Nelly's AS biological molecules notes

Concise set of notes in 2 pages on OCR AS Biology Unit 2, Module1, Topic 1: Biological molecules

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2.1.1 Biological Molecules
+ +
Water is a polar molecule because e s shared in covalent
H H bond between the O atom and H atoms are slightly closer to
O- the O atom so H has a slight positive charge. Oxygen has two
O H+ H+ lone pairs of electrons which makes the other side of the
O- oxygen atom slightly negatively charged so O is
electronegative. This allows hydrogen bonding to take place.
Property Description Usefulness
High specific Lots of E to raise temp. of 1 gram of Stops rapid temperature changes in
heat capacity substance by 1°C as H bonds need breaking. organism so temp. is kept stable
High latent heat Lots of heat E to change a liquid to a gas as A cooling mechanism as it carries away a
of evaporation hydrogen bonds need to be broken lot of the heat energy from a surface
Very cohesive Water molecules attract as they're polar Water can flow easily- great transport
Lower density Water molecules held further apart in ice Insulating layer on top of water so the
when solid than water so ice floats water below doesn't freeze habitat
Good solvent Dissolves ionic substances. + end will attract Mineral ions dissolved in water can be
and surround a negative ion and vice versa transported around the organism's body
Proteins are made of one or more polypeptide
Amino Acids (KEY: amino group, variable (or residual) group, carboxyl group, peptide bond)
If R is H, this
molecule is glycine H2O
(smallest a. acid) Amino acid 1 Amino acid 2 Dipeptide
Primary structure: A sequence of amino acids in a polypeptide chain held together by peptide bonds
Secondary structure: Hydrogen bonds form between the ­NH and ­COOH groups of the amino acids
in the chain. This makes it coil into an alpha helix or fold into a beta pleated sheet
Biuret Test: Add few drops of sodium hydroxide solution so alkaline
& then copper (II) sulphate solution (+ve result = blue purple)
Tertiary Structure
-Coiled or folded further
-Hydrophilic and phobic
interactions: Hydrophobic R groups
tend to clump together so
hydrophilic R groups are pushed to
the outside
Beta-pleated sheet -Disulphide bonds: the sulphur
atoms on two molecules of amino
acid cysteine bond
Quaternary structure: the way polypeptide chains are assembled -Ionic interactions: weak between
- +
together influenced by tertiary structure or the protein's final 3D R groups and R groups on different
structure. Hb has 4 polypeptide chains (2 and 2 ) Each has a parts of the molecule
-Hydrogen Bonds: weak, between
prosthetic group (non-polypeptide structure needed for activity + -
H and H in different R groups on
of protein) called Heam groups which contain an iron (Fe2+) ion. the polypeptide chain

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Protein Description Example
Fibrous Tough, rope shaped Collagen forms supportive tissues made of 3 polypeptide chains coiled
found in connective into triple helix, chains interlinked with strong covalent bonds Minerals
tissue bind to helix, making it rigid.
Globular Round, compact, Haemoglobin carries O2 around the body.…read more


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