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DNA, RNA and Protein Synthesis= CH 10

DNA, RNA and Protein Synthesis= CH 10. Griffith’s Experiments. Showed that hereditary material can pass from one bacterial cell to another The transfer of genetic material from one cell to another or organism to organism is called transformation

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DNA, RNA and Protein Synthesis= CH 10

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  1. DNA, RNA and Protein Synthesis= CH 10

  2. Griffith’s Experiments • Showed that hereditary material can pass from one bacterial cell to another • The transfer of genetic material from one cell to another or organism to organism is called transformation • Heat killed virulent bacteria can transfer their disease causing ability to harmless bacteria

  3. Griffith’s Experiments

  4. Avery’s Experiments • Showed that: DNA is the hereditary material that transfers info btwn bacterial cells • Cells missing RNA and Protein could transform R into S cells • Cells missing DNA could not transform cells

  5. Hershey-Chase Experiment • DNA not protein is the genetic material • DNA of viruses enters bacterial cells and this causes the bacterial cell to produce more viruses containing DNA • Protein doesn’t enter cells

  6. Discovery Of Structure • 1953: Watson and Crick put together a model of DNA using Franklin’s and Wilkins’s DNA diffraction X-rays

  7. Molecular Structure of DNA • DNA is composed of 2 strands made of 4 kinds of nucleotides • Each nucleotide consists of 3 parts: • one 5-carbon sugar (deoxyribose) • one phosphate group, and • one of 4 bases • adenine (A), guanine (G), thymine (T), cytosine (C).

  8. Structure of a nucleotide • Sugar & Phosphate are “sides” of ladder and Bases are the “rungs” & attach to sugars

  9. 2 categories of DNA bases:PurinesvsPyrimidines PURINES = A, G = SMALL WORD, BIG BASES = 2 RINGS = PuAG PYRIMIDINES = T, C = BIG WORD, SMALL BASES= 1 RING = PyTC

  10. Purines vs Pyrimidines • Chargaff showed that • % of A always = % of T • % of G always = % of C • Purines always with pyrimidines • BIG BASE ALWAYS WITH SMALL

  11. DNA Structure

  12. Complementary base pairing rules • Base pairs are formed by hydrogen bonding of A with T (2 H bonds), and G with C (3 H bonds)

  13. DNA Replication

  14. DNA Replication = inS phase of cell cycle • An enzyme (helicase) breaks the H bonds between base pairs and unZIPS the strands = replication fork

  15. DNA Replication • Another enzyme (DNA polymerase) attaches the complementary base to the original DNA strand

  16. DNA Replication • Results in DNA molecules that consist of one "old" strand and one "new" strand • Known as semi-conservative replication b/c it conserves the original strand).

  17. DNA Errors in Replication • Changes = mutation • Proofreading & repair prevent many errors • Unrepaired mutation can cause cancer

  18. Flow of Genetic Material:DNA → RNA → Proteins

  19. RNA Structure • RNA differs from DNA • RNA uses ribose as the sugar not deoxyribose. • RNA bases are A, G, C, and uracil (U). • G-C • A-U • Single Stranded • Shorter than DNA • Can Leave the nucleus

  20. 3 Types of RNA • rRNA - ribosomal • mRNA - messenger • tRNA - transfer

  21. Messenger RNA (mRNA) • Made from DNA in nucleus using RNA Polymerase • Is the “Blueprint" for a protein • Carried to ribosomes in cytoplasm after “stop” is reached • Carries message from nucleus to cytosol

  22. Ribosomal RNA (rRNA) • rRNA + protein makes a ribosome • Site where proteins are assembled in cytoplasm

  23. Transfer RNA (tRNA) • Carries correct AA to ribosome/ mRNA complex

  24. Transcription • DNA → RNA • uses RNA Polymerase (binds at “promoter” region) • Process similar to DNA replication • Begins with a START codon and ends with a STOP codon • Makes rRNA, tRNA or mRNA • Message is “transcribed” from DNA code to RNA code

  25. Transcription

  26. Protein Synthesis: Translation • Making of protein at the rRNA using mRNA and tRNA • Each base triplet in mRNA is called a codon -specifies an amino acid to be included into a polypeptide chain • Uses genetic code to determine amino acid

  27. Genetic Code • Universal for all forms of life • 61 triplets specifying amino acids • 3 “stop” codes • Stop codes = UAA, UAG, UGA • StartCodon = AUG = methionine

  28. From DNA to Proteins

  29. Translation • RNA → PROTEIN • mRNA leaves nucleus goes to ribosome • Begins when ribosome attaches to start codon • tRNA gets specific amino acid (floating free in cytosol), anticodon matches codon of mRNA and A.A. • tRNA brings its AA to ribosome and attaches it to growing chain of AA (protein) • stops at “stop” codon

  30. Chapter 11Gene ExpressionTURN “ON” GENES to REGULATE PROTEIN AND GENE EXPRESSION

  31. Role of Gene Expression • Activation of a gene that results in transcription and production of mRNA • Only a fraction of a cell’s genes are expressed at any one time • You only express genes or make proteins when NEEDED!

  32. Gene Expression in Prokaryotes -Studies in 1960’s by French scientists -Started with simple intestinal prokaryotic cell= Escherichia coli = E. coli

  33. Bacteria adapt to changes in their surroundings by using proteins to turn groups of genes on and off in response to various environmental signals • The DNA of Escherichia coli is sufficient to encode about 4000 proteins, but only a fraction of these are made at any one time. E. coli regulates the expression of many of its genes according to the food sources that are available to it

  34. - Scientists discovered how genes in this bacteria metabolize lactose when present • -lactose = disaccharide…needs to be broken down into galactose and glucose

  35. Gene Expression in Prokaryotes • When lactose is absent, E. coli will not produce the protein…is repressed • When lactose is present, E. coli will produces the 3 structural enzymes • Meaning this will make the “protein” or go through induction…..so it can break down lactose!

  36. Gene Expression in Prokaryotes • http://www.phschool.com/science/biology_place/biocoach/lacoperon/genereg.html • GREAT ANIMATION TO REVIEW AT HOME!

  37. Gene Expression in Prokaryotes • Operon: series of genes coding for specific products = “lac” operon • Operon = structural genes + promoter + operator

  38. Gene Expression in Prokaryotes • Promoter: segment of DNA recognized by RNA polymerase which then starts transcription • Operator: segment of DNA that acts as “switch” by controlling the access of RNA polymerase to promoter

  39. Prokaryotic On & Off switches • Transcription can be turned “on or off” depending on what the cell needs • When turned “off” a repressor protein is bound to DNA in front of the gene • To turn a gene “on” an inducer (lactose) binds to the repressor, causing it to fall off….then gene is expressed

  40. Repression Activation

  41. Gene Expression in Eukaryotes • Have not found “operons” in eukaryotes • Genomes are larger & more complex • Organized into introns and exons • Through removal of introns from pre- mRNA

  42. Controlling Transcription in Eukaryotes

  43. Removal of Introns After Transcription

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