Chromosomes and DNA Replication

1. Chromosomes and DNA Replication

2. What We Will Be Covering • DNA and Chromosomes • Length and Structure • DNA Replication

3. DNA and Chromosomes • DNA is stored as chromosomes • Chromosomes are organized structures of DNA that contain large numbers of nucleotides • Large numbers of nucleotides that are expressed are often called genes

4. DNA and Chromosomes • DNA can be extremely long • A chromosome for an E. coli bacterium living in your gut is 4,639,221 base pairs

5. DNA and Chromosomes • The E. Coli DNA when stretched out would be 1.6 centimeters • The bacteria is only 1.6 micrometers • That is one thousand times smaller than the DNA • It is like fitting a 300m rope into your backpack

6. DNA and Chromosomes • Eukaryotic cells contain even more DNA • Humans contain about a meter of DNA per cell • In order to fit DNA into a cell, it must be coiled

7. DNA and Chromosomes • Eukaryotic chromosomes pack DNA and Protein together • It is called chromatin • Chromatin consists of DNA tightly coiled around proteins called histones

8. DNA and Chromosomes • By coiling the DNA around histones, it decreases its overall length • Histones are then coiled

9. Copying Information • What happens when you make a hand drawn copy of a picture? • Is it then really the same image?

10. Demo • Try this… • Have one partner sit facing the blackboard, one sit facing the opposite direction • The partner that faces the direction of the board will describe and the other partner will draw

12. Now Switch

13. Copying Information • What happens when you put a piece of paper in a copier? • Can you then copy the copy? • Does DNA need to be exactly copied in order to give the same information?

14. Copying Information • DNA can be easily copied based on its structure • If you split DNA in half, you can easily tell what the other half should look like

15. Review • Base pairs match up to only one other base pair • Adenine to Thymine • Guanine to Cytosine • This is because of the structure of the hydrogen bonds of the DNA

16. Review Guanine Cytosine Adenine Thymine Cytosine Guanine Thymine Adenine

17. DNA Replication Steps • Unzip DNA • Add Base Pairs to both unzipped strands • Proofread the 2 new strands

18. DNA Replication • Before a cell divides, it goes through a process called DNA replication • This is where a cell copies its DNA to create new complementary strands • Complementary strands are the DNA that is created from the existing DNA strands

19. DNA Replication • DNA replication is carried out by a series of enzymes • These enzymes “unzip” a molecule of DNA base pairs • Each half of the unzipped pairs serve as a template for the new strand

20. DNA Polymerase • DNA Polymerase is the principal enzyme involved with DNA Replication • It has 2 main functions. • It “polymerizes” or creates a complex compound by linking together nucleotides • It also proofreads and corrects any mistakes that happen in the DNA strands

21. DNA Polymerase • DNA polymerase serves a second function of checking the new strand for errors • “Proof reads” the DNA strand • Reduces mess-ups in copying DNA • Maximizes the odds that the copied DNA will be an exact copy • What might mess-ups be called?

22. DNA Helicase • DNA Helicase is an important enzyme that is involved in DNA replication • This enzyme unzips the DNA strand • Its job is to separate the DNA strand and make sure it does not reattach

23. DNA Helicase • DNA base pairs hold each other together by hydrogen bonds • Helicase separates the DNA strand by taking away the hydrogen bonds that hold DNA together

24. Enzymes At Work • There are a host of other enzymes working in DNA replication • They all serve the purpose to copy DNA with complete accuracy

25. Enzymes At Work

26. In Summary • DNA is a long series of base pairs that must be coiled in order to be stored • The structure of DNA is allows it to be easily copied • DNA that is copied is unzipped, held open and then completed

27. DNA Replication Animation Animation 2