Carbohydrates Flashcards
Elements Contained
Hydrogen (H)
Oxygen (O)
Carbon (C)
Carbohydrates
Organic molecules used as source of energy in all organisms and as structural materials in cell walls
The General Formula for a carbohydrate
Cn(H2O)n
The 3 main groups of carbohydrates
Monosaccharides - Mono=1
Disaccharides - Di=2
Polysaccharides - Poly=Many
Monosaccharides
Monosaccharides are single sugar units that form the building blocks for the larger carbohydrates.
They are classified according to the number of carbons:
Trioses=3C eg glyceraldehyde
Pentoses=5C eg ribose, deoxyribose (in RNA/DNA)
Hexoses=6C eg alpha and beta glucose, fructose and galactose
Glucose
- Is the most common monosaccharide
- Is a Hexose sugar with the formula C6H12O6
- exists in both straight chain and ringed form (rings form when glucose is dissolved in water)
Isomer
Same chemical formulae but different structural formulae
2 isomers of glucose
1) Alpha-Glucose
2) Beta-Glucose
Disaccharides
Sugars formed when 2 monosaccharides join during condensation reaction.
The 3 we need to know are:
Glucose+Glucose=Maltose+Water
Glucose+Fructose=Sucrose+Water
Glucose+Galactose=Lactose+Water
Chemical formula Disaccharide
C6H12O6=C12H22O11 + H2O
Reducing sugars
All the monosaccharides and many of the disaccharides are reducing sugars
Biochemical Test for Reducing Sugars
- Add Benedicts Reagent to a solution with water
- Heat
- Blue to Brick-Red colour
Biochemical test for non-reducing sugar
- Hydrolyse/heat with acid (acid hydrolysis)
- Neutralise, with alkali/sodium hydrogen carbonate
- Add Benedicts Reagent
- Heat-Blue to Brick-Red colour
Polysaccharides
Polysaccharides are all: -Polymers of glucose -Macromolecules -Insoluble The 4 polysaccharides we need to know are: -Starch -Glycogen -Cellulose -Chitin
Starch
Starch is a polymer of Alpha-Glucose and made up of 2 chains-Amylose and Amylopectin
Amylose
Amylose is formed by a series of condensation reactions that bond alpha glucose molecules together into a long chain forming many glyosidic bonds
Amylopectin
Amylopectin consists of a straight chain of alpha glucose units with branch points occurring at approx. every twelfth glucose units the straight chain. The branch points form when carbon 6 of a glucose molecule positioned above the chain forms a glyosidic bond with carbon 1 of a glucose molecule positioned above the chain.
Starch Biological Importance
Starch is only stored in plants as an energy store. Animals store glycogen. Starch is hydrolysed by the enzyme amylase
Starch Structure
- Polymer of alpha-glucose
- made up of amylose and/or amylopectin
- so it has 2 polysaccharides
- glyosidic bonds/ 1-4 and 1-6 linkages
- amylose coil/starch coiled/amylopectin branched; not compact
- glucose all same way up
- consists of single chains
Starches Function and Properties
Function:
-Energy store in plant cells only
Properties:
-Insoluble so doesn’t affect osmotic potential in cell
-Can’t diffuse out of cell
-Coiled making it compact so stored lots in small space
-Starch as few free ends for enzyme hydrolysis so it is an excellent long term storage molecule - not broken down quickly
Biochemical test for starch
- Add iodine
- Turns from orange-brown to blue-black colour
Glycogen
Its a polymer of a alpha-glucose and it is an energy store in animal cells mainly in the liver and skeletal muscles. Glycogen has a similar structure as amylopectin but there is significantly more branching
Glycogen function and properties
Function:
-Energy store in animal cells only
Properties:
-Has many more branches so it can hydrolyse rapidly to meet the higher energy demands of animals
Cellulose
Its a polymer of Beta-Glucose and it has structural role in plant cell walls
Cellulose Structure
- Polymer of Beta-Glucose
- With 1-4 glyosidic bonds
- Adjacent glucose molecules are rotated by 180’/head up and head down
- Hydrogen bonds form between OH groups adjacent parallel chains/reference to cross linking
- Forming microfibrils
- Straight chain only/no branches; not parallel
- Cellulose (cross linked) in straight chains
- Linked with hydrogen bonds
Cellulose functions and properties
Function:
-Structural role in plant cell walls
Properties:
-Strength or stability-long chains cross linked by hydrogen bonds
-Freely permeable due to spaces between fibres so water can pass to cell membrane
Chitin Structure
- Polymer of beta-glucose
- It has some - OH groups replaced by nitrogen-containing acteylamine groups
Chitin function and properties
Function:
-Structural role in forming the exoskeleton of many invertebrates and cell walls in fungi eg yeast
Properties:
-Strong-long chains cross linked by hydrogen bonds
-Waterproof
-Lightweight
