The document discusses the structure and classification of proteins. It notes that proteins are composed of chains of amino acids and can be classified based on chain length. There are four levels of protein structure: primary, secondary, tertiary, and quaternary. The primary structure is the amino acid sequence. Secondary structure involves twisting of the chain into alpha helices or beta sheets. Tertiary structure describes the three-dimensional folding, and quaternary structure refers to the arrangement of multiple folded chains. Proteins play diverse roles in organisms, including enzymatic catalysis, oxygen transport, structure, and defense.

1. Prepared by : HafizYaseen khan

2.  Protein structure
 Classification of protein

3.  Large complex organic molecule
 Made up of chain of amino acids
 Play a diverse role in living organism
 Proteins made up of such elements as carbon
, hydrogen , oxygen, nitrogen , sulphur and
sometimes phosphorus

4.  Made up of chains of amino acids
 classified by number of amino acid in a chain
 Peptides: fewer than 50 amino acids
 Polypeptides : more than 10 amino acids
 Protein: more than 50 amino acids

5.  Biochemists have distinguished several level
of structural organization of proteins.They
are
 Primary structure
 Secondary structure
 Tertiary structure
 Quaternary structure

6.  The primary structure of protein refers to the linear
sequence of amino acids present in the polypeptide
chain
 Amino acids are covalently linked by peptide bonds
 Each component amino acid in a polypeptide is
called a “ residue” or “ moiety”

7.  Higher level of organization of proteins are
dependent on primary structure
 Many genetic diseases result from abnormal amino
acids sequences
 If the primary structures of the normal and mutated
proteins are known , this information may be used
to diagnose or study the disease

9.  The arrangement of protein by twisting of
the polypeptide chain
 The most common types of secondary
structures are alpha helix and beta pleated
sheets
 Both structures are held in shape by
hydrogen bond

10.  Spiral structure
 Stabilized by H bonding between carbonyl oxygen
and amide hydrogen
 Most helices are around 10 residues long
 Each turn of an alpha helix contains 3.6 amino acids
 A very diverse group of proteins contain alpha
helices
 For example keratins whose structure is nearly
entirely alpha helical
 Keratins are a major component of tissues such as
hair and skin

11.  Formed when two or more polypeptides line
up side by side
 The surface of beta sheets appear pleated
and these structures are therefore called beta
pleated sheets
 Stabilized by H bonds
 Size between adjacent amino acids are 3.5A`

13.  Some of the common structural motifs
combining alpha helices and beta sheets
These are:
 Beta alpha Beta unit
 Greek key
 Beta meander
 Beta barrel

15.  Tertiary structure is the three dimensional
conformation of a polypeptide
 The common features of protein tertiary
structure reveal much about biological
functions of the proteins

16. The function of a protein depends on its
tertiary structure. If this is disrupted , it loses
its activity examples
 Denatured enzyme lose their catalytic power
 Denatured antibodies can no longer bind
antigen

17.  Polypeptide chains containing more than 200
residues usually fold into two or more globular
clusters known as domains
 Basic functional and 3 dimensional structure of
protein
 Domains often have a specific function such as the
binding of a small molecule

18.  The following four types of interactions
cooperate in stabilizing the tertiary structures
 Hydrogen bond
 Ionic bond
 Disulphide bridges
 Hydrophobic interactions

19.  Arrangement of polypeptide subunit is called
quaternary structure
 Consists of two or more polypeptide chains
 Held together by non covalent interactions
 For example : Hydrogen bond, ionic bond etc

20.  Proteins are large complex organic molecule
 primary structure is the linear sequence of amino
acids in a polypeptide chain
 Secondary structure is twisted polypeptide chain
 Tertiary structure is a three dimensional shape
 Quaternary structure is arrangement of two or more
tertiary polypeptides that make up a protein

22.  Proteins make up about 15% of the mass of the average
person
 Enzyme act as biological catalyst
 Storage and transport: Hemoglobin
 Defenece : antibodies
 Ligaments and arteries mainly form by elastin protein
 Muscle : proteins in the muscle respond to nerve impulses by
changing the packing of their molecules ( actin and myosin)
 Hair , nail and skin ; protein keratin as main component

23.  Fibrous proteins:
 These proteins have a rod like structure
 They are insoluble in water
 They can be stretched and contracted like thread
 Form structure of the tissue
 Present where support is required
 Examples : collagen, keratin, elastin etc

24.  Spheroid or ovoid in shape
 Enzymes are mostly globular in shape
 Subdivided into two types of protein
i. Albumins: water soluble
ii. Globulin : soluble in dilute salt solution

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