1. THE STRUCTURE AND FUNCTION
OF MACROMOLECULES
2) Proteins :- Many Structures, Many Functions
1. A polypeptide is a polymer of amino acids connected in a specific sequence
2. A protein’s function depends on its specific conformation
2. Their functions include structural support, storage, transport of other
substances, intercellular signaling اإلشاراتبينالخلوية , movement, defense
against microbes and work as enzymes in the cell that regulate
metabolism األيض.
Humans have tens of thousands of different proteins, each with their
own structure and function.
All protein polymers are constructed from تتركبمن the same set of 20
monomers, called amino acids.
Polymers of proteins are called polypeptides ببتيداتعديدة .
A protein consists of one or more polypeptides folded and coiled
into a specific conformation
3. - The physical and chemical characteristics صفاتof the R group
determine تحددthe unique characteristics of a particular amino acid.
Side chain
Amino
group
Carboxyl
group
General Formula
of the Amino
Acid: C
H
R
N
H
H
C
OH
O
- The side chain R links with ترتبطبـ different compounds
***
- Monomer of amino acid includes a hydrogen atom, a carboxyl group,
an amino group, and a variable متغيرةR group (or side chain), all
covalently bonded to C atom.
- Differences in R groups produce the 20 different amino acids.
5. 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.
6. The Peptide Bond الرابطةالبيبتيدية
Peptide bond formed between the carboxyl group of one amino acid
and the amino group of the other by dehydration.
OH
C C
H
R
N
H
H
O
H
C
H
R
N
H
C
OH
O
Peptide bond
Polypeptide (Protein)
Dehydration
نزعالماء
Amino acids Peptide
7. 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 عدةمرات creates 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 C-
terminus).
• 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.
8. The folding إلتفافof a protein from a chain of amino acids
occurs spontaneously ذاتيا.
There are three levels of structure:
primary أولى, secondary ثانوى, and tertiary ثالثىstructure, are
used to organize the folding within a single peptide
chain.
Quaternary باعىُرstructure arises when two or more
polypeptides (proteins) join to form another kind of
protein.
9. 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 تغييرطفيف in the
primary structure can affect a
protein’s conformation and
ability to function.
10. Sickle cell disease المنجليةخالياالدم :
an abnormal hemoglobin because of a single amino acid
substitution تغيير.
These abnormal hemoglobin crystallize, deforming كسرُيthe red blood
cells and leading to clogs إنسدادin tiny blood vessels .أوعية
11. 2. The secondary structure:
Results from hydrogen bonds at regular intervals علىأبعادمتساوية along the
polypeptide backbone.
A. Coils الحلزونى(α-helix)
are typical shapes
that develop from
secondary structure
B. Folds (β-pleated sheets)
الشيتجعـدُمال . Composed
of several parallel α-helix
coils attached by H bonds
12. An example for folds (β-pleated sheets) الشيتجعدُمال :
Is the structural properties of silk الحريرbecause of the presence of so
many hydrogen bonds makes each silk fiber stronger than steel.
13. 3. Tertiary structure:
is determined by a variety of interactions among خاللR groups and
between R groups and the polypeptide backbone.
These interactions include weak bonds like hydrogen bonds
among polar areas, ionic bonds between charged R groups, and
hydrophobic interactions and Van der Waals interactions among
hydrophobic R groups.
- Also include disulfide bridges,
strong covalent bonds that form
between the sulfhydryl groups
(SH) of cysteine monomers,
stabilize the structure.
14. 4- The quaternary structure:
Results from the aggregation تجمعof two or more
polypeptide chains.
Collagen is a fibrous protein of three polypeptides that are
supercoiled, and function in connective tissues.
Hemoglobin
is a globular protein with
two copies of two kinds
of polypeptides (2α and
2β).
Collagen Hemoglobi
n
16. It is the change of protein’s conformation in response to
إستجابةلـ the physical and chemical conditions.
For example, alterations تغييرin pH, salt concentration,
temperature, or other factors can denature يفردa protein.
These forces break the hydrogen bonds, ionic bonds, and disulfide
bridges that maintain the protein’s complicated shape.
Some proteins can return to their original shape again
after denaturation, but others cannot.
19. 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
20. Lipids are an exception among macromolecules because
they do not have polymers.
The unifying feature الصفةزةٍـيَمُمال of lipids is that they all
have little or no affinity for water المتزجَـتبالماء .
This is because their structures are dominated by non-polar
covalent bonds.
Lipids are the components كوناتُمof fats, and are highly
diverse in form and function.
Although fats are not polymers, they are large
molecules assembled from تتكونمن smaller molecules by
dehydration reactions.
A fat is constructed from two kinds of smaller
molecules, glycerol and fatty acids أحماضُهنيةد .
21. A fat is composed of three fatty acids linked with one glycerol molecule.
Fats are classified into Saturated مشبعand Un-saturated غيرمشبع fats
OH
H H
C
C
CC
C
C H
HH
H
H H
H
H
H
O
OC
C
C
H
H
H
H
OH
OH
H
H
Dehydration
Fatty AcidGlycerol
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.
Ester link
22. The many non-polar C-H bonds in the long hydrocarbon skeleton
make fats hydrophobic.
In a fat, three fatty acids are joined to glycerol by an ester linkage, رابطة
إستيريةcreating a triacylglycerol( = triglyceride) .
23. 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 حامضدهنىغيرمشبع - formed by the
removal of H atoms from the carbon skeleton.
24. 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 التصلبالشريانى .
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 ََْردَهةﭽالَـ).
B)- Un-saturated Fats الغيرمشبعةالدهون
25. The major function of fats is energy storage.
A gram of fat stores more than twice as much energy as
a gram of a polysaccharide.
Humans and other mammals store fats as long-term
energy reserves كمخزونطاقةطويلالمدى in adipose cells خاليادهنية .
26. 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.
27. When phospholipids are added to
water, they self-assemble تتشكلذاتيا
into aggregates تجمعاتwith the
hydrophobic tails pointing toward
the center and the hydrophilic
heads on the outside.
This type of structure is called a
micelle .الزهرة
• At the surface of a cell phospholipids
are arranged as a bilayer طبقةمزدوجة .
– Again, the hydrophilic heads are on
the outside in contact with the aqueous
solution المحلولالمائى and the
hydrophobic tails in the core .المركز
– The phospholipid bilayer طبقةمزدوجة
forms a barrier حاجزbetween the cell
and the external environment البيئة
.الخارجية
• They are the major component of cell
membranes.
28. 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 المادةالخام from which all other
steroids are synthesized.
• Many of these other steroids are hormones, including the sex
hormones.
• While cholesterol is clearly an essential molecule, high levels of
cholesterol in the blood may contribute to Atherosclerosis تصلبالشرايين
29. F a t s
(Composed of Lipids)
Saturated Unsaturated Phospholipids
Animal Fats Vegetable Fats Bi-layer of cell
membrane
Hydrogenation
ََْردـَهــــــــةﭽَـ
Steroids
Sex Hormones
& Cholesterol
***
30. CHAPTER 5
THE STRUCTURE AND
FUNCTION OF
MACROMOLECULES
THE STRUCTURE AND FUNCTION
OF MACROMOLECULES
4- Nucleic Acids:
The Informational Polymers
1. Nucleic acids store and transmit
hereditary information المعلوماتالوراثية
2. A nucleic acid strand is a polymer
of nucleotides
3. Inheritance is based on
replication of the DNA
double helix
