
muscle pain/weakness, or fast breathing because
these could be signs of a serious side effect
Diabetes Pills:
Glitazones

These help insulin in your body work better
Diabetes Pills:
Names of Glitazones

Avandia and Actos

Only come as brand name pills
Diabetes Pills:
Things to know about glitazones
The more common side effects of these
are weight gain and swelling
 People with heart failure should discuss
this with their doctor before taking
 Occasional blood work to test the liver is
recommended, although liver problems
on this medicine are very rare
 These pills usually take 6 to 12 weeks
before you can see their full benefit on
blood sugar
 These are expensive

Diabetes Pills:
Meglitinides

These tell the pancreas to make more insulin

These are taken with meals, so you skip a dose if you skip a
meal
Diabetes Pills:
Names of Meglitinides

Prandin® and Starlix®

Only come as brand name pills
Diabetes Pills:
Meglitinides

Things to know

Main side effect to watch out for is low sugars


Might have a lower chance of having lows compared with
sulfonylureas
These are expensive