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Chapter 2

Chapter 2. An Introduction to Genes and Genomes. Central Dogma. Central Idea of Genetics!. DNA RNA PROTEIN. Transcription. Translation. DNA Replication Animations. http://www.johnkyrk.com/DNAreplication.html

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Chapter 2

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  1. Chapter 2 An Introduction to Genes and Genomes

  2. Central Dogma

  3. Central Idea of Genetics! DNA RNA PROTEIN Transcription Translation

  4. DNA Replication Animations • http://www.johnkyrk.com/DNAreplication.html • http://www.bioteach.ubc.ca/TeachingResources/MolecularBiology/DNAReplication.swf • http://www.wiley.com/college/pratt/0471393878/student/animations/dna_replication/index.html • http://www.mcb.harvard.edu/Losick/images/TromboneFINALd.swf • http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swf • http://207.207.4.198/pub/flash/24/menu.swf • http://www.dnatutorial.com/

  5. DNA Replication • When a cell divides, it is essential that newly created cells contain exact copies of the DNA • Somatic cells divide by mitosis – one cell divides to produce daughter cells with an identical copy of the DNA • Gametes divide by meiosis – a parent cell divides to create four daughter cells with half the number of chromosomes (haploid cells)

  6. Semiconservative Replication Prior to cell division, DNA replicates itself by semiconservative replication

  7. Semiconservative Replication • Two complementary strands of the double helix are pulled apart • Two strands become templates for copying new strand • Two new strands of DNA are formed • Each new double helix contains one original parent strand and one newly synthesized strand

  8. Steps of DNA Replication (p. 34) • DNA Helicase • Replication Fork • Single-strand binding proteins • Origin of replication • RNA primers and RNA primase • DNA polymerase • 5’ to 3’

  9. Figure 2.9 – Semiconservative Replication of DNA

  10. Steps of DNA Replication (p. 34) • DNA Helicase – enzyme that separates the two strands of nucleotides by breaking the hydrogen bonds • Replication Fork – two strands separate and form a replication fork • Single-strand binding proteins – attach to each strand and prevent them from reforming double helix • Origin of replication – place where separation of strands occur • RNA primers and RNA primase – the enzyme primase create short sections of RNA called RNA primers to bond to parent strand • DNA polymerase – enzyme that binds to RNA primer and begins to copy new strand. DNA uses the parent strand as a template • 5’ to 3’ – DNA polymerase creates new strand in the 5’ to 3’ direction, always adding nucleotides to the 3’ end

  11. Leading and Lagging Strands in DNA Replication • DNA can only proceed in a 5’ to 3’ direction • Leading strand – continuous replication towards the replication fork • Lagging strand – discontinuous replication away from the replication fork • Short pieces of DNA are made called Okazaki fragments • DNA ligase – the enzyme that bonds the Okazaki fragments

  12. Protein Synthesis DNA (Transcription) Messenger RNA (Translation) Protein

  13. Protein Synthesis • Genes within DNA are copied into messengerRNA molecules (mRNA) in a process called transcription • mRNA molecules, which are exact copies of DNA, are deciphered into instructions for making a protein in a process called translation

  14. Transcription

  15. Transcription http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html http://www.johnkyrk.com/DNAtranscription.html http://www.biostudio.com/d_%20Transcription.htm http://207.207.4.198/pub/flash/26/transmenu_s.swf http://learn.genetics.utah.edu/units/basics/transcribe/

  16. Transcription Copying the Code • Transcription occurs in the section of DNA containing the gene. Adjacent to most genes is a promoter region, specific sequence of nucleotides that allow RNA polymerase to bind at a specific location next to the genes. 2. The enzyme RNA polymerase unwinds the DNA double helix and copies one strand of DNA into RNA. RNA polymerase separates the DNA strand and proceeds in a 5’ to 3’ direction along the DNA template to copy a complementary strand of RNA. 3. When RNA polymerase reaches the end of the gene, it encounters a termination sequence. The newly formed mRNA is released from the RNA polymerase and DNA. • Multiple copies of mRNA can be transcribed from each gene during transcription • Besides mRNA, Two other types of RNA are produced by transcription, transfer RNA (tRNA), ribosomal RNA (rRNA), and microRNA (miRNA).

  17. Transcription • The process of making RNA by copying part of the DNA sequence into a complementary RNA sequence

  18. Transcription • Requires enzyme RNA polymerase • RNA Polymerase binds to DNA and separates strands • RNA Polymerase uses DNA as template and assembles complementary RNA strands

  19. Transcription

  20. Transcription Animations • http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html • http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

  21. mRNA Processing • Initial mRNA copied from a gene is a primary transcript (pre-mRNA) – it is not fully functional • There are genes that contain stretches of DNA that do not code for proteins –these stretches of DNA are still transcribed into mRNA. These non-coding sections are called introns • Exons are the protein coding sequences of a gene. • Introns and exons are copied during transcription of mRNA • Before mRNA can be used to make a protein, the introns must be removed and the exons must be spliced together

  22. mRNA Processing • Alternative splicing can join together certain exons and cut out others. Alternative splicing allows several different proteins products to be produced from the same gene sequence • A gene contains several exons and splicing doesn’t always occur in the same way. As a result, multiple proteins can be produced from a single gene. • This process creates multiple mRNAs of different sizes from the same gene. Each mRNA can then be used to produce different proteins with different functions.

  23. Two other types of mRNA processing: 1. At the 5’ end of the mRNA, a guanine base containing a methyl group is added. • Known as the 5’ cap • Plays a role in ribosome recognition of the 5’ end of mRNA during translation • In a process called polyadenylation, a string of adenine nucleotides around 100 to 300 nucleotides in length is added to the 3’ end of the mRNA • Known as the poly(A) tail. • Protects the mRNA from degradation in the cytoplasm, increasing its stability and availability for translation • Following processing, a mature mRNA leaves the nucleus and enters the cytoplasm where it is now ready for translation

  24. RNA Editing Exon Intron DNA • The introns are cut out of RNA molecules. • The exons are the spliced together to form mRNA. Pre-mRNA mRNA Cap Tail

  25. RNA Editing • RNA Editing • The DNA of eukaryotic genes contains sequences of nucleotides, called introns, that are not involved in coding for proteins. • The DNA sequences that code for proteins are called exons. • When RNA molecules are formed, introns and exons are copied from DNA.

  26. Translation • The ultimate function of a gene is to produce a protein. • Translation is using the information in mRNA to synthesize a protein from amino acids.

  27. Protein Review • Proteins are made by joining • AMINO ACIDS • Each protein contains a combination of the 20 amino acids • The function of the protein is determined by number and sequence of amino acids • (A polypeptide is a protein!) Protein 1 Protein 2

  28. Genetic Code • The genetic code is the “language” of mRNA instructions. • A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid. Each codon specifies a particular amino acid that is to be placed on the polypeptide chain.

  29. http://cluelessaboutdna.blogspot.com/2008/01/more-about-genetic-code-start-codons.htmlhttp://cluelessaboutdna.blogspot.com/2008/01/more-about-genetic-code-start-codons.html

  30. Genetic Code RNA Sequence - U C G C A C G G U Codon Sequence – U C G – C A C – G G U Use the Amino Acid Guide to determine amino acid – U C G – C A C – G G U Amino acid sequence – U C G – C A C – G G U Serine – Histidine – Glycine

  31. Translation • Translation is the decoding of an mRNA message into a polypeptide chain (protein). • Translation takes place on ribosomes. • During translation, the cell uses information from messenger RNA to produce proteins.

  32. Translation 1. Messenger RNA is transcribed in the nucleus, and then enters the cytoplasm where it attaches to a ribosome.

  33. Translation 2. The ribosome “reads” the mRNA codon and the corresponding amino acid is brought to the ribosome by the tRNA Amino Acid Amino Acid codon

  34. Translation 3. The ribosome forms bonds between the amino acids to form the protein Bond formed

  35. Translation 4. Translation continues until the ribosome reaches a stop codon on the mRNA and releases the protein (polypeptide)

  36. The BIG Picture!

  37. Translation Animation • http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html • http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf

  38. Translation The genetic code • Ribosomes read the code and produce proteins. Proteins are formed by joining the building blocks called amino acids. • A chain of amino acids linked together by covalent bonds is a polypeptide. Some proteins consist of a single polypeptide chain, while others contain several polypeptide chain that must wrap and fold around each other to form complicated three-dimensional structures. • Proteins can contain combinations of up to 20 different amino acids.

  39. Genetic Code • The genetic code is a universal language of genetics used by all living organisms. • The code works in three-nucleotide units called codons which are contained within mRNA molecules. • Each codon codes for a single amino acid. • There are 64 different potential codons corresponding to all possible combinations of the four possible bases assembled into three nucleotide codons.

  40. http://www.cbs.dtu.dk/staff/dave/roanoke/genetics-finalex-spr98.htmhttp://www.cbs.dtu.dk/staff/dave/roanoke/genetics-finalex-spr98.htm

  41. http://scienceblogs.com/oscillator/2010/02/expanding_the_genetic_code.phphttp://scienceblogs.com/oscillator/2010/02/expanding_the_genetic_code.php

  42. Translation What amino acid is coded by the following codons? ACC Threonine CGC Arginine AGC Serine UUA Leucine GUA Valine

  43. Translation • Also contained in the genetic code are codons which tell ribosomes where to begin translation and end translation. • The start codon, AUG, codes for the amino acid methionine and signals the starting point for mRNA translation. • Stop codons terminate translation. UGA is a commonly used stop codon in many mRNA, but UAA and UAG are other stop codons. Stop codons do not code for amino acids; they simple signal the end of translation.

  44. Translation Ribsomes • Each ribosome contains two subunits, the large and small subunit. • There are specific sites, called the A site and the P site, into which tRNA molecules can bind.

  45. Translation tRNA molecules • At one end of each tRNA is an amino acid attachment site. • tRNA molecules carry their amino acids to the ribosome • Bind with the ribosomes at the A site. • At the opposite end of each tRNA molecule is three-nucleotide sequence called an anticodon. • Different amino acids have different anticodon. • Anticodons are designed to complementary base pair with codons in mRNA.

  46. Stages of translation • The three major stages of translation in eukaryotes: • Initiation • Elongation • Termination.

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