Phys 214. Planets and Life
Dr. Cristina Buzea
Department of Physics
Room 259
E-mail: cristi@physics.queensu.ca
(Please use PHYS214 in e-mail subject)
Lecture 14. Molecular components of cells.
February 8th, 2008
Contents
Textbook pages 163-164
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Molecular components of cells
Carbohydrates
Lipids
Nucleic acids
Proteins (amino acids)
Vitamins, Metals, Porphyrins
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Movie: Carl Sagan: “Origin and Evolution of life on Earth” 33 minutes
Molecular components of cells
Carbohydrates
• Stoichiometric formula (C•H2O)n
• Provide energy to cells -sugars (glucose, fructose,
lactose) and starches (polymers of glucose)
• Make important cellular structures (celulose - fibers
of cotton and linen, main constituent of wood)
• Most important - Glucose - is metabolized by nearly
all known organisms
• Aerobic organisms metabolize glucose and oxygen to
release energy (byproducts CO2 and H2O)
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MOST important role - short-term energy storage
(much simpler to metabolize than fats or proteins)
Glucose C6H12O6
Molecular components of cells
Lipids
• known as fats – insoluble in water -> absorb
less water -> weight less than carbohydrates;
C-H bonds more metabolically useful – more
potential energy stored - long term storage of
energy
• Phospholipids – cell membranes – form
bilayers
Phosphate - one polar end soluble in water
(hydrophilic),
Chains of hydrocarbons - a nonpolar end
insoluble in water (hydrophobic)
• Critical role in the origin of life spontaneously form membranes in water
• MOST important role- major ingredient of
cell membrane
Molecular components of cells
Nucleic acids
Most important role - the storage
and transfer of information
DNA - The basic hereditary
material on Earth
RNA (ribonucleic acid) - helps
carry out instructions
contained in DNA
More on DNA and RNA in the
following lecture
Molecular components of cells
Proteins
The basic molecular building blocks of
proteins are amino acids.
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Amino refers to the amino group
(N & 2 H); also contain a carboxyl
group (COOH).
Different amino acids - distinguished
by different sets of atoms bonded to
the central carbon
Amino acids found in protein in life on
Earth are all left-handed molecules.
Amino group
More than 70 amino acids identified, but life
on Earth uses only 20! => all life on
Earth has a common ancestor.
Molecular components of cells
Dual amino acid structure = dipeptide
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Amino acids link by dehydration reaction (amino group towards carboxyl)
Protein = hundreds to thousands of aminoacids – polypeptides
Peptide units can rotate about carbon bonds –rotation angles restricted by repulsive
forces when too closed together; overall rotation arrangement = conformation
=>the polypeptide chain folds
Folding rule for protein - result of - restricted conformation of the chain; hydrophobic
sides fold to minimize contact with water; attractive interactions between side
chains; two primary shapes of proteins – either a spiral helix or a pleated sheet
Molecular components of cells
Proteins
• basic functioning of living
organisms
• Vast array of functions
• Structural elements
• Enzymes - important to almost all
biochemical reactions, including
copying genetic material, serving as
catalysts
• Most important - enzymes facilitate replication of DNA and
the reading of the genetic code
IgG
Hemoglobin
Representations of the 3D structure of the protein triose
phosphate isomerase.
Left: all-atom representation.
Middle: backbone conformation.
Right: Solvent-accessible surface representation.
Insulin
Glutamine synthetase
Molecular surface of several proteins showing their comparative sizes. From left to right: Antibody (IgG),
Hemoglobin, Insulin (a hormone), and Glutamine synthetase (an enzyme).
Molecular components of cells
Vitamins
• nutrients that higher organisms cannot
manufacture by themselves – but are
essential to living functions
• Primary role – co-enzyme – much smaller
than protein enzyme itself; they fit within
the functional shape of the protein to
enable beneficial interactions with other
small molecules
• Vitamin C (ascorbic acid) – most
mammals except humans
Metals (Fe, Mg) co-factors
Many reactions require inorganic minerals in a
soluble form
Metal ions help in catalysis
Vitamin B12
Molecular components of cells
Porphyrin
Central metal ions – bound by N
atoms contain in heterocyclic
rings
Metals absorb and emit light –
they are strongly coloured
Chlorophyll – reflects green
Hemin - contained within a
protein called hemoglobin –
Fe can reversibly bind O2
(red); is carried in the
bloodstream of animals to
transport oxygen from the
lungs to cells
Chlorophyll
Movie
• Movie: Disk 2, Chapters 5-8
Emmy award winning series - Cosmos, by Carl Sagan:
“Origin and Evolution of life on Earth” 33 minutes
(16:43-45:32 + updates 2 minutes)
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Next lecture
The major grouping of life on Earth
Metabolism
DNA and heredity