Test

• DNA


  Deoxyribonucleic Acid, the molecule that transmits traits (genes) from parent to offspring
• Miescher


  • Isolated a substance known as "Nuclein" from white blood cells
  • Said that nuclein was composed of an Acid portion (he called it nucleic acid) and an alkaline portion (later shown to be a protein)
• Research after Miescher


  • Nuclein was made up of a series of strand-like complexes of nucleic acids and proteins tightly bound together
  • These strands were called Chromosomes
• Levene


  • Isolated two types of Nucleic acids distinguished by type of sugar in them
  • RNA - Ribonucleic Acid (contains a 5 Carbon sugar called "Ribose")
  • DNA - Deoxyribonucleic Acid (contains a 5 carbon sugar called "Deoxyribose (deoxy = no oxygen))
  • Showed that nucleic acids are made up of long chains of individual units called nucleotides
  • Said that DNA and RNA contained equal amounts of nucleotides (this was an error, later disproved)
• Nucleotide


  A structure composed of a 5 carbon sugar, phosphate group and a Nitrogen base
• Nitrogen Bases in DNA

  • Adenine (A)
  • Guanine (G)
  • Cytosine (C)
  • Thymine (T)
• Nitrogen Bases in RNA

  • Adenine (A)
  • Guanine (G)
  • Cytosine (C)
  • Uracil (U)
• Griffith


  • Studied bacteria and pneumonia
  • Found that dead pathogenic bacteria passed on their pathogenic properties to live non-pathogenic bacteria
  • Called this the Transforming Principle
• Transforming Principle


  The idea that genetic information can be transferred from one organism to another
• Avery, MacLeod, McCarty experiment

  1. Treated pathogenic bacteria with protein destroying enzyme (transformation still occurred)

  2. Treated the pathogenic bacteria with DNA destroying enzyme (transformation stopped)

  3. Treated bacteria with RNA destroying bacteria, but not DNA (transformation occurred)
• They proved that DNA was the material responsible for the transforming principle
• Chargaff


  • Overturned Levene's conclusion about nucleotides
  • Found that the four nucleotides were NOT present in equal amounts, but in varying proportions
  • The nucleotide composition from members of the same species is constant
  • In any sample of DNA, the amount of Adenine = Thymine and Guanine = Cytosine (Chargaff's Rule)
• Chargaff's Rule


  In any sample of DNA the amount of Adenine = Thymine and Guanine = Cytosine
• Hershey and Chase experiment

  • Used radioactive labeling on DNA of one phage and protein coat of another phage
  • Allowed phages to infect bacteria (E. coli)
  • First sample (radioactive phage DNA) the bacteria became radioactive, surrounding fluid did not
  • Second sample (radioactive protein coat of phage) the bacteria did not become radioactive, the surrounding fluid did
  • Concluded that only the DNA from the virus entered the bacterial cells, therefore transmission of genetic material from the virus to bacteria happened only because the DNA was injected into the bacteria
• DNA became known as the molecule that transmits genetic information
• Wilkins and Franklin


  • Did work on determining the structure of nucleic acids and DNA
  • Took X-rays of DNA that proved it had a "helical" or "twisted" shape
  • Found that DNA had 2 distinct and repeating patterns
  • Found that Nitrogenous bases were "hydrophobic" and contained within the center of the helical structure
  • Found that the sugar-phosphate backbone was "hydrophilic" and was located on the outside
• Watson and Crick


  • Worked on different models of the "helical" structure using the knowledge of Wilkins and Franklin
  • Produced the structural model of DNA that is still in use today
  • They called their model the "DOUBLE HELIX"
• DNA


  • Long molecule made up of TWO (2) strands of nucleotides bound together in the shape of a double helix (twisted Ladder)
  • Found in the nucleus of cells
  • Each rung of the ladder is composed of repeating units called Nucleotides
• Nucleotide


  Subunit of the DNA molecule made up of a Phosphate Molecule, 5 carbon sugar (Deoxyribose in DNA, Ribose in RNA), and a Nitrogen base (A, T, C or G)
• Nitrogen Bases


  • Molecules containing nitrogen that form the "rungs" in the DNA double helix
  • Adenine bonds with Thymine, Guanine bonds with Cytosine
  • Purines (Adenine and Guanine) have a double ring structure, Pyrimidines (Thymine and Cytosine) have a single ring structure
• In the DNA molecule 1 Pyrimidine bonds with 1 Purine (Hydrogen bonds keep them together)
• DNA is 'antiparallel'


  The phosphate bridges (backbone) of the molecule run in opposite directions in each strand, the 5' end of one strand is opposite the 3' end of the other strand and vice versa
• RNA


  • Single stranded nucleic acid found inside and outside the nucleus of cells
  • Structure similar to DNA except RNA has 5 carbon sugar called "Ribose" and 4 nitrogen bases (Adenine, Guanine, Cytosine, Uracil)
• Types of RNA


  • mRNA - Messenger RNA (found in the nucleus, carries genetic message to ribosomes)
  • tRNA - Transfer RNA (found in the cytoplasm, brings amino acids to ribosomes)
  • rRNA - Ribosomal RNA (found at the ribosomes, helps make up ribosomes)
• Chromosomes


  • Consist of one linear double stranded DNA molecule wrapped around proteins called histones
  • The DNA is wrapped around a group of 8 histone molecules making a "bead-like" structure called a Nucleosome
  • The nucleosomes fold back upon themselves making a condensed structure called a chromosome
• Composition of a Chromosome

  • 60% protein
  • 35% DNA
  • 5% RNA
• Gene


  Small segment of DNA found on a chromosome that codes for specific traits in organisms
• Genome


  The sum of the entire DNA carried within the cells of an organism
• Exons


  Portions of DNA in a gene that are called "Coding Regions" and code for specific proteins
• Introns


  Portions of DNA in a gene that are "noncoding" and were once called "junk" or "nonsense" DNA
• DNA Replication


  • The process of making a copy of the DNA molecule
  • DNA Replication is Semi-conservative, meaning each new molecule contains one strand of parental DNA and one strand of new DNA
• DNA Replication


  1. Initiation

  2. Elongation

  3. Termination

  4. Proofreading and Correction
• Initiation


  1. Enzymes called helicases unzip and open up the DNA creating Replication Forks

  2. DNA Polymerase inserts itself in the replication fork and begins to add NEW nucleotides, one at a time, to create a new complementary strand
• Elongation


  1. At the 3' exposed end of the DNA molecule (Leading Strand), DNA Polymerase adds new nucleotides from 5' to 3' direction

  2. Short copies of DNA are made in spurts called Okazaki fragments on the Lagging Strand, in the opposite direction to the Leading Strand

  3. DNA Ligase stitches together the Okazaki fragments to make a complete strand of DNA
• Termination


  • The stopping of the copying of the DNA molecule, normally when replication forks meet each other or the end of a linear piece of DNA is reached
  • Results in strands of DNA that are SHORTER than the originals due to the removal of RNA primers
• Telomeres


  • Segments of highly repetitive nucleotide sequences at the ends of chromosomes that do not contain coding genes
  • In humans, telomeres consist of the sequence TTAGGG repeated several thousand times
  • As more DNA replications happen, the length of telomeres shortens, directly relating to the death of a cell
• Telomerase


  An enzyme related to keeping telomeres long, helps maintain the longevity of a cell
• Proofreading and Correction


  The process whereby DNA polymerase moves along the newly completed DNA strand looking for mismatched nucleotides and corrects them by inserting the correct nucleotides
• Protein Synthesis


  The process whereby the instructions from DNA are used to create polypeptides that make up a protein, also known as Gene expression
• Polypeptide


  Long chains of amino acids, 2 or more polypeptides joined together = a protein