Short Note on Starch

3456 Words Sep 6th, 2012 14 Pages
Starch
From Wikipedia, the free encyclopedia
Starch

Identifiers
CAS number
9005-25-8

EC-number
232-679-6

RTECS number
GM5090000
Properties
Molecular formula variable Molar mass variable Appearance white powder
Density
1.5 g/cm3
Melting point decomp. Solubility in water none Hazards
MSDS
ICSC 1553

EU Index not listed
Autoignition
temperature
410 °C (verify) (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Infobox references

Structure of the amylose molecule

Structure of the amylopectin molecule

Granules of wheat starch, stained with iodine, photographed through a light microscope
Starch or amylum is a
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The same type of bond is found in the animal reserve polysaccharideglycogen. This is in contrast to many structural polysaccharides such as chitin, cellulose and peptidoglycan, which are bound by beta bonds and are much more resistant to hydrolysis.
[edit]Biosynthesis
Plants produce starch by first converting glucose 1-phosphate to ADP-glucose using the enzyme glucose-1-phosphate adenylyltransferase. This step requires energy in the form of ATP. The enzyme starch synthase then adds the ADP-glucose via a 1,4-alpha glycosidic bond to a growing chain of glucose residues, liberating ADP and creating amylose. Starch branching enzymeintroduces 1,6-alpha glycosidic bonds between these chains, creating the branched amylopectin. The starch debranching enzyme isoamylase removes some of these branches. Several isoformsof these enzymes exist, leading to a highly complex synthesis process.[8]
Glycogen and amylopectin have the same structure, but the former has about one branch point per ten 1,4-alpha bonds, compared to about one branch point per thirty 1,4-alpha bonds in amylopectin.[9] Amylopectin is synthesized from ADP-glucose while mammals and fungi synthesize glycogen from UDP-glucose; for most cases, bacteria synthesize glycogen from ADP-glucose (analogous to starch).[10]
[edit]Properties
[edit]Structure This section does not cite anyreferences or sources. (March 2012)

While amylose was traditionally thought to
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