3.1.2 Carbohydrates Flashcards
What is an organic molecule?
A molecule that contains carbon
What are the monomers of carbohydrates?
Monosaccharides which are soluble
The general formula is (CH2O)n where n is between 3 and 7
What are the common monosaccharides?
Glucose, fructose and galactose
All contain 6 carbon atoms
How are monosaccharides joined?
A condensation reaction joins two monosaccharides together using a glycosidic bond (an oxygen atom connected diagonally) and produces one molecule of water
What is a disaccharide?
Two monosaccharides joined together
What are the main disaccharides?
Maltose: two glucose molecules
Sucrose: a glucose molecule and a fructose molecule
Lactose: a glucose molecule and a galactose molecule
What are the isomers of glucose?
Alpha and beta
Beta glucose has the OH and H swapped round
What are polysaccharides?
Long chains of monosaccharides joined in a condensation reaction
What are reducing sugars?
Sugars that donate electrons to other chemicals
All monosaccharides and some disaccharides are reducing sugars
What is the process and result of the Benedict’s test?
Benedict’s test: when a reducing sugar in liquid form is heated with Benedict’s reagent (alkaline solution of copper(II) sulphate) it forms an insoluble red precipitate of copper oxide
Blue=none, green=very low, yellow=low, orange=medium, red=high
How are glycogen, starch and cellulose formed?
Glycogen + starch = condensation of alpha glucose
Cellulose = condensation of beta glucose
What are the types of glycosidic bond?
(1,4) = between carbon 1 on one glucose and carbon 4 on another glucose, forms a straight chain (1,6) = glycosidic bonds between (1,4) chains, called branching
What is starch?
Plant-based
Collective term for amylose (1,4) and amylopectin (1,6)
Amylose coils due to hydrogen bonding of monosaccharides, straight chains of amylopectin also coil
Insoluble- doesn’t affect water potential
Unbranched state forms a spiral coil- compact
Large- doesn’t diffuse out of cells
When hydrolysed it forms alpha glucose- easily transported and readily used in respiration
Branched form has many ends- many enzymes can act simultaneously so that glucose is released rapidly
What is glycogen?
Animal based
Insoluble- doesn’t draw water out of the cell by osmosis
Compact- a lot can be stored in a small space
More branched than starch- glucose monomers are released more rapidly
What is cellulose?
Plant based
Only exits in straight chains- stacks to form a dense cell wall that stops the plant cell from bursting
Lots of hydrogen bonds: very strong structure even though single hydrogen bonds are very weak
Cellulose molecules group to form microfibrils then group to form fibres- very strong
