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The Structure of DNA

The Structure of DNA. DNA or Protein?. Walter Sutton discovered chromosomes were made of DNA and Protein However, scientists were NOT sure which one (protein or DNA) was the actual genetic material of the cell. DNA!.

martha-stevenson
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The Structure of DNA

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  1. The Structure of DNA

  2. DNA or Protein? • Walter Sutton discovered chromosomes were made of DNA and Protein • However, scientists were NOT sure which one (protein or DNA) was the actual genetic material of the cell

  3. DNA! • Frederick Griffith in 1928 showed the DNA was the cell’s genetic material • In 1944, Oswald Avery demonstrated that DNA is the material responsible for transformation.

  4. DNA’s role Revealed • In 1952, Alfred Hershey and Martha Chase, proved that the DNA of a virus is injected into the bacterial cells. That then causes the bacterial cells to produce more viral DNA and proteins.

  5. DNA • DNAis often called the blueprint of life. • In simple terms, DNA contains the instructions for making proteins within the cell that make up you.

  6. Why do we study DNA? We study DNA for many reasons: • Important to all life on Earth • Medical benefits such as cures for diseases • Better food crops

  7. What is a Gene? • Gene – segment of DNA that is located in a chromosome and that codes for a specific hereditary trait. • Basic unit of heredity. • Each cell in the human body contains about 25,000 to 35,000 genes, which carry information that determines your traits. • Our genes are on our chromosomes.

  8. Chromosomes and DNA • Chromosomes are made up of a chemical called DNA and proteins. • Chromosomes come in pairs, and there are hundreds, sometimes thousands, of genes in one chromosome. • There are 46 chromosomes in each human cell. • Draw and explain Figure 2 Chromosome structure on p.119 on the left side of your notebook.

  9. DNA • Deoxyribonucleic acid • Stores hereditary information • Found in all cells • Organic Comound made up of C, H, O, N and P

  10. Watson & Crick in the 1950’s built the 1st model of DNA With the help of Chargraff’s observations and Wilkins and Franklin’s photographs (x-ray diffraction)

  11. The Shape of DNA • DNA is a very long polymer. • The basic shape is like two strands twisted around each other, like a winding staircase. • This is called a double helix. • Read the first paragraph on p. 194; then summarize what you read in your notes.

  12. The Double Helix Molecule • The DNA double helix has two strands twisted together.

  13. What are Nucleotides? • Each DNA strand is made of linked nucleotides. • Nucleotides are the subunits of DNA • Each nucleotide is made up of 3 parts: 1. phosphate group 2. 5 carbon sugar (deoxyribose) 3. nitrogen base

  14. One Strand of DNA phosphate • The backbone of the molecule is alternating phosphates and deoxyribose sugar • The teeth are nitrogenousbases. deoxyribose bases

  15. O -P O O -P O O -P O O O O O O O C C ribose ATP Nucleotides One deoxyribose together with its phosphate and base make a nucleotide. Nitrogenous base O Phosphate C C C Deoxyribose O

  16. One Strand of DNA nucleotide • One strand of DNA is a polymer of nucleotides. • One strand of DNA has many millions of nucleotides.

  17. Four nitrogenous bases • Cytosine C • Thymine T • Adenine A • Guanine G DNA has four different bases:

  18. N N C N C C C N N C Two Kinds of N Bases in DNA • Pyrimidines are single ring bases. • Purines are double ring bases. N N C O C C N C

  19. N O N N C C O C C O C C C N C N C thymine cytosine Thymine and Cytosine are pyrimidines • Thymine and cytosine each have one ring of carbon and nitrogen atoms.

  20. O N N N C C N C C C C N N N C N C C Guanine Adenine C N N Adenine and Guanine are purines • Adenine and guanine each have two rings of carbon and nitrogen atoms.

  21. Two Stranded DNA • Remember, DNA has two strands that fit together something like a zipper. • The teeth are the nitrogenous bases but why do they stick together?

  22. O N C N N C C C N N C N N C O C C N C Hydrogen Bonds • The bases attract each other because of hydrogen bonds. • Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA. • The bonds between cytosine and guanine are shown here with dotted lines

  23. O N C O C C C N C N N C C C N N C C N Hydrogen Bonds, cont. • When making hydrogen bonds, cytosine always pairs up with guanine • Adenine always pairs up with thymine • Adenine is bonded to thymine here

  24. Chargraff’s Rule: Adenine and Thymine always join together A T Cytosine and Guanine always join together C G

  25. The earth is 150 billion m or 93 million miles from the sun. DNA by the Numbers • Each cell has about 2m of DNA. • The average human has 75 trillion cells. • The average human has enough DNA to go from the earth to the sun more than 400 times. • DNA has a diameter of only 0.000000002 m.

  26. What is the complimentary strand according to the base pairing rules:ATCCATTGGACGA

  27. TAGGTAACCTGCT

  28. DNA Replication What: The process of making a copy of DNA. When: DNA replication occurs during the synthesis (S) phase of the cell cycle, before a cell divides. How Long: One chromosome can be replicated in about 8 hours.

  29. Step 1 : DNA replication • Double helix unwinds • DNA helicasesopen the double helix by breaking the hydrogen bonds that link the complementary nitrogen bases.

  30. Replication Fork • The areas where the double helix separates are called replication forks because of their Y shape. Once the 2 strands are separated, additional proteins attach to each strand, holding them apart.

  31. Step 2: DNA replication • At the replication fork, enzymes known as DNA polymerases add nucleotides to the exposed nitrogen bases, according to the base-pairing rules. • As it moves along, two new double helixes are formed.

  32. Step 3: DNA replication • Process continues until all of the DNA has been copied and the polymerases are signaled to detach. • Results in two identical DNA strands.

  33. Checking for Errors • Errors sometimes occur and the wrong nucleotide is added to the new strand. • An important feature of DNA replication is that DNA polymerases have a “proofreading” role. • It can backtrack to remove the incorrect nucleotide. • Reduces errors in DNA replication to about one error per 1 billion nucleotides.

  34. RNA

  35. RNA Differs from DNA 1. RNA has a sugar ribose DNA has a sugar deoxyribose 2. RNA contains the nitrogen base uracil (U) so.. A pairs with U and C pairs with G DNA has thymine (T) 3. RNA molecule is single-stranded DNA is double-stranded Just like DNA…RNA is made up of the subunits called nucleotides.

  36. Structure of RNA

  37. Three Main Types of RNA . • Messenger RNA (mRNA) carries genetic information to the ribosomes • Ribosomal RNA (rRNA), along with protein, makes up the ribosomes • Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized • More recently discovered RNA: • Interference RNA (RNAi) inhibit gene expression

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