Molecular Biology and DNA
Chapter 10
• Nucleic acid group
• Structure resembles a
twisted ladder
• Phosphate/Sugar group
makes up the rungs of ladder
• 4 nitrogen bases make up
the steps: A, T, G, C
• Structure verified in 1953 by
Watson and Crick
• Rosalind Franklin credited
with helical shape discovery.
• Having two sides makes it a
“double helix”
4 nitrogen bases pair specifically
• Adenine always bonds with
Thymine
• Cytosine always bonds with
Guanine
• Remember “At Times,
Go Crazy” AT-GC
- Each DNA molecule has a
specific order of bases…thus
each individual has a specific
DNA
- The way the bases pair up will
designate which protein will be
formed influencing phenotype of
individuals
- Thus, you share the same bases
as a goldfish or a corn plant, just
different amounts of them!
When a cell duplicates, where does
the extra DNA come from?
• Each cell must duplicate DNA exactly
• Order of bases must be the same
• Replication is semi-conservative…uses
part of the original molecule to make new
molecule.
• Base pairing is important…exact bases
must match up to make sure the order is
the same
• Replication takes place every time mitosis
and meiosis takes place
Process of making RNA from DNA
is called TRANSCRIPTION
• ½ of a DNA strand becomes
a template, or pattern, for the
RNA molecule
• Free floating bases in the
nucleoplasm will pair up with
bases on the DNA creating
the RNA molecule, called
messenger RNA or mRNA
• All T’s will be replaced in the
RNA with a U. A, G and C all
remain paired the same as in
DNA
Once in the cytoplasm, TRANSLATION from
RNA to protein can begin
• mRNA attaches to a
ribosome site in the
cytoplasm where a rRNA
(ribosomal RNA) is located
• Free-floating in the
cytoplasm are nucleotide
bases to pair up on the
mRNA. These are called
tRNA for transfer RNA. They
transfer the bases to the
correct site for pairing to
make the correct sequence
of bases for the protein.
Translation results in a chain of
amino acids being formed.
• Each base group of 3 forms a code for an amino
acid.
• Different amino acids linked together form a
protein.
• Since the bases are universal among organisms
the code is interchangable.
• Proteins will be formed according to the cell that
is coding them and the job they need to do
• Amino acids come from food you eat and then
digest
Flow of genetic information in
making a protein is important
• DNA is in nucleus and
cannot leave
• Double strand prevents this
• Cell must “copy” info on DNA
molecule to a single stranded
molecule to get the message
into the cytoplasm
• This is where proteins are
made
• RNA becomes the copy that
carries a DNA code into the
cytoplasm
• RNA is single stranded and
has the base Uracil in place
of Thymine
Occassionally, a base is out of order
and the protein cannot form right.
• This creates a mutation
• Bases can be added or
deleted to create
mutations
• Added bases bump the
chain up one base,
deleted bases shift the
chain back one base
• Enzyme checkers make
sure deletions happen
very infrequently
Viruses…living or non-living? This
is a good question!!
• Don’t contain any of the 5
properties of living organisms
• Do contain genes and have
structure
• Must insert their own DNA
into another cell’s DNA
before it can replicate
• Then each time a cell
replicates by mitosis, it also
replicates the virus
• In order to eliminate the
virus, you must eliminate
each cell infected by it
• Plants and animals are
susceptible to viral infections
Occassionally a virus can be used
for a good reason.
• Viral vectors can be used to carry desirable
DNA into cells that lack it.
• Example is the DNA for breaking down mucus
lacking in people who have Cystic Fibrosis
• DNA for human insulin has also been
transferred this way to create insulin made in
the lab instead of taken from slaughtered cattle
and pig pancreases
• This helps lessen the chances of allergic
reactions to the insulin
Recombinant DNA Technology allows
us to create unique organisms.
• Many products we depend on
today are created by mixing
DNA from one or more
organisms together.
• Insulin, vaccine for hepatitis B,
human growth hormone, EPO
protein to treat anemia
• Many “GM” crops are
produced this way
• Corn, soybeans, alfalfa, wheat,
oats, rice with beta-carotene,
potatoes with edible vaccine,
strawberries with antifreeze
FORENSIC SCIENCE AND DNA
• DNA fingerprinting common in solving many types of
crime cases
• Some involve paternity or maternity, others involve
murder or kidnapping or burglarly, etc.
• Any cells with DNA left by a criminal can have DNA
extracted from them for testing
• Sometimes use mitochondrial DNA instead of nuclear
DNA (chloroplasts contain DNA, too, incase a plant
ever becomes a murder!!!)
• Order of bases for individuals will be unique
• Also used in verifying species claims on food products
(caviar from specific fish)
• Helps in identification of fossils, bones and pieces of
organisms