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Lecture 1
Cell Biolgy ٢٢٢
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Cell Biolgy ٢٢٢
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Cell theory and the cell
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All animals consist of certain structural units
A term cell was used by Robert Hook in1965
Cork Cells were thought to have been these cells.
Cells are the fundamental units of life.
Anton von Leeuwenhoek was first to observe one
celled living things. Examples of these were bacteria
and paramecium.
The concept that the cell is the basic unit of life is
known as the cell theory, which put by Schlieden an
Schwann
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Cell are divided into two main classes:
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Prokaryotic cells: lacks a nuclear envelope,
smaller and simpler than eukaryotic cells,
absence of nucleus, their genomes are less
complex, they do not contain cytoplasmic
organelles or cytoskeleton.
Eukaryotic cells: have a nucleus in which the
genetic material is separated from the
cytoplasm.
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Chapter I:
Biological chemistry of the cell
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Chapter I: Biological chemistry of the cell
This chapter focus on five major topics:
1- types of molecules within the cells
2- the structure and function of each type
Molecular constituents of cells
Cells are composed of :
1- Macromolecules Organic molecules (carbon containing
molecules like: lipids, proteins, nucleic acid,
carbohydrates)
2- Inorganic ions (water, salts, acids and bases)
3- Organelles (mitochondria, Golgi apparatus, nucleus)
4- Traces of Vitamins and minerals
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These constituents differ according to
Cell type & Cell function
.Molecular constituents of cells
(Water)
(Acids)
(Bases)
(Salts)
(Inorganic
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(Biological
Molecules)
(Organic)
(Nucleic
acids)
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(Proteins)
(Lipids)
(Carbohydrate
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1- water
Water is the most abundant compound found in
living organisms (about 80%).
Properties of Water
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Water as a Biological Solvent
- Cellular molecules bathed in water
- Water is an excellent solvent (a fluid in which
something can be dissolved) for
many substances because of its polar nature.
- Polar substances and ions dissolve in water
because opposite charges are
attracted. Ions are attracted to the appropriate
ends of water molecules which
keep the ions dispersed in the water - or dissolved.
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Why Is water Polarity Important?
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Many macromolecules are also polar and
readily dissolve in water
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Promotes the stability of large molecules
through hydrogen bonding
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Forces non polar substances to aggregate
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Makes water cohesive
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1- water
1- Strictly hydrophobic molecules, including most lipids, do not mix
well with water
2- Some molecules have both hydrophobic and hydrophilic ends.
Such molecules are said to be amphipathic.
3- Amphipathic molecules make good emulsifiers because they can
attract both hydrophobic substances and hydrophilic substances
to them.
Water in Biochemical Reactions
• The breakdown and assimilation of many molecules of living
organisms involves water. Water is needed to breakdown
carbohydrates, lipids and proteins during digestion. The
formation of large biological molecules from smaller building
blocks releases water
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There are four classes of biological
molecules
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The four classes of biological molecules contain very large molecules
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1- Carbohydrates
2- Proteins
3- Lipids
4- Nucleic acids
They are often called macromolecules because of their large size
They are also called polymers because they are made from identical
building blocks strung together
The building blocks are called monomers
A cell makes a large number of polymers from a small group of
monomers
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Proteins are made from only 20 different amino acids, and DNA is built from
just four kinds of nucleotides
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The monomers used to make polymers are
universal
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Hydrolysis
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Short polymer
Dehydration
reaction
Unlinked
monomer
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Monomers are linked
together to form polymers
through dehydration
reactions, which remove
water
Polymers are broken
apart by hydrolysis, the
addition of water
All biological reactions of
this sort are mediated by
enzymes, which speed up
chemical reactions in cells
Longer polymer
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LIPIDS
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Lipids are water insoluble (hydrophobic,
or water fearing) compounds
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They are soluble in organic solvents like chloroform, ether and
benzene
They are important in energy storage, They contain twice as
much energy as a polysaccharide
They are Amphipathic (possess hydrophilic and hydrophobic
characteristics) macromolecules
lipids have 4 major roles in cells
The major component of cell membranes
Play an important roles in cell signaling both as steroid hormones
and as messenger molecules that convey signals from cell
surface receptors to targets within the cell
Provide an important form of energy storage
They are carriers of fat-soluble vitamins (A, D, E and K)
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Lipids
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Simple lipids (fats, triglycerides): three fatty acids bonded
to the C3 alcohol glycerol
Complex lipids: simple lipids that contain additional
elements such as phosphorus, nitrogen, sulfur, or small
hydrophilic organic compounds (e.g., sugars)
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Lipid categories
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Lipids may be divided into the following categories:
fatty acyls
Glycerophospholipids
sphingolipids
Neutral fats
Plasmalogens
Steroids
Waxes
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1- Fatty acids
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Fatty acids are major constituents of
biological lipids
The simplest lipids
fatty acid are formed of two parts:
- The hydrophilic head (COOH)
which found in contact with the
water of the environment and the
internal part of the cell
- The hydrophobic tail (long
Hydrocarbon chain, most frequently
containing 16 - 18 carbon atoms)
which is unable to interact with
water
This hydrophobic nature is
responsible for the formation of
biological membranes
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Types of Fatty acids
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Saturated fatty acids
Fatty acids with the maximum number of
hydrogens are called saturated fatty acids
Most animal fat is saturated fat. Saturated fats,
such as butter and lard, will pack tightly together
and will be solid at room temperature
- Unsaturated fatty acids
Fatty acids contain one or more double bonds
between carbon atoms called unsaturated fats
because they have fewer than the maximum
number of hydrogens.
This causes kinks or bends in the carbon chain
because the maximum number of hydrogen
atoms cannot bond to the carbons at the double
bond
Plant and fish fats are usually unsaturated fats.
They are usually liquid at room temperature.
Olive oil and cod liver oil are examples.
The balance between saturated and unsaturated
fatty acids is important in maintaining the
optimum degree of fluidity of a given membrane.
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The salts of fatty acids have an ionic polar
head group, the carboxylate and a long
non-polar hydrocarbon chain.
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2- Neutral fats
- Fats are lipids made from one molecule of glycerol and three
molecules of fatty acids
- Fatty acids link to glycerol by a dehydration reaction
- They are mostly energy-storage molecules
- Fats are often called triglycerides because of their structure
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3- Phospholipids (Glycerophosphatides
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complex lipids containing phosphate groups;
play a major structural role in cytoplasmic membranes
structurally similar to fats but the third carbon atom of glycerol
is bound to a phosphate group, which in turn attached to
another small polar molecules such as choline, serine
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