Unit 1 - Biological Molecules Flashcards
define monomers
smaller units from which larger molecules are made
define polymers
large, complex molecules made from joining long chains of many monomers together
give 3 examples of monomers
monosaccharides
amino acids
nucleotides
define condensation reaction
two molecules join together with the formation of a chemical bond and a water molecule is released
define hydrolysis reaction
breaks (hydrolyses) a chemical bond between two molecules using a water molecule to form monomers
what are the properties of water & why are they important?
- a metabolite in many metabolic reactions including condensation & hydrolysis
- an important solvent in which metabolic reactions occur
water readily dissolves O2, CO2, ammonia, urea & enzymes - has high specific heat capacity, which buffers changes in temperature
organisms are mostly H2O so maintains constant body temperature - has a large latent heat of vaporisation, providing a cooling effect with little water loss through evaporation - evaporation of sweat (mostly H2O) in mammals (thermoregulation)
- has strong cohesion between water molecules
supports columns of water in xylem of plants (transpiration stream)
provides surface tension where water meets air - vital for supporting small organisms e.g. pondskaters
define monosaccharides & what are the common monosaccharides?
the monomers from which larger carbohydrates are made
e.g. glucose, galactose, fructose
how is a glycosidic bond formed?
in a condensation reaction between two monosaccharides
a water molecule is released
a glycosidic bond is a type of covalent bond
what happens in a hydrolysis reaction involving a disaccharide?
a water molecule is added to the disaccharide to hydrolyse the glycosidic bond
how is a disaccharide formed?
condensation of two monosaccharides
how are maltose, sucrose & lactose formed?
maltose is formed by condensation of two alpha glucose molecules
sucrose is formed by condensation of a glucose molecule & a fructose molecule
lactose is formed by condensation of a glucose molecule & a galactose molecule
define isomers
molecules with the same molecular formula but different structural formula
what are the isomers of glucose?
alpha glucose - hydroxyl group is below the plane of the ring on carbon-1
beta glucose - hydroxyl group is above the plane of the ring on carbon-1
what is the name for a sugar with 5 carbon atoms & with 6 carbon atoms?
5 - pentose
6 - hexose
how are polysaccharides formed?
many monosaccharides are joined together by glycosidic bonds in a condensation reaction
(1 water molecule released per glycosidic bond)
what are the structures & functions of starch?
polymer of alpha glucose that is the store of glucose (energy) in plants
1. spiral/helical shape
compact, lots of glucose can be stored in a small volume
- large & insoluble
cannot leave the cell
does not affect the water potential/osmosis - can be branched
several ends, each end can release glucose by hydrolysis for respiration/transport when needed
what are the structures & functions of glycogen?
polymer of alpha glucose that is the store of glucose in animals/bacteria
similar to starch but shorter chains & more branching
1. highly branched (more than starch)
more ends so faster hydrolysis so more alpha glucose released because animals have a higher metabolic rate than plants
- large & insoluble
cannot leave the cell
does not affect the water potential/osmosis - helical shape
compact - lots of glucose stored in a small volume
what is the structure & function of cellulose?
plant cell wall (structural support)
polymer of beta glucose, which causes straight, unbranched chains
each cellulose polymer can form hydrogen bonds with a different parallel polymer because of the polar hydroxyl groups
(hydrogen bonds are individually weak but collectively strong)
cellulose molecules are bundled into microfibrils which are grouped into fibres
this causes the cell wall to be rigid & prevents the cell bursting so it stays turgid
what is the test for starch?
iodine test
add 2 drops of iodine solution (iodine dissolved in potassium iodide solution) & shake
positive result is a colour change from orange-brown to blue-black
what is the test for reducing sugars?
benedict’s test
add 2cm3 of benedict’s reagent (an alkaline solution of copper (II) sulphate)
heat in water bath at 80 degrees/boiling for 5 minutes
positive result is a brick red, orange, yellow or green precipitate forms according to the concentration of the reducing sugar (brick red shows highest concentration)
what is the test for non-reducing sugars?
hydrolysis then benedict’s test
add 2cm3 of dilute hydrochloric acid to sample
boil in a gently boiling water bath for 5 minutes to hydrolyse the glycosidic bonds between the monosaccharides
neutralise the solution by slowly adding sodium hydrogen carbonate solution (test with pH paper to check the solution is alkaline)
add 2cm3 of benedict’s reagent (an alkaline solution of copper (II) sulphate)
heat in water bath at 80 degrees/boiling for 5 minutes
positive result is a brick red, orange, yellow or green precipitate forms according to the concentration of the reducing sugar (brick red shows highest concentration)
negative result for benedict’s test before hydrolysis then a positive result after hydrolysis
what is the test for lipids?
emulsion test
add 5cm3 ethanol & shake thoroughly to dissolve the lipid
add 5cm3 distilled water & shake gently
positive result is a colour change from colourless to white emulsion
what is the test for proteins?
biuret test
add 2cm3 biuret reagent
positive test is colour change from colourless to lilac
what are 2 groups of lipid?
triglycerides
phospholipids