CHAPTER 9 SECTIONS 2 & 3

Stores and passes on genetic information from one generation to another. Sugar: deoxyribose DNA Deoxyribonucleic acid

DNA STRUCTURE Shaped like a spiral staircase, or twisted ladder. Double Helix

DNA – Scientists who mapped its structure Chargaff’s 1949 Observations: The amount of adenine always equaled the amount of thymine (A = T) The amount of cytosine always equaled the amount of guanine (C = G)

DNA – Scientists who mapped its structure Wilkins & Franklin’s Photographs Using x-ray diffraction, in 1952 Developed high-quality photographs of strands of DNA Suggested that DNA was a tightly coiled helix with 2 or 3 strands of nucleotides

DNA – Scientists who mapped its structure Watson & Crick’s 3-D DNA model in 1953 “Watson & Crick, took a stick and built the DNA model.”

DNA STRUCTURE The outer parts of the ladder are made of: a sugar (deoxyribose) + a phosphate.

DNA STRUCTURE The rungs (steps) of the ladder are pairs of nitrogen bases… …held together with weak hydrogen bonds.

DNA STRUCTURE 1.ADENINE = A 2.GUANINE = G 3.CYTOSINE = C 4.THYMINE = T They are represented by their capital letter.

Base Pair Bonding Rules A DENINE WITH T HYMINE (“Stick” Family) T & A C YTOSINE WITH G UANINE (“Curve” Family) C & G

DNA STRUCTURE QUESTION ? CAN T JOIN WITH A AND G JOIN WITH C YES NO

CORRECT MOVE ON

SORRY REVIEW MORE

DNA STRUCTURE ACTCATGGTCATG TGAGTACCAGTAC This is an example of a genetic code that may be found in your body.

DNA STRUCTURE The combinations of the nitrogen bases is the code that produces the genes for a particular trait.

DNA STRUCTURE Because there can be so many different combinations of the bases, the code can be limitless

DNA STRUCTURE EXAMPLE: ATCGTCAGG May be for hair color. BUT ATCGTCAGC May be for eye color

Stop Begin DNA Model

DNA Replication Replication: to make anReplication: to make an identical copy of identical copy of Occurs during the “S” phase of the cell cycle. (Just before mitosis)

DNA Replication Also known as: Semi-Conservative Replication – –semi: half – –Conserve: to save or reuse – –Replicate: to copy exactly

Semi-conservative Replication To reuse half of the original DNA strand to make an exact copyTo reuse half of the original DNA strand to make an exact copy

DNA REPLICATION 1.DNA Ladder Splits (unzips) enzyme DNA helicase

2.Free floating nitrogen bases begin to pair on each strand Attached by the enzyme DNA polymerase (the glue) Semi-conservative Replication

Semi-conservative Replication (attaching bases)

3. Two new identical DNA chains are formed Semi-conservative Replication

DNA REPLICATION

FYI Each human chromosome is replicated in about 100 sections that are 100,000 nucleotides long. An entire human chromosome can be replicated in about 8 hours!

hill.com/sites/ /student_view0/chapter1 4/animations.html# DNA Animation View “DNA Replication Fork”