Carbohydrates Flashcards
What are general features of carbs?
-only contain C,O,H
-divided into 3 groups: monosaccharides, disaccharides and polysaccharides
-2 monosaccharides join in a condensation reaction to form a disaccharide and also produces a glycosidic bond.
-many monosaccharides join in many condensation reactions to form a polypeptide.
What is an isomer?
A molecule with the same molecular formulae but different arrangement of atoms. They can be structural /optical.
What are monosaccharides
Single sugars like glucose fructose and galactose
What are types of monosaccharides
Hexose, pentose , triose
What are uses of monosaccharides
-atp production
-formation of other carbs, starch, cellulose and glycogen
-formation of other molecules, DNA & RNA
Properties of monosaccharides
- small so can move across membranes using protein carriers
-polar (soluble in H2O) so easily transportable and diffuse for use as respiratory substrate.
-lower wp
-reducing sugars
Biochemical test for reducing sugars:
Add Benedict’s reagent and heat.
Red precipitate = positive, blue = negative
It can be made fully quantitative by using a dilution series , weighing the mass of the precipitate and using a calibration curve.
Why don’t we use Benedict’s test for diabetes?
It’s not specific - it detects all reducing sugars not just glucose
It provides qualitative readings
Cannot be used to test coloured substances like blood
Cannot measure blood glucose levels continuously
What are disaccharides?
2 sugars like maltose, sucrose and lactose. Forms when 2 monosaccharides join by a condensation reaction forming a glycosidic bond whilst producing H2O.
Maltose= a-glucose + a-glucose
Sucrose= a-glucose + fructose
Lactose = a-glucose + galactose
Uses of disaccharides
Make polysaccharides and hydrolysed for monosaccharides for respiration
Properties of disaccharides
Soluble in water/ polar
Hydrolysed before they can cross
membranes
Sucrose = non-reducing, maltose and lactose = reducing
Biochemical tests for non-reducing sugars
First conduct negative reducing sugars test
Add acid and boil
Neutralise
Add Benedict’s reagent and heat
Positive = red precipitate
Negative = blue precipitate
Where are maltose sucrose and lactose hydrolysed?
In the epithelial cells of the ileum
What are polysaccharides?
Many monosaccharides join by many glycosidic bonds formed by many condensation reactions
What do the properties of polysaccharides depend on?
Number of monosaccharides in the chain, the type of monosaccharides, how they’re joined (branched or not), overall shape of the molecule
What are the three polysaccharides?
Starch, cellulose and glycogen
Describe starch
-polymer of a-glucose held by glycosidic bonds
- 1-4 and 1-6 glycosidic bonds formed more ends for larger SA for hydrolysis by enzymes which releases more glucose
-plant storage molecule
- large and insoluble so doesn’t affect wp of cell as it can’t pass across the cell membrane.
-all glucose molecules lie upwards
-its a helical structure so can be compressed for storage
-consists of 2 polysaccharides (amylose and amylopectin)
Test for starch
Add iodine (potassium iodide)
Blue/black = positive
Orange = negative
Describe glycogen
- polymer of a-glucose held by glycosidic bonds
- 1-4 and 1-6 glycosidic bonds
- storage molecule in animals and fungi
- insoluble and doesn’t affect wp
- all glucose molecules lie in one direction
-helical
-more branched than starch because animals move more so require more hydrolysis of glucose for respiration
