Proteins are an important class of biological macromolecules which are the polymers of amino acids.

2. Proteins are an important class of biological
macromolecules which are the polymers of amino
acids.
are biochemical compounds consisting of one or
more polypeptides typically folded into
a globular or fibrous form in a biologically functional
way.

3. • Biochemists have distinguished several levels of structural
organization of proteins. They are:
– Primary structure
– Secondary structure
– Tertiary structure
– Quaternary structure

4. • The primary structure of protein refers to the
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”
• By convention, the 10 structure of a protein
starts from the amino-terminal (N) end and
ends in the carboxyl-terminal (C) end.

5. Secondary structure refers to
highly regular local sub-structures.
These secondary structures are
defined by patterns of hydrogen
bonds between the main-chain
peptide groups.
They have a regular geometry,
being constrained to specific
values of the dihedral angles ψ
and φ on the Ramachandran plot.
Both the alpha helix and the beta-
sheet represent a way of
saturating all the hydrogen bond
donors and acceptors in the
peptide backbone.

6. • Tertiary structure is the three-dimensional conformation of
a polypeptide.
• The common features of protein tertiary structure reveal
much about the biological functions of the proteins and
their evolutionary origins.
• The function of a protein depends on its tertiary structure.
If this is disrupted, it loses its activity.

7. Quaternary structure is a larger assembly of several protein
molecules or polypeptide chains, usually called subunits in
this context.
The quaternary structure is stabilized by the same non-
covalent interactions and disulfide bonds as the tertiary
structure. Complexes of two or more polypeptides are called
multimers.

8. Chemical properties of proteins
1. Hydrolysis
 Proteins can be hydrolyzed (the peptide bond) by acid or enzymes to
give peptides and free amino acids (e.g. soy sauce, fish sauce.)
 Modifies protein functional properties
- E.g. increased solubility.
 Increases bio availability of amino acids
- Excessive consumption of free amino acids is not good however.

9. 2. Maillard reaction (carbonyl - amine browning)
 Changes functional properties of proteins
 Changes color
 Changes flavor
 Decreases nutritional quality (amino acids less available)

10. 3. Alkaline reactions
Soy processing (textured vegetable protein)
 Denatures proteins
 Opens up its structure due to electrostatic
repulsion
 The peptide bond may also be hydrolyzed

11. are specialized proteins involved in defending the
body from antigens (foreign invaders). One way
antibodies destroy antigens is by immobilizing them
so that they can be destroyed by white blood cells.

12. are proteins that facilitate biochemical reactions. They are
often referred to as catalysts because they speed up
chemical reactions. Examples include the enzymes lactase
and pepsin. Lactase breaks down the sugar lactose found in
milk. Pepsin is a digestive enzyme that works in the stomach
to break down proteins in food.

13. are messenger proteins which help to coordinate certain bodily
activities. Examples include insulin and oxytocin. Insulin
regulates glucose metabolism by controlling the blood-sugar
concentration. Oxytocin stimulates contractions in females
during childbirth.
are responsible for movement. Examples include actin and
myosin. These proteins are involved in muscle contraction and
movement.

14. are carrier proteins which move molecules from one
place to another around the body. Examples include
hemoglobin and cytochromes. Hemoglobin transports
oxygen through the blood. Cytochromes operate in
the electron transport chain as electron carrier proteins.

15. Intracellular Trafficking and Protein
Transport
 Trafficking : Endoplasmic Reticulum to Golgi to cell membrane

16. Endoplasmic Reticulum
• Helps move substances within cells
• Network of interconnected membranes
• Two types :
– Rough endoplasmic reticulum
– Smooth endoplasmic reticulum

17. Rough Endoplasmic Reticulum
• Ribosomes attached to surface
– Manufacture protiens
– Not all ribosomes attached to rough ER
• May modify proteins from ribosomes

18. Smooth Endoplasmic Reticulum
• No attached ribosomes
• Has enzymes that help build molecules
– Carbohydrates
– Lipids

19. Golgi Apparatus
• Involved in synthesis of plant cell wall
• Packaging & shipping station of cell
The Golgi apparatus is an organelle found in most eukaryotic
cells. . The primary function of the Golgi apparatus is to process
and package macromolecules, such as proteins and lipids, after
their synthesis. It is important in the processing of proteins for
secretion.

21. Liquid droplets
Endocytosis - process by which particles,
solutes, membrane proteins (including receptor-
ligand complexes) and lipids are taken up by
vesicles from the PM. Also used by parasites
and bacteria to get into the host cell.
- Pinocytosis - uptake of extracellular fluid
through endocytosis.
Endocytosis
Trafficking : ER to Golgi to PM
- Phagocytosis - uptake of pathogens as a
defense, clearance of cell debris.

22. - where proteins from ER are further
processed sorted for transport to final
destinations: outside cell, PM, or lysosomes
Exocytosis - fusion of vesicles derived from TGN with the PM resulting
in insertion of transmembrane proteins into PM or secretion of soluble
proteins into extracellular space.
Trafficking from ER to Golgi complex:
- Transport vesicles (TV): bud from mb of
one organelle & fuse with mb of next
organelle .

24. Trafficking : ER to Golgi to Lysosome
Receptors take up cargo via receptor-mediated endocytosis
,into clathrin-coated endocytic vesicles which bud into cell
from PM and fuse with early endosomes.
Early endosomes mature into late endosomes, with recycling
of membrane components back to PM.

28. REFERENCE
 Voet, Donald; Voet Judith. Biochemistry, 3rd edition, John
Wiley and sons.
 Champe, Pamela.C, Harvey, Richard A, Ferrier Denise R
(2005). Lippincott’s Illustrated Reviews: Biochemistry, 3rd
edition. Lippincott William and Wilkins.
 McKee Trudy, McKee James R (2003), Biochemistry: The
molecular basis of life, 3rd edition, McGraw Hill.
 http://esciencenews.com/articles/2011/06/01/new.antibiotics.a.s
tep.closer.with.discovery.bacterial.protein.structure
 http://www.eurekalert.org/pub_releases/2010-04/sri-
srs042610.php
 http://www.physorg.com/news/2011-10-cell-survival-protein-
reveals.html

29. Thank You
That’s all