Why carbohydrates
This presentation is the property of its rightful owner.
Sponsored Links
1 / 63

Why Carbohydrates? PowerPoint PPT Presentation


  • 41 Views
  • Uploaded on
  • Presentation posted in: General

Why Carbohydrates?. Play a number of important roles in biochemistry: Major energy sources Play a key role of processes that take place on the surfaces of cells. eg. cell-cell interactions Essential structural components of several classes organisms.

Download Presentation

Why Carbohydrates?

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Why carbohydrates

Why Carbohydrates?

  • Play a number of important roles in biochemistry:

    • Major energy sources

    • Play a key role of processes that take place on the surfaces of cells. eg. cell-cell interactions

    • Essential structural components of several classes organisms.

Eg. Cellulose: components in grass and trees


Carbohydrates

Consist of 3 sub-classes

- monosaccharide

- oligosaccharide

- polysaccharide

* saccharide = 1 unit sugar, normally

refers to glucose

Carbohydrates


Carbohydrate

Carbohydrate

  • General formula – Cn(H2O) n

  • Only the simple sugars (monosaccharides) fit this formula.

  • Oligosaccharides and polysaccharides are based on the monosaccharides unit and have slightly different formula.

  • Oligosaccharides?

  • Polysaccharides?


Zatilfarihiah rasdi

  • Compounds containing C, H and O

  • Produced in plants by photosynthesis

    6CO2 + 6H2O  C6H12O6 + 6O2

  • All have C=O and –OH functional group.

  • The C=O may be as HC=O or by itself.

  • As HC=O( aldehyde) so the sugars are also known as aldoses . Just as C=O, the sugars are also known as ketoses.


Zatilfarihiah rasdi

  • Suffix – ‘ose’ indicates that molecule is a carbohydrate.

  • Major roles in energy metabolism ( energy storage and energy transport ) and structural component.


Zatilfarihiah rasdi

Monosaccharides

-monosaccharides is a molecule of single sugar unit.

e.gglucose, galactose, mannose, fructose, xylose

  • Are the simplest sugars

  • Can be used for fuel

  • Can be combined into polymers

    - Glucose, galactose, and mannose are 6C molecules or aldohexoses.

    - Xyloseis a 5C molecule/aldopentose.


D glucose

D-Glucose

  • This is a Fischer Formula

  • 6C monomeric molecule

  • Is an aldohexose

  • D to denote the –OH on C5 is on the right side of the C chain


Zatilfarihiah rasdi

  • Emil Fischer ( 1852 -1919 ) was a German-born scientist who won the noble prize in chemistry.


Stereochemistry of monosacharides

Stereochemistry of monosacharides

  • Anomers :- Sugars that differ only in the configuration around the anomeric carbon (carbonyl becomes a new chiral; C1)

  • Epimers :- Sugars that differ only by the configuration at one C atom ( excluding the anomeric carbon )


Zatilfarihiah rasdi

  • Enantiomers :- Molecules that are superimposible mirror images of one another.

  • Isomers : Isomers are molecules with the same molecular formula, but different arrangements of atoms.


Zatilfarihiah rasdi

  • Stereoisomers : molecules that differ from each other only in their configuration ( three dimensional shapes )also called optical isomers. Glucose n Galactose.

  • Diastereomers :non superimposable,non mirror image stereoisomers. ( L- Threose with both D n L erythrose. )


Zatilfarihiah rasdi

  • The figures show the two isomeric forms that are mirror images of each other → stereoisomers.

  • The two forms differ in the position of –OH group bonded to the central C.

  • the mirror-image stereoisomers are also called enantiomers,

  • D-Glyceraldehyde and L-Glyceraldehyde are enantiomers.

Fig. 16-1b, p.435


Zatilfarihiah rasdi

Epimers


Zatilfarihiah rasdi

Mirror image


Zatilfarihiah rasdi

diastereoisomers

The aldotetroses have two chiral C ; C-2 and C-3.

Therefore, the stereoisomers of aldotetroses are 22, or four possible stereoisomers.

Diastereoisomers that differ from each other at only one chiral C are known as epimers.

D-erythrose and D-threose are epimers.

Fig. 16-3, p.437


Zatilfarihiah rasdi

Haworth projections formula


The most abundance monosaccharide in nature

The most abundance monosaccharide in nature.


Glucose anomers

Glucose Anomers


Oligosacharides

Oligosacharides

-oligosaccharides is a chain containing

2-10 sugar units.

-Two sugar units also called Disaccharides.

-The name is derived from the Greek word oligos, meaning "a few", and from the Latin/Greek word sacchar which means "sugar"

- These sugar units join to one another by glycosidic linkages.

- Maltose and Lactose: Alternative Glycosidic Linkages (1,4)

- Sucrose: glucose-α-1,2-fructose


Examples

Examples

  • Maltose, a cleavage product of starch (e.g., amylose, is a disaccharides with an α(1,4) glycosidic linkage between the C1 hydroxyl of one glucose and the C4 hydroxyl of a second glucose. Maltose is the α anomer, because the O at C1  points down from the ring.


Zatilfarihiah rasdi

  • Sucrose, common table sugar, has a glycosidic bond linking the anomeric hydroxyls of glucose and fructose. Because the configuration at the anomeric carbon of glucose is α (O points down from the ring), the linkage is designated α(1,2).

  • Lactose, milk sugar, is composed of glucose and galactose with β(1,4) linkage from the anomeric hydroxyl of galactose.


Disaccharide synthesis

Disaccharide Synthesis

Energy +

The reactions, the names of the sugars, and whether they are mono- or disaccharides is what you should know (also, “Glycosidic linkage”)


Zatilfarihiah rasdi

Dehydration reaction in the synthesis of maltose. The bonding of two glucose units forms maltose. The glycosidic link joins the number 1 carbon of one glucose to the number 4 carbon of the second glucose. Joining the glucose monomers in a different way would result in a different disaccharides.

(a)

CH2OH

CH2OH

CH2OH

CH2OH

O

O

O

O

H

H

H

H

H

H

H

H

1–4glycosidiclinkage

HOH

HOH

HOH

HOH

4

1

H

H

H

H

OH

OH

O

H

OH

HO

HO

OH

O

H

H

H

H

OH

OH

OH

OH

H2O

Glucose

Maltose

Glucose

CH2OH

CH2OH

CH2OH

CH2OH

O

O

O

O

1–2glycosidiclinkage

H

H

H

H

H

HOH

HOH

H

2

1

H

OH

H

HO

H

HO

Dehydration reaction in the synthesis of sucrose. Sucrose is a disaccharide formed from glucose and fructose.Notice that fructose,though a hexose like glucose, forms a five-sided ring.

H

(b)

HO

H

O

O

HO

CH2OH

CH2OH

OH

H

OH

H

H

H

OH

OH

H2O

Glucose

Sucrose

Fructose

Figure 5.5


Reducing non reducing sugar

Reducing & Non Reducing Sugar

  • Sugars exist in solution as an equilibrium mixture of open-chain and closed-ring (or cyclic) structures.

  • In the open-chain form, the carbon atom that contains the C=O bond is called the carbonyl carbon.

  • Sugars that can be oxidised by mild oxidising agents such as Benedict's Solution, Fehling's Solution,and Tollen's Reagen are called reducing sugars because the oxidising agent is reduced in the reaction.

  • Reducing sugar: one that has a free aldehyde group and this aldehyde is easily oxidized.


Zatilfarihiah rasdi

+ Ag (NH3)2 Being reduced

Tollens’ agent


Zatilfarihiah rasdi

  • A non-reducing sugar is not oxidised by mild oxidising agents.

  • All common monosaccharides are reducing sugars.

  • The disaccharides maltose and lactose are reducing sugars.

  • The disaccharides sucrose is a non-reducing sugar (both anomeric groups are involved in glycosidic linkage)


Zatilfarihiah rasdi

Polysaccharides

  • are the complex carbohydrates

  • is a macromolecule, containing >1000 sugar units/monomers.

  • They are made up of chains of monosaccharides (the sugars) which are linked together by glycosidic bonds, which are formed by the condensation reaction.


Zatilfarihiah rasdi

  • The linkage of monosaccharides into chains creates chains of greatly varying length, ranging from chains of just two monosaccharides, which makes a disaccharide to the polysaccharides, which consists of many thousands of the sugars.

  • the molecule can be straight chain or branched.

  • e.g amylose, cellulose are straight.

  • e.g xanthan gum, amylopectin are branched.


Zatilfarihiah rasdi

  • the monomers can be of 1 type (homopolysaccharide)

  • e.g starch ( poly D-glucose) or

  • Mixed types (heteropolymers)

  • e.g xanthan gum which are glucose-glucose-mannose- glu.acid-mannose

  • the importance of glycosidic linkage:

    • β-glycosidic linkage: cellulose and chitin –structural material

    • α-glycosidic linkage: starch and glycogen – carbohydrate storage polymers in plants and animals


Xantham gum

Xantham gum


Cellulose

Cellulose

  • Cellulose is a major component of plant cell walls. It is an unbranched polymer with about ten thousand glucose units per chain.

  • Hydroxyl groups (-OH) project out from each chain, forming hydrogen bonds with neighbouring chains which creates a rigid cross-linking between the chains, making cellulose the strong support material that it is.


Zatilfarihiah rasdi

  • Despite the combined strength of cellulose, it is fully permeable to water and solutes which makes it ideal for allowing water and solutes into and out of the cell.

  • It is the most abundant organic substance in the living world and it has been estimated that more than half the total organic carbon on the planet is in cellulose.


Cellulose1

Cellulose

Know the difference


Cellulose2

Cellulose

Cellulose is a Structural polysaccharide


Glycogen

Glycogen

  • Glycogen is a branched polysaccharide found in nearly all animal cells and in certain protozoa and algae.

  • In humans and other vertebrates it is principally stored in the liver and muscles and is the main form of stored carbohydrate in the body, acting as a reservoir of glucose (which the glycogen can be broken down into) for when the body is being starved of food.

  • The structure of glycogen consists of long polymer chains of glucose units connected by an alpha acetal linkage.

  • All of the monomer units are alpha-D-glucose, and all the alpha acetal links connect C 1 of one glucose to C 4 of the next glucose.


Zatilfarihiah rasdi

  • The no. of branch points is significance for two reasons:

  • More branched polysaccharides, more water soluble.

  • More branched polysaccharides, more potential targets of enzyme to allow a quicker the mobilization of glucose.


Starch

Starch

  • Starch is similar to glycogen, however it is found in plant cells, protists and certain bacteria. The starch granules can be seen in the cell through a light microscope. The starch granules are made up of two polysaccharides, amylose and amylopectin.

  • Amylose is an unbranched molecule made up of several thousand glucose units, coiled helically into a more compact shape. Amylopectin is also compact but has a branched structure and is made up of twice as many glucose units as amylose.


Chitin

Chitin

  • Chitin is closely related in structure to cellulose, also being an unbranched polysaccharides. However, instead of the hydroxyl groups (-OH), the chains have the following structure –NH.CO.CH3 replacing it.

  • Chitin is a polysaccharide found in the outer skeleton of insects, crabs, shrimps, and lobsters and in the internal structures of other invertebrates.

  • It is the main source of production of chitosan, which is used in a number of applications, such as a flocculating agent, a wound healing agent, a sizing and strengthening agent for paper, and a delivery vehicle for pharmaceuticals and genes.


Zatilfarihiah rasdi

CH2OH

O

OH

H

H

OH

H

H

H

NH

O

C

CH3

OH

(b) Chitin forms the exoskeleton

of arthropods. This cicada

is molting, shedding its old

exoskeleton and emerging

in adult form.

(c) Chitin is used to make a

strong and flexible surgical

thread that decomposes after

the wound or incision heals.

(a) The structure of the

chitin monomer.

Figure 5.10 A–C

  • Chitin, another important structural polysaccharides

    • Is found in the exoskeleton of arthropods

    • Can be used as surgical thread


Arthropods

arthropods


Functions general

FUNCTIONS ( GENERAL )

  • Carbohydrates are one of the most important components especially in foods. Carbohydrates may be present by itself as monosaccharides, oligosaccharides or polysaccharides, or they may be physically associated or covalently bound to other molecules as glycoproteins ( to proteins), as glycolipids( to lipids ) .

  • Some carbohydrates are digestible by humans and therefore provide an important source of energy, whereas others are indigestible. Indigestible carbohydrates form part of a group of substances known as dietary fiber, which also includes lignin.


Zatilfarihiah rasdi

  • Consumption of significant quantities of dietary fiber has been shown to be beneficial to human nutrition, helping reduce the risk of certain types of cancer, coronary heart disease, diabetes and constipation.

  • Carbohydrates also contribute to the sweetness, appearance and textural characteristics of many foods. It is important to determine the type and concentration of carbohydrates in foods for a number of reasons.


Summary

Summary

  • Monosaccharides ,the simplest carbohydrates,are classified as aldoses or ketoses.

  • The cyclic hemiacetal ( have aldehyde group) and hemi ketal ( have ketone group)forms of monosaccharide have either the α or β configuration at their anomeric carbon but are conformationally variable.

  • Sugars that can be oxidised by mild oxidising agents are called reducing sugars because the oxidising agent is reduced in the reaction.

  • Polysaccharides consist of monosaccharide linked by glcosidic bond.

  • The storage polysaccharides starch and glycogen consist of α- glycosidically linked glucose residues.


  • Login