Download Proteins

Dr. Tarek El Sewedy
Department of Medical Laboratory Technology
Faculty of Allied Medical Sciences
Structure And Function of proteins
INTENDED LEARNING OUTCOMES
By the end of this lecture, students will learn:
1.
Protein structure , function , reactions.
Lecture Content
• Levels of Protein structure: Primary, Secondary, Tertiary and Quaternary.
• Protein structure
• Classification of proteins.
• Hydrolysis of proteins.
• Denaturation of proteins.
Proteins
 Proteins are Macromolecules consisting of long sequences of amino acids in
peptide linkage.
 Protein accounts for almost 20% of total body weight.
 The human body is made up of approximately 100 trillion cells - each one
has a specific function.
 Each cell has thousands of different proteins, which together make the cell
do its job - the proteins are tiny machines within the cell.
 One gram of protein or carbohydrate contains 4 calories, while one gram of fat has
9 calories.
Levels of protein structure
 There are 4 levels of protein structure:
1.
Primary
2. Secondary
3. Tertiary
4. Quaternary
1. Primary structure of proteins
 Describes the order of the amino acids joined together
to make the protein (exact sequence of amino acids
before folding).
 The end of the peptide chain with the -NH2 group is
known as the N-terminal, and the end with the COOH group is the C-terminal
2. Secondary Structure
 It is the simple folding of a protein to create simple
structures.
 The secondary structure of a protein or polypeptide is due
to hydrogen bonds forming between amide and carboxyl
groups.
 There are two possible types of secondary structure:
1.
Alpha helix, the hydrogen bonding causes the
polypeptide to twist into a helix.
2.
Beta sheet the hydrogen bonding enables the
polypeptide to fold back and forth upon itself like a
pleated sheet.
Tertiary structure
 Refers to the three-dimensional structure of the entire polypeptide chain.
 result from four different bonds:
1.
Ionic interactions
2.
Hydrogen bonds
3.
van der Waals forces
4.
Disulphide bond
Quaternary Structure
 It is the interaction between several
chains of polypeptide subunits.
 Not all proteins have quaternary
structure, since they might be
functional as monomers.
 The quaternary structure is stabilized
by the same range of interactions as
the tertiary structure.
 Hemoglobin is an example of a
heterotetramer
Proteins could be classified by
1. Shape
 Globular
 Fibrous
2.Function
3. structure
1.
Catalytic as enzyme
 Simple
2.
Structural as collagen, keratin
 Conjugated
3.
storage as ferritin (store iron).
4.
Protective as immunoglobulins
5.
Regulatory : hormones as insulin
6.
Communication as neurotransmitters
7.
Motion as actin/myosin; in muscle
8.
Transporter proteins as hemoglobin.
9.
Carrier as albumin.
 Glycoprotein:
Immunogloulin.
 Metalloprotein:
Hemoglobin
 Nucleoprotein:
RNA bound
protein
 Phosphoprotein:
casein
 Lipoprotein: Low
density lipoprotein
(LDL), HDL.
Fibrous proteins
• Water insoluble and found as structural
materials, e.g. collagen, keratin.
Globular proteins
• Compact, roughly spherical, water soluble
and comprise all other types of protein as
albumins and globulins.
Hydrolysis of proteins
 Hydrolysis of proteins results in breaking down the
peptide bonds to give amino acids thus it disrupts the
primary structure of protein .
 Hydrolysis can be achieved by Enzymes as Proteases.
 Biological role of hydrolysis:
1.
Convert inactive prohormones into active hormones. ex;
Proinsulin (inactive) → Insulin (active).
2. Digestion of protein by enzyme as trypsin and pepsin.
Inactive form
Hydrolysis
Active form
Protein denaturation
It is a process in which proteins can lose their structures and function,
without breaking the peptide bonds by denaturing agents such as:
1.Heat, U.V radiation.
2.Heavy metal as mercury.
3.Soaps.
4.Organic acids as acetic acid.
5.Strong acids and bases as sulfuric acid and sodium hydroxide.
Note: Denaturation disrupts 2ry,3ry,4ry structure of protein not 1ry
structure.
•
All proteins have unique shapes that
define their roles and interaction with
other proteins.
•
Environmental factors and genetic
mutations can affect a protein's
structure, or three-dimensional shape,
causing it to misfold.
•
Misfolded proteins can no longer
perform their functions leading to
various diseases.
•
Misfolded proteins often clump
together, forming aggregates.
•
The aggregates are toxic to some cells
such as neurons and lead to diseases
such as Alzheimer's Disease.
‫رحمه مسعد عبد اللطيف‬
‫نورهان أشرف السيد‬
ASSIGNMENTS
• Selected students are requested to prepare slides about one of the
following topics (To be delivered before next lecture):
• Digestion of proteins
• Essential amino acids.
• Non essential amino acids
• Physical properties of amino acids.
• Chemical properties of amino acids.
• Disease resulting from disturbance in amino acid metabolism.
• Ketone bodies and amino acids
• Translation of RNA
Suggested readings:
Principles of Biochemistry, Donald J. Voet, Judith G.
Voet, Charlotte W. pratt; Willey, 3rd ed.