KEGS Biology Blog


Monday 10th September 2012 Section 1
September 10, 2012, 1:28 pm
Filed under: Uncategorized

Glycosidic Bonds, Amylose, Amylopectin, Glycogen and Starch

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Alpha glucose are bonded by a condensation reaction- a type of reaction in which two molecules join together by way of covalent bonding to form one larger molecule. A water molecule is produced in the process. The bond formed during this reaction is called a glycosidic bond. The glycosidic bonds that Alpha and Beta glucose form can be referred to as 1,4. This is in reference to the two specific carbon atoms which join together in the bond.

Glycosidic bonds can be broken down through a hydrolosis reaction. This is a reaction in which water is added to break the molecule into two.

When Beta glucose molecules join, one of them flips 180 degrees on a horizontal axis to ensure the hydroxide atoms are compatible(are both going up instead of one up, one down). These form 1,4 bonds. Cellulose forms long chains of these; the long chains make it useful for structure and rigidity.

Polymers of Alpha glucose:

Amlyase: Unbranched, forms long, straight chains(a helix). Forms 1,4 bonds. It is found in plants, and used for the storage of energy.

Amylopectin: Branched, has long branches for extra storage. Has 1,4 and 1,6 bonds. Also found in plants, and used for energy storage.

Starch: Branched, forms helices. Consists of chained amylose molecules and branched amylopectin. It is stored in the chloroplasts of plants. It can be broken down into glucose.

Glycogen: It is made up of Alpha glucose ‘subunits.’ It has shorter 1,4 bonds than usual. It is more compact than starch, and forms glycogen granules in animal cells.

Neither glycogen nor starch dissolve, and both hold glucose molecules in chains so they can be easily broken off to provide energy.

Alex Molyneux
12F

Comment by alexmolyneux

This website gives a good overview of monosaccharides and polysaccharides:
http://www.s-cool.co.uk/a-level/biology/biological-molecules-and-enzymes/revise-it/carbohydrates

Comment by danielwatt

can someone please go into more detail on the structure of starch in relation to its function ? my notes arent comprehensive enough (Miss Campbell’s) cover work

Comment by halima95

Starch is the main energy source material in plants. Cells get energy from glucose. Plants store excess glucose as starch (when needed, the plant will break it down to provide the glucose). Starch is insoluble in water, so it doesn’t cause water to enter cells by osmosis (which would make them swell). This makes it good for storage. Starch is a mixture of two polysaccharides of AMYLOSE and AMYLOPECTIN:-

Amylose: A long, unbranched chain of alpha-glucose monosaccharides. The angles of the glycosidic bonds give it a coiled strucure (almost cylinderical). This makes it compact. Therefore it is excellent for storage because you can fit more into small space.

Amylopectin: A long, branched chain of alpha-glucose with side branches. They allow the enzymes that break down the molecule (carbohyrases, e.g amylase) to get to the glycosidic bonds easily. This means that the glucose can be released quickly.

Comment by Deelan Vadher

In addition to Starch (above), here are my notes on Glycogen and Cellulose:

Glycogen: The main energy storage material in animals. Animal cells get energy from glucose, but since glucose cannot be stored, it is converted into glycogen first, then stored. Glycogen is a polysaccharide composed of alpha-glucose monosaccharides. It contains many side branches. These branches mean that stored glucose can be released quickly which is important for energh release in animals. It is also a very compact molecule, therefore excellent for storage. It is also insoluble in water, therefore doesn’t bloat cells by osmosis (good for storage). As it is a large molecule, it can store large amount of energy.

Cellulose: The major component of cell walls in plants. Cellulose is made up of long, unbranched chains of beta-glucose. The bonds between the sugars are straight, so the cellulose chains are also straight. The cellulose chains are linked together by hydrogen bonds to form strong microfibrils. These strong fibres mean that cellulose provides structural support for cells (e.g. in plant cell walls)

Comment by Deelan Vadher




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