https://www.youtube.com/watch?v=hpaki7F4HR0
http://www.wisconline.com/objects/index_tj.asp?objID=AP13304
 Cells contain thousands of different proteins, each
performing a specific task.
 Examples: Enzymes, immunoglobulins (used in
immune response), haemoglobin (oxygen carrier in
blood), keratin (In hair and fingernails), fibrin (helps
blood clot), collagen (in bones, skin, tendons).
 Consist of long chains of amino acids (amino acid
polymers) folded into specific 3-D shapes.
Amino Acids
 There are 20 different amino acids each with a
different side chain.
 The common structure of all amino acids is:
- A central Carbon atom to which are attached an
amino group, carboxyl group, a hydrogen atom
and side chain (R).
Amino Acid general structure
Properties
 Contain acidic (carboxyl) and basic (amino) functional
groups.
 Can be polar, non-polar, or charged (acidic or basic)
depending on the nature of their side chains.
How proteins are formed
 Proteins consist of chains of amino acids
(polypeptides) that are twisted and coiled into a
specific shape or conformation.
 Polypeptides are made in the cytoplasm of cells during
protein synthesis.
 The amino acids in the cytoplasm come from the food
eaten or are made from simpler compounds.
How proteins are formed con’t
 Of the 20 amino acids, 8 cannot be made from simpler
compounds and must be obtained from diet. These
are essential amino acids.
 During protein synthesis, bonds called peptide
bonds are formed between amino acids by a
condensation reaction.
 http://www.johnkyrk.com/aminoacid.swf
Protein Structure
 The structure of a protein determines its function! Eg.
A structural protein will be roughly linear in shape and
will from strands or sheets (fibrous proteins)
 Many enzymes and other functional proteins are
globular (rounded, spherical shape).
 There are four levels of structure:
1. Primary
 The unique sequence of amino acids in a polypeptide
chain.
 Determined by nucleotide sequence in DNA.
 If one amino acid is out of order, the entire protein
could be useless!
2. Secondary
 As the protein grows in length, it coils and folds
creating the protein’s secondary structure.
 In some polypeptides, repeated H bonds cause it to
twist into a coil called an α-helix. (Eg. -keratin in hair,
sections of the enzyme lysozyme in saliva, sweat and
tears)
 When two parts of the chain lie parallel to each other
and are bonded by H-bonds, β-pleated sheets are
created. (Eg. Proteins in spider webs)
3. Tertiary
 This structure results from the nature of the different
amino acids interacting with the environment.
 For example, polar amino acids are attracted to water
so they interact with it while non-polar amino acids
will congregate in the centre, away from the water.
 This causes the polypeptide to fold into a certain shape
– the tertiary structure.
 http://www.johnkyrk.com/aminoacid.swf
4. Quaternary
 Shape of a protein resulting from 2 or more
polypeptides coming together. Eg. Collagen, keratin,
haemoglobin
 -Sometimes a chaperone protein may help the
protein fold into its quaternary structure.
Collagen
Haemoglobin
Denaturing Proteins
 The 3-D shape of a protein can be destroyed or
changed due to changes in temperature, pH, ionic
concentration, etc. This is called denaturation.
 When the structure is destroyed or changed, the
proper function cannot be carried out.
 Sometimes protein denaturation can be useful. We do
it every day when we cook meat or curl/straighten hair.
Questions
 Page 28, #19-24
 Bring a device with internet access for a quiz next
class!!