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Introduction: polarity of the molecule determines its ability
to interact with water and dissolve in water
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Chemistry of the Cell.
Table salt with water
The molecular composition of cells.
Four major classes of biomolecules and their essential features:
carbohydrates, lipids, amino acids/proteins and nucleotides and nucleic acids.
Basic structure of a plasma membrane. Impact of polarity on the functional
properties of biomolecules, lipophylicity and hydrophylicity.
Na and Cl are
charged and
can interact
with water!
Dr. Sergey Kasparov – room E9
The main text for this lecture is:
Vander’s Medical Physiology.
Some additions from Germann and Stanfield
and Cooper’s textbooks
Introduction: polarity of the molecule determines its ability
to interact with water and dissolve in water
REMEMBER: polar, charged molecules dissolve in water!
Introduction: polarity of the molecule determines its ability to interact
with water and dissolve in water
Olive oil with water
Water
But if oil does not
dissolve in water,
what does it
dissolve in?
Oil contains
mainly
nonpolar
molecules!
REMEMBER: non-polar, uncharged molecules DO NOT
dissolve in water!
Introduction: polarity of the molecule determines its ability
to interact with water and dissolve in water
Fight for the electron:
Consider mixing…
Table salt with water
Olive oil with water
+
ELECTRONS
Ions comprising
NaCl are able to
interact with
water
Oil contains
mainly nonpolar
molecules!
Carbon
Hydrogen
NOT polarised
ELECTRONS
Carbon
Oxygen
Polarised
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Four major classes of biomolecules and their essential features: carbohydrates, lipids, amino acids/proteins and
nucleotides/nucleic acids.
Carbohydrates…
Proteins… are long chains of subunits, called amino acids.
are highly polar molecules composed of “carbon atoms and water”.
Monosaccharide
Disaccharide
Glucose
GLUCOSE
Fructose
SUCROSE
1. Are highly polar, well soluble in water.
2. Exist as monomers, dimers and polymers.
3. Important sources of energy, components of cell
membranes and the backbone of nucleic acids
4. Glucose is the ONLY source of energy for the brain.
5. Glycogen is abundant most abundant in liver but is
also present in muscles. The only brain cells which
contain glycogen are called astrocytes.
GLYCOGEN
6. There are about 10 “glycogen storage diseases” due
to various mutations in enzymes involved in its
synthesis and degradation.
Polysaccharide
Four major classes of biomolecules and their essential features: carbohydrates, lipids, amino acids/proteins and
nucleotides and nucleic acids.
Lipids… are composed largely of carbon and hydrogen atoms and
therefore are nonpolar.
All amino acids have the same
backbone but different side
chains. It is the side chains
which actually make all the
difference!
Amino acids get connected together and form
long chains (sometimes > 1000 amino acids).
These chains are called PROTEINS
1 Fatty acid
Glycerol
2 Triglycerol (fat)
4 Steroid
3 Phospholipid
1. Fatty acids are nonpolar, waterinsoluble molecules. They are used
to store energy.
2. Phospholipids have a polar “head”
and nonpolar fatty acid “tails”.
They are amphipathic. In water
they form clusters. In the cells
they are the essential component
of all membranes.
3. Steroids have 4 cycles of carbon
atoms
and
are
important
components of plasma membrane
and
also
act
as
signalling
molecules.
Phospholipids: the building blocks of cellular membrane
Macro-molecular complex protein haemoglobin
consists of 4 individual protein chains
Phospholipid bi-layer is
the key component of all
cellular membranes
The structure and function of proteins are determined
by the amino acid composition.
Structural and functional blocks/parts of a protein is often referred to as
“domains” (e.g. “catalytic domain” or “regulatory domain”).
The key aminoacids which are responsible for the function of a domain are
usually conserved throughout evolution. We can trace some of the domains in
our proteins back to the yeast cells.
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Nucleic Acids (DNA and RNA) contain and
handle the information in the cell.
H
RNA = ribonucleic acid
DNA = deoxyribonucleic acid
The plasma membrane of a cell consists of the
phospholipid bi-layer and numerous proteins embedded
in it.
REMINDER: polar molecules solve well in water. And non-polar … in what?
DNA is built of numerous
nucleotides connected via
phosphoric acid residues
Nucleic Acids (DNA and RNA) contain and
handle the information in the cell.
1. DNA and RNA are polymer molecules. Their subunits are called
nucleotides.
2. Four different nucleotides are found in DNA and RNA (3 are the same in
both)
3. Sequence of nucleotides is the genetic code of the cell as it determines
the sequence of amino acids in the proteins
Other interesting facts about nucleic acids:
1.
2.
3.
4.
5.
6.
RNA can not only carry information but also perform functions,
similar to proteins: in the ribosome where the proteins are
made it is the RNA which obviously joins the amino acids
together. There are also “rybozymes” – species of RNA which
can attack and destroy other RNAs.
Nucleotides give rise to ATP. ATP is the universal energy
currency of the cell but also perhaps the most archaic cell-to
cell signalling molecule.
Viruses have genomes encoded in either DNA or RNA form.
Some viruses can use RNA as a template to generate DNA (e.g.
information flows in reverse direction).
DNA is almost always double-stranded while RNA is usually
single-stranded. Because of that RNA often folds on itself
forming hairpin-like structures.
NOT all the DNA in the cell is located in the nucleus,
mitochondria have their own genomes which are different from
the main one.
In order for a molecule to be inside the lipid bi-layer it needs to …
= non-polar,
hydrophobic
COOH
NH2
= polar or
charged,
hydrophilic
Some Functions of (INTEGRAL) Membrane proteins
Receptor – detects chemical signals
A channel (leak)
Anchoring/connecting
effect
Carriers
A gated channel
Chemical reactions
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The Key Points:
1. Polar & charged molecules dissolve in water while non-polar dissolve in
oil/fat/lipid media
2. Carbohydrates (sugars) exist as monomers, dimers or polymers. They are
polar molecules and are serve as sources of energy and components of
other molecules, such as nucleic acids.
3. There are 4 main classes of lipids (fatty acids, triglycerides,
phospholipids and steroids). Most lipids are water-insoluble but
phospholipids are amphipathic (= have hydrophobic “tails” and hydrophilic
“heads”). They are the essential components of all membranes.
4. Proteins are long stretches of amino acids. Their structure and function is
determined by the sequence of amino acids. They are responsible for all
cellular activities / functions.
5. Nucleic acids (RNA and DNA) are long stretches of nucleotides. There are
4 kinds of nucleotides in RNA and DNA. DNA encodes all the information
in the cell and encodes all the proteins while RNA is responsible for the
transfer of this information to the places where the proteins are being
produced.
6. Some proteins are embedded into the cell membrane. This is possible
because their sequences have parts enriched in hydrophobic (non-polar)
amino acids. These parts form “membrane-spanning domains”.
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