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Proteins

Topic 2
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Changing the order of one amino acid can lead to genetic diseases

➢ Polypeptide and protein have a slightly different meaning
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A protein is an organic substance consisting of covalently bonded amino
acids and it is ready to carry out its function
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Example: enzymes, antibodies

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Proteins

Topic 2
...
4
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Biology SL

Different part of the protein start to bond with each other
with hydrogen bonds

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The shape of this structure depends on how they are bonded
with each other

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Tertiary protein structure
■

A shape described as globular

■

α-helices and β-pleated sheets bind either with one another or with
others on their kind forming a unity => globular protein
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■
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Determined by the secondary protein structure

In most cases the organisation stops here

Quaternary protein structure
■

Two or more polypeptides or globular proteins combined together to
make a single functional protein

■

Example: haemoglobin, if it’s not folded like this, it doesn’t function

➢ If the smallest detail is different ( a folding or an amino acid), this specific protein
stops being this protein or it stops functioning
➢ Important proteins:

Protein

Function

Rubisco

The enzyme that catalyses the first
reaction of the carbon-fixing reactions of
photosynthesis

Insulin

Reduce the blood sugar levels and increase
the sugar in body cells

Immunoglobulin

Antibody that recognises antigens as part
of the immune response

Rhodopsin

A pigment found in retina, useful in low
light conditions

Collagen

Main component of connective tissue,

which is abundant in skin, tendons and
ligaments

Spider silk

Protein used by spiders for making webs,
drop lines, nest building, etc
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Biology SL

The unique proteome
➢ Every individual has a unique genome
○

All the genetic material of an individual

➢ Since we all have a unique DNA, we have a unique sequence of amino acids
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This means that each individual has a unique set of proteins our cells can
synthesize
■

Called proteome

■

Almost the same in all individuals, but with a few exceptions

Denaturing proteins
➢ The secondary, tertiary and quaternary structures are dependent on intramolecular
forces
○

Weak hydrogen bonds are formed between different parts of the molecule

➢ If a protein is heated, the hydrogen bonds break, due to the increased molecular
motion
○

Loss of its normal three-dimensional shape and function

○

As long as the covalent bonds remain intact, the protein will return to its
original shape, if it is returned to its normal temperature

➢ When a fluid environment is flooded with either hydrogen ions (acid) or hydroxyl
ions (base), the extra charges can prevent normal hydrogen bonding
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Thus the protein will not take on its normal shape and will not function as it
should

➢ In both cases the protein has been denatured
➢ The bond between the amino acids is called peptide bond and it is a covalent bond

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