Chapter 10

1. Chapter 10 DNA, RNA and Protein Synthesis

2. 1) How did scientist discover that genes are made of DNA • DNA • - Deoxyribonucleic Acid • - Molecule of heredity • - Contains the genetic information in all living things • Genes • - genetic informational units • -A length of DNA codes for proteins

3. Historical Look at DNA • Late 1800’s • Scientist new of genes and that heritable information was contained in genes. • Studies of cell division showed that genes are located on threadlike structures called chromosomes • Chromosomes are composed of DNA and protein. Genes are made of DNA and protein.

4. 1920’s • Frederick Griffith transformed bacteria in an experiment to find a vaccine to prevent pneumonia • Griffith used two strains of streptococcus pneumonia bacteria • The R-strain did not cause pneumonia • The S-strain was deadly • Injected mice with the weakened R-strain to produce an immune response, mice did not die • Injected mice with the S-stain, killed mice • He then heat killed the S-strain, injected mice, mice did not die • He then mixed the live R-strain and dead S-strain, mice died • Autopsied mice and found living form of S-strain • S-strained transformed the living, but harmless R-strain into a harmful one • Discovered genes are made of DNA

6. 1940’s • Oswald Avery and colleagues, made and extract of the S-strain (heat killed) bacteria • They treated it with enzymes that would destroy proteins, lipids and carbohydrates but not DNA • Transformation still occurred, the enzyme did not destroy DNA • They then used an enzyme that would destroy DNA, transformation did not occur • They concluded that when the S-strain (heat killed) bacteria and the R-strain were mixed, fragments of the DNA from the S-strain entered some R-strain making it a deadly strain, concluding that the fragments contained genes needed to cause disease.

7. 1940’s • Chargaff analyzed relative amounts of nucleotides in DNA and found equal amounts of Adenine and Thymine and equal amounts of Cytosine and Guanine

8. 1950’s • Rosalind Franklin and Maurice Wilkens used X-ray diffraction to study the structure of DNA • Took photo’s to determine the shape • They knew it was helical shaped • Knew it had a uniformed diameter (2 nanometers)

10. 1953 • James Watson and Francis Crick proposed a new model for DNA • Used Franklins photo’s to determine the structure • Noted that DNA consisted of two separate strands of linked nucleotides • Contains a phosphate group linked to a sugar that are covalently bonded making up a sugar phosphate backbone • The two DNA strands are held together by hydrogen bonds • DNA strands are a ladder like structure that is twisted • The rungs of the ladder are made up of complementary nitrogenous bases, bonded together by hydrogen bonds • Twisted double helix

12. Structure and Review of Nucleic Acids • Composition of a nucleotide. Nucleic acids are composed of nucleotides. • Nucleotides can be broken down even further to yield three components • Phosphate • Sugar • Base

13. Overview of DNA • A. The Scientist’s Who Discovered DNA Were: Watson and Crick • B. Structure of the Nucleic Acid • Phosphate • Sugar • Base

14. C. Overview of DNA • . Nucleotides are joined together in DNA by bonds between the phosphate component of one nucleotide and the sugar component of the next nucleotide.

15. DNA

16. Detailed representations of DNA

17. D. DNA • . DNA has four Nitrogenous Bases: • Adenine • Cytosine • 3. Guanine • Thymine Purines (double rings) - adenine and guanine Pyrimidines (single rings) - cytosine and thymine

18. E. Watson – Crick Model of Base Pairing • A single ring always bonds with a double ring • Adenine bonds with Thymine • Cytosine bonds with Guanine

19. The Four Nucleotidesof DNA DNA Thymine DNA Cytosine DNA Adenine DNA Guanine

20. Watson and Crick Model of Base Pairing (view it as a ladder) • Sugar phosphates form the sides of the ladder • Nitrogen bases are held together by weak hydrogen bonds and form the rungs of the ladder • Base pairing is called complimentary rather than identical • Double helix • (A – T, C –G) The amount of A=T, the amount of C=G

21. The Watson-CrickModel of DNA Structure Hydrogen bonds form between complementary bases DNA is a double helix of two nucleotide strands Complementary base pairs hold the two DNA strands together

22. DNA Replication F. How Does DNA Replication Ensure Genetic Constancy? DNA Replication - Cells reproduce themselves in the process of cell division - One cell will divide to produce two daughter cells exactly like the parent cell - Cell division must ensure that each daughter cell receives exact copies of genetic information from parent - In order for this to occur, DNA must replicate itself – that is to make exact copies Process is know as DNA Replication.

23. G. DNA Replication • Enzymes are involved • DNA Helicase – breaks apart the double helix • DNA Polymerase – adds nucleotides to the original strand making new DNA molecule • Replication produces two DNA double helices – each contain one original (old) strand and one new strand • Chromosomes contain one DNA double helices • Replication results in two identical DNA double helices passed within chromosomes to each of the new daughter cells

24. DNA Replication Steps • Steps of Replication: • 1. DNA Helicase is an enzyme that breaks apart the double helix. The bases are held together with weak hydrogen bonds that are broken apart by DNA helicase enzyme • 2 . DNA Helicase uses energy of ATP to break apart the hydrogen bonds between the complimentary bases • 3. The DNA starts to separate and unwind • 4. DNA Polymerase is an enzyme that plays a critical role in DNA synthesis

25. DNA Replication • 5. DNA polymerase recognizes an unpaired nucleotide base in the parental strand and matches it up with free nucleotides (Example – DNA polymerase matches up a unpaired adenine with a free floating thymine) • 6. While helicase moves along the parental DNA double helix separating the parental strand, one DNA polymerase moves along in the same direction, adding nucleotides. • 7. You end up with two daughter double helix strands of DNA.

27. The SemiconservativeReplication Model One DNAdouble helix SisterChromatids Both strands of original DNA serve as templates DuplicatedChromosome Chromosome Daughter chromosomes half old, half new

28. DNA Has Proof Reading Abilities • The Enzyme DNA Polymerase Has Proofreading Ability • Replication errors can result in mutations – is a change in a nucleotide sequence) • DNA polymerase has proofreading ability • 1 mistake per 10,000 base pairs occurs • DNA polymerase can repair damage • If errors are not fixed you get mutations

29. DNA’s Primary Function: • DNA’s Primary Function is to • Provide instructions to Make proteins

30. H. Transcription • - How Does DNA Provide the Instructions to Make Proteins? DNA uses a messenger in the process called transcription • - DNA needs to use a messenger to carry the instructions on how to make proteins to the ribosomes. • - DNA is found in the nucleus and uses a “messenger” to carry the instructions from DNA out to the ribosomes. • - DNA uses messenger RNA

31. I. RNA and Transcription What is RNA and how is it different from DNA?RNA =Ribonucleic Acid

32. Comparision of DNA and RNA Nucleus and Cytoplasm Nucleus Deoxyribose Ribose Adenine, Thymine, Guanine, Cytocine Adenine, Cytosine, Guanine, Uracil DNA mRNA, tRNA, rRNA

33. J. Types of RNA: - Messenger RNA (mRNA) – Carries the instructions from DNA (gene) to make a protein - Ribosomal RNA (rRNA) – Part of ribosomes where protein synthesis takes place - Transfer RNA (tRNA) – Transfers amino acids to the ribosome to make a protein

34. K. Transcription: Re-writing DNA into RNA - Simply stated, one gene (DNA) is re-written into MRNA in the nucleus. - A gene is a segment of DNA that can be copied or transcribe into MRNA.

35. K. Transcription Transcription consists of the following steps:1.DNA separates into 2 strands (one strand is the template). RNA Polymerase binds to a segment of DNA and initiates transcription to start2.RNA Polymerase (enzyme) adds free nucleotides to the complimentary DNA strand3.RNA Polymerase reaches a sequence of nucleotides that marks the end of a gene4. 3 base pairs of mRNA = triplet codons that will correspond to an amino acid.Draw diagram

36. Transcription

37. L. How is the sequence of Messenger RNA translated Into a protein? • mRNA acts a intermediate between the permanent storage form of DNA and the process that uses the information – Translation = Protein Synthesis • The language of RNA is in the form of codons – which are groups of three nucleotides, such as AUG, GCC or AAA. • This is called the triplet code. • The sequence of codons on the mRNA determines the sequence of amino acids. • Each codon codes for a specific amino acid. • There are only 20 amino acids that code for all the thousands of proteins made. • Some codons are used for more than one amino acid and some are used as stop codons.

38. Translation – Protein Synthesis

39. Translation – Protein Synthesis Steps • A single strand of DNA serves as a template for mRNA • mRNA carries the sequences of nucleotides to the ribosomes • AUG signals translation to begin • tRNA picks up individual amino acids and takes them to the ribosome • The amino acids are bonded together in a chain by peptide bonds and a protein is synthesized • Translation ends when one of the stop codns (UAA, UAG, and UGA) in the mRNA is reached • Diagram

40. Translation

41. The End.