What does DNA look like DNA has A

What does DNA look like? • DNA has. . • A sugar/phosphate backbone • 4 Chemical bases Sugar

The bases • It is composed of 4 chemical bases: Adenosine (A), Thymine (T), Cytosine (C) and Guanine (G). • A always pairs with T • C always pairs with G • The pairs are held together by hydrogen bonds (WNC’s).

What does DNA do? • DNA is the genetic code. • It determines our physical characteristics: from our hair color to what we are allergic to. • Our DNA codes for 20 amino acids which are the building blocks of life.

What Is DNA Replication • DNA Replication is the process in which the DNA within a cell makes an exact copy of itself. – Why does DNA replicate? – During which phase of the cell cycle does DNA replicate?

DNA Replication models

The Three Possible DNA Replication Models • Conservative- would leave the original strand intact and copy it. • Dispersive-would produce two DNA molecule with sections of both old and new along each strand. • Semiconservative –would produce DNA molecule with both one old strand one new strand.

DNA Replication occurs during Interphase Replication fork Replication bubble Hydrogen bond DNA replication is the process where an entire double-stranded DNA is copied to produce a second, identical DNA double helix.

DNA Replication DNA helicase • Helicase unwinds the double helix starting at a replication bubble. • The two strands separate as the hydrogen bonds between base pairs are broken. • Two replication forks form and the DNA is unwound in opposite directions.

DNA Replication • Helicase has completed unwinding the DNA strand. • Single strand Binding Proteins (SSB) keep the two strands from re-annealing (coming back together).

DNA Replication Leading Strand Primase RNA Primer Lagging Strand • Primase is an RNA polymerase that makes the RNA primer. • These primers “tell” the DNA polymerase where to start copying the DNA.

DNA Replication Leading Strand 5’ 3’ Direction of Replication DNA Polymerase 5’ Direction of Replication Lagging Strand 3’ • The DNA polymerase starts at the 3’ end of the RNA primer of the leading stand CONTINUOUSLY. • DNA is copied in 5’ to 3’ direction. • DNA polymerase copies the lagging strand DIS- continuously.

DNA Replication • The dis-continuous pieces of DNA copied on the lagging strand are known as Okazaki fragments.

DNA Replication Another DNA Polymerase removes the RNA primers and replaces them with DNA.

DNA Replication ligase Finally the gaps in the sugar phosphate backbone are sealed by DNA ligase There are now 2 identical double helices of DNA.

DNA Replication ANIMATION • http: //www. wiley. com/college/pratt/047139 3878/student/animations/dna_replication/in dex. html