Biomolecules: Carbohydrates Flashcards
(20 cards)
Main elements in Carbohydrates
Carbon, Hydrogen, Oxygen 1:2:1 ratio
Carbohydrate means hydrate (water of) carbon aqueous Reflects the 2:1 ratio of hydrogen to oxygen
Examples of carbohydrate
sugars, starches, glycogen, cellulose, chitin
Function of sugars and starches
Sugars and starches are energy sources for cells
Function of cellulose and chitin
indigestible and act as structural component
Importance of carbohydrates
- Constitute the structure. of cells and tissues
- Participate and regulate metabolic reactions
- Transmit info
- Provide energy
Glucose
One sugar unit - Monosaccharides e.g. glucose for metabolic fuel
C6H12O6
Most abundant, a hexose sugar
Oxidised by the cell in cellular respiration
Used as a compound in the synthesis of other compounds such as amino acids and fatty acids
Mechanisms have evolved to keep it at a relatively constant level in the blood
Diabetes is a breakdown of the mechanism
Glycosidic Bond- Joins the sugars together
Monosaccharides can join together to create polymers of Disaccharides and Polysaccharides
Common Disaccharides
Sucrose, Lactose, Maltose
Sucrose
Glucose alpha (1-2) fructose. From cane or beet and hydrolysed by the enzyme Invertase an equimolar mixture of glucose(1 mole) and fructose(1 mole)
Lactose
Galactose Beta (1-4) glucose. Occurs in milk and hydrolysed by lactase or Beta Galactosidase. Lactose intolerance is nausea pain, cramps, diarrhoea due to the osmotic effects when lactose is built up in the ileum.
Maltose
Glucose alpha (1-4) glucose. Homodimer of glucose units. Occurs as a by- product of starch hydrolysis. Degraded to glucose by Maltase.
Polysaccharides
Means ‘many sugars’
1000s of mono rings joined by glycosidic linkages usually glucoses
Most abundant carbs in nature
E.g. starches, glycogen, cellulose, chitin
Long chained or branched
Enzymatic or acid hydrolysis during digestion will release mono
Homopolysaccharides many of the same monosaccharide e.g. Glucans Mannans
Storage Polysaccharides
Plants - starch two forms of starch alpha amylose and amylopectin
Animals - Glycogen
Deposited as granules in the cytoplasm
Starch
Homopolymer of alpha Glucose units joined by glycosidic bonds
Alpha Amylose
- a long unbranched chain of glucose units linked by alpha (1-4) bonds
- Not water soluble but forms hydrated micelles *
- In the micelles the polymer from a helical coil
Amylopectin
- highly branched polymer,
- branch length 24-30 glucose residues,
- backbone linkages = alpha (1-4)
- branch points = alpha(1-6)
Hydrolysis of starch
Alpha amylase enzyme - found in saliva and pancreatic juices,
important in digestion of starch,
Cleaves alpha (1-4) bonds randomly to produce mixture of glucose and maltose
ii)Beta Amylase enzyme
Found in malt
Cleaves single maltose units successfully from the non-reducing end of the polymer
Specific for alpha(1-4) bonds
ii)Both alpha and beta amylase degrade alpha amylose to completion
Degrade amylopectin but cannot breakdown alpha (1-6)bonds
Products are dextrins short chain -> limit dextrin
Debranching enzyme alpha(1-6) glucosidase is needed for the completion of degradation
Polysaccharide- cellulose
Most abundant carb in the planet
Makes up over 50% of carbon compounds
Structural carb e.g. wool is 50% cellulose cotton is 90% cell walls are cellulose
Bonds between glucose units are beta 1-4 glycosidic linkages
Humans and most animals don’t have the enzyme to breakdown cellulose
Polysaccharide-chitin
Structural carb found in animals
Main component in cell wall of fungi
External skeleton of insects and crayfish
Glycoproteins
Integral membrane proteins
Secreted proteins e.g. antibodies
Contain oligosaccharides in glycosidic linkage to serine threonine or asparagine
Phosphorylated sugars
Occurs as intermediates in energy yielding metabolism e.g glucose 6 phosphate in glycolysis
Phosphorylation also makes sugars anionic and can be involved in glycosidic bonding as reactive intermediates
