Specification Revision Notes- Biological Molecules

So I had a look through the specification and went through each requirement in the first section (Biological Molecules) and made a few notes mainly from my text book and revision guide. I haven't had time to do any other units yet but if I find it has been useful I'll do the other topics as well. Please tell me what you think, and good luck for the exam!

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  • Created on: 31-05-13 15:14
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Specification- 2.1.1- Biological Molecules
(a) describe how hydrogen bonding occurs between water molecules, and relate this, and other
properties of water, to the roles of water in living organisms
A molecule of water is one atom of oxygen joined to two atoms of hydrogen shared
by electrons. Because the shared negative hydrogen electrons are pulled towards
the oxygen atom, the other side of each hydrogen atom is left with a slight positive
charge. The unshared negative electrons on the oxygen atom give it a slight negative
charge so makes the water a polar molecule: one negative charge and one positive
The negatively charged oxygen atoms of water attract the positively charged hydrogen atoms of
other water molecules. This attraction is called hydrogen boding which gives water useful
Properties of water due to hydrogen bonds-
1. High specific heat capacity (energy needed to raise temperature of 1g by 1degreeC)
The hydrogen bonds between water molecules can absorb a lot of energy, so it takes a lot
of energy to heat it up. This is useful for living organisms because it stops rapid temperature
changes, allowing them to keep their temperature fairly stable.
2. High latent heat of evaporation It takes a lot of energy (heat) to break the hydrogen
bonds between water molecules. This means that water has a high latent heat of
evaporation as a lot of energy is used up when it evaporates. As a result, it means water is
useful in organisms to cool down in hot temperatures.
Properties of water due to its polarity-
1. Cohesion (attraction between molecules of the same type) They're very cohesive so
tend to stick together which helps water flow. This makes water a good transport medium.
2. Good Solvent A lot of important substances in biological reactions are ionic (made from
one positively charged atom/molecule and one negatively
charged atom/molecule). Because water is polar, the
positive end of a water molecule will be attracted to the
negative ion and the negative end will be attracted to the
positive ion. This means ions will get surrounded by water
molecules and dissolve. This therefore makes water a
useful solvent for other polar molecules.
(b) describe, with the aid of diagrams, the structure of an amino acid
All amino acids have the same general structure- A carboxyl group (COOH), an amino group (HNH)
attached to a carbon atom. The difference is the variable R group (there are 20 different
(c) Describe, with the aid of diagrams, the formation and breakage of peptide bonds in the
synthesis and hydrolysis of dipeptides and polypeptides.

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Two or more amino acids can join together to form a polypeptide in a condensation reaction. This
occurs Between the OH on the carboxyl group on one amino acid and the H on an amino group on
another amino acid. These molecules take part in the condensation reaction and are replaced with a
peptide bond released a water molecule in the process.
Hydrolysis is the reverse of a condensation reaction.…read more

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A quaternary structure involved several different polypeptide chains held together by bonds and
describes the way in which they're assembled. Eg. Haemoglobin has four polypeptide chains
bonded together.
(h) describe, with the aid of diagrams, the structure of a collagen molecule
It's a fibrous protein and made up of 3 polypeptide chains wound around each other. Each of the
three chains is itself a coil, made up of 1000 amino acids. Hydrogen bonds form between the chains
to give strength.…read more

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State the structural difference between alpha and beta glucose
Both alpha and beta have a similar molecular formula, however at C1 in alpha helix the OH molecule is
below and in beta helix the OH molecule is above the carbon atom.
(l) Describe, with the aid of diagrams, the formation and breakage of glycosidic bonds in the
synthesis and hydrolysis of a disaccharide (maltose) and a polysaccharide (amylose).…read more

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Explain how the structures of glucose, starch, glycogen and cellulose relate to their functions
in living organisms
Glucose- It's the main energy source in animals and plants so the structure makes it soluble so it can
be easily transported. The chemical bonds also contain lots of energy.
Starch- Starch is the main energy storage material in plants.…read more

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Benedict's test), starch (iodine solution)
and lipids (emulsion test). ffdsuffdsfds
Protein (Biuret Test) Add a few drops of sodium hydroxide solution Blue Purple layer
to make it alkaline. Then add some copper(II)
sulphate solution.
Reducing Sugars Add Benedict's reagent (blue) to a sample and Blue Orange/Red
(Benedict's test) heat it without boiling.
Non-reducing Sugars If the previous test is negative, like sucrose, If it's positive, it
you first have to break them down into could be either
monosaccharides.…read more

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Benedict's solution that's left after the test so the higher the
glucose concentration, the lower the absorbance of solution.…read more


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