Biochemistry, Digestion, and Absorption of Carbohydrates

Carbohydrates

Major food source and energy supply for the body, and are stored primarily in the liver and muscle glycogen

What is the general formula of a carbohydrate?

Cn(H2O)n

Name a disorder of CHO metabolism.

Diabetes mellitus

Name the functions of carbohydrates

1. Provide energy for life processes.

2. Precursors for biosynthesis of biological substances and contribute to cell structure and signaling.

Carbohydrates are classified based on four properties, name them

1. Number of carbons in chain

2. Number of sugar units

3. Location of the carbonyl functional group

4. Stereochemistry of compund

Aldehyde

Carbonyl on first or last carbon

Ketone

Carbonyl on an internal carbon

Carbohydrates have two types of functional groups

-C=O and -OH, which are the carbonyl and hydroxyl groups.

Carbonyl

• group can be classified as an aldehyde or ketone.

Hydroxyl

• Bonded to all carbons in the chain except those in the carbonyl group

What are the most common disaccharides?

The most common disaccharides are sucrose, lactose, and maltose. These are formed by the condensation of two monosaccharide units.

Which sugars are reducing substances?

Maltose and lactose

__________ + __________ = Maltose

Glucose + Glucose

__________ + __________ = Lactose

Galactose + Glucose

__________ + __________ = Sucrose

Glucose + Fructose

Polysaccharides

long chains of monosaccharides linked together by glycosidic bonds, serving as energy storage or structural components in organisms.

What are the two most important polysaccharides?

Glycogen and starchare the two major

Polysaccharides that are found in plants are ______ and ______

Starch and cellulose

What is the major polysaccharide found in animals?

glycogen

D and L designations refer to position of _______ group on carbon atom next to the last(bottom) CH2OH group

Hydroxyl

D-dextro isomer has hydroxyl group is on the _____.

right side of the chiral carbon

L- levo isomer has hydroxyl group on ______.

Left

Most sugars in the body are __ isomers.

D isomers

What is mutarotation and why is it important?

Mutatrotation is the constant change in optical rotation of glucose (alpha or beta) until constant value is attained.

It is important in systems that use glucose oxidase(enzyme) to measure glucose levels. Glucoe oxidase only reacts with beta-D-glucose

Describe the reducing power of the monosaccharides.

They are strong reducing agents due to the presence of aldehyde or ketone groups, enabling them to donate electrons to reduce other compounds.

What enzyme is released from the salivary glands and acts on starch and glycogen, producing maltose and intermediate dextrins?

Amylase

Once food reaches the stomach, amylase is inactivated by what?

the acidic environment of gastric juice.

What happens when the food passes through the stomach and arrives in the small intestine?

The gastric secretions are neutralized by bile and pancreatic secretions, allowing for enzymatic digestion of carbohydrates to continue. Pancreatic amylase acts on dextrins to produce disaccharides

In the jejunum, what happens?

Mucosa produces disaccharidases that break down into monosaccharides such as glucose, fructose, and galactose, which are then absorbed into the bloodstream.

Where do the monosaccharides go after absorption?

Enter the portal circulation for transport liver for further processing and distribution.

The monosaccharides can be used for

1. Energy production

2. Storage as glycogen in the liver

3. Storage as triglycerides in adipose tissue

4. Conversion to keto acids, amino acids, or protein

Metabolism

A sequence of enzyme-catalyzed chemical reactions that occurs in the living cell

Anabolic reactions

result in synthesis of molecules

1. Typically require electrons

2. Pathways require energy to proceed

Catabolic reactions

Break down of molecules

1. Typically donate electrons

2. Use coenzymes NAD or FAD as electron carriers

3. Pathways produce energy

What are the three stages of catabolism?

1. Breakdown of macromolecules into smaller units

2. Acetyl-Co-A production

3. Acetyl-Co-A oxidation(citric acid cycle) and electron transfer(oxidative phosphorylation)

Glycogenesis

The process of converting glucose into glycogen for storage in the liver and muscles.

Glycogenolysis

The process of breaking down glycogen into glucose when energy is needed.

Gluconeogenesis

The metabolic pathway that converts non-carbohydrate substrates into glucose, primarily in the liver.

Glycolysis

The metabolic pathway that breaks down glucose into pyruvate, yielding energy in the form of ATP.

Lipogenesis

Formation of fat

Lipolysis

Breakdown of fat into fatty acids and glycerol.