Carbohydrates Flashcards
What is the general formula for carbohydrates?
(CH2O)x
Why are monosaccharides soluble in water?
- polar hydroxyl groups form hydrogen bonds with water making them soluble
What are ‘hexose’ and ‘pentose’ sugars?
- hexose: 6 carbons
- pentose: 5 carbons
How is a disaccharide formed from 2 monosaccharides?
- join together during a condensation reaction
- forms a 1,4 glycosidic bond
- water molecule produced
- hydroxyl group from one joins to a hydrogen from the other
How is the disaccharide sucrose formed?
glucose + fructose
How is the disaccharide lactose formed?
galactose + glucose
How is the disaccharide maltose formed?
glucose + glucose
How is glucose made available for respiration?
- 1,4 glycosidic bond is broken using a water molecule
- in a hydrolysis reaction
- catalysed by an enzyme
Describe the difference between alpha and beta glucose
- alpha glucose on carbon 1 has the hydroxyl group below the ring
- beta glucose on carbon 1 has the hydroxyl group above the ring
What is amylose?
- compact, insoluble
- angle of 1,4 glycosidic bond cause it to twist into helix
- made of alpha glucose
What is amylopectin?
- every 25 glucose units, a condensation reaction occurs between a C1 and a C6 of two glucose molecules
- made of alpha glucose
What is the structure of glycogen?
- every 6 glucose units glycogen branches due to 1,6 glycosidic bond
What impact does glycogen having more branches than amylopectin have?
- glycogen has more ‘free ends’ where hydrolysis of glucose takes place
- so more glucose released per unit time for use in respiration
What are the roles of glucose and how do its properties enable this?
- respiratory substrate
- building blocks for larger molecules, like starch, glycogen and cellulose
- polar so soluble in water (and cell cytoplasm) transport medium
- energy trapped within the C-H bonds
- hydroxyl groups can form glycosidic bonds with other monosaccharides
What are the roles of starch and glycogen and how do its properties enable this?
- chemical energy store in plants (starch), animal and fungi (glycogen)
- helical structure (stabilised by H bonds) makes it compact (less space needed for it to be stored)
- insoluble (no osmotic effect)
- (amylopectin in starch) is branched so has many ‘free ends’ for adding or removing glucose (respiration)
How is it possible for beta glucose to from 1,4 glycosidic bonds and what is the effect on the cellulose molecule?
- flipping every other glucose 180oC ensures OH groups are close enough to form bond
- effect is chain is straight and not coiled
Where is cellulose found?
Plant cell walls
Why is cellulose so strong?
- crosslinks (hydrogen bonds) between the cellulose molecules
- staggered ends offer more strength as there’s no weak points
What makes up cellulose?
- lots of cellulose molecules makes the microfibril
- lots of microfibril makes the macrofibril
- lots of macrofibril make the cellulose fibres
Explain how the structure of cellulose is related to its function?
- straight chain molecule
- many H bonds between individual chains
- staggered ends that give strength to fibres
- all make it good for strength in a plant cell wall
Explain why beta glucose, when polymerised, leads to the production of cellulose instead of starch
- in beta glucose OH group at carbon 1 is above the ring
- so alternate molecules rotate 180
- this means OH groups are close enough to react
- in a condensation reaction forming a glycosidic bond
- produces a straight chain molecule: cellulose
