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About how many cells are our bodies made of?

About how many cells are our bodies made of?. TRILLIONS! How many of those cells contain your DNA? All of them! All of your cells contain a complete copy of your genome (DNA)!. Your life started as just 1 cell. How do we come from 1 cell & end up as trillions?.

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About how many cells are our bodies made of?

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  1. About how many cells are our bodies made of? TRILLIONS! How many of those cells contain your DNA? All of them! All of your cells contain a complete copy of your genome (DNA)!

  2. Your life started as just 1 cell. How do we come from 1 cell & end up as trillions? That 1 cell divided over & over again as you grew! All of those new cells need copies of your DNA, right? HOW DOES THAT WORK?

  3. DNA Replication

  4. Remember! • In April 1953, James Watson & Francis Crick discovered the double-helical structure of DNA. • Your genetic endowment is the DNA you inherited from your parents. • Nucleic acids are unique in their ability to direct their own replication! • The resemblance of offspring to their parents depends on the precise replication of DNA & its transmission from 1 generation to the next!

  5. How is DNA copied? • DNA Replication: the process of copying DNA • Because DNA is double stranded, we can separate the 2 strands & create a new strand using 1 strand as a template. • Our end product is 2 identical double stranded DNA molecules! • The 2 strands are called complementary!

  6. During DNA Replication: • DNA is unwound & unzipped by the enzyme Helicase. • The strands are held apart by single-stranded binding proteins (ssbps).

  7. New DNA strand New DNA strand During DNA Replication 2. Each original DNA strand is used as a template (model) to make a new DNA strand with base pairing.

  8. During DNA Replication 3. The enzyme Primase lays down an RNA Primer a few base pairs long to which the new DNA can be added.

  9. During DNA Replication 4. Another enzyme, DNA Polymerase, adds new nucleotides to the RNA Primer.

  10. DNA Polymerase always reads 3’-5’ & synthesizes the new strand from 5’-3’. This occurs in the direction following Helicase, which is opening up the replication fork. For this reason, the new strand is called the leading strand.

  11. 5. Another DNA Polymerase also proofreads the new DNA to check for errors. 6. Meanwhile, on the other strand, the lagging strand, Primase & DNA Polymerase synthesize DNA from 5’-3’ away from the replication fork. • These small spurts of replication form what are known as Okazaki Fragments.

  12. DNA Polymerase only works in 1 direction! One strand is read & synthesized continuously while the other is synthesized in fragments!

  13. During DNA Replication 7. The Okazaki Fragments are joined together by the enzyme Ligase. 8. On both strands, the RNA Primer is replaced with DNA nucleotides by DNA Polymerase.

  14. When replication is complete, each DNA molecule is made of 1 old strand & 1 new strand (the semi-conservative model of replication).

  15. During DNA Replication 9. The new DNA molecules are rewound by the enzyme Gyrase.

  16. Chromosome Arrangement – Prokaryotic Cells (Bacteria) • Prokaryotic cells have 1 circular chromosome that is free-floating in the cytoplasm. • Remember! Prokaryotic cells do not have a nucleus! • When prokaryotic cells copy their DNA, the process begins at 1 point in the chromosome & moves around the circle in both directions until complete.

  17. Chromosome Arrangement – Eukaryotic Cells • Eukaryotic cells have more chromosomes than prokaryotic cells & DNA Replication begins at hundreds of places & continues in both directions until each chromosome is completely copied!

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