Presentation on theme: "A quick review! AKA: What you SHOULD know by now. DNA is copied during the S phase of the cell cycle. What is a gene? A segment of DNA that codes for a."— Presentation transcript:
A quick review! AKA: What you SHOULD know by now. DNA is copied during the S phase of the cell cycle. What is a gene? A segment of DNA that codes for a protein or RNA molecule. The structure of chromosomes: A chromosome consist of DNA tightly coiled around proteins.
Changes in DNA are called Mutations. Original DNA strand: ABCDEFG Types of mutations: 1)Deletion: ABCEFG – a nucleotide is missing 2) Substitution: ABKEFG – a nucleotide is substituted (K for C). 3) Insertion: ABGCDEFG – a nucleotide is inserted (G). All other nucleotides are present. 4) Translocation: ABCDJEFG – a nucleotide is brought in that is not in the original strand at all. 5) Replication: ABBCDEFG – a nucleotide is repeated.
And, last but not least- don’t forget Mendel’s Theory of Heredity: 1)For each inherited character, an individual has 2 copies of the gene- one from each parent. 2)There are alternative versions of genes. 3)When two different alleles occur together, one of them may be completely expressed, while the other may have no observable effect on the organism’s appearance. 4)When gametes are formed, the alleles for each gene in an individual separate independently of one another.
Chapter 9. Pg 189 DNA: The Genetic Material Section 1 Key Terms: Vaccine: a substance that is prepared from killed or weakened disease-causing agents, including certain bacteria. Virulent: Describes an organism that is able to cause disease. Transformation: A change in genotype caused when cells take up foreign genetic material. Bacteriophage: AKA ‘phage’; it is a virus that infects bacteria. QUIZ TOMORROW ON THESE TERMS.
A Little History Frederick Griffith was researching a vaccine for pneumonia and discovered that genes could be changed when cells take up foreign material. This change in genetic material is called transformation.
In order to find a vaccine, he used two strains of bacteria. The two strains were called Steptococcus pneumonia or S. pneumoniae. One strain was enclosed in a capsule made of polysaccharides that protected it from the immune system. This characteristic, helped make this strain be able to cause pneumonia. This ability to cause disease makes an organism virulent. This strain was virulent. The capsule around strain one strain causes the bacteria to grow with smooth edged colonies in a petri-dish. This is call the “S bacteria” or Smooth strain. Mice infected with the S bacteria died. The second strain did not have a polysaccharide coat, so it was unable to cause disease. In a petri-dish, this bacteria causes round edged colonies. It is referred to as the‘Rough Strain’ or ‘R-strain ’. Mice infected with the R bacteria did not die. S. pneumonia
This is what he knew, but he didn’t know why it happened.
Griffith wanted to know what was causing the death. He knew the only difference between the two strains was the presence of a capsule on the S strain. So, he injected dead S strain into the mice. This left only the capsule alive in the mice. But, the mice did not die. ____________________________________ Next, he made a vaccine of weakened S strain bacteria, by raising their temperature. This produced “heat-killed” bacteria. Heat killing bacteria allows bacteria to stay alive, but prevents them from being able to reproduce. The mice still lived. ___________________________________ This meant that the capsule was not the cause of death. Next, he mixed the harmless R strain bacteria with the harmless heat killed bacteria. This mixture killed the mice. When he examined the dead mice, he found that the harmless R strain had acquired capsules and became harmful S bacteria while in the mice. This change is called transformation, but he didn’t know how it had occurred.
100 years later, Oswald Avery and his team discovered that DNA was the source of this transformation, not proteins. His experiments showed that DNA contained the instructions of making the capsule around the bacteria.
Viral Genes & DNA Although Avery had shown that DNA was responsible, many scientists still believed protein was responsible. They knew protein had many important responsibilities in a cell but, they didn’t know much about DNA. 1952: Alfred Hershey & Martha Chase. At this time, it was known that viruses were made of DNA or RNA and were surrounded by a protective protein coat. These are called bacteriaphages or phages. They are viruses that infect bacterial cells. Once inside the cell, they reproduce and create more viruses. The bacteria cell ruptures and the new viruses are released.
Hershey & Chase concluded that the DNA of viruses is injected into the bacterial cells, while most of the viral proteins remain outside. The injected DNA molecules causes the bacterial cells to produce more viral DNA and proteins.
Homework: DUE TUESDAY Page 193 # 1 and # 6. NOW Section 1 Vocabulary quiz.
Section 1 Bellwork Quiz Take out one sheet of paper. Match the terms with the correct definition. A)Vaccine B)Virulent C)Transformation D)Bacteriaphage 1) This describes a microorganism or virus that causes disease and that is highly infectious. 2) A virus that infects a bacteria. 3)A substance prepared from killed or weakened pathogens and introduced into a body to produce immunity. 4)The transfer of genetic material in the form of DNA fragments from one cell to another or from one organism to another.
Section 1 Scientist Bellwork Answer the following questions using the choices below. Write the correct letter. 1)Who discovered transformation? 2)Who performed the first experiment that correctly identified the molecule that carries genetic info as DNA and not proteins? Choices: A)Oswald Avery B)Martha Chase C)Frederick Griffith D)Alfred Hershey
Section 2: The structure of DNA Key Terms: 1. Double Helix 2. Nucleotide 3. Deoxyribose 4. Base-Pairing Rules 5. Complementary Base Pair Quiz tomorrow on these terms.
Watson and Crick Found the model of DNA. This model showed how DNA was able to serve as the genetic model. They discovered: -That a DNA molecule is a double helix. -That each strand is made up of linked nucleotides. -Each nucleotide is made up of three parts: 1) A phosphate group (same for each nucleotide in a molecule of DNA). 2) A 5-carbon sugar molecule (deoxyribose- same for each nucleotide in a molecule). 3) A nitrogen-containing base (may be adenosine, guanine, thymine, or cytosine).
DNA Nitrogen Bases: There are 2 groups and 4 bases. PurinesPyrimidines Purines are nucleotides that are bulky and double-ringed. Pyrimidines are nucleotides that are small and single- ringed. The nitrogen base in a nucleotide can be Thymine, Cytosine, Adenine, or Guanine.
Base Pairing Rules Purines (Adenosine or Guanine) are always paired with pyrimidines (Thymine or Cytosine). An Adenosine base on one strand always pairs with the Thymine base on the opposite strand with 2 hydrogen bonds. A Guanine base on one strand always pairs with the Cytosine base on the opposite strand with 3 hydrogen bonds. This pairing is due to the structure and size of the nitrogen bases. The hydrogen bonds keep the two strands of DNA together. The strictness of base pairing rules results in two strands of DNA that contain complementary base pairs. This means that the sequence of bases on one strand will determine the sequence of bases on the other strand.
Who discovered this stuff? Chargaff: 1948, Erwin Chargaff discovered that for each organism he studies, the amount of adenine always equaled the amount of thymine and that the amount of guanine always equaled the amount of cytosine. Now, we know why. Wilkins and Franklin: Developed high X-ray diffraction photographs of strands of DNA. These photos suggested that DNA resembled a tightly coiled helix and was composed of three chains of nucleotides. Watson and Crick: They took this info and their knowledge of chemical bonding and determined the structure of DNA.
Homework Study Section 2 terms and end of section questions (pg 197 #1,4,5,6). Be ready for a Bellwork Quiz on vocabulary.
Section 2 Vocab Quiz Take out one sheet of paper. Number your paper 1-5. Match the terms (the correct letter) with the correct definition. 1. Double helix 4. Base-Pairing Rules 2. Nucleotide 5. Complementary Base Pairing 3. Deoxyribose a. The rules stating that cytosine pairs with guanine and adenine pairs with thymine in DNA, and that adenine pairs with Uracil in RNA. b. In a nucleic-acid chain, a subunit that consists of a sugar, a phosphate, and a nitrogenous base. c. A characteristic of nucleic acids in which the sequence of bases on one strand is paired to the sequence of bases on the other. d. The spiral staircase structure characteristic of the DNA molecule. e. A five-carbon sugar that is a component of DNA nucleotides.
Sec 3: The Replication of DNA DNA Replication: the process of making a copy of DNA. Steps of DNA Replication: 1)An enzyme called DNA helicase breaks the hydrogen bonds that link the two DNA strands together. The double helix unwinds and the two original DNA strands separate. Once the two strands are separated, additional proteins attach to each strand in order to hold them apart and keep them from wrapping back together. The areas where the strands are held apart are called replication forks. 2) At the replication fork, DNA polymerases add complementary nucleotides to each strand, according to the base pairing rules. 3) Two DNA molecules form that are identical to the original DNA molecule.
1)DNA helicases separate the two original DNA strands. 2)DNA polymerases add complementary nucleotides to each strand. 3)Two DNA molecules form that are identical to the original DNA molecule.
Checking For Errors If an error occurs and the wrong nucleotide is added to the strand, this is corrected with DNA polymerases. As DNA polymerases are adding nucleotides, they can only move on to the next one if the previous one is correctly paired to its complementary base. If there is a mismatch, then the DNA polymerases can move backwards and make the correction. This “proofreading” reduces errors in DNA replication to about one error per 1 billion nucleotides.
The Rate of Replication In prokaryotes, DNA molecules are circular. So, there are two replication forks that form at a single point and replicate DNA by moving away from each other until they meet on the other side of the DNA circle. If eukaryotes (humans) were done in this same way, it could take 33 days to replicate a strand of DNA.
Each human chromosome is replicated in about 100 sections that are 100,000 nucleotides long, each section have its own starting point. Since this means that multiple replication forks are working at the same time, an entire human chromosome can be replicated in 8 hours. This process occurs at multiple places throughout the strand of DNA, until replication is complete.