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Structure and Function of DNA 4 3 5 9 2 7 1 8 6 10 RNA, what’s different from DNA? RNA has the base uracil (U) (Instead of thymine (T) in DNA) The RNA sugar has 2 OH groups vs 1 in DNA (Ribose vs deoxyribose) Names of structures? 2 1 4 3 5 Complementary = DNA: A-T, C-G; RNA: A-U, C-G What are the structures? And, which is which? Name of structure? What type of bond is this? Complementary = DNA: A-T, C-G; RNA: A-U, C-G Learning check 1. Along one strand of a DNA double helix is the nucleotide sequence GGCATAGGT. Want is the sequence for the other DNA strand? ___ ___ ___ ___ ___ ___ ___ ___ ___ 2. A molecule of DNA contains 2 polymer strands called _________ made by bonding many monomers called ____________ together. Each monomer contains 3 parts: __________, _________ and _________. 3. DNA and RNA are polymers of _______ monomers. 4. What type of bond joins the bases of complementary DNA strands? What is the flow of Genetic Information? From DNA 1 To RNA To Protein In 2 stages 2 DNA is transcribed The result is mRNA mRNA is then translated The result is a sequence of amino acids in a polypeptide But, what is the correspondence… Between nucleotides of an RNA And the amino acids of a polypeptide What are the 4 types of nucleotides? DNA: ATCG RNA: AUCG How do we get to protein? There are 20 amino acids in protein Each designated by a single letter How do the 4 nucleotides specify 20 amino acids? Amino acids are identified by triplets of bases which Specify all the amino acids What are the triplets of bases called? Cod ons The genetic code is The relationship between nucleotide sequence And amino acid sequence One DNA codon (3 nt) => one RNA codon (3 nt) => one amino acid How is this read? Learning check 1. How many nucleotides are necessary to code for a polypeptide that is 100 amino acids long? 2. An organism’s genetic information is stored within the sequence of ___________. 3. The genetic information is transcribed into a sequence of ____________. 4. (the answer to #3) are then translated into a sequence of ______________. 5. The nucleotide sequence of a DNA codon is GTA. The mRNA complementary sequence codon is _____. 6. The above codon codes for the _________ amino acid. Did you know that the genetic code is shared by all organisms? All 20 amino acids are common to all living systems The code is the same in different species After genes have been transferred, (one species to another) They can be transcribed and translated What does this allow for? Mixing genes from various species Tobacco plant expressing firefly gene Overview: What is the flow of genetic information? DNA RNA Protein In eukaryotic cells where does transcription occur? The nucleus Where is mRNA synthesized? The nucleus Where does translation occur? The cytoplasm What happens to protein as it is made? It coils It folds It forms a 3-D shape And, several polypeptide chains bind together What are each of these shapes called? How do genes control structures and activities of cells? Via transcription & translation processes Learning check 1. Information in a gene is a specific linear sequence of ____________ in DNA. 2. The gene serves as a template in ____________. 3. The gene produces a ___________ strand of mRNA. 4. mRNA specifies a linear sequence of ___________. The Genetic Basis of Cancer In recent years, scientists have learned more about the genetics of cancer What have they identified? That cells escape from control mechanisms This causes changes in some of the cells genes Or changes in the way certain genes are expressed Cancer causing genes First discovered in a chicken virus What is a (chicken) virus? Molecules of DNA or RNA Surrounded by protein How do they work? Become a permanent resident in host cells And, insert their nucleic acid into DNA Of host chromosomes What happens when they insert into a host cell? They make the host cell cancerous Is there something unique about the virus nucleic acids? They contain a gene that causes cancer Called an oncogene (tumor gene) In many cases we all have some of these genes… They are called ‘proto-oncogenes’ They are normal genes that can become oncogenes They are found in many animals They code for growth factors What do these growth factors do?? They are proteins that stimulate cell division Or, are others that affect the cell cycle What happens when these proteins malfunction? Uncontrolled cell growth - cancer What causes the proto-oncogene to malfunction? A mutation must occur Several types of mutations can occur A mutation within a gene An error in DNA replication = many gene copies The normal location of the gene is changed Proto-oncogene Gene mutation oncogene Hyperactive! Growth stimulating protein Multiple gene copies Gene location moved New promoter Normal growth stimulating protein, but in excess! In all cases, normal gene expression is changed => cell division Which cancer is one of the best understood? Colon cancer What is the progression of colon cancer? Begins as an unusually frequent division of normal-looking cells in the colon lining Several (4 or more) mutations are needed Activation of cellular oncogene And inactivation of 2 tumor-suppressor genes These mutations result in altered signal transduction pathways Then see full-fledged cancer cells Typical colon cancer progression - mutations Count the mutations… Normal cell Malignant cell What do the mutations lead to? Increased cell division And, structure of cell grossly altered Typical colon cancer progression – oncogene & TSG What are the cellular changes? DNA changes? Increased cell division Growth of benign tumor Growth of malignant tumor Oncogene activated Tumorsuppressor gene inactivated 2nd Tumorsuppressor gene inactivated What are cancer causing agents called? Carcinogens What is the carcinogen for these cancers? 1 Tobacco 2 UV radiation Microscopic changes that happen when a person smokes Normal lung tissue Abnormal lung tissue • Ciliated columnar epithelia • H = cilia sweep mucus • J = goblet cell produces mucus • L = basal layer of cells • Columnar cells becoming crowded out • Displaced by basal cells • Fewer cilia, reduced capability • Chemicals in tobacco toxic to cilia, paralyzing • Smokers cough Exam 3 Next Tuesday, 11/20/07 The exam covers: Chapter 8, Mitosis & Meiosis Chapter 10 Structure / Function of DNA Some cancer: Pages 128-129 & 211-215