We are starting our DNA Unit Today! Please do the following: pick up handouts have out your notebook

In 1952, Alfred Hershey and Martha Chase, proved that the DNA of a virus is injected into the bacterial cells. That then causes the bacterial cells to produce more viral DNA and proteins. 3 Radioactive 32 P was injected into bacteria!

Nucleus

A T G C

DNA’s two strands run antiparallel 3’-5’ & 5’-3’

Photo by Brocken Inaglory Photo by Infrogmation

Human Chromosomes

Chromosomes come in pairs, and there are hundreds, sometimes thousands, of genes in one chromosome. There are 46 chromosomes in each human cell. Except for gametes (egg and sperm) which have

ATCCATTGGACGA What is the complimentary strand according to the base pairing rules? ATCCATTGGACGA

Pyrimidines are single ring bases; thymine and cytosine Purines are double ring bases; adenine and guanine The complimentary bases are held together by weak hydrogen bonds. G C TA

DNA Replication - Why Replicate? Remember: ALL cells need genetic material….DNA! So….before a cell can divide & make a new cell (a daughter cell), the DNA must be replicated (copied). If a cell doesn’t get a copy of DNA, it is USELESS and essentially DEAD!

DNA Replication DNA → DNA (copy) DNA is a HUGE molecule, in fact it is so HUGE it cannot exit the nucleus EVER ! Sooo… DNA Replication occurs in the NUCLEUS!

3 EASY STEPS STEP 1: ◦DNA Unzips ◦DNA Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds 5’ 3’

STEP 1: ◦DNA Unzips ◦DNA Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds 3 EASY STEPS

STEP 1: ◦DNA Unzips ◦DNA Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds 3 EASY STEPS

STEP 1: ◦DNA Unzips ◦DNA Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds 3 EASY STEPS

STEP 1: ◦DNA Unzips ◦DNA Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds 3 EASY STEPS

Replication Fork The areas where the double helix separates are called replication forks because of their Y shape. Once the 2 strands are separated, additional proteins attach to each strand, holding them apart. 34

STEP 2: ◦Complimentary Base Pairing ◦DNA Polymerase adds matching nucleotides 5’ 3’ 3 EASY STEPS

5’ 3’ 3 EASY STEPS STEP 2: ◦Complimentary Base Pairing ◦DNA Polymerase adds matching nucleotides

5’ 3’ STEP 2: ◦Complimentary Base Pairing ◦DNA Polymerase adds matching nucleotides 3 EASY STEPS

5’ 3’ 3 EASY STEPS STEP 2: ◦Complimentary Base Pairing ◦DNA Polymerase adds matching nucleotides

5’ 3’ 3 EASY STEPS STEP 2: ◦Complimentary Base Pairing ◦DNA Polymerase adds matching nucleotides

5’ 3’ 3 EASY STEPS STEP 2: ◦Complimentary Base Pairing ◦DNA Polymerase adds matching nucleotides

5’ 3’ 3 EASY STEPS STEP 2: ◦Complimentary Base Pairing ◦DNA Polymerase adds matching nucleotides

5’ 3’ 3 EASY STEPS STEP 2: ◦Complimentary Base Pairing ◦DNA Polymerase adds matching nucleotides

5’ 3’ 3 EASY STEPS STEP 2: ◦Complimentary Base Pairing ◦DNA Polymerase adds matching nucleotides

5’ 3’ 3 EASY STEPS STEP 2: ◦Complimentary Base Pairing ◦DNA Polymerase adds matching nucleotides

5’ 3’ 3 EASY STEPS STEP 2: ◦Complimentary Base Pairing ◦DNA Polymerase adds matching nucleotides

5’ 3’ 5’ 3’5’ 3’ 3 EASY STEPS STEP 2: ◦Complimentary Base Pairing ◦DNA Polymerase adds matching nucleotides

STEP 3: ◦DNA Ligase Rezips DNA 5’ 3’ 5’ 3’5’ 3’ 3 EASY STEPS

DNA REPLICATED! Two IDENTICAL copies of DNA; one copy goes into each new cell Blue – Original DNA Green – New DNA DNA replication is a semi-conservative process; there is not 1 new set and 1 old set. Each set of DNA contains 1 old strand and 1 new strand. 5’ 3’ 5’ 3’5’ 3’

Checking for Errors  Errors sometimes occur and the wrong nucleotide is added to the new strand.  An important feature of DNA replication is that DNA polymerases have a “proofreading” role.  It can backtrack to remove the incorrect nucleotide.  Reduces errors in DNA replication to about one error per 1 billion nucleotides. 49