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‫الحمد هلل رب العالمين‬
‫الذي هدانا لهذا وما كنا لنهتدي لوال أن هدانا هللا‬
‫والصالة والسالم على أشرف األنبياء والمرسلين العالمين‬
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‫‪222Cell Biology‬‬
Lecture 3
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Cellulose
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It is a polymer of glucose that forms Plant Cell Walls
cellulose is the most abundant organic molecule on
Earth
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Chitin
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Is a Polysaccharide used by insects and crustaceans to
build an exoskeleton
Found in cell wall of fungi
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Hyaluronic acid
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Found in
connective tissues
1,3 glycosidic bond
1,4 glycosidic
bond
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Inulin
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Found in some plantes,
formed of fructose
units (b 1,2 glycosidic
bond)
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Glycogen
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Is a storage
polysaccharide
composed of
glucose, which is
hydrolyzed by
animals when
glucose is needed
Highly branched
molecules
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Starch
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Is a storage
polysaccharide
composed of
glucose
monomers
and found in
plants
Starch helix
may be
unbranched or
branched
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Other polysaccharides
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Formed of Mannose
units
Found in Yeast
(branched) and in
Some plantes
( non-branched)
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Paramylum
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Homopolsaccharides, found in Euglina
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Dextrin
Branched polysaccharides , produced by some
bacteria
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Complex polysaccharides
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Polysaccharides can combine with other classes of
macromolecules to form complex polysaccharides:
 Glycoproteins: polysaccharides + proteins
 Glycolipids: polysaccharides + lipids
 Cellular functions
 Cell-surface receptor molecules; typically reside on
external surfaces of the membrane
 Glycolipids important in cell walls of gram-negative
bacteria
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PROTEINS
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Are a polymer built from various combinations of 20 amino acid
Monomers
Are the most abundant macromolecules in cells found throughout cell
Have an important structural and enzymatic roles
Transmit information between cells (e.g : protein hormones)
Provide a defense against infection (e.g antibodies)
Account for more than 50% of the dry mass of cells.
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Proteins divided into two groups based on its function in the cells:
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Structural proteins : Integral parts of cellular structures (Fibrous proteins
(Collagen) , cartilage, skin and bone (keratin(. tubulin, actin like protiens,
microtubules and ,Microfilaments
Dynamic proteins : Catalytic proteins; catalysts for chemical reactions, cell
metabolism (hormones , insulin, erthrproetin and thyroxine, hemoglobinhemocyanin-myoglobin
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PROTEINS
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Proteins can be divided into three main classes, which
correlate with typical tertiary structures:
1- Globular proteins: Almost all are soluble and many
are enzymes.
2- Fibrous proteins: Fibrous proteins are often structural,
such as collagen, the major component of connective
tissue, or keratin, the protein component of hair and nails
3- Membrane proteins: Membrane proteins often serve
as receptors or provide channels for polar or charged
molecules to pass through the cell membrane.
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Amino Acids
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Most consist of carbon, hydrogen, oxygen, and nitrogen; 2 of 22
contain sulfur, 1 contains selenium
All contain two important functional groups
 Carboxylic acid group (-COOH)
 Amino group (-NH2)
Amino acid monomers held together by covalent bonds Peptide
bonds.
Polypeptides: thousands or millions of amino acids Have two
distinct ends: one terminating in an a amino group (the amino- or
N- terminus) and the other is an a carboxylic group (carboxyl or
C-terminus)
Protein consists of a specific amino acid sequence
The amino acid sequence of protein determines its three
dimensional structure and its chemical reactivity .
Side chains of amino acids impart its chemical properties
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Peptide bond
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The amino acids in a polypeptide chain are linked by
Peptide Bonds
This bond links the carboxyl group of one amino
acid to the amino group of the next amino acid
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Conjugated proteins
A conjugated protein is a protein that functions in
interaction with other chemical groups
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Nucleoproteins: chromosome
o Chromoprotein: haemoglobin
o Phosphproteins: found in milk
o Glycoproteins : contain oligosaccharide chains
covalently attached to their polypeptide side-chains,
they play a role in cell-cell interactions
o Lipioproteins: enzymes, transporters
o
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Levels of protein structure
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Protein can have four levels of structure:
1- Primary structure
2- Secondary structure
3-Tertiary structure
4-Quaternary structure
Primary structure
Primary structure: sequence of amino acids in a polypeptide
-The correct amino acid sequence is determined by the cell’s genetic
information
-The slightest change in this sequence affects the protein’s ability to
function
-Sickle cell disease is manifested by an inability of hemoglobin in red
blood cells to carry oxygen, the primary function of hemoglobin.
This blood disorder is the result of change in a single amino acid
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Four levels of protein structure
Four Levels of Protein Structure
Primary structure
Amino acids
Hydrogen
bond
Secondary structure
Alpha helix Pleated sheet
Tertiary structure
Polypeptide
(single subunit
of transthyretin)
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2- Secondary structure
Secondary structure: the
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regular arrangement of amino
acids within localized regions
of the polypeptide
Folds in polypeptide that form
a more stable structure, often
involving hydrogen bonding
between R groups
There are two types of
secondary structure:
Helical structure called an
alpha helix (α-helix) (region
of polypeptide chain coils
around itself
Pleated sheet (β sheet(: two
parts of polypeptide chain lie
side by side with hydrogen
bonds between them.
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Tertiary structure
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Tertiary structure: additional folding of polypeptide to result in greater stability
and unique three-dimensional shape
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Forms exposed regions or grooves in the molecule that are important for binding
other molecules
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Disulfide bonds: bonds between -SH groups from two different amino acids
In most proteins combination of alpha helix and beta sheets connected by loop
regions of polypeptide chain, fold into compact globular structures called Domains
(the basic unit of tertially structure)
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Quaternary structure
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Quaternary structure: occurs in
proteins composed of two or
more polypeptides
 Subunit: each polypeptide
in the protein, held together
by either/both covalent and
noncovalent linkages
 Homodimer: protein
containing two identical
subunits
 Heterodimer: protein
containing two nonidentical
subunits
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‫وفقنا هللا وإياكم لما فيه خير أمتنا اإلسالمية‬
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