Chemistry in Focus 3rd edition
Tro
Chapter 16
Biochemistry and Biotechnology
Brown Hair, Blue Eyes,
and Big Mice
• Study of the molecular blueprints that are genes
has increased our understanding of how we
think, how we behave, and what diseases we
might develop.
• We understand not only how a molecular
sequence works, but how to take it from one
organism and implant it in another.
• 4 type of molecules in living organisms
–
–
–
–
Lipids
Carbohydrates
Proteins
Nucleic acids
Lipids and Fats
• Lipids are cellular components that are
insoluble in water, but extractable in
nonpolar solvents.
– Fats, oils, fatty acids, steroids, some vitamins
• They form the structural components of
biological membranes and reservoirs for
long-term energy storage.
• They contain twice as much energy per
gram than any other class of biochemical
compounds.
– Efficient energy storage
Fatty Acids
• One type of lipid
• Organic acid with a long hydrocarbon tail
• General formula RCOOH:
Triglycerides
• Fats and oils are a combination of glycerol
and three fatty acids.
Tristearin
• Structure/property relationships
– Long hydrocarbon chains: nonpolar,
immiscible with water
– Energy is extracted via oxidation of these long
chains (as in gasoline).
– Chains are saturated: efficient packing, solids
– Fat is conveniently stored in the body.
• Provides thermal insulation
Triolein
• Main component of olive oil
• Double bonds in R groups interferes with
efficient packing, liquid at room
temperature
Trilinolenin
• Polyunsaturated fat: multiple double bonds in
the hydrocarbon chains
– Animal fats tend to be saturated.
– Plant fats tend to be unsaturated.
• Variations in structure serve different purposes
in the human body.
Carbohydrates
• Chemical formulas are multiples of CH2O,
carbon and water
• Function in the body as short-term energy
storage
• Chemical structure related to:
• Carbohydrates are polyhydroxy
aldehydes, or ketones, or their derivatives.
Glucose
• This is a dynamic system, but at any
instant more molecules are in the ring
form.
Glucose Properties
• Hydroxyl groups mean strong hydrogen
bonding with each other and with water.
• Solubility in body fluids leads to function
as a quick energy source.
• Since it is partially oxidized, it yields less
energy per gram than octane or lipids.
• Balance between efficient energy storage
and ease of access to that energy
Fructose
• Isomer of glucose
• Two CH2OH groups mean it is more
soluble in water and sweeter.
– Takes less to offer same sweetness
Saccharides
• Monosaccharides – carbohydrates composed of a
single ring
• Disaccharides – joined monosaccharides, double ring
structures
Complex Carbohydrates
• Polysaccharides
– Most common are starch and cellulose
– Subtle molecular difference (the oxygen linkage
between rings and subsequent nature of resulting
hydrogen bonds) means a dramatic macroscopic
result.
– Human enzymes cannot cut chains of cellulose.
Proteins
• The body CAN
metabolize proteins.
• The body metabolizes
proteins ONLY as a
last resort.
• Proteins have much
more important other
work to do in the
body.
Protein Functions
• Compose much of the physical structure of
the body (muscle, hair, skin)
• Act as enzymes to control chemical
reactions
• Act as hormones to regulate metabolic
processes
• Transport oxygen from lungs to cells
• Act as antibodies
• Protein molecules are long chains of repeating
units of amino acids.
– Differences among amino acids arise from different
R groups.
• Changing the number and order of these amino
acids changes the functionality of the protein.
• The simplest R group is the hydrogen atom,
and the amino acid is glycine.
The Peptide Bond
• The acidic end of one amino acid reacts with
the amine side of another to form a peptide
bond.
• Two linked amino acids is called a dipeptide.
• Chains with 50 units or less are polypeptides;
chains with over 50 units are called proteins.
Sickle Cell Anemia
• Hemoglobin (Hb) is a medium size protein
with a molecular formula that contains
close to 10,000 atoms:
C2952H4664O832S8Fe4
• Replacing polar glutamate with nonpolar
valine at one position, on two of these
chains, lowers the solubility of Hb resulting
in red blood cell deformation.
Protein Structure
• The structure of a protein is finely tuned to
achieve a specific function.
• We characterize protein structure in four
categories:
– Primary
– Secondary
– Tertiary
– Quaternary
Primary Structure
• The amino acid sequence held together by
peptide bonds
• Abbreviations like gly-val-ala-asp are used
to note the sequence of the amino acid.
Secondary Structure
• The way the amino
acid chain orients
itself along it axis
– Alpha-helix
– Pleated sheet
Alpha-Helix
• Helical shape is maintained by hydrogen
bonds between different amino acids
along the protein chain.
• α-keratin is an alpha-helix and is
responsible for the elasticity of hair and
wool.
• It works like a spring.
Pleated Sheet
• Protein forms zig-zag
chains that stack
neatly
• Silk is pleated sheet
• Inelasticity due to full
extension of protein
chains
• Softness due to
sliding of sheets past
each other
Tertiary and Quaternary Structure
• Tertiary structure is the bending and folding due to
interactions between amino acids on the chain.
– Completely extended
– Globular or ball-like
• Overall shape of the particular protein strand
• Arrangement of subunits of the protein chain in space
is quaternary structure.
Interactions of R Groups to Determine
Tertiary and Quaternary Structure
Common Proteins: Hemoglobin
• Entire structure not known until late 1950s
• HB folds to hold four flat molecules called heme
groups.
– Pick up oxygen at lungs
– Release it at cells undergoing glucose oxidation
• Interior of Hb molecule is highly nonpolar.
– Repels water
– Allows oxygen in and out
• Exterior is polar
– Hemoglobin is soluble in water.
α-Keratin
• Composes hair and wool
• α-helix structure maintained by hydrogen
bonding
• Hair
– 3 α-helices in a coil held by hydrogen bonds
(easy to change) and disulfide linkages
(require chemical treatment)
Lysozyme
• Acts as an enzyme
• Cleaves polysaccharide
units within cell walls
– Walls explode killing the
bacteria
• In nasal mucus and tears
• Discovered by Alexander
Fleming in 1922
Insulin
• Acts as a hormone
• Synthesized in the
pancreas
• Small (51 amino acids)
• Promotes entry of glucose
into muscle and fat cells,
lowering blood glucose
level
• Diabetics must inject
insulin.
Nucleic Acids
• The templates from which all proteins are
made
• Two types
– DNA (deoxyribonucleic acid)
• Occurs in cell information center
– RNA (ribonucleic acid)
• Occurs throughout interior of cells
Nucleotides
Nucleotides
• Phosphate and sugar groups are identical in
every nucleotide.
• Four different bases
–
–
–
–
A, adenine
T, thymine
C, cytosine
G, guanine
• Codon
– A group of three bases that codes for one amino acid
• With minor exceptions, the code is universal; it is
identical in all organisms, from bacteria to
humans.
DNA
• Occurs in chromosomes, found in the
nucleus of most cells of the human body
– There are 46 in humans
• Each set of DNA contains all the DNA
required to specify an entire person.
– Organs make those proteins specific for their
own functioning.
– But the blueprint is there for everything else
too
DNA Replication
• Mechanism elucidated by Watson, Crick,
and Franklin in 1953
• Complementary base units are formed
(with the help of enzymes) after the
double-helix unzips.
– Two daughter DNA strands formed
• Daughter DNA molecules are identical in
every way to the parent.
Protein Synthesis
• Genes are sections of DNA, thousands of base
pairs long.
• When the gene for a protein is needed, that
section of DNA unwinds.
• A messenger RNA (mRNA) is formed, which is a
complement to the unwound section.
• expression
• mRNA goes to a ribosome where protein
synthesis occurs.
• Cells express only the proteins specific to their
function.
Viruses
• Definition lies somewhere between life and
non-life.
– Difficult to kill, do not respond to antibiotics
• Require the machinery of a host cell to
reproduce
– Virus inserts it own DNA into the
chromosomes of the host.
– Host then expresses viral DNA
• Common cold, flu, measles, polio,
smallpox, ebola
AIDS
• HIV causes AIDS
• HIV attacks immune system
cells, releasing its RNA.
• Reverse transcriptase forms
viral DNA from the RNA
• An enzyme inserts the DNA
into the chromosomes of the
host cell.
• Cell dies, releasing daughter
HIVs
Recombinant DNA Technology
• Employs restriction enzymes which cut DNA in
specific places
• DNA pieces can be separated by gel
electrophoresis.
– Even single genes can be isolated.
• A DNA strand from one organism (a human)
can be introduced into another (a bacterium).
• Bacterium are cultured, replicating DNA.
• This is a source for the protein coded for by that
DNA.
Pharmaceuticals
• Insulin
– Animal insulin is not tolerated by all diabetics.
– The gene that codes for the production of
human insulin was copied and expressed by a
bacteria.
– Human insulin factory
– Most diabetics take genetically engineered
insulin today.
• Human growth hormone
Agriculture
• Bacteria, without the
protein that
accelerates ice crystal
formation on crop
leaves, have been
engineered.
• What impacts might
this (and similar
technologies) have on
the environment?
Genetic Screening
and Disease Therapy
• Can we screen for genes that may indicate
predisposition to disease?
– And should insurance companies have
access to this information?
• Genetic engineering techniques might one
day be used to treat genetic disease
directly.
– CF, Huntington’s disease, MD
CLONING
• When egg DNA is modified,
whole new organisms can
develop.
• Science fiction is now
possible in reality.
• Embryonic cloning has been
achieved in animals.
• By nuclear transfer, cloning of
adult organisms has been
achieved in animals.
Therapeutic Cloning
and Stem Cells
• Reproductive cloning is generally viewed as unethical.
• Therapeutic cloning is regarded as acceptable.
– Goal is to produce embryonic stem cells that are genetically
identical to the adult donor
– These are the master cells normally present in embryos,
days after the fertilization of an egg.
• Therapeutic cloning offers the potential to make stem
cells that are a perfect genetic match to the donor of
the DNA from whom the stem cells are cloned.
– No rejection by the immune system
– Fraught with controversy