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DNA.

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Presentation on theme: "DNA."— Presentation transcript:

1 DNA

2 DNA D= Deoxyribose Sugar NA= Nucleic Acid DEOXYRIBONUCLEIC ACID

3 DNA The material that contains information that determines inherited characteristics

4 DNA Shaped like a double helix A spiral staircase structure

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6 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

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9 Nitrogen Bases Adenine Thymine Cytosine Guanine

10 Nitrogen bases Purines: double ring Pyrimidine: Single ring

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

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

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14 EXAMPLE TATGGAGAGTC ATA

15 EXAMPLE TATGGAGAGTC ATACCT

16 EXAMPLE TATGGAGAGTC ATACCTCTC

17 EXAMPLE TATGGAGAGTC ATACCTCTCAG

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

19 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

20 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

21 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

22 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

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25 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

26 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


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