Download Amino Acids and Proteins

Amino Acids and Proteins
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Proteins are macromolecules (polymers)
They are made up of monomers which are known as amino acids
Amino Acids
structure of amino acids
The simplest amino acids has R = H as its side chain.  Glycine
There are 20 different amino acids involved in protein synthesis
Each amino acid has a different side chain;
a. If it is oxygen or nitrogen polarity, hydrophilic
b. If it is hydrogen and carbon  hydrophobic
1.
2.
3.
Peptide Bonds
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All proteins contain NITROGEN and some contain SULPHUR because
amino acids do. This is significant to how proteins bond.
Proteins contain peptide bonds
These join amino acids together
Many amino acids joined by peptide bonds form a macromolecule
which is a polypeptide.
If 100+ amino aids present = protein.
Condensation hydrolysis
Protein Structure
Primary Structure
Secondary Structure
Tertiary Structure
Quaternary Structure
 Sequence of amino acids
 Sequence determined by genetic
code in genes (DNA)
 Chain of amino acids that coil
helix or pleated sheet
 Hydrogen bonds hold in structure
on place (configuration)
 Secondary structure coils/ folds
into complex 3D shape (v.
precise)
 Held together by bonds between
side chains
 Proteins of greater than one
polypeptide have quaternary
structures either GLOBULAR or
FIBROUS
If primary structure is wrong the tertiary structure is wrong and
hence the protein will not function correctly
Protein shape determines its function
4 Types of bonds hold protein structures together
1. HYDROGEN BONDS
 Occur between polar groups. (any 2 polar amino acids)
 Broken by pH and high temperature
2. DISULPHIDE BRDGES
 Occur between cysteine molecules (type of amino acid)
 S=S ; covalent bond; very strong
 Broken by reducing agents
3. IONIC BONDS
 Occur between ionized amines and carboxylic acid groups
 Electrons from one atom leave its outer shell and enter the outer shell
of another atom.
 Gainer  reduced  -ve ion
 Loser  oxidised  +ve ion
 Form weak attractions between bonds (weaker than covalent bonds)
4. HYDROPHOBIC INTERACTIONS
 Helps some proteins as water hating ‘hydrophobic’ groups point
inwards, therefore hold structure together
 Occurs between non-polar side chains
Protein shape related to function
Globular
Fibrous
Globular – e.g. Haemoglobin
 4 polypeptide chains with disulphide bridges
 nearly spherical
 at the centre of each polypeptide  Fe containing haem group. This is
a non-protein prosthetic group which combines with protein 
conjugated protein
 present in red blood cells, carries oxygen from lungs to respiring cells
as oxyhaemoglobin
Globular – e.g. Enzymes
 enzymes are a type of a protein- each enzyme has a specific shape,
with an active site that locks onto the substrate molecule.
 amino acids with hydrophilic side chains towards the outside
 hydrophobic inwardly facing
 therefore, water molecules can surround the molecule hence it is
soluble.
Globular – e.g. Hormones (Insulin)
 is a hormone that reduces blood glucose levels.
 Globular = good for transport
 Disulphide bonds hold the molecule in shape
 It’s a small molecule – so it’s easily transported and absorbed by cells
Fibrous – e.g. Collagen/Keratin/Elastin
 long strands
 insoluble
 chains are interlinked by strong covalent bonds
 polypeptides laid down in sheets
 collagen/Elastin  SKIN
 Keratin  nails and hair
 Collagen/elastin  skin
 Actin/myosin  muscle
Biuret Test
 Detects presence of proteins
 Amine groups in side chains of some amino acids of a protein are at
the site of ionized peptide bonds react with copper ions to form a
complex with a violet colour
 Biuret reagent 2 chemicals used in succession
1. dilute alkali (KOH, NaOH)
2. dilute Cu2SO4(aq)
 violet purple = +ve test