Transcript forensic science

DNA & RNA
The Nucleic Acids
Remember: Each chromosome is a very long DNA
molecule that contains many genes. The DNA controls
the production of proteins within a cell.
Gene: A segment of DNA that is part of a chromosome
that is responsible for inherited traits such as eye
color, hair color, skin color, etc.
It directs the protein production that controls the cell.
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DNA: (Deoxyribonucleic Acid):
•Is an organic molecule composed of nucleotides.
•Is a molecule that is common to all living things,
from bacteria to humans.
•It is the blueprint of an organism; DNA is made of
chains of nucleotides shaped much like that of a
spiraling ladder, and they called it a double helix.
•A DNA molecule can NOT be viewed with a
compound light microscope.
•In 1953, Watson and Crick constructed the first
model of DNA, and they called it a double helix.
•Rosalind Franklin-used x-ray diffraction to
determine that a chromosome has DNA in a
spiraled shape.
Structure of DNA: (DNA is composed of
nucleotides.)
Nucleotides of DNA have three Parts:
1. Deoxyribose (a five carbon sugar)
2. Phosphate group
(these two bond together to make up the sides of the ladder)
3. 1 of 4 Nitrogen Bases
Adenine (A)
Guanine (G) *These hydrogen, weak, bonds together
Cytosine (C) form the rungs of the ladder.
Thymine (T)
The 2 bases on the same rung of the DNA ladder are
referred to as a base pair.
In DNA
Cytosine always bonds with guanine, and
Thymine always bonds with adenine!
C=G
G=C
T=A
A=T
•Base Pairing Rules. The strictness of base-pairing
results in 2 strands that are complementary, which
means the sequence of bases on one strand
determines the sequence of bases on the other strand.
Example:
1st strand of DNA has
T C GAAT T
The other strand must have
AG C T TAA
•All organisms contain chromosomes composed of
DNA made up of nucleotides with adenine, thymine,
guanine, and cytosine.
•The reason organisms can be different from each other
even though their genetic material is made of the same
molecules is because the order of nucleotides in two
different organisms are different.
•It is the sequence of nucleotides that forms the genetic
information of an organism.
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•How can organisms be different from each other if their
genetic material is made of the same DNA: A, T, C, G?
•They are the different because the order of nucleotides
in the 2 organisms is different.
Example: A squirrel differs from a rosebush because the
order of nucleotides in its DNA is different.
Replication:
During mitosis and meiosis the cells divide. Each time a
cell divides it must make a copy of its DNA. Replication is
the process by which DNA is duplicated, forming two
identical copies from one original.
These are the steps of replication:
1. The enzyme helicase, in DNA breaks the hydrogen
bonds between the nitrogen bases that hold the two
strands together, unzipping the DNA molecule.
2. As the DNA continues to unzip, free nucleotides
from the surroundings in the nucleus bond to the
single strands base pairing by DNA polymerase.
3. The enzyme ligase forms the sugar-to-phosphate
bonds that connect nucleotides on each strand of
DNA. It also adds hydrogen bonds between
nitrogen-bases & “zips” the strand back up.
4. Since DNA polymerase adds the free nucleotides, it
also acts as a spell-checker. Errors occur once for
every billion nucleotides due to DNA Polymerase
Replication of DNA
doesn’t begin at one
end of the molecule and
proceed to the other. It
occurs simultaneously
at many points on the
molecule, speeding up
to process. Replication
is completed when the
entire molecule has
been unzipped and
replicated.
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Each new DNA molecule
has one nucleotide strand
from the original DNA
molecule (template) and one
nucleotide strand that has
been newly synthesized
(complementary strand)
from free nucleotides in
the cell.