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UNIT
1: CELLULAR FUNCTIONS
·
proteins can either have
a structural purpose, or they can be functional by effectively directing and
controlling the chemical reactions in life processes
·
about 50% of all of the
body’s dry weight is protein
·
proteins are polymers of
amino acid monomers
·
every amino acid
contains the same parts (see Figure 1.27, p. 23)
·
all amino acids contain
the following parts attached to the central carbon:
·
there are 20 different
side chains that an amino acid can have, therefore, 20 different amino acids
exist in living systems
·
each R group (or side
chain) possesses its own unique chemical character, therefore each different
amino acid possesses unique biological properties
·
the properties of amino
acids reflect the properties of the individual R groups, themselves, that they possess
·
R groups can be polar,
non-polar, and electrically charged
·
proteins can be small,
straight-chained molecules, or they can be globular, 3-D structures that are
over 1000 amino acids long
·
the formation of the polypeptide chain or polymer protein
chain is done through a series of condensation, or dehydration synthesis,
reactions (see Figure 1.28, p. 23)
·
the – OH of the “head”
end of one amino acid combines with one of the Hs of the amino group of the
“tail” end of the adjacent amino acid, to form water
·
the resulting bond
between the two amino acids is called a peptide bond
·
this dimer possesses an
amino group “tail” and a carboxyl group “head” that will both eventually
dehydrate and combine with other amino acids as the chain grows
·
a protein’s shape is
very important to its function
·
if the sequence of the
amino acids of a polypeptide molecule is incorrect (i.e. even if one amino acid
is substituted with a different one) the entire protein shape may be altered, or
enough of it so that it is rendered useless!
·
after the primary structure of a protein is
established – the polypeptide chain, a protein (depending on its function) may
develop one, two, or three more structures; secondary, tertiary, and quaternary
structures (see Figure 1.29a, b, c, and d, p. 24)
·
the secondary structure
forms from the twisting within the chain itself, resulting in an a-helical, b-pleated bent sheet, or random coil
shape
·
the twisting and bending
occurs because of intramolecular dipole-dipole,
·
if the secondary
structure contains amino acids with sulfur-containing side chains, further
covalent, ionic, hydrogen, and non-polar interactions occur
·
sometimes covalent
bonds, that help maintain the tertiary structure together, actually form –
called disulfide bridges – formed
between the sulfur of one side chain and the sulfur of another
·
quaternary structures
occur when two or more tertiary structures interact to form a globular protein
structure
·
along with the
intramolecular ionic, covalent, dipole-dipole, H-bonding, and disulfide bridge
interactions, a protein’s environmental conditions also play a major role in
maintaining its 3-dimensional structure and shape
·
the structure of a
protein is extremely sensitive to pH, temperature, chemicals, and ionic
concentration
·
if any one of these
conditions fall outside a favorable range, the shape of a protein may change,
and therefore its ability to function properly may also be affected
·
when a protein changes
shape, it is denatured
·
hemoglobin is a
globular, quaternary protein
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it consists of 4
tertiary groups, two identical a-chains, and two identical b-chains
·
at the centre of a
hemoglobin molecule exists a system of hydrocarbon rings called a porphyrin ring
system
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at the centre of this
heme group is an iron molecule
·
this is the part of the
molecule that binds to oxygen and gives blood its red colour
·
the centre of the heme
group for the blood of marine worms is a magnesium atom, giving their blood a
green colour
·
blue crabs have copper,
giving their blood a blue colour
Homework: 1-6, p. 25