The document provides a comprehensive overview of carbohydrates, including their types, structures, and metabolism. It discusses monosaccharides, disaccharides, and polysaccharides, detailing their roles in nutrition and digestion. Additionally, it outlines metabolic pathways such as glycolysis, glycogenolysis, and gluconeogenesis, emphasizing the importance of carbohydrates as energy sources for the human body.

1. Carbohydrates
Types and characteristics and
metabolism

2. Introduction
GREATEST CONTRIBUTOR
TO HUMAN ENERGY
INTAKE.
ALL CELLS CAN USE
CARBOHYDRATES AS A
SOURCE OF ENERGY
CAN BE STORED IN THE
FORM OF GLYCOGEN OR
CAN BE CONVERTED INTO
OTHER MOLECULES.
DIETARY FIBERS ARE
CLASSIFIED AS
CARBOHYDRATES,
ALTHOUGH THEY
PROVIDE A LIMITED
AMOUNT OF ENERGY. ITS
ROLE IS MAINLY IN THE
DIGESTIVE FUNCTION

3. Carbohydrates classification

4. Monosaccharides
3 monosaccharides (simple units of sugar) are important in
nutrition:
–Glucose
–Fructose
–Galactose
They share the same chemical formula C6H12O6, but they have different
characteristics and structures.

5. Monosaccharides - Structure
The monosaccharides that are relevant to human nutrition may be classified based on carbon number and
include the trioses, tetroses, pentoses, and hexoses..
The six-carbon hexoses are the most common form of monosaccharides in the human diet. These include
glucose, galactose, and fructose. Glucose is the principal carbohydrate found in human circulation and is
often referred to as blood sugar.

6. Although it is common to represent
monosaccharides as straight-chain
structures, in an aqueous environment there
is a reaction between the aldehyde group
(COOH) of carbon 1 and the hydroxyl group
(OH) of carbon 5.
Many carbohydrates have the same chemical
formula but vary in structure, making them
isomers. For instance, glucose, fructose,
galactose, and mannose have different
structures but the same formula: C6H12O6.
Monosaccharides -
Structure

7. Monosaccharides D and L series
When looking at a monosaccharide as a straight chain, the
position of the hydroxyl group on the asymmetric carbon
farthest away from the carbonyl group (C=O) is used to
designate the D and L isomer series.
Specifically, if the OH group is on the right side, then the
monosaccharide is classified within the D series. If the OH
group is on the left side, the monosaccharide is classified
within the L series.
One of the most important distinctions in nutrition
between the D and L series is that the D isomers are the
predominant naturally occurring form, whereas the L
series isomers tend to result from chemical synthesis.
D-Glucose is the
most predominant
naturally occurring
form in food

8. Monosacharides
The hydroxyl group attached to the anomeric carbon can exist on either side of the ring structure,
thus creating another type of stereoisomer—anomers—designated and
⍺ β.
The -OH group of the β isomer resides on the same side of the ring as the 2CH2OH next to the
carbon atom that determines D or L configuration.
The Anomery of sugars characterizes the bond between monosaccharides on which digestive
enzymes depend.
Only -bond can be digested by humans. The
⍺ β-bonds will be fermented by bacteria in the large
intestine.

9. Disaccharides
Disaccharides are simple sugars composed of 2 monosaccharides linked by glycosidic bond.
Specific bond designations, such as α1–4 (Maltose), α1–2 (Sucrose), and β1–4 (Lactose), are used to
describe the bond and explain the necessary specificity of disaccharidase enzymes.
The three most common disaccharides are:
• LACTOSE = Glucose + Galactose (Milk sugar)
• SUCROSE = Glucose + Fructose (Saccharose)
• MALTOSE = glucose + Glucose (Seeds and digestion products of more complex carbohydrates)
Lactose is the only disaccharides of animal origin.

10. Disaccharides
The term sugar more often refers to monosaccharides and disaccharides:
• They all have a sweet taste.
• Fructose is the sweetest
• Honey is a natural syrup, corn syrup is also known as glucose syrup and resists crystallization, HFCS is used in the food
industry, Agave syrup is rich in fructans and made from the agave plant.

11. Polysaccharides or complex carbohydrates
Polysaccharides are composed of repeating monosaccharide units, most commonly glucose.
Although their length may vary, they are rather long, and the covalent bonds in the primary structure are found between
carbons 1 and 4.
For branched polysaccharides, a bond is typically found between carbons 1 and 6
The position of the bonds, known as either the α or β configuration, determines the properties and digestive fate of these
compounds because of the ability of digestive enzymes to recognize only a particular configuration.
There are several types of polysaccharides, which are simplified here into several categories: oligosaccharides, starch,
glycogen, Cellulose, and fiber.

12. Plant Starch
The most common digestible polysaccharide.
It is the form of CHO storage in plants.
It is a homopolysaccharide because it consists exclusively of monomers.
Its 2 forms: amylose & amylopectin are both polymers of α-D-glucose.
•The amylose is linear, has unbranched chain, in which solely glucose units are attached through α(1-4) glycosidic bonds. In water, amylose chains adopt a helical conformation.
•-Amylopectin, is a branched-chain polymer, which branch chains occur through α(1-6) bonds.
Both Amylose and Amylopectin occur in cereal grains, potatoes, legumes, and other vegetables. Amylose contributes about 15-20% and
amylopectin 80-85% to the starch content in food.

13. Glycogen
Glycogen is the major form of stored carbohydrate in animal tissues, localized primarily in liver and skeletal muscle.
The structure of glycogen is similar to amylopectin but is more highly branched.
The glucose units within glycogen serve as a readily available source of glucose.
When dictated by the body’s energy demands, glucose units are sequentially removed by enzymatic hydrolysis from the nonreducing
ends of the glycogen chains.
The liberated glucose molecule then enters energy-releasing pathways of metabolism = glycogenolysis (discussed later).
Essentially no glycogen is consumed in meat products, despite muscle being a primary location for glycogen storage. During meat animal
processing, the glycogen in muscle is quickly hydrolyzed to glucose, which in turn is converted to lactic acid

14. Cellulose
Cellulose is the major component of cell walls in plants and, like starch, is a homopolysaccharide of glucose.
It differs from starch because the glycosidic bonds connecting the glucose units are β(1-4), what makes the
molecule resistant to the digestive enzyme α-amylase.
Because cellulose is not digestible by mammalian digestive enzymes, it is defined as a dietary fiber and is not
considered an energy source.
However, colonic bacteria can digest it, resulting in several digestion products including short-chain fatty acids
that provide energy to the body and play important roles in the gastrointestinal tract.

15. Polysaccharides are the most abundant
carbohydrates in the food supply. Disaccharides,
mainly sucrose and lactose, are also abundant in
food. Before these dietary carbohydrates can be used
by the body’s cells, they must first be hydrolyzed into
their constituent monosaccharides within the
gastrointestinal (GI) tract.
Only monosaccharides can be absorbed into intestinal
mucosal cells (enterocytes).
The hydrolytic enzymes involved in digestion of
complex carbohydrates and disaccharides are
collectively called glycosidases or, alternatively,
carbohydrases.
Glucose and fructose, when present in food as
monosaccharides, require no digestion prior to being
absorbed into intestinal cells.

16. Digestion
Digestion of the starches, amylose and amylopectin, starts in the mouth.
The key enzyme is salivary a-amylase, a glycosidase that specifically hydrolyzes a(1-4) glycosidic linkages. a-Amylase is unable to hydrolyze the b(1-4) bonds of
cellulose, the b(1-4) bonds of lactose, the a(1-2) bonds of sucrose, and the a(1-6) linkages that form branch points in amylopectin.
Given the short period of time that food is in the mouth before being swallowed, this phase of digestion produces mostly oligosaccharides (dextrins), but few
mono or disaccharides.
The salivary a-amylase action continues in the stomach until the gastric acid penetrates the food bolus and lowers the pH sufficiently to inactivate the enzyme.
The dextrins move into the duodenum and jejunum, where they are acted upon by pancreatic a-amylase. The presence of pancreatic bicarbonate in the
duodenum elevates the pH to a level favorable for enzymatic function.
Pancreatic a-amylase continues to hydrolyze a(1-4) glycosidic bonds to produce maltose, maltotriose, and limit dextrins

17. Membrane
transport of
monosaccharides
Fourteen members of the GLUT family
have been identified in humans. GLUTs
are distributed throughout the body
and function to transport glucose and
other molecules by facilitated
diffusion.
Transport may be bidirectional
depending on the substrate
concentration gradient.

18. Integrated metabolism in tissues

19. The metabolic pathways of carbohydrate metabolism
●● Glycogenesis: The synthesis of glycogen
●● Glycogenolysis: The breakdown of glycogen
●● Glycolysis: The oxidation of glucose to pyruvate
●● Gluconeogenesis: The synthesis of glucose from noncarbohydrate sources
●● Pentose phosphate pathway (hexose monophosphate shunt): The production of five-
carbon monosaccharides (pentoses) and nicotinamide adenine dinucleotide phosphate
(NADPH)
●● Tricarboxylic acid (TCA) cycle: The oxidation of acetyl- CoA to yield CO2 and high-
energy electrons.

21. The goal of glycolysis, glycogenolysis, and the citric
acid cycle is to conserve energy as ATP from the
catabolism of carbohydrates. If the cells have
sufficient supplies of ATP, then these pathways and
cycles are inhibited. Under these conditions of excess
ATP, the liver will attempt to convert a variety of
excess molecules into glucose and/or glycogen.

22. Glucose
transport
into cells
The fate of G6P varies
according to the needs
of the body and is
under hormonal
control to be directed
towardsglycogenogene
sis, glycolysis, the
pentose pathway,
gluconeogenesis, or
glucose.

23. Overview of
metabolism

24. - Anabolism is the synthesis of complex molecules from simpler molecules including the formation of macromolecules from monomers by
condensation reactions.
Anabolic reactions describe the set of metabolic reactions that build up complex molecules from simpler ones
•• Monosaccharides are joined via glycosidic linkages to form disaccharides and polysaccharides
•• Amino acids are joined via peptide bonds to make polypeptide chains
•• Glycerol and fatty acids are joined via an ester linkage to create triglycerides
•• Nucleotides are joined by phosphodiester bonds to form polynucleotide chains
Catabolism is the breakdown of complex molecules into simpler molecules including the hydrolysis of macromolecules into monomers
Catabolic reactions describe the set of metabolic reactions that break complex molecules down into simpler molecules
The breakdown of organic molecules via catabolism typically occurs via hydrolysis reactions
Hydrolysis reactions require the consumption of water molecules to break the bonds within the polymer

25. Major metabolic hormones

26. Insulin-
mediated
Glucose uptake

27. Blood sugar
insulin cycle

28. Insulin regulation of metabolism

29. Glucagon regulation of metabolism

30. Adrenaline or epinephrine
Epinephrine (adrenalin) is produced in the adrenal glands
(adrenal medulla) from the amino acid tyrosine, which itself can
be synthesized from the essential amino acid phenylalanine.
Epinephrine, norepinephrine, and dopamine are important
molecules in the response to stress
The effects of epinephrine include the breakdown of glycogen
(Glycogenolysis) in skeletal muscle and the liver and fat
breakdown (lipolysis) in adipose tissue. This serves to make
fuel available for skeletal muscle and the heart during times of
increased activity.

32. Overview of metabolsim

33. Overview of Glycolysis
Glycolysis is a series of 10 reactions that convert one six-
carbon glucose molecule to two three carbon pyruvate
molecules. The net ATP yield of glycolysis is two ATP
molecules, with the potential for two more via the glycerol
phosphate shuttle, which allows for the reducing equivalents
of the NADH generated in the cytosol to be transferred to
mitochondrial FADH2. Glycolysis also allows entry points for
the catabolism of other monosaccharides, such as fructose
and galactose

34. Glycogenogenesis = Glycogen synthesis

35. Glycogen degradation
Glycogen degradation
(glycogenolysis) is catalyzed by
the active phosphorylase
(phosphorylase a)
enzyme. This enzyme is activated
by epinephrine. Meanwhile,
glucagon and epinephrine both
participate in the activation of
phosphorylase in hepatocytes.

36. Pentoses Phosphate pathway
The primary importance of the pentose phosphate pathway is the reduction
of NADP+ to NADPH, which can be used for reducing equivalents for the
synthesis of certain molecules (i.e., fatty acids).
Also, this reaction pathway allows for the creation of ribulose-5-phosphate,
which may be isomerized to ribose-5-phosphate and used in nucleotide
biosynthesis. The reactions of the pentose phosphate pathway can be
described as either oxidative or nonoxidative.
The oxidative phase allows the production of NADPH used in the
biosynthesis of fatty acids and cholesterol.
The non-oxidative phase allows the production of Ribose-5-phosphate for
the synthesis of DNA and Fructose-6-P and Glyceraldheide-3-P intermediate
in Glycolysis.

38. Gluconeogenesis
Production of glucose from non-carbohydrate substrates:
•- Amino acids
•- Lactate
•- Glycerol (Triglycerides)
Occurs during prolonged fasting of > 1 day.
Occurs mainly in the liver

39. Lipogenesis from increased CHO intake

40. Lipogenesis from increased CHO intake
Increased dietary carbohydrate intake may result in increased liver lipogenesis.
Although insulin is released in response to carbohydrate intake and is well known for its lipogenic effects,
some evidence suggests that glucose alone can enhance liver lipogenesis. Increased intake of
carbohydrate can lead to gene expression of a variety of glycolytic and lipogenic pathways that play a
role in converting glucose to fatty acids.