Download Genes, Chromosomes, and DNA

DNA Replication
DNA Length
• DNA molecules are surprisingly
long.
• The nucleus of a human cell
contains more than 1 meter of
DNA.
• DNA must be folded and coiled in
order to fit in such a small space.
Structure of Chromosomes
• Chromosomes are made up of
chromatin.
– Chromatin is DNA tightly coiled
around proteins called histones.
– DNA and histone molecules form
packets called nucleosomes, which
fold enormous lengths of DNA into
tiny spaces.
DNA Replication
• DNA is a double helix (two
strands wound around each
other).
• Each strand has ALL the info
needed to reconstruct the
other half by the mechanism
of base pairing.
Base Pairing
• If you separate the two strands, the
rules of base pairing allow you to
reconstruct the sequence of the other
strand.
• A=T
• G=C
• Before mitosis (cell division), the cell
duplicates its DNA in a process called
replication.
DNA Replication
• During DNA replication:
– The DNA molecule separates into 2
strands.
– 2 new complementary strands are
produced following the rules of base
pairing.
• Each strand of the double helix of
DNA serves as a template for the
new strand.
How DNA Is Replicated
• DNA replication is carried out by
a series of enzymes.
• The enzymes “unzip” (separate
the strands) of a molecule of
DNA.
• The unzipping occurs when the
hydrogen bonds between the
base pairs are broken.
How DNA Is Replicated
• Each strand serves as a template for
the attachment of complimentary
bases.
– Example: TACGTT produces
ATGCAA (complimentary)
• Each DNA molecule resulting from
replication has one original strand and
one new strand.
Enzymes in DNA Replication
• The principle enzyme involved in DNA
replication is called DNA polymerase.
• It attaches (or polymerizes) individual
nucleotides to produce DNA.
• DNA polymerase also “proof-reads”
each new DNA strand, helping to
maximize the odds that each molecule
is a perfect copy of the original DNA.