Transcript Protein is a polymer of amino acids

Principals of General Zoology (Zoo-103)
Zoology Department, 1431-1432H
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2- Proteins
1. A polypeptide is a polymer of amino acids connected in a specific sequence
2. A protein’s function depends on its specific conformation
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2-Proteins
 Their functions include structural support, storage, transport of
other substances, intercellular signaling ‫اإلشارات بين الخلوية‬, movement,
and defense against microbes.
 Some proteins works as enzymes in the cell that regulate
metabolism ‫ األيض‬by accelerating ‫ تسريع‬chemical reactions.
 All protein polymers are constructed from ‫ تتركب من‬20 monomers,
called amino acids.
 Polymers of proteins are called polypeptides ‫ببتيدات عديدة‬.
 A protein consists of one or more peptides (polypeptides) folded
and coiled into a specific conformation
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- Protein is a polymer of amino acids (constructed from 20 amino
acids) (to form Polypeptides).
- These components include a hydrogen atom, a carboxyl group, an
amino group, and a variable ‫ متغيرة‬R group (or side chain).
H
H
General Formula
of the Amino
Acid:
N
Amino
group
H
C
R
O
C
OH Carboxyl
group
Side chain
- The side chain R links with ‫ ترتبط بـ‬different compounds
- Differences in R groups produce the 20 different amino acids.
- The physical and chemical characteristics ‫ صفات‬of the R group
determine ‫ تحدد‬the unique characteristics of a particular amino acid.
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Types of Amino acids ‫األحماض األمينية‬
1. Hydrophobic: the amino acids that have hydrophobic R groups
(non-polar).
2-
Hydrophilic: the amino acids that have polar R groups,
making them hydrophilic.
3- Ionized: the amino acids with functional groups that are charged
(ionized) at cellular pH (7). So, some R groups are bases, others are
acids.
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The Peptide Bond ‫الرابطة‬
‫البيبتيدية‬
Peptide bond formed between the carboxyl group of one amino acid
and the amino group of the other by dehydration.
H
N
H
H
O
H
H
C
C
N
C
R
OH H
Peptide bond
Amino acids
Peptide
O
C
OH
R
Dehydration
‫نزع الماء‬
Polypeptide (Protein)
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•
•
•
•
•
Amino acids are joined together when a dehydration reaction removes a
hydroxyl group from the carboxyl end of one amino acid and a hydrogen
from the amino group of another. The resulting covalent bond is called a
peptide bond.
Repeating the process over and over ‫ عدة مرات‬creates a long polypeptide chain.
– At one end is an amino acid with a free amino group the (the N-terminus)
and at the other is an amino acid with a free carboxyl group the (the Cterminus).
The repeated sequence (N-C-C) is the polypeptide backbone.
Attached to the backbone are the various R groups.
Polypeptides range in size from a few monomers to thousands.
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Levels of Protein Structure
•
The folding ‫ إلتفاف‬of a protein from a chain of amino
acids occurs spontaneously ‫ذاتيا‬.
There are three levels of structures:
1. Primary ‫أولى‬,
2. Secondary ‫ثانوى‬,
are used to organize the folding within a single peptide chain.
3. Tertiary ‫ثالثى‬,
4. Quaternary ‫رباعى‬:
ُ structure arises when two or more polypeptides
(proteins) join to form another kind of protein.
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1. Primary structure:
It is a single peptide
chain of amino acids.
–
Lysozyme, an enzyme that
attacks bacteria, consists of a
polypeptide chain of 129
amino acids.
–
A slight change ‫ تغيير طفيف‬in the
primary structure can affect a
protein’s conformation and
ability to function.
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2- The secondary structure:
Results from hydrogen bonds at regular intervals ‫ على أبعاد متساوية‬along
the polypeptide backbone.
A. Coils ‫( الحلزونى‬α-helix)
are typical shapes
that develop from
secondary structure
B.
Folds (β-pleated sheets)
‫الشيت ال ُمجعـد‬. Composed
of several parallel αhelix
coils attached by H bonds
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•
Tertiary structure:
is determined by a variety of interactions among ‫ خالل‬R groups and
between R groups and the polypeptide backbone.
These interactions include:
1.
2.
3.
4.
Hydrogen bonds among polar areas,
Ionic bonds between charged
R groups, and hydrophobic
interactions,
Van der Waals interactions
among hydrophobic R groups.
Disulfide bridges, is formed
between the sulfhydryl groups
(SH) of cysteine monomers,
stabilize the structure.
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4- The quaternary structure:
Results from the aggregation ‫ تجمع‬of two or more
polypeptide chains.
A. Collagen is a fibrous protein of three polypeptides that
are supercoiled, and function in connective tissues.
A. Hemoglobin is a
globular protein
with two copies
of two kinds
of polypeptides
(2α and 2β).
Collagen
Hemoglobin
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The 4 forms of protein
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Hydrophobic (non-polar R group)
Amino
acids
Hydrophilic (polar R group)
Ionized (charged functional groups)
Peptides
Primary
structure
Secondary
structure
Single chain
of amino acids
H bonds
e.g. Lysozyme
Coils &
Folds
e.g. silk
Polypeptides
Tertiary
structure
1- Hydrophobic
Interaction
(Van der Waals
interaction);
Proteins
Quaternary
structure
two or more
polypeptide
chains
2- H bonds;
e.g. Collagen
3- Ionic bonds;
& Hemoglobin
4- Di-sulfide
bridges;
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3- Lipids;
The Hydrophobic Molecules
1. Fats store large amounts of energy
2. Phospholipids are major components of cell membranes
3. Steroids include cholesterol and certain hormones
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1)- Fats:
• Lipids are an exception among macromolecules
because they do not have polymers.
• The unifying feature ‫ الصفة ال ُم َميـٍزة‬of lipids is that they all
have little or no affinity for water ‫ال تـَمتزج بالماء‬.
– This is because their structures are dominated by non-polar
covalent bonds.
• Lipids are the components ‫ ُمكونات‬of fats, and are highly
diverse in form and function.
• Although fats are not polymers, they are large
molecules assembled from ‫ تتكون من‬smaller molecules by
dehydration reactions.
• A fat is constructed from two kinds of smaller
molecules, glycerol and fatty acids ‫أحماض دُهنية‬.
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Glycerol
O
H
C
OH
Ester link
H C
OH
H
OH
C
OH
H C
H
C
H
H
C
H
H
C
H
H
C
H
H
C
Fatty Acid
H
H
Dehydration
H
A fat is composed of three fatty acids linked with one glycerol molecule.
Fats are classified into Saturated ‫ مشبع‬and Un-saturated ‫ غير مشبع‬fats
Glycerol consists of a three C skeleton with an OH group attached to each C.
A fatty acid consists of a carboxyl group (COOH) attached to a long
carbon skeleton, often 16 to 18 carbons long.
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• Fatty acids may vary ‫ تختلف‬in length (number of carbons) and in the
number and locations of double bonds.
– If there are no carbon-carbon double bonds, then the molecule is a
saturated fatty acid ‫( مشبع‬has H at every possible position).
•If there are one or more carbon-carbon double bonds, then the
molecule is an unsaturated fatty acid ‫ حامض دهنى غير مشبع‬- formed by the
removal of H atoms from the carbon skeleton.
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A)- Saturated Fats ‫الدهون المشبعة‬
The Fatty acid components are saturated (there is no double bonds
between the carbons. All C are linked with H.
Thus, it is saturated with H.
Most animal fats are saturated.
They are solid at room temperature.
Saturated fats-rich diet results in Atherosclerosis ‫التصلب الشريانى‬.
B)- Un-saturated Fats ‫الغير مشبعة‬
‫الدهون‬
These double bonds are formed by the removal of H atoms.
Most vegetable fats (oils) and fish fats are unsaturated.
They are liquid at room temperature.
They can be synthetically converted to saturated (solid) by adding H
(Hydrogenation ‫)ال َهد َْرﭽـَة‬.
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2)- Phospholipids;
Are major components of cell membranes
• Phospholipids have two fatty acids attached to glycerol and a
phosphate group at the third position.
– The phosphate group carries a negative charge.
• The interaction of
phospholipids with
water is complex.
• The fatty acid tails are
hydrophobic, but the
phosphate group and
its attachments form a
hydrophilic head.
• Thus, it is amphipathic
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3)- Steroids:
Include cholesterol and certain hormones
• Steroids are lipids with a carbon skeleton consisting of four fused
‫ ملتحمة‬carbon rings.
– Different steroids are created by varying functional groups attached to
the rings.
• Cholesterol, an important
steroid, is a component in
animal cell membranes.
• Cholesterol is also the precursor ‫ المادة الخام‬from which all other
steroids are synthesized.
• Many of these other steroids are hormones, including the vertebrate
sex hormones.
• While cholesterol is clearly an essential molecule, high levels of
cholesterol in the blood may contribute to Atherosclerosis ‫تصلب الشراييت‬
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Fats
(Composed of Lipids)
Saturated
Unsaturated
Phospholipids
Steroids
Animal Fats
Vegetable Fats
Bi-layer of cell
membrane
Sex Hormones
& Cholesterol
Hydrogenation
‫َهـد َْرﭽـَــــــــة‬
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