DNA: Structure and Replication Ch9

Learning Goal Students will have a clear understanding of the structure of DNA, how genetic information is stored and how DNA replicates itself. When asked, a student will be able to describe and detail each step of DNA replication.

1 Students do not understand much of DNA, or replication if anything at all.

2 Students understand the basics of the structure of DNA but do not understand how information is stored or how replication works

3 Students understand the structure of DNA and how information is stored and how replication works as a whole

4 Students understand DNA, how info is stored, and all the specifics of DNA replication.

“A genetic material must carry out two jobs: duplicate itself and control the development of the rest of the cell in a specific way.” -Francis Crick

Wikipedia Type in DNA repair-deficiency disorder Tell me what the different disorders cause.

What do you Remember? What do you know about DNA? How does it relate to chromosomes? Spool

DNA is highly packaged. Bacterial cell exploding with DNA See Long sheet

So, how does one go about it? How is it we discovered the function of something that is so tiny? Cells are microscopic and it took us long enough to discover them. How do we find something so tiny it fits in a tiny portion of a cell?!

Many Scientists build on Each other Friedrich Miescher, 1871 Isolated white blood cell nuclei from pus Found an acid substance with nitrogen and phosphorus He called it “Nuclein,” later called nucleic acid

Next Archibald Garrod, 1902 Linked inheritance of “inborn errors of metabolism” with the lack of particular enzyme proteins Alkaptonuria(can’t break down tyrosine) Hm..is it possible proteins are the genetic material?

Next.. Frederick Griffith, 1928 This is the first scientist that took the first step in identifying DNA as the genetic material. He noticed that mice with a certain type of pneumonia had one of two types of Diplococcus pneumoniae bacteria- rough or smooth.

Rough Vs. Smooth Rough Type Mice injected with type R bacteria did not develop pneumonia. Smooth Type Smooth because they are enclosed in a sugar capsule. Mice injected with smooth developed pneumonia.

Type S and R When Smooth was heated, it killed the pnemonia, but left the DNA intact and they no longer produced pneumonia in mice.

BUT When Griffith injected mice with a mixture of type R plus heat killed type S, neither which was deadly, the mice died of pneumonia. When he cultured, they contained live type S bacteria. WHAT?! Griffith termed this “transformation” https://www.youtube.com/watch?v=4LU71ubTCZA

pg173

“The transforming Principle” Avery, MacLeod, and McCarty, 1944 To test whether protein or DNA was genetic material… Treated type R bacteria with protease and DNase DNase prevented transformation Therefore DNA is the transforming principle, not protein

And next..DNA is genetic Material Alfred Hershey and Martha Chase, 1953 They actually radioactively tagged certain areas of viruses to see WHAT is being transmitted. They tagged the Protein Coat, and the Viral DNA

Hershey-Chase Experiment Look in your book pg 174 YOU tell ME what this says?

Video Time! Discovery Streaming (6min)

The Structure of DNA(note out of order!) Levine, 1929 Identified the sugar, ribose 1929, identified deoxyribose Three parts of a nucleotide Sugar Phosphate Base

Deoxyribonucleic Acid (DNA ) Subunits are deoxyribonucleotides Composed of: ( coloring time!!!) Sugar - deoxyribose Phosphate group Base - one of four types: adenine (A), thymine (T) guanine (G), cytosine (C)

DNA Deoxyribose. Ose=sugar Phosphate Bases G, A, C & T

Main two pieces of evidence of structure: 1)DNA base Pairs 1952 Erwin Chargaff observed: Within an individual there were equal amounts of base pairs. Adenine = Thymine (equal amounts of) Guanine = Cytosine(equal amounts of) Because Complementary bases pair by hydrogen bonds: A with T Gwith C I remember AT the Genetics Council

2nd major piece of evidence of structure:helix shape Maurice Wilkins and Rosalind Franklin Franklin spent 100 hours just trying to capture this picture. The clue from photo 51 X-ray diffraction indicated DNA is a helix She understood it was a helix. The X indicates a helix and the darkened regions reveal symmetrically organized subunits

But guess what? Grr. Wilkins showed Rosalind’s picture to James Watson behind her back. And the race was on. And guess who won? And guess who doesn’t receive the credit?

Watson and Crick’s Model of DNA A sugar and phosphate “backbone” Two nucleotide chains in a helix. Hydrogen bonds hold the two strands together DNA strands are antiparallel

Runs 5’ to 3’

Movie time After Movie,(6min) Practice. Guided DNA molecule. Worksheet. OR beads(depending)

RECAP!!! What did Griffith Do? What did Hershey/Chase do? What about Rosalind Franklin? Watson and Crick?

Anti-parallel-Sugars point in opposite directions(anti-parallel) Note: Configuration of reading top to bottom and bottom to top have sugars pointing opposite directions, making them antiparallel. Opposing directions=antiparallel

Orientation of DNA 3’ 5’ The 5’ and 3’ hydroxyl groups attach phosphate groups The directionality of a DNA strand is due to the orientation of the phosphate-sugar backbone and the CARBON # in the sugar. Um. Why 5’ to 3’? Flip to pg. 178. The carbons are numbered 1-5. On the left, the sugar orientation presents so that 5’ is at top, and 3’ at the bottom of the sugar molecule. On the right, however, it is rotated, so 3’ is at top, and 5’ is at the bottom. Check it out! Flip the book upside down. 5’ 3’

Molecular Definition of a Gene A gene is a segment of DNA (spool of thread) It directs the formation of RNA to produce protein (in other words, a gene instructs how to produce a protein) The protein (or functional RNA) creates the phenotype(huh? The gene produces the protein, the protein creates what you are going to see) Information is conveyed by the sequence of the nucleotides (Ever hear of binary? Or even written language. Different patterns mean different words)

Chromatin Yesterday, I got the question “so HOW does DNA fit into such a tiny space?” I responded by tight packaging. And this is how it does it… Chromatin is Composed of DNA and associated proteins DNA winds around histone proteins (these are called nucleosomes) Other proteins wind DNA more tightly to form a chromosome During mitosis, replication and mRNA production DNA is unwound

Pg 179 Spool thread around my finger!

Replication What comes to mind when I say Replication? When does Replication occur in mitosis?

DNA replication Production of new copies of the DNA molecules occurs in interphase prior to cell division

Replication..the hows Double-stranded DNA unwinds. Flip to pg 182 in your book. Double-stranded DNA unwinds. The junction of the unwound molecules is a replication fork. A new strand is formed by pairing complementary bases with the old strand. Two molecules are made. Semi Conservative Replication-Each has one new and one old DNA strand Two sister chromatids are formed

Enzymes in DNA replication Flip to pg 182 in your books! Demo(as we go through following slides)

1st-3rd steps in replication 1)Helicase protein binds to DNA sequences called origins and unwinds DNA strands. For all you nurses..helicase is like cracking a chest open. It allows access. 2) Binding proteins hold the strands open(like those large spreaders to hold the chest cavity open) 3)Primase makes a short stretch of RNA to get the replication happening. Start replicating here! Primase=primer, get it?

4th and 5th step in replication DNA polymerase does two things, it 4)adds DNA nucleotides to the RNA primer and and 5)replaces incorrect nucleotides What is a nucleotide? (one section of sugar, and?)

6th and 7th Steps in replication ALWAYS creates new bases in a 5’ to 3’ direction Discontinuous synthesis produces (aka, screws up!)5’ to 3’ DNA segments called Okazaki fragments

And LASTLY 7)Exonuclease enzymes remove RNA primers 8)Ligase forms bonds between sugar-phosphate backbone And Ligase also joins Okazaki fragments and seals other nicks.(it’s the epoxy or spackle of the DNA world)

*yawn* long story short DNA unwinds, breaks, builds a new chain then mends, and voila, two new chains.

And now its time for.. Da da da da! DNA worksheet DNA movie