-Literally hydrated carbon
-Carbon molecules rich in hydroxyl groups with a general formula:
- 3 carbon sugars (triose)
- can contain a ketone group 4C- tetroses 5C- pentose
- or a aldehyde group(DNA+RNA) 6C- hexose (Glucose + galactose etc) 7C - heptose
Steroisomerism in monosaccharides
1) ISOMERS - same molecular formular but different structures
1:1) CONSTITUTIONAL ISOMERS - differ in order of attachment of atoms
1:2) STEREOISOMERS: same order of attachment of atoms but differ in spatial arrangement of atoms
1:2:1) ENANTIOMERS: Non super imposable mirror image
1:2:2) DIASTEREOISOMER: Stereoisomers that are not mirror images
1:2:2:1) ANOMERS: Differ in configuration of atoms at the anomer carbon formed on a ring closure.
1:2:2:2) EPIMERS: Differ at one of several asymmetric carbon atoms
Extra info on monosaccharides
- Most vertebrae monosaccharides are in the D-isoform
- Monosaccharides with MORE than 3 carbon atoms have more than 1 asymmetric carbon atom existing as enantimers and diastereoisomers
- Number of possible isomers = 2(to the power of)n
n= number of asymmetric carbon atoms
EG > 6C with 4 asymmetric carbon atoms = 16 possible isomers for this hexose sugar.
- Common monsaccharides in Bio:
5 carbon - D-ribose and D-deoxyribose
6 carbon - D-gluocse and D-mannose (only differ at the 2nd carbon) D-galactose and D-fructose.
Monosaccharides as ring structures
- Exist as ring structures:
- Naming carbons:
..Exist in ring structures in solution
This cyclic form generates another isomeric form called an anomer
a- form the OH group on the opposite side of carbon 6
B- form the OH group on the same side as carbon 6
Plants have evolved enzymes to produce starch from a-D-glucose and cellulose of B-D-glucose. The majority of life have evolved enzymes to metabolise a-D-glucose
Only snails and some fungi can degrade cellulose.
- Steric problems prevent planar conformation
- Steric hindrance :
-functional groups get in eachothers way on a molecule
i.e the size or polarity of the functional group
-some monosaccharides do not exist because of this.
Chair and boat conformations
-different angle of bonds affected by the environment eg pH, temp etc.
-each carbon has a tripod formation of H-bonds coming from it. Eg axial (straight up or down) and equatorial (diagnanolly stemming from the carbon).
-Sugars join together to form large molecules (disaccharides)
-They form together and a glycosidic bond is formed in a condensation reaction (removal of water)
-monosaccharides have MANY hydroxyl groups so they can be linked in a variety of ways
- Common disaccharides
Sucroce <-sucrase-> glucose and fructose
From sugar cane and sugar beet releases fructose and glucose
Lactose <-lactase-> glucose and galactose
Present in milk
Maltose <-maltase-> glucose + glucose
ENZYMES THAT DEGRADE DISACCHARIDES ARE PRESENT ON THE EXTERNAL FACE OF MICROVILLI IN THE EPETHILIAL CELLS OF THE SMALL INTESTINE.
Glycogen and starch
- Large molecuar weight polymers of glucose
- Animals and plants require glucose for energy production
- BUT they cannot store glucose at high concentrations due to osmotic problems
- OSMOSIS: the diffusion of water molecules across a partially permeable membrane, from an area of higher water potential to and area of lower water potential
- The main energy storage polymer in plants- a plant breaks down starch when its in need of more energy
- Insoluble - doesn't cause osmotic problems like water entering the cells making them swell.
- Mixture of two polysaccharides of alpha-glucose:
-> AMYLOSE: a long, unbranched chain of a-1,4 glucose.
Angles of the glycosidic bond give it a coiled structure, making it compact (good for storage).
-> AMYLOPECTIN: a long, branched chain of a-1,4 glucose. Its side branches of a-1,6 glucose allow the enzymes that break down the molecule to get at the glycosidic bonds easily so the glucose can be released quickly.
The branches link every 30 glucose molecules, resulting in a compact structure.
- When starch is digested it is broken down to maltose my amylase (released by salivary glands and the pancreas).
- Maltose is then broken down to a-glucose by maltase - released by the intestinal epithelium.
STARCH <-amylase-> MALTOSE <-maltase-> a-GLUCOSE
- The main energy storage polymer in animals
- Another polysaccharide of a-glucose
- Structure is very similar to amylopectin but with side branches of a-1,6 glucose every 10 glucose molecules rather than 30
- This means there are many more branches and a much more compact shape.
- It also means that stored glucose can be released quickly which is important for energy release in animals.
Cellulose B-1-4 links and Starch a-1-4 links
- 10'15 tonnes of cellulose is produced each year by plants
- We havent evolved enymes that can degrade B-1-4 links so we cannot degrade cellulose so we cannot degrade cellulose
- Only slugs, snails and fungi can degrade cellulose
Other important carbohydrates
-Present in our lungs, stomach, nose etc
-Act as lubricants and a protective coating
-present in our extracellular matrix providing support to muscles and cartilidge
- Blood group patterns (A, B and O) on red blood cells are determined by sugars