biochem cho (1)

7/30/2019 Biochem CHO (1)

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Carbohydrates

- are a group of naturally occurring carbonyl

compounds (aldehydes or ketones) that alsocontain several hydroxyl groups

- include single sugars (monosaccharides) and

their polymers, the oligosaccharides andpolysaccharides.


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- the most abundant organic molecule in nature (each year,

photosynthesis converts more than 100 billion metric tons

of CO2 and H2O into cellulose and other plant products)

- essential for life because of its wide range of function and

widely distributed in plants and animals

- Plants: synthesized from CO2 and H2O through

photosynthesis, store as starch or converted to

cellulose


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- Animals: synthesized from Lipids and CHONthrough Gluconeogenesis but the bulk is fromplants

Glucose

- primary CHO, most important source of fuel ofmost organisms

- physiologic sugar since all CHO are convertedto glucose for further metabolism


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Functions

1. Source of Energy

- 1 gram of CHO = 4 calories2. Storage form of Energy

- plants (starch), animals (glycogen)

3. Structural component of many organisms

- cell membrane, bacterial cell

4. Provides building blocks for many processes of

body metabolism


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Structure

- Carbon containing the functional group (aldehyde or ketone

group) should have the lowest possible number

-Penultimate Carbon: D and L isomer is determined


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Haworths Projection Formula (Cyclic form)

- ring is formed due to reactions:

a. aldehyde and the alcohol group (Hemiacetalring)

b. ketone group and alcohol (Hemiketal ring)

- rules: Structure in the left side (above the ring)

Structure in the right side (below the ring)

Bulky group (placed above the ring)


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-Pyranose

- the hydroxyl (OH) of5thcarbon reacts with

the 1st

carbon and the oxygen comprising theoxygen ring

- Furanose

- the 1stcarbon reacts with 4rth carbon

- Pyranose form is more stable than furanose form


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Classification

A. Monosaccharide (CnH2nOn)

- simple sugars, named based on:

1. the no. of Carbon atoms

2. based on the reaction group present

- aldehyde (aldoses)- ketone (ketoses)

- important monosaccharide:

1. Ribose and Deoxyribose (5C)2. Glucose, Fructose, Galactose (6C)


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B. Disaccharides

- yield two molecules of monosaccharide whenhydrolyzed

- e.g. sucrose, lactose, etc.

C. Oligosaccharide- contains 2- 12 monosaccharide units

- e.g. Malto-riose

D. Polysaccharide

- contains more than 10 monosaccharide units

- e.g. Starch, Glycogen etc.


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Sugars Exhibit Various Forms of Isomerism

- Isomers are compounds that have the samechemical formula but differ in structural

configuration and properties

- Isomers is due to the presence of asymmetriccarbon (attached to 4 different atoms/groups)

- study of Isomerism is focused on Glucose due to

its clinical importance


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- application of polarized light, there is rotationeither to the right (Dextrorotatory (+)) or to theleft (Levorotatory (-))

- D and L isomer is also

known as Enantiomers,

means mirror images ateach other


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(3) Alpha and beta anomers

- Isomerism occurs about position 1, the

carbonyl or anomeric carbon atom, togive a mixture:

1. -glucopyranose (38%)

2. -glucopyranose (62%)

- less than 0.3% is represented by and anomers of glucofuranose


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Beta : OH in C1 is above the rinAlpha: OH in C1 is below the ring

Ketosis: C2 is involve.


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- hemiacetal ring formation (aldehyde) andhemiketal ring (ketose)

- Interco version of alpha and beta is termed as

Mutarotation, rotation is also either Dextro (+)or Levo (-)

- In mutarotation, there is opening of ring of ringand assume free aldehyde or ketone group


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(4) Epimers

- Isomers as a result of variations in configurationof the OH and H on carbon atoms 2, 3, and 4 of

glucose

-biologically, the most

important epimers of

glucose are mannose

(C2) and galactose (C4)


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(5) Aldose-ketose isomerism

- Fructose has the same molecular formula asglucose but differs in its structural formula (ketogroup in position 2, the anomeric carbon)

- Glucose has potential

aldehyde group in

position 1 of the

anomeric carbon


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6. Boat and Chair conformers

- differs in the shape of the ring

- originates from pyranose form- chair is more stable than the boat conformation


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Monosaccharide

Aldoses

and

ketoses family


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Some hexose derivatives important in biology


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Derived sugars

1. Sugar acids

- produced when monosaccharide undergooxidation

C1 - aldonic type (Gluconic acid)

C6 uronic type (Glucoronic acid)

C1 and C6 aldaric (Glucaric acid)


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2. Sugar alcohol

- product of reduction of sugar

- e.g. Sorbitol or D-glucitol (sweetener)Mannitol (plasma expander)

3. Sugar amines

- known as amino sugars (NH2 attached in C2)

- constituent of: Antibiotics, Glycoproteins

Glycosaminoglycans


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4. Sugar phosphates

- product of phosphorylation of sugar

- phosphorylation important step in glucosemetabolism

5. Deoxy-sugars

- removal of Oxygen from carbon

- Hydroxyl group is replaced with H-ion

- e.g. Deoxyribose (DNA component)


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6. Glycosides- formed when CHO is linked to non-CHO suchas aglycone or another sugar through glycosidiclinkage

- aglycone maybe: methanol, phenol, sterol,glycerol or a base (e.g. Adenine)

- can be found in drugs, dyes, vegetables,

animal tissues

- important in the field of medicine


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B. Disaccharides

- formed when the anomeric hydroxyl group of

one monosaccharide is bound glycosidically

with one of the OH groups of another (acetal

complementation)

- type of linkage:

1. head to tail (common)

2. head to head (no free functional group,

non-reducing sugar)

.


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(1) Maltose

- occurs as a breakdownproduct of the starches

contained in malt(malt Sugar) and as

an intermediate in

intestinal digestion

- the anomeric OH group of one glucose moleculehas an -glycosidic bond with C-4 in a secondglucose residue


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2. Lactose (milk sugar,

- is the most important

carbohydrate in the

milk of mammals

- Cows milk contains 4.5%

lactose, while human

milk contains up to 7.5%

- In lactose, the anomeric OH group of galactoseforms a - glycosidic bond with C-4 of a glucose


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(3) Sucrose

- serves in plants as

the form in whichcarbohydrates are

transported, and as a

soluble carbohydrate

reserve

- non-reducing sugar


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Polysaccharides

- polymer of several molecules of sugars, areubiquitous in nature

- can be classified into three separate groups,based on their differentfunctions

1. Structural polysaccharides-provide mechanical stability to cells,

organs, and organisms


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Structural polysaccharide

- structural component of cells and tissues1. Cellulose

2. Chitin

3. Glycoprotein

4. Glycosaminoglycans


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2. Waterbinding polysaccharides- are strongly hydrated and prevent cells and

tissues from drying out

3. Reserve/Storage polysaccharides

- serve as carbohydrate stores that releasemonosaccharides as required

- due to their polymeric nature, they areosmotically less active, hence can be storedin large quantities within the cell


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Storage polysaccharides

- source of energy or storage form of CHO1. Starch

2. Glycogen

3. Inulin

4. Dextrin


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Structure

Homopolysaccharides- contain only a single

type of monomer

Heteropolysaccharides- contains two or more

different kinds


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Starch

- the most important vegetable reservecarbohydrate and polysaccharides from plantcell walls

- consist of glucose as building block (glucanor glucosans)

- abundant in fruits- important in human diet (50 70%)


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Structure:

1. Amylose

- linear form consisting of 250 300 glucose

units (alpha 1-4 linkage)

- 15 20%, soluble in water, when in solutionform a helix

2. Amylopectin

- branched form with alpha 1-6 linkage in thebranch (every 12 18 glucose units)

- 80 to 85%, water insoluble


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Glycogen

- the reserve carbohydrate of higher animals, isstored in the liver and musculature in particular

- formation and breakdown of glycogen are subjectto complex regulation by hormones and otherfactors

- structure: similar to amylopectin but highly

branched (every 8 10 units)


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Inulin- a fructose polymer, is used as a starch substitute in

diabetics dietaryproducts

- it serves as a test substance for measuring renalclearance

Chitin

- a homopolymer from 1-4-linkedN-acetylglucosamine,

- most important structural substance in insect andcrustacean shells, thus , the most common animalpolysaccharide

- also occurs in the cell wall of fungi.


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Dextrin

- formed in the course of hydrolytic breakdown ofstarch

- yield maltose upon hydrolysis by amylase

- contains 7 10 glucose units

- used in malt preparation for beverages

- widely used in infant feeding which facilitatesdigestions (prevents large heavy curds of milk inthe stomach)


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Cellulose

- structural polysaccharide of plants

- linear polymer ofB-D-glucose joined byB 1-4glycosidic bond

- cellobiose as building block

- could not be digested by humans due to lack of

B-1-4 glycosidase enzyme- food sources: Fruits, vegetables and other fibrous

foods


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Physiologic function

- serves as a roughage (cleansing of Intestine)

by increasing the fecal bulk thereby decreasingthe transit time of bowel preventing the effectsof toxins and microorganisms in the colon

- decrease in fecal bulk will increase transit timeof bowel, increase exposure to carcinogens(waste product of metabolism or in-situproduction)


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Glycoproteins

- high CHON content than CHO

- found in cell membrane or tissues

- widely distributed and perform several functions

- contains sialic acid responsible for its (-) charge

- substances made up of glcoproteins:

a. Blood group Ag

b. Enzymes d. Collagen

c. Transport proteins e. Antibodies (Ab)


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Glycosaminoglycans

- known as Mucopolysaccharide or Proteoglycan

- special heteropolysaccharide made up ofUronicacid andAmino sugars as building block

- present in matrix where in collagen, elastin andbone minerals are embedded

- relative to connective tissue function


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- responsible for the lubricating function of mucousmembrane

- almost all exist as proteoglycan (uronic acid isattached to a CHON):

a. Chondroitin

b. Heparin

c. keratan

d. Heparan


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Types of Glycosaminoglycans and their repeatingDisaccharides

1. Hyaluronic acid

- largest consist of

400 25,000 linearpolymer of repeating

disaccharide

- main constituent ofground substance of

Connective tissues


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2. Chondroitin

- acts as water bed

around cells and fibers

- types:

a. Chondroitin-4-SO4

b. Chondroitin-6-SO4

c. Dermatant sulfate


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3. Heparin

- naturally occurring

anticoagulant

- present in Mast cells

Lining of arteries

Liver, lungs and skin


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4. Keratan sulfate

- present in corner of the eye and nucleus of

Intervertebral disc

- repeating disaccharide:

N-acetylglucosamine-B-1,3-D-galactose


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Summary of Function

1. Component of ground substances or C.T.

e.g. Hyaluronic Acid, Chondroitin

2. Structural component of cell membrane

3. Lubricant in joint spaces

e.g. Hyaluronic Acid

4. Anti-coagulante.g. Heparin


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END

biochem cho (1)

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