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Ch 12- DNA and RNA Frederick Griffith carried out experiments to find out how bacteria produce pneumonia – Used mice and injected them with samples of.

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Presentation on theme: "Ch 12- DNA and RNA Frederick Griffith carried out experiments to find out how bacteria produce pneumonia – Used mice and injected them with samples of."— Presentation transcript:

1 Ch 12- DNA and RNA Frederick Griffith carried out experiments to find out how bacteria produce pneumonia – Used mice and injected them with samples of bacteria- heat killed bacteria and harmless bacteria-no mice died – Mixed the samples of bacteria and mice died from pneumonia Transformation- process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria Griffith hypothesized some factor was transferred from the heat killed cells into the live cells- transforming factor might be a gene

2 Oswald Avery decided to repeat Griffith’s work in 1944 – Wanted to find which molecule in heat killed bacteria was most important for transformation – Made extract from heat killed bacteria, treated it with enzymes that destroyed proteins, lipids, carbohydrates and RNA- transformation still occurred – Repeated experiment, used enzymes that would break down DNA-transformation did not occur Avery and other scientists discovered that the nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next

3 Alfred Hershey and Martha Chase perform experiment in 1952 using bacteriophages – Bacteriophages- virus that infects bacteria, composed of DNA or RNA core and a protein coat – Used different radioactive markers to label the DNA and proteins of bacteriophages – The bacteriophages injected only DNA into the bacteria, not proteins Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein

4 Components and Structure of DNA What is the overall structure of DNA molecule? – DNA has a double helix, in which two strands are wound around each other – DNA is made up of nucleotides- made up of 3 parts; deoxyribose molecule, phosphate group, and nitrogenous base 4 kinds of nitrogenous bases in DNA – Adenine, cytosine, guanine, thymine Base Pairing – A=T and G=C always unless there is a mutation or error – Discovered by Watson and Crick

5 Sec 2- Chromosomes and DNA Replication Where is prokaryote’s DNA found? Eukaryotes have as much as 1000 times more DNA than prokaryotes Where is eukaryote’s DNA found? DNA molecules are very long and folded into tiny chromosomes Chromosomes contain both DNA and protein Chromatin- consists of DNA that is tightly coiled around proteins called histones Nucleosome- beadlike structure made up of DNA and histone molecules – Fold enormous lengths of DNA into tiny space in nucleus Strands of nucleosomes are tightly coiled and supercoiled to form chromosomes


7 DNA Replication DNA replication – DNA molecules separates into two strands by helicases – Then produces two new complementary strands following the rules of base pairing – Each strand of the double helix of the DNA serves as a template, or model, for the new strand DNA replication is carried out by series of enzymes – Enzymes unzip a molecule of DNA – DNA polymerase- principal enzyme that is involved in replication, proofreads each new DNA strand, polymerizes individual nucleotides to produce DNA Video Clips for Biology! Animation Quiz 2 - DNA Replication Fork

8 Sec 3- RNA Protein Synthesis Genes- coded DNA instructions that control the production of proteins within the cell DNA must be copied into RNA- they contain coded information for making proteins Structure of RNA – Consist of long chain of nucleotides made up of 5- carbon sugar, phosphate group, and nitrogenous base Differences between DNA and RNA – Sugar in RNA is ribose instead of deoxyribose – Single stranded – Contains uracil in place of thymine

9 Types of RNA What is the function of RNA? – Protein synthesis – Controls the assembly of amino acids into proteins 3 main types of RNA: messenger RNA, ribosomal RNA, and transfer RNA – Messenger RNA (mRNA)-carry copies of instructions from DNA to rest of cell – Ribosomal RNA (rRNA)- type of RNA that combines with protein to make ribosomes – Transfer RNA (tRNA)- transfers each amino acid to the ribosome as it is instructed to by mRNA

10 Transcription Process in which RNA molecules are produced by copying part of nucleotide sequence of DNA into a complementary sequence in RNA How does this happen? – RNA polymerase binds to DNA and separates the DNA strands – RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA How does RNA polymerase know where to start and stop making an RNA copy of DNA? – Will only bind to promoters- signals in DNA, have specific base sequences – Similar signals to stop transcription Video Clips for Biology! Tutorial 12.1 Transcription

11 Genetic Code Genetic code- known as the language of mRNA instructions Codon- consists of three consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide-64 possible – UCGCACGGU- this sequence is read three bases at a time UCG-CAC-GGU- the codons represent the diff amino acids – Serine-Histidine-Glycine – Polypeptide- long chains made up of amino acids Start codon= AUG Stop codon= UGA, UAA, UAG

12 Translation Process in which a mRNA message is decoded into a polypeptide chain – Takes place on ribosomes – Production of proteins What happens during translation? – Messenger RNA is transcribed in the nucleus, and released into cytoplasm – Translation begins at AUG (start codon), as each codon of the mRNA moves through ribosome, amino acid is brought into ribosome by tRNA, amino acid is transferred to growing polypeptide chain tRNA has 3 unpaired bases (anticodon)- complementary to one mRNA codon – Polypeptides join assembly line, continues until one of the three stop codons is reached – Protein synthesis – Video Clips for Biology! Video Clips for Biology!

13 Sec 4- Mutations Mutations- changes in the genetic material, mistakes during copying of DNA Gene mutations- changes in a single gene – Point mutation- involving changes in one or a few nucleotides, occur at single point Examples- substitutions- one base is changed to another – Frameshift mutation- mutation that shifts the “reading frame” of the genetic message by inserting or deleting a nucleotide Examples- insertions and deletions- may change every amino acid that follows point of mutation

14 Chromosomal mutations- changes in the number or structure of chromsomes – May change locations of genes on chromosomes – May change number of copies of some genes Examples – Deletion- involves the loss of all or part of a chromosome – Duplications- produce extra copies of parts of a chromosome – Inversions- reverse the direction of parts of chromosomes – Translocations- occur when part of one chromosome breaks off and attaches to another

15 Significance of Mutations Are all mutations harmful? Mutations may cause changes in protein structure or gene activity- harmful Mutations are source of genetic variability in a species- beneficial Cause of many genetic disorders Polyploidy- organism has extra sets of chromosomes. What good is this? – Polyploid plants are stronger and larger

16 Sec 5- Gene Regulation How does the cell determine which genes will be expressed and which will remain “silent”? Gene appears as a confusing jumble of 4 letters- patterns within those letters – Promoters- binding sites for RNA polymerase – Start and stop signals for transcription Cells filled with DNA binding proteins that help regulate gene expression

17 Gene Regulation Operon- group of genes that operate together – In E. coli three genes are turned off and on together to tell bacterium to use sugar lactose as food- lac operon – The lac genes are turned off by repressors and turned on by the presence of lactose Operator- regulatory region on one side of operon’s three genes – Lac repressor, DNA binding protein, binds to O region and prevents RNA polymerase- turns operon “off”

18 Eukaryotic Gene Regulation Principles of gene regulation between prokaryotes and eukaryotes are pretty similar- there are some important differences Most eukaryotic genes are controlled individually – Have regulatory sequences that are much more complex than those of lac operon Why is gene regulation in eukaryotes more complex than in prokaryotes? – Cell specialization

19 Development and Differentiation Do cells in multicellular organisms just grow and divide during embryonic development? – Differentiation- cells become specialized in structure and function Hox genes- series of genes that control the differentiation of cells and tissues in the embryo – Careful control of expression in these genes is essential for normal development

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