GENETICS 1 Classification, Heredity, DNA & RNA. Classification, Objectives At the end of this sub section you should be able to: Heredity, DNA and RNA

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1 Classification, Heredity, DNA and Objectives At the end of this sub section you should be able to: RNA Heredity and Variation Gene Expression DNA structure DNA Profiling Protein Synthesis 1. Discuss the diversity of organisms 2. Define the term species and heredity 3. Distinguish between inherited and acquired variation & give examples 4. Define the term gene and outline their role 5. Define the term gene expression 6. Know the structure of a chromosome 7. Outline the complex structure of DNA double helix 8. Name the four bases and the base pairs in DNA 9. Discuss the bonding in the DNA molecule 10. Distinguish between coding and non-coding structures 11. Define triplet/codon & base 12. Outline the structure of RNA 13. Name the bases in RNA 14. Discuss the replication of DNA 15. Define and discuss the stages involved in DNA profiling, give two uses 16. Define and give the use genetic screening 17. Explain the genetic code and how genes control cell activities by producing proteins 18. Describe the formation of mrna 19. Describe the function of a ribosome in protein synthesis 20. Understand the process of translation that leads to the formation of a new protein 21. Know that the shape of a protein determines its function 22. Outline the steps in protein synthesis 23. Discuss the role of mrna 24. Detail the process of transcription including the role of trna

2 Taxonomy: The science of classifying organisms Classification: Involves placing organisms into similar groups or categories based on similar traits Species: A group of similar organisms that are capable of naturally interbreeding with each other, but not with other such groups, to produce fertile offspring. - All species have different characteristics (Variation) between individual members. E.g: humans can be African American, Caucasian, Asian etc, all with different hair colour, eye colour, height, etc. Acquired Variation: Traits which are not genetically inherited but instead are learned or developed during life. E.g: speaking a language, reading, counting, driving a car. Inherited Variation: are controlled by genes and inherited from our ancestors. E.g: height, ear size, eye colour. Heredity/Genetic inheritance: passing on of features/traits from one generation to the next by means of genes. - Characteristics are traits/features that are genetically inherited. Just because you inherit the gene does not mean it is expressed ( heredity + environment). Gene: Section of DNA that required for the production of a protein. Unit of inheritance. Coding DNA. - Non-coding/Junk DNA: makes up 97% of a chromosome, in between the 3% that is genes, it has no known function. - Gene Expression involves the precise way in which the genetic information in a gene is decoded in the cell and used to make a protein. The way in which genes are read and their sequence used to make a protein. A gene is expressed if it is switched on in a particular cell. DNA in chromosomes is tightly packaged by Histone protein. Chromosomes are 40% DNA, 60% Histone.

3 DNA & RNA DNA: Deoxyribonucleic acid. RNA: Ribonucleic acid. DNA was discovered by Watson and Crick. It is arranged in a double helix shape. Nitrogenous Bases: Adenine, Thymine, Guanine, Cytosine. Backbone consists of phosphate, sugar (deoxyribose) molecules Complementary base pairs: Adenine Thymine (Uracil in RNA), Guanine Cytosine. A Nucleotide consists of a phosphate group, a deoxyribose sugar and a single base. The bases fall into two families: - Purines are double-ringed molecules: Adenine & Guanine - Pyrimidines are single-ringed molecules: Thymine & Cytosine Hydrogen bonds hold the base pairs together; - A-T has 2 hydrogen bonds, G-C has 3 hydrogen bonds DNA RNA A, T, G, C (Thymine) A, U, G, C (Uracil) Double-stranded Single-stranded Found in Nucleus Found in Nucleus and Cytoplasm The Genetic Code: DNA encodes proteins. Proteins are made up of combinations of hundreds or even thousands of Amino Acids joined together in a specific sequence. Amino Acids are coded for by 3 bases bound together in a particular sequence. This is called a triplet or codon. - Amino Acid: The basic building blocks of proteins. Approximately twenty in total. Building blocks of a protein. - Triplet/Codon: Group of three consecutive bases which code for an Amino Acid. Base = Letter, Triplet = Word, Gene = Paragraph, Genome = Book

4 Replication of DNA: Single-stranded chromosomes become double-stranded. DNA Replication Occurs during Interphase before the cell enters mitosis - The double Helix unwinds - A special enzyme breaks the bonds/separates the base pairs - Extra DNA bases in the cytoplasm enter the nucleus and an enzyme attaches them to the exposed complementary bases. - Each side of the molecule acts like a template for two new strands - Two new strands are now formed (each identical to each other and the original strand) - Each new piece of DNA rewinds to form a double helix, now a double stranded chromosome joined at centromere. DNA Profiling/Genetic Fingerprinting: is a method of making a unique pattern of bands from the DNA of a person, which can then be used to distinguish that DNA from other DNA. - DNA Profiles: can be used to establish whether biological tissue at a crime scene matches or does not match a suspect and to determine whether a person is or is not the parent of a child.

5 DNA profiling involves: - Cells are broken down to release DNA from the nucleus. - Restriction enzymes cut the DNA at specific sequences. - The DNA fragments are separated according to size by gel electrophoresis. The sample is added to a gel, an electric current is passed from one end to the other and causes the fragments to separate. - Radioactive material is added to the gel, it attaches to the bands of DNA and gets photographed to produce a DNA fingerprint. Applications of DNA profiling include: Forensic Analysis & Paternity Tests Genetic Screening: means testing DNA for the presence or absence of a particular gene or an altered gene, specific to a disease. Genes can have mistakes made during replication called mutations. These mutations can result in a protein not functioning properly and result in a disease. - Adult screening: Cystic fibrosis or Sicklecell anaemia. - Foetal screening: Cells can be removed from the placenta or fluid. - Genetic Counselling: couples with a history of genetic disorders in their family can receive advice and tests to let them make informed decisions about having children.

6 Protein Synthesis Genes are responsible for the formation of protein. The protein could be new body cells or enzymes. The base sequence of the DNA determines the properties of the new protein produced. Each 3 base group (triplet/codon) produces an amino acid. The amino acids form a protein. Synthesis occurs in the ribosomes in the nucleus of a cell. For Protein Synthesis you need: A supply of nitrogen bases (A, U, G, C) cytoplasm A supply of amino acids cytoplasm Instructions as how to join the amino acids together genetic code/triplets An assembly line ribosomes A messenger to carry information from DNA to ribosomes mrna Each mrna strand carries: 1. a start codon (AUG below) 2. a series of codons each of which will form a particular amino acid 3. a stop codon (UAA below) Three steps: Initiation, Transcription and Translation Transcription: is the copying of a sequence of genetic bases from DNA into messenger RNA (mrna). DNA mrna Translation: is the conversion of a sequence of genetic bases on mrna into a sequence of amino acids. mrna Protein Steps Initiation (In nucleus): An enzyme called RNA polymerase moves along DNA until it finds gene start site and unwinds and separates the double-stranded DNA until it reaches a a stop site at the end of a gene. Transcription (In nucleus): RNA bases (A, U, G, C) from the cytoplasm enter the nucleus and attach to one of the exposed strands. The RNA polymerase joins the bases together to form a strand of mrna. The single-stranded mrna strand then leaves the nucleus and enters the cytoplasm.

7 Translation (In Ribosome in cytoplasm): The mrna strand forms weak bonds with the rrna in a ribosome. (Ribosome made of rrna and protein). As it moves through the ribosome, complementary trna anti-codons attach to the exposed complementary mrna codons, one at a time. Starting at the triplet just after the start codon and stopping just at the stop codon. Each amino acid detaches from the trna and is joined together in a string by the ribosome. The trna s leave the ribosome pulling the mrna through it as they go. Once the stop codon is reached, the completed string of amino acids leaves the ribosome and folds into a functional protein. The shape of a protein determines its function. Every protein has a specific job to do and will only work correctly if it is in the correct shape.

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