1-Biological Molecules Flashcards
Metabolism
All biological processes that take place within living organisms.
Monosaccharides
Sweet tasting soluble substances with the general formula “(CH2O)n” where n can be any number from 3 to 7.
E.g. Glucose is C6H12O6 and is a hexose (6-carbon) sugar.
2 arrangements of alpha and beta glucose.
Alpha glucose has H above carbon-1.
Beta glucose has H below carbon-1.
Test for reducing sugars (Benedict’s Test)
For all monosaccharides and some disaccharides.
- Heat the sample with Benedict’s solution (copper(ii)sulfate).
- If the the blue solution turns orange-brown due to a red precipitate (copper(i)oxide) forming then a reducing sugar is present.
Condensation reaction of disaccharides
2 monosaccharides join together by a water molecule being removed. The bond formed is called a glycosidic bond.
1) Glucose + Glucose ——>
2) Glucose + Fructose ——>
3) Glucose + Lactose ——>
1) Maltose
2) Sucrose
3) Lactose
Hydrolysis
When water is added to a disaccharide under suitable conditions the glycosidic bond is broken and water molecule is added to form 2 monosaccharides.
Test for non-reducing sugars
1) Make sure sample is in liquid form.
2) Add 2cm3 of sample to 2cm3 Benedict’s reagent in a test tube.
3) Place test tube in boiling water for 5 minutes. If solution doesn’t change colour then reducing sugar isn’t present.
4) Add another 2cm3 of sample to 2cm3 dilute HCl and boil to hydrolyse the disaccharide into its respective monosaccharides.
5) Add sodium hydrogencarbonate to neutralise the HCl.
6) Retest and if a orange-brown solution is formed now then a non-reducing sugar was in the original sample.
Polysaccharides
Very large, insoluble molecules formed by condensation reactions forming glycosidic bonds between monosaccharides. This feature makes them suitable for storage, e.g. starch. However the polysaccharide cellulose is used to give structural support for plants instead of being used for storage.
Test for starch
1) Add 2cm3 of sample into a test tube.
2) Add 2 drops of iodine solution and shake/stir.
If solution goes blue-black then starch is present.
Structure of starch
Chains of alpha-glucose monosaccharides linked by condensation reactions formed by condensation reactions. Chains can be branched or unbranched. The unbranched chain is wound into a tight coil to make the molecule very compact.
Function of starch
1) Insoluble so water isn’t drawn into cells by osmosis.
2) Large and insoluble so doesn’t diffuse out of cells.
3) Compact so a lot can be stored in a small space.
4) When hydrolysed forms alpha-glucose which is easily transported and readily used in respiration.
5) Branched variant has many ends which can each be acted on by enzymes at the same time so more glucose monomers are released very rapidly.
Structure of glycogen
Similar structure to starch but has shorter chains and is more highly branched. Only in bacteria and animal cells, not plant cells.
Function of glycogen
1) Insoluble so doesn’t draw water on by osmosis.
2) Insoluble so doesn’t diffuse out of cells.
3) Compact so a lot can be stored in small places.
4) Highly branched so is broken down by enzymes more rapidly to form glucose monomers used in respiration.
Structure of cellulose
Straight unbranched chains of beta-glucose which run parallel to each other and allow hydrogen bonds to form between them. Cellulose molecules are grouped together to form microfibrils which are arranged in parallel groups called fibres.
Function of cellulose
Provides support and rigidity
Lipids
Contains C, H, O
Insoluble in water
Soluble in organic solvents (alcohols/acetone)
Role of lipids
Source of energy — when oxidised they provide 2x energy of carbohydrates for the same mass and release water.
Waterproofing — since they’re insoluble they are useful for being waterproof.
Insulation — slow conductors of heat wand retain body heat. Also act as electrical insulators.
Protection — acts as a buffer around delicate organs, e.g. kidneys.
Triglycerides
Consist of 3 fatty acids joined to a glycerol molecule by ester bonds formed in a condensation reaction. When hydrolysed produces 3 fatty acids and a glycerol.
Structure and Properties of triglycerides
Good source of energy due to a high ratio of energy-storing C-H bonds to C atoms.
Low mass:energy ratio so are good storage molecules because less mass carries more energy which is beneficial to animals as it reduces the mass they have to carry around.
Large and non-polar so are insoluble in water so their storage doesn’t affect osmosis in cells or water potential.
High H:O atom ratio so when oxidised provide an important source of water.
Phospholipids
Hydrophilic phosphate head which interacts with water (but not fat) joined to 2 hydrophobic fatty acid tails that mix readily with fat but orient themselves away from water. These 2 distinct ends make the molecule polar.
Structure and Properties of phospholipids
Polar so form a bilayer within cell surface membranes. As a result a hydrophobic barrier is formed inside and outside the cell.
Can form glycolipids by combining with carbohydrates in the cell surface membrane which are important for cell recognition.
Test for lipids
1) Add 2cm3 of sample to test tube and add 5cm3 of ethanol.
2) Shake thoroughly to dissolve sample in solution.
3) Ad 5cm3 of water and shake gently .
4) If a cloudy white emulsion forms then a lipid is present.
5) A control can be conducted by repeating the process with water instead of lipid and solution should remain clear.
Amino acids
Basic monomer unit which combine to form the polymer polypeptides. Consist of a carbon atom attached to 4 different chemical groups:
1) —NH2 basic amino group
2) —COOH acidic carboxyl group
3) —H hydrogen atom
4) —R group which is a variety of different chemical groups.
Formation of peptide bond
A condensation reaction where the —H of the amino group of an amino acid and the —OH the the carboxyl group of another amino acid is removed to link the 2 amino acids to form a dipeptide. Dipeptide can be broken down into its respective amino acids by hydrolysis.
