Carbohydrates Flashcards
Carbohydrate
A group of molecules containing carbon, hydrogen and oxygen in the ratio Cn(H20)n
Carbohydrate percentage composition of a cell
Around 10%
Use of carbohydrates
Energy source - released from glucose during respiration
Energy store - e.g. starch
Structure - e,g, cellulose
Form parts of larger molecules such as nucleic acids
Monosaccharide
The monomeric unit for disaccharides and polysaccharides e.g. glucose, fructose and galactose
Properties of monosaccharides
- Soluble in water
- Taste sweet
- Form crystals
Triose sugar
3-carbon monosaccharide
Pentose sugar
5-carbon monosaccharide
tend to occur as a ring structure
Hexose sugar
6-carbon monosaccharide
Tend to occur as a ring structure
The difference between alpha glucose and beta glucose
On alpha glucose, the OH group on carbon 1 is below the plane of the ring
On beta glucose, the OH group on carbon 1 is above the plane of the ring
Condensation reaction
A reaction in which two molecules are joined together by means of a glycosidic bond to form a larger molecule, and at the same time a water molecule is released
Glycosidic bond
The bond between two monosaccharides during a condensation reaction
Polysaccharide
A polymer consisting of many monosaccharide monomers covalently bonded together
How does glucose release energy?
When glucose is broken down into simpler molecules such as water and carbon dioxide. The breaking of the bonds releases energy in the form of ATP
Word equation of respiration
glucose + oxygen -> carbon dioxide + water+ ATP
Why can plants and animals digest alpha glucose but not beta glucose?
Plants and animals do not have the right enzymes that has the complementary shape to beta glucose
Sucrose
- Commonly known as table sugar
- White, odourless and crystalline powder
- Composed of alpha glucose and fructose
- Formula C12H22O11
- Hydrolysis can be accelerated using sucrase
- Transported around in the phloem (translocated)
Lactose
- Commonly known as milk sugar
- Composed of alpha glucose and galactose
- Has both a alpha and beta form
- Hydrolysis can be accelerated using lactase
Maltose
- Product of starch hydrolysis
- Composed of two alpha glucoses
- Has both an alpha and beta glucose structure
- Found in germinating seeds as a break down product of starch
- In animals, starch is hydrolysed by amylose
Oligosaccharide
A saccharide made up of 3~10 monosaccharides
Makes up the receptor sites on glycoproteins and glycolipids
Starch
- Polymer made from alpha glucose linked through 1:4 and 1;6 glycosidic bonds
- Stored in chloroplasts or in membrane bound starch grains
- Starch can be broken down into glucose to use for respiration
- Composed of amylose and amylopectin
- Insoluble in water so it doesn’t affect the cell’s water potential
Glycogen
-Used as a stored energy store
-Stored in animal cells in muscle and the liver
-Polymer made from alpha glucose linked through 1:4 and 1:6 glycosidic bonds
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Why is glycogen a good storage molecule
- It can be easily hydrolysed to produce ATP
- Highly branched making it very compact so a large amount can be stored in a small volume
- Insoluble in water, thus doesn’t affect the cell’s water potential
Glycogen storage disease (glycogenoses)
Genetic metabolic disorders involving enzymes regulating glycogen metabolism
Can result in muscle cramps, enlarged liver and low blood sugar
Accumulation of abnormal metabolic by-products can damage the liver and kidneys
Cellulose
- Polymer made from beta glucose linked by 1:4 glycosidic bonds
- Structural molecule
- Totally permeable
- Mechanically very strong
