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Module 1: Biological Molecules
Proteins, carbohydrates, lipids and nucleic acids are key biological
macromolecules with important roles in living organisms.

2.1.1 Biological Molecules
A.Water
Structure
Water is a very small molecule consisting of two hydrogen atoms covalently
bonded to an oxygen atom. The covalent bond is very strong, making it…

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molecules have enough energy
to break apart.
Density The hydrogen bonds between Due to their high water
water molecules pull them content, most organisms
closely together, making water have a density close to that
relatively dense ­ about 1gcm3 .

of water, making it easy for
them to swim.
Ice…

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Water can form ions: These ions can be used in
H2O OH


+ H+ reactions such as
photosynthesis.
Cohesion Water forms hydrogen bonds Cohesion and adhesion allow
& with other polar substances, water to enter and move
Adhesion sticking to them. This is known along very narrow spaces in
as…

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C.Peptide Bonds
Making Peptide Bonds
Amino acids can join together to form
long chain polypeptides and proteins.
This occurs through protein synthesis
on the ribosomes of cells. The amino
acids are joined together using a
condensation reaction (where water is
also formed). This joins the amino
group form one amino…

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The shape of an alpha helix or beta fold is maintained by hydrogen bonds
forming between the amino acids in the backbone of the chain, not between
the R groups. Although hydrogen bonds are weak individually, when many of
them are present it creates a strong structure.

Alpha Helix
The…

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Examples of proteins with a tertiary
structure are antibodies, channel proteins and enzymes.
The polypeptide chains in haemoglobin also
have a tertiary structure. They each wind
themselves around a haem group (a little group
of atoms with an iron ion in the centre), curling
up into a ball, forming a…

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Haemoglobin
In a haemoglobin molecule, the quaternary structure consists of 4 polypeptide
subunits, including 2 alpha globin chains and 2 beta globin chains. These fit
together, forming the complete structure of this globular protein.
Haemoglobin contains 4 haem groups, which aren't made up of amino acids
but form an essential…

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Must have a very precise shape as this determines their function. They
therefore have a very precise primary structure, always being made up of
exactly the same sequence of nonrepeating amino acids, in a chain that is
always of the same length.
E.g. Haemoglobin, enzymes, antibodies and some hormones such…

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Monosaccharides
These are simple reducing sugars made up of one unit. They have the general
formula of (CH
2O) n, where n =39, and include glucose, fructose and

galactose.
Glucose is a sugar which contains 6 carbon atoms, so is a hexose. It can exist
in two forms (isomers), known…

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Lactose = galactose + glucose
Sucrose = fructose + glucose. This is a small and soluble molecule used for
transport in the phloem in plants, and to make fruits sweet.

Polysaccharides
Polysaccharides are macromolecules which are insoluble in water and don't
taste sweet. They are noncrystalline structures and are all…

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