LO

Made By: JOYA HOSSAM

Facilitation Committee
Concepts:
1. Proteins in cells.
2. Function of protein in the cell.
3. Protein classification.
4. Enzyme structure, functions and factors
affecting rates.
Proteins in cells
-Every protein is made of one or more polypeptide.
-Polypeptide are chain of amino acids linked by peptide bonds.
-There are 20 different amino acids found in proteins of living
things.
-Each polypeptide chain may consists of hundred or thousands
of 20 different amino acid.
-Arrange in a sequence specific to each protein.
-The shape of the protein is critical to its function.

Steps of translation
1-Two ribosomal subunits TRNA, MRNA join together.
-tRNA carrying amino acid Methionine at one end and The
anticodons Uac at other end pairs with start codon Aug on the
mRNA .
-The first amino acid nearly all polypeptide is methionine but
this amino acid may be removed.
2-After form amino acids the first TRNA Then exits the
ribosome the ribosome Then Moves A distance of one cadon
along the mrna.
3-The polypetide chain continues T0 grow as MRNA Moves
along The ribosome A new trna move in carryng an amino acid
for the next MRNA Codon the growing polypeptide chain
Moves from one TRNA To amino acid attached To the next trna.
4-The ribosome reaches The stop codon The newly Made
Polypeptide falls of. 5-end
Amino acid monomer
-All amino acids share a common structure.
-PH of amino acid is 7.4 neutral as carboxyl group has negative
charge (coo-) and amino group has positive charge (RNH+3 ).
-The physical and chemical properties of the side chain
determine the unique characteristics of a particular amino acid,
thus affecting its functional role in a polypeptide.

Amino acid polymer

-When two amino acids are positioned so that the carboxyl
group of one is adjacent to the amino group of the other.
-they can become joined by a dehydration reaction
with the removal of a water molecule.
- The resulting covalent bond is called peptide bond.
-R group together called polypeptide backbone.
Primary structure
-The primary structure of a protein is a linked series of amino
acids with a unique sequence.
-Example Transthyretin is made up of four identical
polypeptide chains, each composed of 127 amino acids
-Protein is determined not by the
random linking of amino acids,
but by inherited genetic info.

Secondary structure
-Most proteins have segments of
their polypeptide chains
repeatedly coiled or folded in
patterns that contribute to the
protein’s overall shape.
-These coils and folds, collectively referred to as secondary
structure, are the result of hydrogen bonds between the
repeating constituents of the polypeptide backbone (not the
amino acid side chains).
-Within the backbone, the oxygen atoms have a partial negative
charge, and the hydrogen atoms attached to the nitrogen have
a partial positive charge.
-Therefore, hydrogen bonds can form between these atoms.
Individually, these hydrogen bonds are weak, but because they
are repeated many times over a relatively long region of the
polypeptide chain, they can support a particular shape for that
part of the protein.
-One such secondary structure is the helix, a delicate coil held
together by hydrogen bonding between every fourth amino
acid.
-Some fibrous proteins, such as α-keratin, the structural
protein of hair,have the α helix formation over most of their
length.
-α helix formation over most of their length.
-The other main type of secondary structure is the pleated
sheet. As shown above, in this structure two or more strands of
the polypeptide chain lying side by side (called β strands) are
connected by hydrogen bonds between parts of the two
parallel polypeptide backbones.
-β pleated sheets make up the core of many globular proteins
and dominate some fibrous proteins, including the silk protein
of a spider’s web.

Tertiary Structure
-Tertiary structure is the overall shape of a polypeptide
resulting from interactions between the side chains (R groups)
of the various amino acids.
-Hydrogen bonds between
polar side chains.
-Covalent bonds called
disulfide bridges may further
reinforce the shape of a
protein. Disulfide bridges form where two cysteine monomers,
which have sulfhydryl groups (¬SH) on their side chains.
-Hydrophobic interaction” is actually caused by exclusion of
nonpolar substances by water molecules, once nonpolar amino
acid side chains are close together, van der Waals interactions
help hold them together.
-Ionic bonds between positively and negatively charged side
chains also help stabilize tertiary structure.

Quaternary Structure
-Quaternary structure is the overall protein structure that
results from the aggregation of these polypeptide subunits.
-Hemoglobin, the oxygen-binding protein of red blood cells
shown below, is another example of a globular protein with
quaternary structure.
-It consists of four polypeptide subunits, two of one kind (α)
and two of another kind (β).
-Both α and β subunits consist primarily of α-helical secondary
structure.
-Each subunit has a non-polypeptide component, called heme,
with an iron atom that binds oxygen.
protein function
1_Enzymatic proteins
Function : Selective acceleration of
chemical reactions.
Example: Digestive enzymes catalyse the hydrolysis of bonds
in food molecules.

2_Defensive proteins
Function: Protection against disease.
Example: Antibodies inactivate and help destroy viruses and
bacteria.
3_Transport proteins
function: Transport of substances
Examples: Hemoglobin, the iron-containing protein of
vertebrate blood, transports oxygen from the lungs to other
parts of the body. Other proteins
transport molecules across cell
membranes.

4_Storage proteins
Function: Storage of amino acids
Examples: Casein, the protein of milk, is the major source of
amino acids for baby mammals. Ovalbumin
is the protein of egg white, used as an
amino acid source for the developing
embryo.

5_Hormonal proteins
Function: Coordination of an organism‘s activities
Example: Insulin, a hormone secreted by the pancreas, causes
other tissues to take up glucose, thus
regulating blood sugar concentration.

6_Receptor proteins
Function: Response of cell to chemical
stimuli
Example: Receptors built into the membrane of a nerve cell
detect signaling
molecules released by
other nerve cells.

7_Contractile and motor proteins

Function: Movement
Examples: Motor proteins are responsible for the undulations
of cilia and flagella. Actin and myosin
proteins are responsible for the
contraction of muscles.

8_Structural proteins
Function: Support
Examples: Keratin is the protein of hair, horns, feathers, and
other skin appendages.

Enzyme structure, functions and factors affecting

rates
-Enzyme is type of protein with specific sequence of amino
acids.
-Enzymes help speed up chemical reactions in the human body.
They bind to molecules and alter them in specific ways. They
are essential for digesting food and among thousands of other
roles.
-Enzyme activity can be affected by a variety of factors, such as
temperature ,water , hydrogen ion concentration (ph)
,concentration of substrate ,concentration of enzyme and effect
of light and radiation
-Enzymes work best within specific temperature and ph
ranges, and sub-optimal conditions can cause an enzyme to
lose its ability to bind to a substrate.
-hydrolytic enzyme work best in acidic environment in
lysosome but it not work in cytosol Is natural ph.
STEM Fayoum Bio Club