DNA

DNA D= Deoxyribose Sugar NA= Nucleic Acid DEOXYRIBONUCLEIC ACID

DNA The material that contains information that determines inherited characteristics

DNA Shaped like a double helix A spiral staircase structure

NUCLEOTIDES DNA is made of repeating subunits called nucleotides Contains 3 parts 1. Phosphate 2. Sugar (deoxyribose) 3. Base (A,T,G,C) Held together by hydrogen bonds

Nitrogen Bases Adenine Thymine Cytosine Guanine

Nitrogen bases Purines: double ring Pyrimidine: Single ring

Nitrogen bases Purines = Adenine and Guanine Pyrimidine = Thymine and Cytosine

BASE PAIRING One purine always pairs up with one pyrimidine Adenine pairs with Thymine Guanine pairs with Cytosine

EXAMPLE TATGGAGAGTC ATA

EXAMPLE TATGGAGAGTC ATACCT

EXAMPLE TATGGAGAGTC ATACCTCTC

EXAMPLE TATGGAGAGTC ATACCTCTCAG

DNA REPLICATION The process of making a copy of DNA Occurs during the synthesis (S) phase of the cell cycle

Why is Replication Important? It provides copies of genetic material for the new cell If replication did not take place, the new cells would have half as much DNA as the parent cell

REPLICATION STEPS 1. Double helix unwinds Hydrogen bonds are broken by enzymes called DNA helicases The areas where the double helix separates are called replication forks

REPLICATION STEPS 2. Nucleotides are added DNA polymerase (enzyme) moves along each strand of DNA at the replication fork DNA polymerase add the nucleotides to the nitrogen bases according to the base pair ruling Two new double helixes are formed

REPLICATION STEPS 3. New strands are formed DNA polymerase continues working until the DNA has been copied and it is signaled to stop Two DNA strands are produced which include an original and a new strand The nucleotide sequences are identical to each other and to the original DNA molecule

CHECKING FOR ERRORS DNA polymerases “proof read” the new strands If there is a mistake, the DNA polymerase backtracks and removes the incorrect nucleotide A correct nucleotide is then added

Rate of Replication If there were only one replication fork in eukaryotic cells, it would take 33 days to copy the DNA strand Human chromosomes are replicated in about 100 sections An entire Human chromosome can be replicated in about 8 hours