Molecular Genetics DNA - PowerPoint Presentation

1. Molecular GeneticsDNA Structure and ReplicationChapter 11

2. * In the pasts, scientists argued about how genetic information was passed down and influcenced traits. * Some scientists believed in "blending" - that the traits of two parents are mixed.  * This doesn't work when a white flower and a 
  purple flowered plant have a white flowered 
  offspring. * Some scientists also believed that proteins were responsible for passing on traits, not DNA. They thought this because DNA molecules are so simple compared to proteins. History of Molecular Genetics

3. Griffith & Avery * Took pathogenic bacteria (cause disease) and killed 
  them with heat.  * Mixed the dead bacteria with harmless bacteria.   * When they injected the mix into mice, it killed them. * The harmless bacteria must have taken up  something from the dead, harmful bacteria that  transformed the harmless bacteria * It was the DNA! Current Thinking and the Experiments that Led to It

4. Current Thinking and the Experiments that Led to ItAvery, MacLeod, and McCarty * Tested what was being   transferred between the   bacteria...was it DNA?   RNA? Proteins? * Killed virulent bacteria * Subjected a sample to    RNAase, one to Protease, one to DNAase * The samples treated with    RNAase and Protease were still able to transform   harmless bacteria but   DNAase treated sample   could not * DNA must be the agent of    transformation

5. Current Thinking and the
Experiments that Led to ItHershey & Chase * Radioactively labeled DNA and proteins in viruses.  * They allowed the viruses to infect cells * Waited to see whether it was the DNA or the protein that entered   the cells to infect them. * Found DNA to be radioactive and therefore the genetic material

6. Chargaff's Rule * Identified pairing rule of bases * Adenine = Thymine (2 H bonds) * Guanine = Cytosine (3 H bonds) Rosalind Franklin * took the first picture of a DNA molecule using 
  a technique called x-ray crystallographyWatson & Crick  * used Franklin's picture and Chargaff’s ratios and cutouts to determine DNA structure Current Thinking and the Experiments that Led to ItDNA Structure videohttps://www.youtube.com/watch?v=C1CRrtkWwu0

7. Nucleotide - monomer of nucleic acids * DNA Nucleotide Structure - 3 Parts  1. Sugar (deoxyribose)  2. Phosphate group  3. Nitrogenous Base - 4 Kinds  1. Adenine  2. Guanine 3. Cytosine  4. Thymine * Purines and Pyrimidines are ring structures associated with the Nitrogenous base  * Purines - 2 rings  *EX: A and G  * Pyrimidines - 1 rings *EX: T and CDNA Structure

8. DNA is a molecule made of 2 strands of nucleotides * Individual strands are made by connecting sugars and    phosphates of nucleotides with a phosphodiester bond (type of covalent) * Forms sugar - phosphate backbone * The two strands are connected by hydrogen bonds 
  between the bases * The two strands are wound together into a double helix. DNA Structure

9. DNA StructureDirectionality of DNA strands * 3' end - end of each strand that has the hydroxyl group off  the 3rd carbon of the sugar molecule * 5' end - the other end which has a Phosphate group off the 5th carbon of the sugar molecule* Anti-parallel- The 2 DNA strands run in opposite directions to each other

10. DNA Organization * Chromosome - DNA wrapped around histone proteins (before cell division) * Chromatin - loose, uncoiled DNA (during Interphase) * Euchromatin - areas in chromosomes that are loosely opened so it  can be transcribed * Heterochromatin - areas in chromosomes that are compacted and  generally not transcribed* Gene - A segment of DNA that codes for a specific trait  * Telomeres - repeated nucleotide sequences at the ends of chromosomes   * they do NOT code for proteins  * TTAGGG in humans -- it is repeated about 2500 times  * 50 -200 base pairs of telomeric DNA are lost after every cell division  * Cells die after 20 - 30 divisions because telomeres are gone * Telomerase - some cells (bone marrow, stem cells, etc...) contain this enzyme which regenerates telomeres.   * Present in 90% of cancer cells as well DNA Organization

11. * Occurs during Synthesis phase of a cell's life * This is done to prepare for cell division so that each daughter cell is identical and contains all of the necessary chromosomes * Occurs during 2 major stages  1. Splitting the DNA  2. Building the new strandsDNA Replication

12. 1. Splitting the DNA * Helicase - an enzyme that breaks the hydrogen  bonds holding the two strands of DNA together. *starts at TATA boxes * Replication fork - point where the DNA opens  * Single strand binding proteins - hold the strands apart during replicationDNA ReplicationDNA replication simple http://www.dnatube.com/video/365/DNA-Replication

13. 2. Building the new strands * Primase - enzyme that lays down a short RNA primer (necessary for DNA polymerase to attach. This acts as a starting spot. * DNA polymerase – attaches new nucleotides to the growing strand. DNA can only add new nucleotide in the 3’ direction   DNA Replication

14. * Leading and lagging strands* DNA polymerase can only add nucleotides in the 5' - 3' direction (adding to the 3’ end)* Leading strand - runs 5' - 3'. Can be built continuously.* DNA Polymerase III – the enzyme that adds new nucleotides to build the growing LEADING strands.  DNA Replication

15. * Lagging strand - runs 3' to 5'. Must be built in chunks called Okazaki fragments As helicase unzips the DNA strands, RNA primase lays down an RNA primer. DNA polymerase II can now attach to the 3’ end of the RNA primer and adds DNA nucleotides in the 3’ direction. The RNA primer is later replaced with DNA nucleotides by DNA polymerase I.* Ligase - enzyme that stitches fragments of sugar-phosphate covalent bonds togetherDNA Replication

16. DNA ReplicationExtra phosphates on each 
nucleotide provide the 
energy for the process. 
Called "active monomers" 
or "phosphorylated 
nucleotides"DNA replication detailed summaryhttp://www.youtube.com/watch?v=vNXFk_d6y80

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18. DNA ReplicationDNA replication real time videohttp://www.hhmi.org/biointeractive/dna-replication-advanced-detailDNA Replication video detailed!http://www.dnatube.com/video/4197/Process-of-DNA-Replication

19. DNA Replication is often referred to as semi – conservative * Semi-conservative - Each new molecule of DNA is composed of one old (parent) strand one new (daughter) strand DNA Replication

20. Replication and TelomeresTelomere- ends of linear chromosomes with repetitive DNA sequence: TTAGGG Telomeres allow cells to distinguish chromosome ends from broken DNA and protect the DNA during cell divisionTelomeres help to delay cell deathTelomeres shorten with each cell division because DNA polymerase leaves 50-200 bp unreplicated on the lagging strand.Cellular senescence is triggered when telomeres are 4-6 kb

21. DNA Replication and TelomeresTelomerase- enzymes that adds telomeres to end of DNA strand. Only found in embryonic and stem cells (and cancer cells)

22. DNA RepairDNA suffers from environmental stresses, radiation, UV light, and carcinogens, which modify the DNA. In addition, internal errors formed during replication must be corrected * If any mistakes (mutations) are found, nucleases, polymerase and ligase will fix it * Nucleases - enzymes that double check that no mistakes were made  

23. DNA Replication - 
Overview12

24. Molecular GeneticsDNA  RNA  ProteinChapter 12

25. * DNA "makes us who we are" by coding for proteins * These proteins are responsible for our various phenotypes  * EX: DNA determines the color of the protein pigment made in your eyes and the amount of melanin pigment made in your skin that gives you your skin color. * Protein Synthesis - process by which a protein is made from the instructions contained in DNA* Requires help from another nucleic acid called RNA DNA & Proteins

26. * RNA = Ribonucleic Acid* Differences between RNA and DNA 1. RNA is single stranded 2. RNA has Uracil instead of Thymine 3. RNA has ribose, not deoxyribose* Three kinds of RNA 1. Messenger RNA (mRNA) - copies DNA's information and takes it out of the nucleus to a ribosome 2. Transfer RNA (tRNA) - picks up and transfers Amino Acids to the ribosome  * contain an amino acid at one end and an anti-codon at the other 3. Ribosomal RNA (rRNA) - one of the components of ribosomes helps to build the polypeptide chain/proteinRNA Structure & Function

27. RNA Structure & Function

28. * Two main stages of Protein Synthesis 1. Transcription * Occurs in the nucleus  * DNA   mRNA 2. Translation * Occurs at a ribosome  * mRNA  ProteinProtein Synthesis DNA RNA  PROTEIN

29. TRANSCRIPTION- Copying a gene from DNA to RNASteps *Binding/Initiation 1. Helicase splits DNA molecule  2. SSBP's hold DNA open  3. RNA Polymerase attaches to ONE of the DNA  strands at a promoter region  a. Promoter region - TATA box *Elongation 4. RNA polymerase builds a complementary mRNA strand in a 5' to 3' direction  a. Reminder: If there is an A in the DNA, a Uracil will be paired to it (no Thymine in RNA) *Termination 5. RNA stops when it reaches a termination sequence   a. sequence usually involves 'AAAAAAAA'   6. mRNA transcript detaches and DNA strands go back together Transcription

30. Transcription

31. mRNA must be processed before leaving the nucleus because it contains ‘junk’* Steps  1. mRNA transcript receives a cap and tail  a) 5' cap - cap of repeated G's at 5' end   b) 3' poly- A tail - tail of repeating A's at 3' end  * These protect the molecule and control its transport out of the nucleus.   2. Introns are excised and Exons are stitched together  a) Introns - pieces of mRNA that are not needed are  excised by spliceosomes and stay IN the nucleus  b) Exons - needed pieces of mRNA that code for proteins. They EXIT the nucleus and are Expressed. Exons are glued together by SnRP's (small nuclear ribonucleoproteins)* The finished product leaves the nucleus and joins w a ribosome to make proteins. The processing allows several proteins to be made from the same mRNA.mRNA Processing

32. mRNA ProcessingTranscription and Translation cartoon videohttps://www.youtube.com/watch?v=rKxZrChP0P4Transcription real time videohttps://www.youtube.com/watch?v=SMtWvDbfHLo&list=PLRSu0DZ2i6tGdGB8reN_yOyfkGq_AX2mE&index=3

33. * Central dogma- all organisms on earth have nucleic acid (DNA/RNA) that codes for proteins.* Every three “letters” of mRNA is called a codon. Each codon codes for one specific amino acid in the protein that will eventually be made.   DNA: TAC TGC CTC GAA GCC TCG ATC  mRNA: AUG ACG GAG CUU CGG AGC UAG Protein: AUG  Methionine (always at start of chain) ACG  Threonine GAG  Glutamic acid CUU  CGG  AGC  UAG Genetic Code

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36. * Steps of Translation - (now out of the nucleus)  1. Binding/Initiation a. mRNA & tRNA bind to small ribosomal subunit (40sv)  b. Smaller ribosomal subunit binds to larger one (60sv)  2. Elongation a. tRNA molecules bind to mRNA based on matching their anti-codon to mRNA codon  b. Amino acids are dropped off and hooked together via peptide bonds  c. Ribosome moves along mRNA, repeating process of bringing tRNA's in, forming peptide bond, and releasing tRNA's   3. Termination  a. Ribosome reaches a stop codon and the ribosomal complex breaks apartTranslation

37. * Ribsome has three sites  1. A site: where the tRNA is accepted/attaches  2. P site: where the polypeptide (protein) is built by making a peptide bond  3. E Site: where the tRNA exits the ribosomeTranslation

38. Translation* A gene must start with a start codon (initiator) that tells ribosome to start translating (AUG - methionine)* A gene will end with a stop codon (terminator) that tells the ribosome to stop translating  * There are 3 stop codons (no amino acids) (UAA, UAG, and UGA.* Many ribosomes can translate the same mRNA transcript at the same timeTranslation real time videohttps://www.youtube.com/watch?v=TfYf_rPWUdY&list=PLRSu0DZ2i6tGdGB8reN_yOyfkGq_AX2mE&index=4Transcription and Translation cartoon videohttps://www.youtube.com/watch?v=rKxZrChP0P4

39. Products of Translation* Proteins usually have to be processed before they can be used as well. This occurs at the ER* Proteins made on free ribosomes will be used within the cell* Proteins made on ribosomes are sent to Golgi to be shipped out of the cell or used in the cell membrane

40. Protein 
Synthesis 
Overview

41. Gene MutationsMutation - a change in DNA or chromosome* Causes (mutagens)   * Environmental factors  * Chemicals, sunlight  * Replication errors* Point mutation- impacts only one base (this is the most common type of mutation)  * Substitution- a base is replaced with another * Insertion- a new base is inserted – shifts the reading frame  * Deletion- a base is removed – shifts the reading frame * Non-sense mutation - inserts a stop codon that prevents a protein from being made* Mis-sense mutation - changes the protein being made* Silent mutation – Change in DNA, but no change in protein due to ambiguity of code.

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43. Mutations* Gene Mutations are usually neutral or have no affect. There are two reasons for this:    1. Mutations that occur in introns will not be expressed in the protein being made.   2. Mutations that affect the third letter in a codon often don’t change the amino acid  
  (Wobble effect)* Mutations can be harmful or beneficial   * EX: make a protein work more efficiently. * EX: make a protein inactive.* Mutations are an important source of new genetic variety. This is where new traits come from.DNA Mutations and Protein Synthesishttps://www.youtube.com/watch?v=GieZ3pk9YVo&index=2&list=PLIIJseG3DYUK0ijyvRoNqjMia9OvPNVjJ

44.  * Recessive disorders  * Sickle Cell Anemia   * point substitution of A for T on Beta-globin gene  * Cystic Fibrosis   * mutation in the gene cystic fibrosis transmembrane conductance regulator (CFTR) gene  * most common mutation is a deletion of three nucleotides that 
  results in a loss of the amino acid phenylalanine  * Hemophelia - MANY causes  * Tay-Sach's  * mutations of the HEXA gene on chrom. 15   * By 2000, more than 100 different kinds of mutations had been 
  identified in the HEXA gene * Phenylketoneuria  * mutation of PAH gene on chrom. 12   * More than 400 disease-causing mutations have been found in PAH gene. Gene Mutations

45.  * Dominant disorders  * Huntington's * All humans have the Huntingtin gene (HTT) on chrom. 4, which codes for the protein Huntingtin (Htt).   * Part of this gene is a repeated section (CAG) called a trinucleotide repeat  * it varies in length b/w individuals and may change length between generations.   * When the length of this repeated section reaches a certain point, it produces an altered form of the protein, called mutant Huntingtin protein (mHtt)  * This leads to increase in decay rate of certain neurons  * Leads to disease symptoms  * Affects muscle coordination and leads to cognitive decline and dementiaGene Mutations

46. Every cell in your body contains the same DNA, 
but some genes are shut off. ~For example, your eyeball cells don’t need the same proteins as your liver cells.  ~In humans these genes can be shut off by methylating them. There are also regulatory genes that can promote or inhibit the transcription of certain genes.Gene Regulation