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AS 90715 Describe the role of DNA in relation to gene expression

Part two…. AS 90715 Describe the role of DNA in relation to gene expression. The Replication of DNA. Take me to NZQA Documents relating to this standard. Contents. Why replicate? (revision stuff you probably already know) The basics The enzymes Okazaki fragments Fixing errors

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AS 90715 Describe the role of DNA in relation to gene expression

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  1. Part two… AS 90715Describe the role of DNA in relation to gene expression The Replication of DNA Take me to NZQA Documents relating to this standard

  2. Contents • Why replicate? (revision stuff you probably already know) • The basics • The enzymes • Okazaki fragments • Fixing errors • Review Questions

  3. Why replicate? Stuff that any respectful Bio student really should know… Mitosis and Meiosis What are they and where they happen! Meiosis Revision exercise • DNA replicates before it forms a chromatid. I.e. when it still looks like… • Over an organisms life the DNA in the zygote is copied trillions of times with minimal error. Error rates are generally 1 in 50 million base pairs (bp). When we copy this 100,000,000,000,000 times it turns into this

  4. Why replicate? www.cellsalive.com • Each new cell must have a copy of the entire DNA genome. Some of the DNA released from a single human chromosome

  5. DNA Replication - the very basics The basics of DNA REPLICATION • Unwind – Unzip – Add nucleotides – wind it all back up. • If only it could be that simple • Two things make it a little more fiddly • DNA is a VERY LONG double helix chemical molecule • It has a anti-parallel structure

  6. It’s a long Double Helix Anti-parallel structure of DNA • The molecule of DNA in a single human chromosome ranges in size from 50,000,000 bp (1.7 cm) up to 250,000,000 (8.5 cm). Ever tried unraveling a long bit of string? • Check the DNA length calculator

  7. DNA replication forks • Because the DNA chromosome is soooooooooo long it needs multiple replication forks working at the same time. How this is coordinated and how strands are placed back together is beyond the scope of L3 Bio (so don’t worry bout it)

  8. DNA Replication The detail. • 4 different enzymes (see next slide) • DNA polymerase moves along template strand in 3’ to 5’ direction. • McGraw Animation • You tube - Replication song.

  9. The Enzymes

  10. Anti-parallel structure (DNA) • This diagram shows a lot of stuff not yet discussed. • What you need to understand at this point • When an enzyme (DNA polymerase) travels along a strand of DNA it travels in the 3’ to 5’ direction of the original strand DNA Polymerase travels 3’ to 5’ on original strand

  11. Okazaki Fragments An Okazaki fragment is a relatively short fragment of DNA created on the lagging strand. The lengths of Okazaki fragments are between 1,000 to 2,000 nucleotides long in E. coli and are generally between 100 to 200 nucleotides long in eukaryotes. Each Okazaki fragment is joined together by DNA ligase after the primers have been removed. http://www.youtube.com/ Replication animation http://www.youtube.com/ crash course in DNA (summary)

  12. Semi-conservative replication A simple idea really… • S.C.R is simply the formation of two double helix molecules where each molecule contains one of the original strands and one new strand of nucleotides (daughter strand). • This helps to minimise the errors made in replication as each molecule contains a copy of the original nucleotide sequence.

  13. Checking for errors You don’t need to know the detail in this box. But read it cause it is interesting ;-) • In general, DNA polymerases are extremely accurate, making less than one error for every 107 nucleotides added. Even so, some DNA polymerases also have proofreading ability; they can remove nucleotides from the end of a strand in order to correct mismatched bases.

  14. Review Questions http://www.biologycorner.com DNA Quizs

  15. Review Question 2011 NCEA exam – Q1 (b) • When DNA is replicated, each of the parent strands acts as a template. • Explain why there is a difference in the way in which the parallel strands of DNA are replicated. • You may use a labelled diagram to support your answer.

  16. Review Question • What words are hidden under the yellow boxes? Click to show answer Click to show answer Click to show answer Click to show answer

  17. Review Question • Complete the table

  18. Review Question • Add the 3’ and 5’ labels to the diagram Click for answers

  19. Review Question – taken from 2008 NCEA Paper

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