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Ch. 12 – DNA

Ch. 12 – DNA. Introduction to DNA (Sec. 12.1) History, important discoveries, who’s who in genetics Structure of DNA (Sec. 12.1) Genes and the Double Helix Chromosomes and DNA replication (Sec. 12-2) Chromosome structure and function RNA and Protein synthesis (Sec. 12.3)

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Ch. 12 – DNA

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  1. Ch. 12 – DNA • Introduction to DNA(Sec. 12.1) • History, important discoveries, who’s who in genetics • Structure of DNA(Sec. 12.1) • Genes and the Double Helix • Chromosomes and DNA replication(Sec. 12-2) • Chromosome structure and function • RNA and Protein synthesis(Sec. 12.3) • Structure and types of RNA • Transcription, Translation • Mutations (Sec. 12.4) • Types of mutations and their significance • Gene Regulation (Sec. 12.5) • Eukaryotes and Prokaryotes • Differentiation

  2. Where is DNA? Nucleus Chromatin Sec. 12.1 DNA is located in the Nucleus of Eukaryote cells. Prokaryotes don’t have a nucleus so their DNA is floating in the cytoplasm. Chromatin = DNA bound to protein, arranged in units called chromosomes Humans have 46 chromosomes The Double HelixChromosomes are composed of two strands of DNAwrapped around each other, as shown to the left.

  3. History of DNA • Fredrick Griffith (1928) wanted to find out how bacteria caused pneumonia, his experiment: Disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Heat-killed, disease-causing bacteria (smooth colonies) Control(no growth) Harmless bacteria (rough colonies) Heat-killed, disease-causing bacteria (smooth colonies) Griffith found that bacteria can “transform” each other, or share information, like how to kill a mouse I didn’t die? Fred killed Kenny! Live, disease-causingbacteria (smooth colonies) But how? What did they pass to each other? Dies of pneumonia Dies of pneumonia Lives Lives

  4. History of DNA Aye, what yo name is? • Oswald Avery (1944) repeated Griffith’s work and discovered that nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next Alfred and Martha • Alfred Hershey and Martha Chase and the Hershey-Chase Experiment (1952): • Studied viruses that infect bacteria = bacteriophage • Bacteriophages = “bacteria eaters” inject their own DNA into cell and use the cell to produce many copies of themselves, killing the bacteria because it splits open, releasing hundreds of new viruses! Eeek! • What Hershey and Chase found: • Used “markers” or radioactive isotopes • Discovered that the genetic material of bacteriophage was DNA, not protein He aint bout that life doe.

  5. What is DNA? DeoxyriboNucleic Acid • DNA is a molecule made up of Nucleotides • Nucleotides are made up of 3 things: 1. 5- carbon sugar called Deoxyribose 2. A nitrogenous base (contains nitrogen) 3. A phosphate group (P= phosphate) P • There are 2 types of Nitrogenous bases in DNA • 1. Purines= 2 kinds • 2. Pyrimidines = 2 kinds • A = Adenine(AD-uh-neen) • G = Guanine(GWAH-neen) • C = Cytosine(SY-tuh-zeen) • T = Thymine(THY-meen) Adenine goes with Guanine A-G Cytosine goes with Thymine C-T Thymine (DNA only) Uracil (RNA only) These bases, A GCT, are arranged into a sequence, or a gene, like letters of our alphabet are arranged into words. thymine cytosine adenine guanine sugar sugar sugar sugar P P P P

  6. Watson and Crick Watson and Crick identified and linked together key pieces of research, and along with their own discoveries, described the basic structure of DNA The “twisted ladder” shape of DNA became known as the double helix. The 2 DNA strandswind around each other, like a winding staircase James Watson Francis Crick Hee hee, my dear Watson we’ve discovered the secret to life! Yes, you bloody fool, we discovered the double helix! • Francis Crick and James Watson (~1953)

  7. Double Helix Structure The 2 strands are held togetherby hydrogen bonds between the bases Adenine and Thymine and between Guanine and Cytosine. Each strand is made up of a chain of nucleotides. Nucleotide Hydrogen bonds Ribose and Phosphates join together forming the backbone of the DNA molecule Sugar-phosphate backbone DNA is a double helix in which two strands are wound around each other (like a twisted ladder). Key Adenine (A) Thymine (T) Cytosine(C) Guanine (G)

  8. Hydrogen Bonds Nucleotide The binding together of the nucleotides with Hydrogen bonds is called Base Pairing Hydrogen bonds G + C= A + T = love Sugar-phosphate backbone Love Forever! H H • Hydrogen bonds (sharing of one electron between 2 Hydrogens) between the nucleotides (AGCT) holds the 2 strands of DNA together with a fairly strong force A=T G=C DNA strand: A G C T G G C T A A T C G Complementary DNA Strand: T A T C A

  9. Who has DNA? All living things do! Fly = 8 • Prokaryotes (bacteria) don’t have a nucleus, and their DNA is found floating in the cytoplasm; usually they have a single strand of DNA, or chromosome • Of course, Eukaryotes are more complicated! • Eukaryote = YOU! And, any organism with their DNA inside the nucleus. Eukaryotes generally have 1000X more DNA than bacteria • Eukaryote DNA is organized into Chromosomes Having MORE chromosomes doesn’t mean an organism is bigger or smarter! Cows are smarter than humans? NO! Chickens are bigger and smarter than dogs? Hmm….. Cows = 60 Cats and Dogs = 38 Chickens = 78 Horses = 64 chromosomes • Humans = 46 chromosomes

  10. How DNA fits into a cell 1. Eukaryotic chromosomes contain DNA wrapped around proteins called histones. 2. DNA and histone together = chromatin Chromosome DNA double helix Histones 3. Wound strands of chromatin are called nucleosomes, and these are tightly coiled and supercoiled to form chromosomes

  11. DNA Replication Replication = the process where DNA makes a copy of itself, base by base, producing 2 new complementary strands , and each strand serves as a template for the new strand. Complementary Strand of DNA Opposite strand: T C G A G G C A G T T A A C DNA strand: A G C T C C G T C A A T T G Complementary Strand of DNA Complementary DNA strands

  12. DNA Replication DNA polymerase= an enzyme that joins two nucleotide bases to produce a DNA moleculeand “proofreads” each copy to make sure it’s correct Nucleotides DNA polymerase Replication Fork Original strand = blue New strand = orange The new strand (orange) is “complementary” to the new strand (blue). Growth Growth During Replication, the new strand is made from the original strand, which serves as a template.

  13. Answer: It has to unwind! Open up!! Unzip!!!! What does DNA have to do 1st, before it can replicate?

  14. How does it…..? Section 12-3 RNA= Ribonucleic Acid • Problem: • DNA is in the nucleus and never leaves • Proteins are made in the cytoplasm • How does the instructions for the protein, the DNA, get out to the ribosomes? • Solution: • DNA doesn’t leave the nucleus, but the information fromDNA does • Send a copy of the instructions! Introducing the messenger service……. RNA

  15. DNA to RNA, the 1st step RNA (ribonucleic acid) = contains coded information for making proteins 1st step in decoding genes = copy part of the nucleotide sequence from DNA to RNA • “I can’t help it, it’s in my genes!” or “It’s genetic.” • Genes = coded DNA instructions that control the production of proteins within the cell • The double helix DNA structure doesn’t explain how a gene works, so to understand that, we have to decode the information within a gene

  16. RNA Structure • RNA is like DNA, but with 3 main differences: • 1. Sugar in RNA is ribose instead of deoxyribose • 2. RNA is generally single-stranded, not double stranded • 3. RNA contains Uracil instead of Thymine (YER-a-sil) Think of RNA this way: Would you give your friend your original CD, or would you give them a copy of it?

  17. Types of RNA Each type of RNA may have a different function, but all RNA has a single goal – to make proteinsIt’s all they care about, all they want to do, they are obsessed with making proteins! • 3 main types of RNA: 1. MessengerRNA (mRNA) 2. RibosomalRNA (rRNA) 3. TransferRNA (tRNA)

  18. Different Functions of RNA • mRNA (messengerRNA) =a messenger service, they carry messages (copies of a gene) fromDNA,in the form of RNA, to the rest of the cell • rRNA (ribosomalRNA) = what makes up aribosome(the organelles that make proteins)thus it’s called “ribosomal”RNA • tRNA (transferRNA) = a molecule that“transfers” amino acidsto the ribosome asdirected by the codedmRNA,to form proteins

  19. Transcription Transcription Process (How it happens): RNA polymerase • Transcription = production of RNA molecules by copying part of the DNA nucleotide sequence into a complementary sequence of RNA • Requires an enzyme called RNA polymerase Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) • RNApolymerase binds to DNA and separates the 2 DNA strands(unzips them) • RNApolymerase only binds to regions of DNA called “promotors” that have specific base sequences that say, “Hey, start here!” • RNApolymerase then uses 1 strand of DNA as a “template” to assemble the strand of RNA

  20. RNA Editing RNA editing is cutting out the introns, and splicing the exons together RNA Exon Intron Exon Intron Exon removed “edited” mRNA removed Exon Exon Exon

  21. The Genetic Code Peptide = protein The Genetic Code = the language of mRNA instructions for making proteins Poly = many! • Proteins – made by joining amino acids into long chains called polypeptides • Any combination of the 20 different amino acids make up a protein • The arrangement of amino acids determines what a protein is and what it does • So, we have the instructions (DNA) for making a protein, but how do we translate that into a protein? • We use the Genetic Code! 20amino acids and only 4 nucleotide bases to code for them, AGCT, sounds impossible, but it’s not.

  22. How it works… • The genetic code is read 3 letters, or bases, at a time, and this forms a sort of “word” • Each 3 letter “word” is in mRNA is known as a codon • Codon = 3 consecutive(in a row)nucleotide bases that specify 1 amino acid to be added to the polypeptide chain Box 64 mRNA sequence = UCGCACGGU UCG CAC GGU Now, read it 3 bases at a time… Each codon represents a different amino acid! Serine – Histidine– Glycine

  23. How It’s Done Some amino acids, like Valine, Serine, Alanine, Arginine, etc. can be specified by more than one codon. Box 65 Some codons, like AUG, specify only 1 amino acid. Ex. AUG can either be a “start” codon, or a Methionine. Box 65 There are 3 “stop” codons that don’t code for any amino acid. Stop codons act like the period at the end of a sentence- they signal the end of the polypeptide sequence. Box 65 4 different bases (AGCT) = 64 possible 3-base codons 4 x 4 x 4 = 64 stop stop 1 2 3

  24. Can You Break the Code? DNA: AAC GTA TGC GAT mRNA: UUG CAU ACG CUA Amino Acid Sequence: Leu His Thr Leu 1 2 3

  25. Translation Translation = occurs in the ribosomes, and is when the cell uses information from mRNA to produce, or assemble, proteins • You have the instructions (sequence of nucleotide bases), but who “reads” them? • The Ribosome “reads” the sequences in a process called Translation You, go there, and you, go here, and stop pushing each other! Get in line, you AA idiots!

  26. Translation cytoplasm nucleus Lysine mRNA Methionine Phenylalanine ribosome tRNA Start codon mRNA

  27. Peptide Bond Growing polypeptide chain ribosome tRNA Lysine tRNA mRNA mRNA ribosome

  28. Roles of RNA and DNA • DNA is the “Master Plan” for a building (your body). • RNA=“Blueprints” • DNA is safely stored in the nucleus, and the copies of DNA, or the RNA, go out into the cytoplasm where the proteins are built. • What else can we compare this process to?

  29. Genes and Proteins • Genes code for enzymes and proteins that do everything from controlling the color of a flower petal to ones that determine your blood type. Genes contain instructions for proteins and enzymes, the molecules that make all life possible. An important genetics concept! • Most Genes contain instructions for assembling proteins. • Many proteins are enzymes, and all enzymes are proteins that catalyze and regulate chemical reactions • Proteins are the tools specifically designed to build or operate a part of a living cell.

  30. Mutations Section 12-4 • Everyone makes mistakes, it’s a part of life. • Genetic mistakes are called Mutations • Mutation = any change in the genetic material • All mistakes aren’t bad, and all Mutations ain’t all bad either! • Types of mutations: • Pointmutations = changes in 1 point, or 1 nucleotide These can be either: Substitutions = 1 base is substituted for another Insertions = 1 base is inserted into the DNAsequence Deletions = 1 base is deleted from the DNAsequence Box 73 The key to remember is a PointMutation occurs at 1point in the DNA sequence

  31. Point Mutations Changes like this are called Frameshift Mutations because they are mutations that shift the “reading frame” by one letter • Changes at a single point, or a single base, can either have NO effect (not change the amino acid specified), or have a HUGE effect • Substitutions do NOT have as big of an effect as…. • Insertions and Deletions usually have a BIG effect on the amino acid sequence • Try adding another letter to the word “CAT” If you add an extra letter to CAT, it either becomes nonsense, or it has a different meaning! CAT CATS CYAT Substitutions do NOT cause Frameshift mutations!!! Insertions and Deletions DO cause Frameshift mutations!!!

  32. Frameshifts No change, mRNA still codes for the amino acid Arg DNA: TAC GCA TGG AAT DNA: TAC GCA TGG AAT mRNA: AUG CGU ACC UUA mRNA: AUG CGU ACC UUA Amino:Met Arg Thr LeuAcids Amino:Met Arg Thr LeuAcids Substitution Insertion DNA: TAT CGC ATG GAA T DNA: TAC GTA TGG AAT mRNA: AUA GCG UAC CUU A mRNA: AUG CAU ACC UUA Amino:Ile Ala Try Leu Acids Amino:Met Arg Thr Leu Acids Big change, mRNA codes for different amino acids!

  33. What about deletions? THE FAT DOG ATE THE PIE If you delete the “H” in the, it moves the whole “reading” frame over one letter! Deletion THE FAT DOG ATE THE PIE TEF ATD OGA TET HEP IE Utter nonsense. The reading frame shift made the sentence change just as a deletion or insertion would change the amino acid sequence of a protein

  34. Types of Mutations • 2. Chromosomal Mutations = involve much larger changes because: • They involve the # or structure of chromosomes themselves • And chromosomescontain 1000’s of genes!!!! • What would happen if you lost a whole chromosome? Added a whole chromosome? Box 76 You’d either be dead, or you’d have a bad disease!

  35. Chromosomal Mutations Box 77 • 4 Types of Chromosomal Mutations: • Deletions = lose part of a chromosome (many genes!) 2. Duplications = gain extra parts of a chromosome, or an extra whole chromosome 3. Inversions = reverse the direction of parts of a chromosome- mixes it up! 4. Translocations = part of a chromosome breaks off and attaches to another chromosome Deletion Duplication Inversion Translocation

  36. Effects of Mutations • Harmful mutations are the cause of many human genetic disorders, like cancer • Mutations that result in a BIG change in the DNA or amino acid sequences are usually harmful- they produce defective proteins or no protein at all! • Beneficial mutations(yes there are some!) can give an organism a survival advantage (evolution • Many mutations are neutral, meaning they have little effect on the expression of genes or the function of proteins coded by the genes

  37. Gene Regulation Section 12-5 • 3 Examples are: • Promotors = binding sites for RNA polymerase • Start and Stop signals = starts and stops transcription • Operons = group of genes that operate together • Not all genes are expressed all the time • Expressed genes = a gene that is transcribed into mRNA, which leads to creating a protein • Humans have ~30-40,000 genes and our bodies can’t be making all those proteins all at once! • In the jumble of DNA, there are patterns, and biologists have identified patterns that represent how gene expression is controlled

  38. Eukaryote Gene Regulation 1. TATAA = the “TATA” box, a sequence that occurs before the start codon, a place where RNA polymerase binds 2. Promotors = sequences that are signals for RNA polymerase found just before the TATA box • Prokaryote = organisms without a nucleus, most are bacteria • Eukaryotes = (YOU!) organisms with their DNA contained in a nucleus (humans, plants, animals, fungi, etc.) • Eukaryote genes are mostly controlled individually and have complex regulatory sequences

  39. Typical Gene Structure Regulatory sites Promoter(RNA polymerase binding site) DNA strand Start transcription Stop transcription Direction of Transcription

  40. Development and Differentiation Hox genes = series of genes that control the differentiation of cells and tissues in the embryo, the BODY PLAN. A mutation in the Hox Genes can completely change the organs that develop in specific parts of the body. • Differentiation = when cells become specialized in structure and function • Early development, in the beginning, all of an embryo’s cells have the ability to become anything- heart, eye, leg, toe, wing, etc. Later development, cells specialize and become the toe, heart, leg or wing cell, and once they have specialized, they lose the ability to be anything else Normal fruit fly Legs instead of antennae! Caused by Human Hox-13 mutation

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