Transcript Year 12 Biology Macromolecules Unit

Chapter 1: M5
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As mentioned before, proteins are large molecules
constructed from amino acids. They’re all made up
of varying combinations of the twenty amino
acids.
Because the combinations can be of any length,
and in any order, the variety of proteins is
potentially infinite. In much the same way as we
have many thousands of words produced from the
same 26 letters. (Though we don’t generally make
words past a certain length, while a protein could
theoretically keep going long after our tongue
would get tied saying the word.)
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Proteins can have a variety of purposes:
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They can have structural roles like hair and muscle
proteins.
They can act as enzymes, to speed up otherwise slow
or awkward chemical reactions.
They can also have other roles critical to cellular
functions.
These proteins are formed from one or more
folded amino acid chains, and it is the shape into
which they are folded which determines their
purpose.
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Protein structure is divided into
four levels:
Primary
 Secondary
 Tertiary
 Quarternary
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Each step represents an
important stage in folding and
shaping the protein to fulfil its
ultimate purpose.
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The primary
structure is
simply the order
of the amino
acids which
make it up.
A single change can make a radically different
protein. E.g. Sickle Cell Anaemia is caused by a
single amino acid substitution in haemoglobin
and is a very serious condition.
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This is the initial folding caused by the
hydrogen bonding between amino acids.
The polypeptide chains may form a variety of
shapes:
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Coils
Helices
Fibrils
Pleated Sheets
Alpha Helix
Beta Sheet
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The tertiary structure is the actual
three dimensional shape of the
polypeptide chain.
This structure forms
spontaneously due to the
attractions and repulsions between
various amino acids (some like
each other better than others).
This is very important for globular
proteins such as enzymes and
hormones which don’t work if
they’re not exactly the right shape.
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The Quarternary
structure doesn’t apply
to all proteins, only to
those made up of more
than 1 polypeptide chain.
The chains first fold into
their 3D shapes before
connecting to each other
using the same
attractions and
repulsions.
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To be discussed on the next slides:
Proteins in the Cell Membrane
 Enzymes
 Antigen-Antibody Binding
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Proteins exist on both the
inner and outer surfaces
of the cell membrane, as
well as in the space
between.
 Most functions of the cell
membrane are carried out
by the proteins
embedded within it.
Some act as chemical receptors for messages from other
cells. These messages are usually hormones, and the
message they carry is determined by the specific 3D
shape of the hormone, which bonds only to a matching
protein. Each protein is then designed to transmit a
specifically matched message through the cell.
Other proteins are designed to allow one-way transport
of certain molecules either into or out of the cell.
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Enzymes are catalysts designed to speed up
reactions in cells that would otherwise take a long
time. Each enzyme has a specific shape designed to
match specific products.
Only the molecules with the complementary shape
can fit with the enzyme. However, the reaction can
run both ways if needed.
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Antigens are foreign molecules which the body
would like to get rid of, they’re usually found
stuck in the membranes of cells.
Antibodies are the bodies defence to antigens.
While it’s starting to sound like a broken record
it’s once again the specific shape which is
important for the antibody to match to the
antigen.
The antibody is designed to deactivate the
antigen when it bonds to it so that the body can
safely dispose of it.