Presentation on theme: "The Molecular Basis of Inheritance"— Presentation transcript:
1The Molecular Basis of Inheritance Chapter 16 NotesThe Molecular Basis of Inheritance
2Concept 16.1Once Morgan showed that genes are located on chromosomes, DNA and proteins became the candidates for the genetic material.- at the time nucleic acids seemed too uniform to be responsible for the multitude of possible traits.
3Concept 16.1The role of DNA in heredity was first studied by using bacteria and viruses.Griffith (1928) was studying streptococcus pneumonia.- used 2 strains (pathogenic and harmless)
5Concept 16.1- Griffith found that when he killed the pathogenic bacteria with heat and then mixed the cell remains with living bacteria of the harmless strain, some of the living cells were converted into the pathogenic form.
6Concept 16.1Transformation: a change in genotype and phenotype due to the assimilation of external DNA by a cell.Avery (1944) purified various chemicals from the heat killed bacteria to recreate Griffith’s experiment. Only DNA worked.
7Concept 16.1More evidence was found from viruses that infect bacteria.A virus is basically DNA enclosed by a protective coat of protein.Bacteriophages (or phages): viruses that infect bacteria
12Concept 16.1 The monomer of nucleic acids are nucleotides - each consists of 3 parts: a nitrogenous base, a pentose sugar called deoxyribose, and a phosphate group.
13Concept 16.1- the base can be adenine (A), thymine (T), cytosine (C), or guanine (G).It was found that even though the DNA varies from one species to another, the amounts of bases are in characteristic ratios
15Concept 16.1Watson and Crick are credited with finding that DNA is formed of two complementary strands called a double helix.- in each rung, a purine (A and G) will bind to a pyrimidine (T and C)- A binds to T, G binds to C
18Concept 16.2During DNA replication, base pairing enables existing DNA strands to serve as templates for new complementary strandsThree theories for DNA replication: conservative, semiconservative, dispersive
20Concept 16.2It was found that the semiconservative model was the actual model used by cells.- the first step is separation of the strand- secondly, each parental strand serves as a template for a complementary strand
25Concept 16.2A series of enzymes carries out the steps of DNA replicationOrigins of Replication: place where replication begins- specific sequence of DNA- may be more than one on a DNA strand- forms a replication fork
29Concept 16.2DNA polymerase adds nucleotides only to the free 3’ end of a growing DNA strand.A new DNA strand can elongate only in the 5’ 3’ direction.- leading strand: DNA strand made by this mechanism; works toward the replication fork
30Concept 16.2To elongate the other strand, polymerase must work in the direction away from the replication fork. This is the lagging strand- Okazaki fragment- DNA ligase: joins Okazaki fragments to make a single DNA strand
36Concept 16.2Enzymes proofread DNA during its replication and repair damage in existing DNA.- DNA polymerase proofreads its work- Mismatch repair: special enzymes fix incorrectly paired nucleotides.- nuclease; nucleotide excision repair