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DNA

Explore the structure of DNA, its replication process, and its role in protein synthesis. Understand how DNA codes for proteins through the genetic code and base pairing. Discover the importance of RNA in protein synthesis.

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DNA

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  1. 1 DNA

  2. 2 DNA DNA stands for deoxyribose nucleic acid This chemical substance is present in the nucleus of all cells in all living organisms DNA controls all the chemical changes which take place in cells The kind of cell which is formed, (muscle, blood, nerve etc) is controlled by DNA The kind of organism which is produced (buttercup, giraffe, herring, human etc) is controlled by DNA

  3. 3 DNA molecule DNA is a very large molecule made up of a long chain of sub-units The sub-units are called nucleotides Each nucleotide is made up of a sugar called deoxyribose a phosphate group -PO4 and an nitrogenous base (A, T, C, G)

  4. 4 Ribose & deoxyribose Ribose is a sugar, like glucose, but with only five carbon atoms in its molecule (found in RNA) Deoxyribose is almost the same but lacks one oxygen atom (found in DNA) Both molecules may be represented by the symbol Pentose (5-carbon) sugars. Always represented by pentagons

  5. 5 The bases Adenine (A) Thymine (T) Cytosine (C) (G) Guanine The most common organic bases are

  6. 6 This is a structure of a NUCLEOTIDE PO4 adenine deoxyribose The deoxyribose, the phosphate and one of the bases Combine to form a nucleotide (Phosphate + sugar + nitrogen base) = nucleotide

  7. Joined nucleotides PO4 PO4 PO4 PO4 sugar-phosphate backbone + bases 7 A molecule of DNA is formed by millions of nucleotides joined together in a long chain

  8. Parts of a Nucleotide A, T, C, G Phosphate + Pentose sugar + Nitrogen Base (deoxyribose) (ribose)

  9. 8 In fact, the DNA usually consists of a double strand of nucleotides The sugar-phosphate chains are on the outside and the strands are held together by chemical bonds between the bases

  10. 10 Bonding 1 Adenine Thymine Guanine Cytosine The bases always pair up in the same way Adenine forms a bond with Thymine and Cytosine bonds with Guanine

  11. 2-stranded DNA PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 9 Covalent bonds found b/t sugars and phosphates Hydrogen bond found between Nitrogen bases sugar Nitrogen base Phosphate

  12. 14 THE DOUBLE HELIX bases sugar-phosphate chain

  13. 13 The paired strands are coiled into a spiral called A DOUBLE HELIX The term “Double Helix” was coined by two British Scientists named James Watson and Francis Crick in the 1950s...but should they have received the Nobel Prize?? If you haven’t already done so. Do a quick search and read about Watson & Crick and Rosalind Franklin. On my webpage, there are questions for you to answer in your notes

  14. 15 A DIY model ofpart of a DNA moleculecan be found at Wal-Mart

  15. 16 DNA replication 1. Before a cell divides, the DNA strands unwind and separate 2. Each strand makes a new partner by adding the appropriate nucleotides 3. The result is that there are now two double-stranded DNA molecules in the nucleus 4. So that when the cell divides, each nucleus contains identical DNA 5. This process is called replication

  16. 17 1. The strands separate PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 During DNA replication, the weak hydrogen bonds between the bases break—and the DNA unzips

  17. PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 18 2-4. Each strand builds up its partner by adding the appropriate nucleotides Two new strands of DNA have been copied

  18. RNA (ribonucleic acid)

  19. Ribonucleic Acid • Single stranded form of DNA • Responsible for Protein synthesis (making proteins) • Travels to the ribosomes (since the DNA cannot leave the nucleus), and aids in protein synthesis There are three types: • Messenger RNA (mRNA)-brings message from DNA • Ribosomal RNA (rRNA)- makes structure of ribosome • Transfer RNA (tRNA)-transfers the amino acid to the site of protein synthesis

  20. DNA vs. RNA (please copy this table)

  21. DNA to Proteins Protein Synthesis

  22. Instructions for making proteins • DNA inside of the nucleus gives instructions for protein synthesis. • The DNA cannot leave the nucleus, so the mRNA must travel to the ribosomes • The RNA helps the ribosomes to make proteins.

  23. Genetic code 1 19 The sequence of bases in DNA forms the Genetic Code A group of three bases (a triplet or codon) controls the production of a particular amino acid in the cytoplasm of the cell The different amino acids and the order in which they are joined up determines the sort of protein being produced

  24. RNA Base Pairing • DNA & RNA share many similarities and differences. • One of the main differences in the base pairing. • There is no THYMINE in RNA…there is URACIL • So A = U • Example • DNA Strand AAT CGC CAT • RNA Strand UUA CGC GUA

  25. Rules of Protein synthesis • 1. You are given a DNA base strand • 2. You must convert it to mRNA • 3. Find the amino acid that codes for the mRNA (p. 292 in Blue textbook has an amino acid chart) • FYI-chains of amino acids make PROTEINS. Example: DNA base strand: AAA CAT mRNA strand: UUU GUA AMINO ACID: Phenylalanine Valine

  26. The Central Dogma (Protein Synthesis) DNA RNA Proteins mRNA travesls through the cytoplasm to the ribosomes where proteins DNA inside of the nucleus gives instructions for Protein synthesis The chains of amino acids make proteins RNA codon: UUU Amino Acid: Phenylalanine DNA codon: AAA

  27. Coding Cytosine Adenine Thymine 21 For example Valine Codes for Cytosine (C) Alanine Codes for Guanine (G) Adenine (A)

  28. Triplet code 22 This is known as the triplet code Each triplet codes for a specific amino acid CGA - CAA - CCA - CCA - GCT - GGG - GAG - CCA - Ala Val Gly Gly Arg Pro Leu Gly The amino acids are joined together in the correct sequence to make part of a protein Ala Val Gly Gly Arg Pro Leu Gly

  29. 23 DNA and enzymes The proteins build the cell structures They also make enzymes (enzymes are proteins) The DNA controls which enzymes are made and the enzymes determine what reactions take place The structures and reactions in the cell determine what sort of a cell it is and what its function is So DNA exerts its control through the enzymes

  30. Genes 24 A sequence of triplets in the DNA molecule may code for a complete protein Such a sequence forms a gene There may be a thousand or more bases in one gene

  31. Question 1 Which of the following are components of nucleotides? (a) deoxyribose (b) amino acids (c) phosphate (d) enzymes (e) organic bases

  32. Question 2 Which of the following represent a correct pairing of bases? (a) adenine with thymine (b) adenine with guanine (c) thymine with adenine (d) guanine with cytosine (e) thymine with thymine

  33. Question 3 DNA molecules are formed from (a) organic bases (b) amino acids (c) deoxyribose (d) nucleotides

  34. Question 4 Which of the following are organic bases? (a) Valine (b) Guanine (c) Thymine (d) Serine

  35. Question 5 Replication of DNA occurs (a) During cell division (b) before cell division (c) at any time

  36. Question 6 A nucleotide triplet codes for (a) a protein (b) an amino acid (c) an enzyme (d) an organic base

  37. Answer CORRECT

  38. Answer INCORRECT

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