reproducesgenetic continuity  When a species reproduces, there is genetic continuity that is maintained from one generation to the next.  WHAT  WHAT is responsible for this continuity?  HOW  HOW does this continuity happen?

ALL organisms  Genetic material present in ALL organisms nucleus  Usually found within the nucleus  Different  Different for each individual within a species DeoxyriboNucleic Acid  DNA = DeoxyriboNucleic Acid NUCLEOTIDE  Polymer made of repeating NUCLEOTIDE monomers

 A molecule made of the following 3 parts: sugar groupdeoxyribose  1. a 5-Carbon sugar group (deoxyribose) phosphate group  2. a phosphate group nitrogen base  3. a nitrogen base – 4 different possibilities! (5 Carbon sugar)

A  Adenine (A) G  Guanine (G)  Purines (2 carbon rings) C  Cytosine (C) T  Thymine (T)  Pyrimidines (1 carbon ring) arrangement so unique  It is the arrangement of these 4 different nucleotides that allows DNA to be so unique!

 Adenine Thymine  Adenine ALWAYS pairs with Thymine double (double bond)  Cytosine Guanine  Cytosine ALWAYS pairs with Guanine triple (triple bond) To Help you Remember: AT C-G

structure of DNA  2 Scientists credited with discovering the structure of DNA in 1953: Watson CrickWatson & Crick  James Watson & Francis Crick (Watson & Crick) DOUBLE HELIX  Watson & Crick Model of structure = DOUBLE HELIX 1962  They received the Nobel Prize (Medicine) in 1962

Rosalind Franklin  The key to Watson and Crick’s discovery was an X-ray diffraction image (known as Photo 51) of DNA recorded by Rosalind Franklin without her permission  Both the image and Franklin’s interpretation of the image were shown to Watson without her permission  Watson, Crick, and Wilkins (the man who gave Watson the image) received the Nobel Prize ▪ Franklin had died 4 years earlier

 Characteristics: DOUBLE  1. DOUBLE stranded molecule phosphate & sugar backbone  2. phosphate & sugar portion of nucleotides form the “backbone” of each strand HYDROGEN BOND  3. Nitrogen base of one strand forms a HYDROGEN BOND with the nitrogen base of a second strand twisted ladder  4. In 3-Dimensional space, it forms a “twisted ladder” (spiral staircase)

make a copy of itself genetic continuity  DNA must be able to make a copy of itself in order for genetic material to be passed on to the next generation and to preserve genetic continuity.  DNA Replication DNA Replication 4 basic steps.  This replication process occurs in 4 basic steps.

HELICASE Unzips the ladder  Step 1 – HELICASE (an enzyme) cause the hydrogen bonds between the nitrogen bases to break (“Unzips the ladder”) DNA POLYMERASE matching up the complimentary nucleotide  Step 2 – DNA POLYMERASE (another enzyme!) is responsible for reading the DNA template and matching up the complimentary nucleotide from the free floating nucleotides present in the nucleus

Base pairshydrogen bonds phosphate group bonds with the sugar backbone  Step 3 – Base pairs form hydrogen bonds and the phosphate group of one nucleotide bonds with the sugar of another to form the “backbone” 2 new strands  Step 4 – Bonding continues along the strands until 2 new strands are formed 2 new EXACT copies of the  RESULT = 2 new EXACT copies of the original DNA molecule! original DNA molecule!

Pink = parent strand Blue = daughter strands

 DNA Replication Simulation DNA Replication Simulation