Unit 3: Molecular Genetics PDF

Unit 3: Molecular Genetics 6.1 – The Molecular Basis of Inheritance  Learning Goal To understand that DNA contains all the genetic information for any living organism.  DNA: Deoxyribonucleic acid DNA is the primary carrier of genetic information in living organisms. Respon...

Unit 3: Molecular Genetics 6.1 – The Molecular Basis of Inheritance  Learning Goal To understand that DNA contains all the genetic information for any living organism.  DNA: Deoxyribonucleic acid DNA is the primary carrier of genetic information in living organisms. Responsible for ensuring the genetic continuity of a species. DNA is the molecular material responsible for the transmission of hereditary information. – Passed through chromosomes (Humans have 46) – The number of chromosomes can vary from species to species.  The chromosomes unravel after cell division takes place and become functional and is spread throughout the new nucleus. Our DNA codes for each protein that our body requires. When a protein needs to be produced the gene that is responsible for coding the protein becomes activated. Gene: the coding region of DNA which contains instructions for building the proteins that are responsible for each inherited trait. The nucleotide sequence is then copied into a molecule of ribonucleic acid (RNA).  RNA moves into the cytosol – sequence is translated by ribosomes into amino acid chains called polypeptides. Polypeptides are modified to form functional proteins – Protein synthesis. How do we know that DNA is inherited?  In 1865, Gregor Mendel presented his findings of his research on patterns of inheritance in garden peas to the Natural Science Society in Brunn, Austria. His results were not widely recognized at the time but over the next few decades scientists found that Mendel’s principles were consistent with emerging theories in biology and with the idea that species change and evolve over time. Today, Mendel’s work is recognized as the foundation of modern genetics. 6 Gregor Mendel (1822-1884) 7 - Mendel discovered through pollinating selected plants that traits become predictable. - Inherited characteristics - Factors from a given trait were passed from parent to offspring. - Genotype coded for phenotype 8 The Genome The complete set of an organism’s hereditary information. 23 homologous pairs of chromosomes – More than 20,000 different genes found in each pair of chromosomes – Combine to form 3 billion base pairs – In February 2001, scientists successfully decoded the human genome through the “Human Genome Project” Frederick Griffith: The Transformation Principle One bacteria takes up DNA from a dead cell of the same species or related species In transformation, there is a decrease in the population There is an increase in genetic variety Griffith’s Streptococcus Experiment An example of transformation Virulent: Extremely infectious R-Strand (no signs of pneumonia S- Strand (contracts pneumonia)  Avery, McLeod and McCarty DNA Transformation Confirmed Completed a similar experiment to Griffith using different strands of Streptococcus bacteria S- Strain bacteria was virulent R- Strain bacteria was not harmful They were trying to determine if the DNA, RNA or Proteins were responsible for making the normally harmless strands virulent. Heat killed the bacteria and treated the dead bacteria with one of three enzymes to destroy one of the three possible transforming substances. Clearly supported that DNA was the transforming substance  Hershey and Chase: DNA the Hereditary Material While you watch the following video, make notes about the procedure and the outcome of the Hershey and Chase experiment. https://www.youtube.com/watch?v=g9JQURwseIY  The Structure of DNA DNA (deoxyribonucleic acid): a chain of units of nucleotides One nucleotide consists of 3 parts: – a phosphate group – a deoxyribose sugar – a nitrogen base (one of four)  There are 4 types of nitrogen bases: – Adenine (A) – Thymine (T) – Cytosine (C) – Guanine (G) These nitrogen bases are found in pairs, creating two strands of nucleotides that form a ladder like appearance This type of pairing is called complementary base pairing (A with T, G with C) – Because of this pairing, the order of the bases in one strand determines the order of the other  DNA is made up of two strands of repeating DNA nucleotides that run in opposite directions (anti- parallel) The sugar and phosphates alternate making up the backbone or "rails" of the "ladder" Nitrogen bases connect at the center creating the "rungs" of the ladder  Complementary acid base pairing occurs – A will only connect with T – C will only connect with G One strand encodes for traits (the coding strand), the other strand is called the non- coding strand  Notice the left rail reads P,S,P,S from top to bottom, and the other rail is flipped and reads S,P,S,P from top to bottom (anti- parallel) The DNA ladder like structure is twisted to form a "double helix"  Wilkins and Franklin: X-Ray crystallography – A sample compound deflects the X-rays creating a specific pattern on a photographic plate. – This can be analyzed to determine molecular structure. Franklin and Wilkins determined that the sugar phosphate backbones were on the outside of the molecule. They also suggested that DNA forms a double helix.  Watson and Crick The building of a DNA model Using information from previous scientist (Wilkins, Griffith, etc.) they were able to build the first accurate model of DNA