Biology: Chapter 2: Biological molecules: Carbohydrates

Biology: Chapter 2: Biological molecules: Carbohydrates

 Sugar quiz

Polysaccharide quiz

• General formula for a carbohydrate is Cx(H2O)y
• Contain elements Hydrogen, Carbon and Oxygen
• Saccharide: Sugar

Common groups:

     Hydroxl Group

        Carbonyl Group

Monosaccharides

• Single sugar molecule
• General formula: (CH2O)n
• All monosaccharides end with -ose eg. glucose, fructose, galactose
• Trioses: 3 carbons, Pentoses: 5 carbons, Hexoses: 6 carbons.
• Source of energy, due to large amount of C-H bonds.
• Building blocks for larger molecules

Molecular and structural formula

• Molecular formula for hexose: C6H12O6
• Below is the structural and ring structure of glucose

• Pentoses and Hexoses have carbon chains long enough to close in on itself and form a more stable ring. Above is an example of a glucose ring structure. 
• Carbon 1 joins to Carbon 5, leaving Carbon 6 out of the ring.
• The hydroxl group in glucose, -OH, can be above or below Carbon 5.
• α Glucose (alpha): -OH is below the ring
• β Glucose (beta): -OH is above the ring
• These are called isomers (two forms of the same chemical).

Disaccharides and Glycosidic bond

• Disaccharides: Two monosaccharides joint together  by condensationeg. Maltose (glucose + glucose), Sucrose (glucose + fructose)
• Condensation: Two Hydroxyl (-OH) groups line up alongside each other. One combines with a H atom from the other to form a H20 molecule, which is the waste product of the reaction.
• The Oxygen becomes the bridge between both molecules, holding them together. This is called a glycosidic bond.
• The reverse of this is called hydrolysis.

Polysaccharides

• Polymers whose subunits (monomers) are monosaccharides, bonded by glycosidic bonds.
• Final unit can be several 1000 monosaccharides long, forming a macromolecule.
• Not sugars
• Energy storage unit for monosaccharides (glucose), since glucose itself cannot be stored therefore is converted into polysaccharides, which are convenient - compact and inert

Starch

•     Mixture of two substances – Amylose and amylopectin
•    Commonly found in chloroplasts – energy storage
•    Never  found in animal cells
•  Amylose: Long, unbroken chain of alpha α glucose molecules bonded by a glycosidic bond through condensation at 1,4 linkages.
• 1,4 linkages: The glycosidic bond is formed between the Carbon 1 of one glucose molecule and Carbon 4 of the next.
• Chains are curved and coil into helical structures – more compact.
•  Amylopectin: Also made of 1,4 linkages, but has shorter chains than amylose and has branches.
•  Branches: Formed by 1,6 linkages – Carbon 1 of one glucose molecule forming a bond with Carbon 6 of another.

Glycogen

•   Similar to Amylopectin – Chains of α glucose made of 1,4 linkages and 1,6 linkages, forming branches.
• More branched than amylopectin
• Clump together to form granules – visible in liver and muscle cells
• Energy storage for animal cells

Cellulose 

•  Structural role – Mechanically strong molecule
•  Polymer of beta β gluclose instead of alpha α glucose.
• In beta glucose, the –OH attached to Carbon 1 is above the ring, but on Carbon 4 it is below the ring
• This means every 2^nd beta glucose in the chain needs to rotate 180 degrees (upside down) to be able to form a glycosidic bond with the glucose in front.
• Strong molecule - Hydrogen bonding between different cellulose molecules 
• The hydrogen bonds are individually weak, but many can form due to large number of Hydroxl (-OH) groups
• Around 60-70 celluolose molecules tightly crosslink to form Microfibrils
• Microfibrils hydrogen bond together to form bundles called Fibres
• Celluloe fibres have high tensile strength but are still freely permeable 
• Found in cell wall - provide support for plant and helps it withstand the large pressures from osmosis