DNA Replication DNA Length DNA molecules are surprisingly

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 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.