Carbohydrates Flashcards
Contain
Only carbon, hydrogen, oxygen
General formula
Cx (H2O) y
3 groups
Monosaccharides - single sugars eg galactose, fructose, glucose
Disaccharides - two sugars eg maltose, sucrose, lactose
Polysaccharides - many sugars eg starch, cellulose, glycogen
Condensation reaction
Two monosaccharides join to from a disaccharides, water is also produced and a glycosidic bond forms
Many monosaccharides join in many condensation reactions to form a polysaccharide
Most common monosaccharide
a Glucose - C6H12O6
Isomer
Molecule with the same molecular formulae but a different arrangement of atoms
Optical isomerism
When the bonds in the molecules can rotate in space to give a different form of the molecule (glucose to B glucose)
B glucose - the hydroxyl group rotates 180 around carbon 1
Fructose and galactose formulae + structure
C6H12O6 - makes it a structural isomer of A and B glucose (different arrangement of atoms, same molecular formulae)
Hexose sugars - 6 carbon atoms
Monosaccharides use
Make ATP - respiration
Formation of other carbohydrates
Formation of other molecules (DNA & RNA)
Properties of monosaccharides
Small, can move across membranes with channel or transport proteins
Soluble in water, easily transportable and diffuse around living organisms to be used as a respiratory substrate
Lower water potential
Reducing sugars
Test for reducing sugars
Add Benedicts reagent, heat
Present - red/brown/orange/green
Absent - blue
Reducing sugars , quantitative
Use standard solution, a colorimeter and calibration curve
Reducing properties come from
The aldehyde or ketone group within the molecule
Disaccharides
Maltose, sucrose, lactose
Bond formed when 2 monosaccharides join by a condensation reaction with a glycosidic bond
Maltose + formulae
Disaccharides formed by condensation of A glucose & A glucose
C12H22O11 as there are 2x glucose and - water since it is a condensation reaction
Sucrose + formulae
disaccharides formed by condensation of A glucose & fructose
C12H22O11 as there are 2x glucose and - water since it is a condensation reaction
Lactose + formulae
Disaccharides formed by condensation of A glucose & galactose
C12H22O11 as there are 2x glucose and - water since it is a condensation reaction
Use of disaccharides
Make polysaccharides
Hydrolysed to make monosaccharides for respiration
Properties of disaccharides
- soluble in water
- need to be hydrolysed before the monosaccharides produced can be transported across membranes
- lower water potential
- maltose + lactose are both reducing sugars
- sucrose is a non-reducing sugar
Lactose and maltose and the reducing sugar test
- if you perform benedicts test on lactose or maltose you get a precipitate
- if you add lactase to lactose or maltase to maltose then perform benedicts test you get double the precipitate
Non-reducing sugars test sucrose
Sucrose will give a blue colour
Test for non-reducing sugars
- add acid, boil
- neutralise
- add benedicts reagent
- heat
Present - red/brown/ orange/ green
Absent - blue
Non-reducing sugars, semi-quantitative
Using standard solutions, a colorimeter and a calibration curve
Maltose hydrolysed
By maltase which is produced by epithelial cells of the ileum
Sucrose hydrolysed
By sucrase which is produced by epithelial cells of the ileum
Lactose hydrolysed
By lactase which is produced by epithelial cells of the ileum
Polysaccharides
Chains of many monosaccharides joined together by condensation reactions with many glycosidic bonds
Three important : starch, cellulose, glycogen
Properties of polysaccharides dependent on
- number of monosaccharide molecules in the chain
- type of monosaccharide in the chain
- how they are joined together (branched or un-branched
- overall shape of the molecule
Starch
Polymer of A glucose molecules
- all atoms lie upwards
- found only in plants, storage polysaccharides (acting as a store of glucose)
- insoluble and doesn’t affect water potential of the cell or solution
- 1-4 and 1-6 glycosidic bonds
Describe structure of starch
- large insoluble chains of A-glucose
- helix
- branched with 1-4 and 1-6 glycosidic bonds
- consists of 2 polysaccharides amylose and amylopectin
Structure related to function starch
Large and insoluble - doesn’t affect water potential, cannot pass across the cell membrane and move out of the cell
Helix - will compress/compact into starch grains which take up less space
Branched - more ends so larger surface area for faster hydrolysis by enzymes to release glucose for respiration
test for starch
iodine or potassium iodide solution
present - blue/black
absent - orange/yellow/brown
food in the stomach
when food is swallowed the enzyme is denatured by the acid in the stomach or hydrolysed by the endopeptidase, pepsin in the stomach
stomach acid pH
1-2
glycogen features
- all atoms lie in 1 direction
- polymer formed by the condensation of A glucose molecules
- found only in animals and fungi and is a storage polysaccharide (acting as a store of glucose)
- glycogen is insoluble and doesn’t affect water potential of the cell or solution
- 1-4, 1-6 glycosidic bonds
structure of glycogen
large and insoluble - doesn’t affect water potential, cannot move past cell membrane and move out of the cell
helix - will compress/compact which takes up less space
branched - more ends, larger surface area, for faster hydrolysis by enzymes to release glucose for respiration
why is glycogen more branched than starch
only found in animals so the more ends increases surface area for faster hydrolysis of glucose by enzymes for respiration.
cellulose features
- polymer formed by condensation of B glucose molecules
- found only in plants and is a structural polysaccharide found in plant cell walls
- cellulose is insoluble and doesn’t affect water potential of the cell or solution
- atoms alternate up and down
- only 1-4 glycosidic bonds
structure of cellulose
long unbranched parallel chains of B-glucose cross-linked by hydrogen bonds to form microfibrils
how is cellulose adapted for its role as a structural polysaccharide
long unbranched chains of B-glucose lie parallel (as there are only 1-4 glycosidic bonds)
allows hydrogen bonds to form between them so they are cross-linked to microfibrils
individual hydrogen bonds are weak however many of them together makes the strong structure that gives them strength and rigidity to the molecule important in cell walls
