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Topic 3: Chemistry of Life - DNA

Topic 3: Chemistry of Life - DNA. 3.3 DNA Structure. Sugar/Phosphate group = sides of the DNA ladder or backbone Nitrogenous Bases = rungs of the DNA ladder. 3.3 DNA Structure. Covalent bonds hold together the sugar of one nucleotide, to the phosphate group of another nucleotide.

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Topic 3: Chemistry of Life - DNA

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  1. Topic 3: Chemistry of Life - DNA

  2. 3.3 DNA Structure • Sugar/Phosphate group = sides of the DNA ladder or backbone • Nitrogenous Bases = rungs of the DNA ladder

  3. 3.3 DNA Structure • Covalent bonds hold together the sugar of one nucleotide, to the phosphate group of another nucleotide. • The backbone/sides of the ladder are alternating sugar/phosphates. • Remember covalent bonds are STRONG, sides of the double helix are never broken!

  4. 3.3 DNA Structure • Hydrogen bonds hold together the complementary nitrogenous bases (rungs of the ladder) • Remember hydrogen bonds are WEAK, our body needs to separate the DNA double helix in DNA replication (S phase of Interphase) • A = T and G = C

  5. 3.3 DNA Structure

  6. 3.3 DNA Structure • Draw and label a simple diagram of the molecular structure of DNA:

  7. 3.3 DNA Structure • James Watson and Francis Crick: 2 British men credited for discovering the double helix shape of DNA and later awarded a Nobel Prize. • Not so fast! They would never have received the prize without Rosalind Franklin's help!

  8. 3.3 DNA Structure • Rosalind was not aware there was a race for the DNA structure, and gladly showed Watson her DNA photograph - which was the key he was missing to finally publish a paper on the double helix. • Rosalind died in 1958 at the age of 30, and Watson and Crick received the Nobel Prize in 1962

  9. Would Rosalind have had a share in the Nobel Prize had she not died so young? • Many say no, she was snubbed out of the prize because she was looking for help and confidence on her work within the scientific community rather than out for glory like Watson and Crick. • She died so young because photographing DNA can take up to 100 hours of radiation exposure per picture - she was around radiation all the time and never protected herself. • She passed away from ovarian cancer.

  10. Homework: • Examine the table below. Compare the amounts of adenine, guanine, cytosine, and thymine found in the DNA of each of the cells studied.

  11. 1. Compare the amounts of A, T, G and C in each kind of DNA. Why do you think the relative amounts are so similar in human liver and human blood cells? • 2. How do the relative amounts of each base in salmon sperm compare with the relative amounts of each base in yeast? • 3. What fact can you state about the overall composition of DNA, regardless of its source?

  12. 3.4 DNA Replication • ★Explain DNA replication in terms of unwinding the double helix and separation of the strands by helicase, followed by formation of the new complementary strands of DNA polymerase. • ★Explain the significance of complementary base pairing in the conservation of the base sequence of DNA • ★ State that DNA replication is semi-conservative.

  13. 3.4 DNA Replication • Before a cell divides (mitosis), it needs to make a complete set of genetic instructions (DNA) for each new cell. • S phase/Interphase = DNA Synthesis • The time where DNA is doubled, otherwise known as DNA Replication • This occurs in the nucleus. • Remember, mitosis produces 2 IDENTICAL daughter cells.

  14. DNA Synthesis/Replication

  15. 3.4 DNA Replication • DNA Replication Step by Step Details: • 1. Unzip the 2 strands. • DNA Helicase (an enzyme) moves along the double helix, unwinding and separating the 2 strands. • The weak hydrogen bonds that hold the bases together are broken.

  16. 3.4 DNA Replication • 2. The unpaired nucleotides are exposed and each single strand now acts as an "old" template to form a new complementary strand. • Free nucleotides move into place (A=T, G=C) • 3. DNA Polymerase is the enzyme that binds the new nucleotides to the old strands. • Two new DNA molecules are rewound, each forming a new double helix.

  17. 3.3 DNA Structure • ★Outline DNA nucleotide structure in terms of sugar (deoxyribose), base and phosphate • ★State the names of the 4 bases in DNA • ★Outline how DNA nucleotides are linked together by covalent bonds into a single strand.

  18. 3.3 DNA Structure • ★Explain how a DNA double helix is formed using complementary base pairing and hydrogen bonds. • ★Draw and label a simple diagram of the molecular structure of DNA

  19. 3.3 DNA Structure • DNA (Deoxyribonucleic Acid) molecules make up the genetic material of all living organisms. • DNA is an extremely long molecule - if uncoiled, the DNA in all the cells in your body would stretch 10 billion miles, from here to Pluto and back! • This long chain of DNA is made up of many subunits called nucleotides.

  20. 3.3 DNA Structure • Although DNA is the genetic material of living organisms and is therefore immensely important, it is made of relatively simple subunits. • These subunits, if you get down to the smallest parts, are made of Hydrogen, Carbon, Oxygen, Nitrogen. • HCON=4 most common elements in all living things, now you know why!

  21. 3.3 DNA Structure • Nucleotides are the building blocks (monomers) of nucleic acids (polymers) • Nucleotide: • 1. Sugar (deoxyribose) • 2. Phosphate group • 3. Nitrogenous base (Adenine, Thymine, Guanine, Cytosine) - A, T, G or C

  22. 3.3 DNA Structure • Classwork/Homework Monday 2/4: • 1. What does DNA strand for and why? • 2. Where are covalent bonds and hydrogen bonds located in DNA? • 3. If there were 6 guanines in a strand of 30, how many C? T? A?

  23. 3.3 DNA Structure • DNA is a twisted ladder, known as a double helix. • Two DNA strands make up the double helix, running in opposite directions of each other. • The 2 strands are held together by base pairs that are complimentary to each other.

  24. 3.3 DNA Structure • DNA is a twisted ladder, known as a double helix. • Two DNA strands make up the double helix, running in opposite directions of each other (antiparallel) • The 2 strands are held together by base pairs that are complimentary to each other.

  25. 3.4 DNA Replication • The two new DNA strands produced are absolutely identical to the original strand because of complementary base pairing. • DNA replication is semi-conservative. • Each new set of DNA has one old strand and one new strand. • This ensures each new cell has an exact copy of the genetic instructions.

  26. 3.5 DNA Transcription and Translation • ★Compare the structure of RNA and DNA • ★Outline DNA transcription in terms of the formation of an RNA strand complementary to the DNA strand by RNA polymerase. • ★ Describe the genetic code in terms of codons composed of triplets of bases. • ★Explain the process of translation, leading to polypeptide formation.

  27. 3.5 DNA Transcription and Translation • ★Explain the process of translation, leading to polypeptide formation (include the roles of mRNA, tRNA, codons, anticodons, ribosomes and amino acids). • ★Discuss the relationship between one gene and one polypeptide.

  28. 3.5 DNA Transcription and Translation • The main role of DNA is to direct the activities of the cell. • It does this by controlling the proteins that the cell produces. • Enzymes, hormones and many other important biochemical molecules are proteins, which control what the cell becomes, what it synthesizes and how it functions.

  29. 3.5 DNA Transcription and Translation • Protein synthesis has 2 steps: • 1. Transcription (in nucleus) • 2. Translation (in cytoplasm) • The sections of DNA that code for specific proteins are known as genes. • Genes have specific sequences of bases in sets of three, called triplets (called it a codon freshman year) • Some triplets control where transcription and translation start and end.

  30. 3.5 DNA Transcription and Translation • Before DNA can be coded into a protein, there is an intermediate molecule (or middle man) that needs to be produced called messenger RNA (mRNA) • RNA = Ribonucleic Acid • Obviously Deoxyribonucleic Acid looks a lot like Ribonucleic Acid - that's because it is! Except with a couple differences...

  31. 3.5 DNA Transcription and Translation

  32. 3.5 DNA Transcription and Translation • First stage of protein synthesis: TRANSCRIPTION • Let's sum up transcription before we break it down: • Transcription= to make an mRNA molecule • Transcription Details: • 1. DNA is unzipped by the enzyme RNA polymerase • a. Transcription begins just like replication - DNA double helix unzips, separating the 2 strands

  33. 3.5 DNA Transcription and Translation • b. But now the enzyme doing the unzipping is called RNA polymerase. • 2. Free RNA nucleotides move into place along one of the 2 DNA strands. • a. These RNA nucleotides have a ribose sugar, phosphate, and A, G, C or U. • b. A Thymine on the DNA strand will bind with the new Uracil of a RNA nucleotide

  34. 3.5 DNA Transcription and Translation • 3. RNA polymerase puts the free RNA nucleotides in the right place using complimentary base pairing. • a. RNA polymerase does double duty in transcription - unzips DNA and attaches new RNA nucleotides to the DNA strand. • b. A=U, G=C • c. The end product (mRNA) is only single stranded, so RNA nucleotides will only bind to one DNA strand, not both!

  35. 3.5 DNA Transcription and Translation • d. The new strand of mRNA is much shorter than the DNA molecule because it is just a copy of one section of the DNA - a gene. • 4. mRNA separates from the DNA strand • a. DNA double helix is zipped up again by RNA polymerase. • b. mRNA moves through the nuclear envelope pores into the cytoplasm (to await translation) • c. mRNA needs to be single stranded to fit through those nuclear pores!

  36. 3.5 DNA Transcription and Translation • Second stage of protein synthesis: TRANSLATION • Let's sum up translation before we break it down: • Translation= a polypeptide (several polypeptide chains make a protein) • Translation Details: • 1. Triplet or Codon: sequence of 3 bases • a. IB uses both terms.

  37. 3.5 DNA Transcription and Translation • b. Each triplet corresponds to a specific amino acid. • c. The order of the triplet determines which amino acid is picked. • d. Triplets are only on the mRNA, so to determine which specific amino acid it codes for, look on the codon chart. • e. Several amino acids chained together makes a polypeptide chain (end product of translation!)

  38. 3.5 DNA Transcription and Translation • 2. Translation is carried out in the cytoplasm by ribosomes and transfer RNA (tRNA) • a. The ribosome binds to the mRNA - where it reads AUG (only start codoc) • b. Ribosome draws in the appropriate tRNA based on its anticodon. • The tRNA anticodon is the exact opposite of the mRNA codon/triplet. • EX: mRNA = AUG, tRNA = UAC, brings amino acid Methionine

  39. 3.5 DNA Transcription and Translation • DNA: TAC GCA CCC ACA GTA TTT ATT • mRNA: • Amino acid chain:

  40. 3.5 DNA Transcription and Translation • DNA: TAC AAC GTA CGG GTA CAC ACU • mRNA: • tRNA: • Amino acid chain:

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