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DNA
Life’s Instruction Manual
or
What Genes are Made Of
What can DNA do?
• 1. Can replicate before cell division.
Remember MEIOSIS and MITOSIS,
chromosomes need to replicate before
they divide
• 2. Can direct protein synthesis. It tells the
RIBOSOME to make a protein.
Why is the DNA the genetic material
• DNA doubles prior to cell division (mitosis)
• DNA divides equally between daughter
cells
• A body cell has 2X the
amount of DNA as a
gamete(egg or sperm)
Discovery of DNA
• 1952 Rosalind Franklin-studies DNA
molecule using x-ray diffraction
• 1953 Watson and Crick- develop double
helix model
The Shape of the DNA Molecule
• DNA is a complex organic molecule with a
double helix shape. (a twisted ladder)
• It consists of 2 phosphate-sugar
backbones connected by a series of
nucleotide bases. (colored letters)
DNA Nucleotide Bases
•
•
•
•
•
Adenine A
Thymine T
Guanine G
Cytosine C
These bases are joined together in a
specific way…
• A with T
G with C
• We call this base pairing.
DNA Structure
DNA Replication
• The bonds between the base pairs are
weak hydrogen bonds and can be broken
easily. This means that the molecule can
unwind and unzip itself.
• Each side of the DNA molecule has all the
information necessary to make a
complementary (second) side.
• Each piece of “old” DNA will act as a
template for a “new” piece of DNA.
DNA Copies Itself!!
• Because of base pairing,
each strand of DNA can
replicate itself making
two new strands of DNA.
• It uses extra nucleotide
bases (in cell) to create
this copy.
• All of the work of DNA
replication is done by
enzymes!!
• The main enzyme is
called DNA polymerase
Semi-Conservative Replication
• The result is that each
new copy of DNA
produced by this
process is made up of
½ original DNA
molecule and ½ new
DNA molecule. This
makes the process
semi-conservative.
RNA
• RNA is a nucleic acid like DNA
• RNA is single stranded.
• RNA does not contain thymine but
instead has the base called uricil which
bonds with adenine.
• RNA has many functions in the cell, most
importantly it is critical in the process of
protein synthesis
Mutations
• What happens when a mistake is made in
replication of DNA?
• Most mutations are NOT helpful!! But every so
often, a beneficial mutation occurs (black moths)
Types of Mutations
Point Mutations – the change in one single
nucleotide base.
substitution – one letter replaces another
in the sequence. (ex. A->G)
insertion – one letter is added to the
sequence. (ex. a new T is added)
deletion – one letter is removed from the
sequence. (ex. a G is removed)
• Make a substitution in the following DNA
ATTGCGTGTG
ATTACGTGTG
Make an insertion in the original sequence
ATTGCGATGTG
Make a deletion in the original sequence
ATGCGTGTG
Larger Mutations
• Inversions – when 2 or more bases
(letters) are switched into reverse order.
• Duplications – when bases are repeated in
the original order more than one time.
• Translocations – when bases are moved
from one area of the sequence to another.
DNA
Mutations
• Sometimes mistakes can be made in the
copying process of DNA. Any change in
the original sequence of base pairs is
called a mutation.
Protein Synthesis
The Central Dogma
• DNA holds the CODE to make Proteins
• RNA transfers the CODE to the Ribosome
• Proteins are strings of amino acids coded
for by DNA
• Proteins are the “workhorses” of the cell
Structure, enzymes, communication, etc.
Transcription
• The DNA
message is
transcribed into
an mRNA
message by
complementary
base pairing
Translation
• The mRNA then
goes into the
cytoplasm to give
the code for a
protein to the
ribosome. tRNA
molecules will
bring the correct
amino acid to the
ribosome.
DNA