Carbohydrates Flashcards
Carbohydrates
Made up of carbon, oxygen and hydrogen Cn (H2 O)n Also called saccharides, sugars Risorsa di energia Intake from diet Chirality in carbohydrates is of extreme importance, different arrangement in three dimensions of the hydroxyl groups changes the chemical properties of the molecule we have: - monosaccharides - disaccharides - polysaccharides
Monosaccharides
Simplest carbohydrates
Carbon chain, aldehyde ( or ketone) and hydroxyls on each carbon atoms
ex. Glyceraldehide, Fructose, Ribose
An aldopentose is a five-carbon saccharide with an aldehyde group.
A ketohexose is a six-carbon saccharide with a ketone group
Have chirality centers
Monosaccharides are found mostly as cyclic forms in solution.
D- Glucose
( monosaccharide)
most common hexose
Also known as dextrose
Building block of the disaccharides sucrose and lactose, and for the polysaccharides such as cellulose and glycogen
D-Galactose
( monosaccharide)
Aldohexose C6H1206
Obtained from the disaccharide lactose
D- Fructose
( monosaccharide)
ketohexose C6H1206
sweetest of the carbohydrates
sucrose + hydrolysis= fructose
D-Ribose
( monosaccharide)
Aldopentose C5H10O5
Component of ribonucleic acid
D-Galactose
Monosaccaride Aldohexose ( C6H12O6) Isomero del glucosio Ottenuto dal disaccaride del Lattosio importante nelle cell membranes Malattia Galactosemia= l'enzima che serve per convertire il d-galactose in d- glucose manca
D-Fructose
Monosaccaride
Ketohexose ( isomero del glucosio)
C6H12O6
Ottenuto dall’idrolisi del sucrose
D-Ribose
Monosaccaride
Aldopenthose C5H10O5
Componente dell’RNA
La sua forma ridotta è il 2- deoxyribose ( del DNA)
Mutarotation
When placed in solution,
- cyclic structures open and close.
- α-D-glucose converts to β-D-glucose and vice versa
- at any time, only a small amount of open chain forms
Oxidation of monosaccharides
- The small amounts of the open-chain form present can be oxidized to the corresponding –onic acid ( Glucose- Gluconic acid)
- have an aldehyde group with an adjacent hydroxyl group that can be oxidized to carboxylic acid by an oxidizing agent such as Benedict’s solution
Reduction of monosaccharides
The carbonyl group can be reduced (Pd + H2 or NaBH4, or enzymatically with the NADH cofactor as a hydride donor) to the corresponding alcohol
Disaccharides
Formed through the condensation of two cyclic monosaccharides:
• One provides the hemiacetal in the form of the anomeric carbon
• One provides an hydroxyl (alcohol)
• The reaction leads to a stable acetal, releasing a water molecule
• The bond established is referred to as an O-glycosidic bond
Lactose
Disaccharide found in breast milk
Is hydrolyzed by the enzyme lactase in the intestine to galactose and glucose
Sucrose
Sucrose, or table sugar,
• consists of α-D-glucose and β-D-fructose.
• has an α,β-glycosidic bond
The glycosidic bond
From a chemical standpoint is an acetal
It’s a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.
The bond is formed between the hemiacetal group of a saccharide (or a molecule derived from a saccharide) and the hydroxyl group of some compound such as an alcohol
In order to favor the synthetic reaction, energy must be provided. A bypass strategy is employed in living cells, forming an intermediate phosphate ester and hydrolyzing a phosphoanhydride bond in a nucleotide.
Polysaccharides
More monosaccharides joined together via O-glycosidic bonds
Single repeating unit (homopolysaccharides, energy storage molecules), or heterogeneous (heteropolysaccharides
Amylose
Poly-α (1,4) glucose
Can be broken down through hydrolysis
Amylopectin
oly-α(1-4) glucose with α(1-6) branches
Amylopectin associates with amylose via non-covalent hydrogen bonding interactions to form starch
Cellulose
Poly-β(1-4)-glucose
Glycogen
Animals store glucose in a polymer called glycogen
Why is it branched?
When glucose is needed, monosaccharides are detached at the non-reducing end of the chain (the glucose with the free —OH at position 4), and branching offers many ends to the enzymes that catalyze the removal
Glycosaminoglycans (GAGs)
Linear polymers of repeating disaccharides
The disaccharide is composed of a uronic acid (sugar with –COOH function) and an amino sugar
Function is mostly to maintain flexibility, absorb mechanical stress, composition of connective tissue (holding cells together), act as lubricants for joints
Synthesized in the Golgi apparatus
Three classes:
- heparin
- dermatan sulfate
- keratan sulfate
Linked to proteins via O-glycosidic or N-glycosidic bonds
Proteoglycans
Heavily-glycosylated proteins with one or more GAGs attached to the core polypeptide
Principal components of the extracellular matrix in animals
Lipids
Organic compounds of biological origin that are soluble in organic solvents
Fatty acids
Simplest type of lipids.
Building blocks of complex lipids
Long acyl chains with terminal carboxylic function
Unsaturated FAs display lower melting points due to less ordered packing of acyl chains
• Addition of water at the double bond (one carbon is reduced, the other is oxidized)
Prostaglandins
Highly potent signaling molecules, despite a rapid turnover. Control muscle contraction, blood pressure. Mediators of inflammation and pain
Arachidonic acid is the precursor. Hormone function
Nomenclature PGXn, where X (letter, A-J) defines a specific set of substituents at the cyclopentane ring.
Triglycerides
Storage molecules for fatty acids
Three FA molecules (no restriction on composition or unsaturation) and a glycerol (triose) molecule.
- Hydrolysis of ester linkage. Catalyzed by strong acids or specific enzymes called lipases.
- Oxidation. Double bonds react and lead to shorter chain FAs and aldehydes. Oxygen and microorganisms facilitate the process
- Saponification. Strong base-mediated hydrolysis (NaOH, KOH) leading to Na+/K+ salt of the FA. Soaps.
Chirality in carbohydrates
Extremely important as different arrangements of the hydroxyl groups changes the chemical properties of the molecule
Isomers in carbohydrates
- Glucose
- Galactose
- Fructose
Ketose
A ketose is a monosaccharide containing one ketone group per molecule
Reducing sugar
Glycans
Polysaccharides conjugated to other molecules, can conjugate with proteins to form glycosylated proteins
