carbohydrates structure & function

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Color Index :● original content ● Important ● Notes● Extra information Editing file

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objectives The structure of carbohydrates of physiological significance.

The main role of carbohydrates in providing and storing of energy.

The structure and function of glycosaminoglycans.

OVERVIEW

Many diseases associated with disorders of carbohydrate metabolism including: Diabetes mellitus - Galactosemia- Glycogen storage diseases - Lactose intolerance

Carbohydrates:

The empirical formula is (CH2O)n, “hydrates of carbon”

Are structural component of cell membranes.

Galactosemia=مشكلة في تحویل المركب

Glycogen storage diseases=مشكلة في تكسیر المركب وتخزینھ

Lactose intolerance=حساسیة من مركبات الالكتوز

Provide important part of energy in diet. Act as the storage form of energy in the body

The most abundant organic molecules in nature.

classification of carbohydrateMonosaccharides

Disaccharide

Oligosaccharide

Polysaccharide

Simple sugar

3-10 monosaccharide units

more than 10 sugar units Homopolysaccharides & heteropolysaccharides

2 monosaccharide units

monosaccharides:

No. of carbon atoms Aldehyde (aldoses)keto (ketoses)

classified according to:

monosaccharide Extra info :https://youtu.be/doe_zZDjU5c

Aldose Ketose

Triose Glyceraldehyde Dihydroxyacetone

Pentose Ribose Ribulose

Hexose Glucose Fructose

isomerism Isomers:Compounds having the same chemical formula but different structural formula.

Extra info:Because the position of individual atoms within a sugar molecule varies, many monosaccharides are isomers of one another. For example, glucose and fructose share the molecular formula C6H12O6, but are structurally different. Differences between isomers are not always as readily apparent as in structural isomers like glucose and fructose.

Aldo-Keto Isomers

Aldose Ketose

ALDEHYDE GROUP

O

R C H

Glucose

KETONE GROUP

O

R C R

Fructose

EpimersCHO dimers that differ in configuration around only one specific carbon atom

-Glucose and galactose, C4 -Glucose and Mannose, C2

Galactose and mannose are not epimers

Extra info : explanationglucose & mannose are epimers in c2 in the second carbon the position of H & OH varriesglucose (OH) RightMannose(OH) Left

Enantiomers (D- and L-Forms)Structures that are mirror images of each other and are designated as D- and L- sugars based on the position of –OH group on the asymmetric carbon farthest from the carbonyl carbon Majority of sugars in humans are D-sugars

Extra info : explanation https://youtu.be/7FR2_VjwKYk

Note : majority of amino acids in humans body are found in L- configuration

α- and β-FormsCyclization of Monosaccharides with 5 or more carbon are predominantly found in the ring form.

- The aldehyde or ketone group reacts with the –OH group on the same sugar.- Cyclization creates an anomeric carbon (former carbonyl carbon) generating the α and β configurations.

Extra info : Explanations For monosaccharide in the D-series:the OH group is down in α anomer,up in β anomer

Note : the structure of these carbohydrates might show that they are an open chain in fact carbs with 5+ carbons are cyclic

MutarotationIn solution,the cyclic α and β anomers of a sugar are in equilibrium with each other, and can be interconverted spontaneously.

(Ficher projection) (Haworth projection)

Aldo-keto

Epimers

D & L forms

α & β anomers

Sugar Isomers

DisaccharidesJoining of 2 monosaccharides

by O-glycosidic bond:

- Maltose (α-1, 4) = glucose + glucose

- Sucrose (α-1,2) = glucose + fructose

- Lactose (β-1,4) = glucose + galactose

Lactose

Polysaccharides

HeteropolysaccharidesHomopolysaccharides

Unbranched:

Ex: Cellulose (β-glycosidic polymer)

Branched:

Ex:

Glycogen and starch (α-glycosidic polymer)

Ex: glycosaminoglycans (GAGs)

Note : Homo : Same type of sugar .Hetero: Different type of sugar .

Glycogen, starch and cellulose are all made of glucose.

Reducing Sugars

Where?

When?

why do we need it?

If the O on the anomeric C of a sugar is not attached to any other structure (Free), that sugar can act as a reducing agent.

Reducing sugars reduce chromogenic agents like Benedict’s reagent or Fehling’s solution to give a colored precipitate.

Urine is tested for the presence of reducing sugars using these colorimetric tests.

Examples MaltoseLactose

Sucrose is non-reducing, Why? sucrose is the combination of Glucose and Fructose(each of them combine with the other in the carbonyl group) and therefore none of them have a free aldehyde or ketone group. (the anomeric C is attached)

Monosaccharides

Complex Carbohydrates❖ Carbohydrates attached to

non-carbohydrate structures by glycosidic bonds (O- or N-type) .

N-Glycosidic

Attachment happens at a Nitrogen atom.

O-GlycosidicAttachment happens at a Oxygen atom.

Examples:

- Purine and pyrimidine bases in nucleic acids.

- Bilirubin.

- Proteins in glycoproteins and proteoglycans.

- Lipids found in glycolipids.

Notes:glycoprotein: proteins that have some sugar attached to it.proteoglycans: carbohydrate having some protein attached to it.Glycolipids:lipids that have some sugar attached to it.

Glycosaminoglycans (GAGs)are large complexes of negatively charged heteropolysaccharide chains.

are associated with a small amount of protein, forming proteoglycans, which consist of over 95 percent carbohydrate.

bind with large amounts of water, producing the gel-like matrix that forms body's ground substance.

The viscous, lubricating properties of mucous secretions also result from GAGs, which led to the original naming of these compounds as mucopolysaccharides.Ground substance are the non-fibrous

protein of our extracellular matrix (the stuff outside the cell of our bodies) in which the other components are held in place.

Glycosaminoglycans (GAGs)

The acidic sugar is either D-glucuronic acid or L-iduronic acid

The amino sugar (usually sulfated) is either D-glucosamine or D-galactosamine

GAGs are strongly negatively-charged: - carboxyl groups of acidic sugars- Sulfate groups

GAGs are linear polymers of repeating disaccharide units [acidic sugar-amino sugar]n

Heparin: Unlike other GAGs, Unlike other GAGs that are

extracellular, heparin is intracellular and serves as

an anticoagulant.

Examples of GAGs:

Chondroitin sulfates: Most abundant GAGs

Hyaluronic acid: Compared to other GAGs, it is unsulfated and not covalently attached to

protein.

Keratan sulfates: Most heterogeneous

GAGs

Resilience of GAGs

chain is extended:They repel each other.

+chain brought together:

slip past each other.

Effect of the GAGs negative charge in solution

GAGs is compressed:water is “squeezed out”

GAGs forced to occupy a smaller volume .

compression is released the GAGs spring back to their

original, hydrated volume.this produces :

Slippery consistency of mucous secretions and synovial (مخاطي)

fluid.

Contributes inresilience of synovial fluid and

vitreous humor of the eye

Note : synovial fluid: سائل یتواجد بین المفاصل و یمنع االحتكاك

vitreous humor: سائل یتواجد داخل العین

Quiz Q1: ribulose sugar is

A) Hexose B) triose C) pentose D) aldose

Q2: the functional group in fructose is

A) aldehyde group B) ketone group C) carboxylic acid group D) amino group

Q3:maltose is made of two monosaccharide

A) glucose+glucose B) glucose+fructose C) fructose+galactose D) galactose+glucose

Q4: Carbohydrates attached to non-carbohydrate structures by

A) glycosidic bond B) covalent bond C) hydrogen bond D) phosphodiester bond

Q1 :What is the isomers?

MCQs SAQ

1)C2)B3)A4)A

MCQs answers

SAQ answer:

Compounds having same chemical formula but different structural formula .

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