Sunday, 20 January 2013

CARBOHYDRATES

CARBOHYDRATES

Includes 

      - sugars

     - glycogen 

     - starches

     - cellulose


- Large diverse group of organic compounds.

- Represent only 2 - 3 %  of total body mass.


MAIN FUNCTION

1. As a source of chemical energy for generating ATP needed to drive metabolic reactions.

2.  A few are used for building structural units.

eg. deoxyribose
     - a type of sugar that is a building block of DNA.



ELEMENTS FOUND IN CARBOHYDRATES

CARBON

HYDROGEN


OXYGEN


The ratio of hydrogen to oxygen atom is usually 2 : 1
  the same as in water.

THE NAME CARBOHYDRATES

- WATERED CARBON 

Carbohydrates generally contain 1 water molecule for each carbon atom.


3 MAJOR GROUPS OF CARBOHYDRATES

1. MONOSACCHARIDES

2. DISACCHARIDES


3. POLYSACCHARIDES


Monosaccharides and disaccharides are simple sugars.


1. MONOSACCHARIDES

mono     = one
sacchar  = sugar

- Simple sugars

- Contain 3 -7 carbon atoms.

 - Designated by names ending in - ose
         - with a prefix that indicates the number of carbon atoms.

eg

Trioses     - monosaccharides with 3 carbon atoms.

Tetroses   - monosaccharides with 4 carbon atoms.

Pentoses   - monosaccharides with 5 carbon atoms.

Hexoses   - monosaccharides with 6 carbon atoms.

Heptoses  - monosaccharides with 7 carbon atoms.


COMMON MONOSACCHARIDES


1. Glucose - The main blood sugar

2. Fructose - Found in fruits.

3. Galactose- In milk sugar

4. Deoxyribose - In DNA

5. Ribose - In RNA.



2. DISACCHARIDES

di = 2

-molecule formed from combination of 2 monosaccharides by dehydration synthesis.

A. SUCROSE / TABLE SUGAR

 - molecules of monosaccharides glucose and fructose combine to form a molecule of disaccharide sucrose.

C12 H22 O11
   not C12 H24 O12
         - Because a molecule of water is removed when 2 disaccharides combine.

B. LACTOSE/ MILK SUGAR

- Glucose + Galactose.

3. MALTOSE

- Glucose + Glucose.


Disaccharides can also be split into smaller simple molecules 

             -by hydrolysis

eg.  A molecule of sucrose may be hydrolysed into glucose and fructose by the addition of water.

ARTIFICIAL SWEETENERS

   -Much sweeter than sucrose.

   - Have fewer calories.

   -  Do not cause tooth decay.

3. POLYSACCHARIDES

 Tens or hundreds of monosaccharides join through dehydration synthesis reactions.

   - usually insoluble in water.

-   Do not taste sweet.

eg . 

1. Glycogen

   - Made entirely of glucose monomers linked to 1 another in branching chains.

   - A limited amount of carbohydrates is stored as glycogen in liver and skeletal muscles.

2. Starches

   - Formed from glucose by plants.

   - Are found in food such as pasta, potatoes.

   - Are the major carbohydrate in the diet.

3. Cellulose

   - Formed from glucose by plants.

   -  Cannot be digested by humans.

   - But does provide movement of food through intestine.

   - Provide bulk to help eliminate feces.



Like disaccharides, polysaccharides such as glycogen and starch can be broken down in to monosaccharides through hydrolysis reaction.

eg.
When blood glucose level falls
   
                    U+2193.svg

Liver cells break down glycogen into glucose

                   U+2193.svg

Release it into blood

                   U+2193.svg

Making it available to body cells.

                   U+2193.svg

Which breaks it down to synthesis ATP.


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