NUCLEIC ACIDS (DNA)

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NUCLEIC ACIDS (DNA)

  1. 1. NUCLEIC ACIDS (DNA) Structure and function
  2. 2. DNA STRUCTURE
  3. 3. DNA double helix structure
  4. 4. Helix • Most DNA has a righthand twist with 10 base pairs in a complete turn • Left twisted DNA is called Z-DNA or southpaw DNA • Hot spots occur where right and left twisted DNA meet producing mutations copyright cmassengale 4
  5. 5. The structure of DNA and RNA • Genetic material of living organisms is either DNA or RNA. • DNA – Deoxyribonucleic acid • RNA – Ribonucleic acid • Genes are lengths of DNA that code for particular proteins.
  6. 6. A BRIEF HISTORY ON NUCLEIC ACID • Frederich Meischer (1844-1895) – Extracted pus from wounds and bandages – Isolated a substance from white blood cells which he named “nuclein” (because it was found in the nucleus of cells).
  7. 7. • Edmund Beecher Wilson (1856-1939) – Establishes that “mother’s” nucleus contain the same number of chromosomes as “father’s nucleus”, and both are present in the offspring… – Therefore half of the information is received from each parent!
  8. 8. • Oscar Hertwig (1849-1922) – Suggests nuclein is needed to inherit characteristics from parents. • Richard Altmann (1852-1900) – Determines nuclein is actually acidic and changes the name to “nucelic acid”
  9. 9. A picture of a DNA molecule using Crystallography by Franklin
  10. 10. • Phoebus Aaron Levene (1869-1940) – Suggested nucleic acids had a highly repetitive sequence… (although he could not describe the repetition patterns) • Albrecht Kossel (1853-1927) – Worked with yeast (why?) – Showed there were 2 types of nucleic acids (and won a Nobel prize for this!)
  11. 11. So what are nucleic acids? • There are 2 types: – DNA (deoxyribonucleic acid) – RNA (ribonucleic acid) • Polymers (i.e made of many monomers joined ogether)
  12. 12. More about nucleic acids • They are in charge of: STORAGE TRANSMISSION USE »Of genetic information
  13. 13. More on nucleic acids • Composed of monomers called nucleotides • Each nucleotide has: – A pentose (5 carbon) sugar – A phosphate group – A nitrogen-containing base
  14. 14. More on nucleic acids (remember there are 2 types: DNA and RNA) DNA bases RNA bases Thymine (T) Uracil (U) Adenine (A) Adenine (A) Cytosine (C) Cytosine (C) Guanine (G) Guanine (G)
  15. 15. Each nucleotide must have: 1. Phosphate group
  16. 16. 2. A single sugar
  17. 17. A single base
  18. 18. pyrimidines purines DNA’s nucleotides
  19. 19. DNA is unique because of the nucleotide sequence • Only 4 nitrogenous bases – thus only 4 nucleotides are found in DNA • What does this mean?
  20. 20. 1. DNA sequences are unique • Nucleotides can join to each other in 2 ways: - As a sequence - By complementary base pairing (not e shown below) A C C G T A T A G The sequence is called the “genetic code” and is UNIQUE to each individual.
  21. 21. How do nucleotides join in a sequence? • Nucleotides can join through covalent bonds between their sugar group AND phosphate group Forming the sugar-phosphate backbone bases are not involved directly in this type of bonding.
  22. 22. Nitrogenous bases – Two types Pyrimidines • Have single ring Thymine - T Cytosine - C Uracil - U Purines • Have double rings of Carbon and Nitrogen atom Adenine - A Guanine - G Base-Pairings: Purines only pair with Pyrimidines AS Biology. Gnetic control of protein structure and
  23. 23. 2. Complementary base pairing • RNA consists of a single strand, but DNA consists of a double strand. • In a double strand, BASES bond to each other. • This IS NOT AT RANDOM, but occurs through COMPLEMENTARY BASE PAIRING • A purine will always bond a pyrimidine.
  24. 24. Complementary base-pairing A T C G Always adenine – thymine cytosine - guanine
  25. 25. Exercise: Which is the complementary strand? A T T A C G C G G C C G T A
  26. 26. • Hydrogen bonds attach nucleotide bases to each other, and determine the bases that CAN join (i.e complementary bases) • C and G make 3 H bonds. • A and T make 2 H bonds.
  27. 27. The hydrogen bonding is one of the causes leading a DNA molecule to twist (like a double helix) • This was discovered by James Watson and Francis Crick (both of whom won a Nobel Prize for this).
  28. 28. The 2 strands run anti-parallel to each other
  29. 29. Questions: 1. Physically, why can’t a guanine (G) in one strand bond with an adenine (A) in another strand?  Guanine and Adenine are both purines.  This means they are slightly larger molecules than Thymine and Cytosine.  If they pair up, the distance between one strand and the other is larger than the average, and surrounding nucleotides could not bond.
  30. 30. 1. Physically, why can’t a guanine (G) in one strand bond with an adenine (A) in another strand?  Guanine can make 3 hydrogen bonds, whereas Adenine can only make 2. This makes the bonding unstable as Guanine ends up with a “lose” end (nonbonded hydrogen)
  31. 31. Questions 2. Why does DNA “need” to have a “coiled” shape? DNA carries ALL the information that makes up an organism. It is present in EVERY nucleus of EVERY cell of the organism. (If DNA was extended side by side, the DNA in our bodies would be long enough to go around the earth!) By coiling DNA (in fact, SUPERCOILING it), DNA can actually fit into the nucleus of each cell.
  32. 32. 2. Why does DNA “need” to have a “coiled” shape?  DNA carries the hereditary information.  By COILING it, the “strong” part (sugar-phosphate backbone) is exposed, rather than the bases.  This confers some “protection” to the information
  33. 33. Summary on DNA structure:  DNA is a ______ helix.  Each strand runs _____________ to the other.  Alternating ______ and _________ molecules form a backbone for each strand.  The two strands backbone sugar and phosphate molecules are held together by ___________ bonds.  The two strands are held together by _________ bonds between complementary base pairs.  There are four nitrogenous bases: two _______, Adenine (A) and Guanine (G) and two __________, Thymine (T) and Cytosine (C).  Adenine and ________ always bond through 2 hydrogen bonds.  Cytosine and _______ always bond through 3 hydrogen bonds.
  34. 34. SUMMERY ON DNA STRUCTURE:  DNA is a double helix.  Each strand runs anti-parallel to the other.  Alternating sugar and phosphate molecules form a backbone for each strand.  The two strands backbone sugar and phosphate molecules are held together by covalent bonds.  The two strands are held together by hydrogen bonds between complementary base pairs.  There are four nitrogenous bases: two purines, Adenine (A) and Guanine (G) and two pyrimidines, Thymine (T) and Cytosine (C).  Adenine and Thymine always bond through 2 hydrogen bonds.  Cytosine and Guanine always bond through 3 hydrogen bonds.
  35. 35. SO HOW DOES DNA STORE TRANSMIT USE genetic information?
  36. 36. REFERENCE • Gavin40 accessed from http://www.slideshare.net/gavin40/nucleic-acids29117862 • Ihmcbiology1213 accessed from http://www.slideshare.net/ihmcbiology1213/dnastructure-15152681 • Campbell & Reece: Chapters, 5, 16.

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