Transcript lec---10

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, movement, and defense
against microbes.
• Some proteins works as enzymes in the cell that regulate
metabolism by accelerating chemical reactions.
• All protein polymers are constructed from 20 monomers, called
amino acids.
• Polymers of proteins are called polypeptides.
• 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 R group (or side chain).
General Formula of the
Amino Acid:
N
H
Amino
group
H
H
C
R
Side chain
O
C
OH
Carboxyl
group
• The side chain R links with‫ ـ‬different compounds
• Differences in R groups produce the 20 different amino acids.
• The physical and chemical characteristics of the R group determine
the
5 unique characteristics of a particular amino acid.
The Peptide Bond
• 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
R
O
C
OH
Dehydration
Polypeptide (Protein)
• 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
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group
of another. The resulting covalent bond is called a peptide bond.
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 of lipids is that they all have little or no
affinity for water.
– This is because their structures are dominated by non-polar covalent
bonds.
• Lipids are the components of fats, and are highly diverse in
•
•
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form and function.
Although fats are not polymers, they are large molecules
assembled from smaller molecules by dehydration reactions.
A fat is constructed from two kinds of smaller molecules,
glycerol and fatty acids.
Glycerol
O
H
C
C
OH
Ester link
OH
H
H
H
C
OH
H
C
OH
C
H
H
C
H
H
C
H
H
C
H
Fatty Acid
H
C
H
H
Dehydration
H
• A fat is composed of three fatty acids linked with one glycerol molecule.
• Fats are classified into Saturated and Un-saturated fats
• 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 in 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 (has H at every possible position).
• If there are one or more carbon-carbon double bonds, then the
molecule is an unsaturated fatty acid - formed by the removal of H
atoms from the carbon skeleton.
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A)- Saturated Fats
• 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.
B)- Un-saturated Fats
• 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
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(Hydrogenation).
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 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
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the
blood may contribute to Atherosclerosis.
The Summary
Fats
(Composed of Lipids)
Saturated
Unsaturated
Phospholipids
Steroids
Animal Fats
Vegetable Fats
Bi-layer of cell
membrane
Sex Hormones &
Cholesterol
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Hydrogenation