DNA and RNA Chapter 12
Section 12-1 DNA
DNA Griffith and Transformation Frederick Griffith bacteriologist studying how certain types of bacteria produce pneumonia Isolated 2 strains of pneumonia from mice Smooth(S) disease causing strain and Rough(R) harmless strain Injected heated (heat-killed) Disease causing strain into mice didn t cause pneumonia Combined harmless strain and heat-killed disease causing strain and injected into mice caused pneumonia
DNA Griffith and Transformation Transformation the two types injected together caused the mice to die! Some transformation had to take place for the harmless bacteria to change into the deadly pneumonia-causing strain! The heat killed bacteria had passed their disease causing ability to the harmless strain! Concluded that some factor had to be transferred between the two strains of bacteria something that heat did not kill! And the offspring of the transformed bacteria also had this factor so he suspected that the factor may be a gene
DNA Avery and DNA Oswald Avery repeated the experiment but isolated the factor that transmitted the disease causing ability Treated bacteria with specific enzymes to destroy only certain parts of the bacteria (proteins, RNA, etc) Only bacteria whose DNA had been destroyed failed to transmit the disease causing ability Showed that DNA was the source of this transformation
DNA - Hershey-Chase Experiment Martha Chase and Alfred Hershey discovered that DNA stores and transmits genetic information Did so by studying bacteriophages (viruses that attack bacteria) These viruses are comprised of a DNA center and a protein coat
DNA - Hershey-Chase Experiment How do bacteriophages work?
DNA - Hershey-Chase Experiment Radioactive Marker Experiment Used radioactive substance as markers in bacteriophages Protein coat Sulfur-35 ( 35 S) DNA core Phosphorous-32 ( 32 P) Marked bacteriophages and bacteria were mixed together and they waited for the virus to inject their genetic material Bacteria were then tested for radioactivity The type of radioactivity detected would tell Chase and Hershey which part of the bacteriophage was transmitting information Nearly all was from 32 P marker in DNA not protein coat
DNA - Hershey-Chase Experiment
DNA Activity Genes are made of DNA, a large, complex molecule. DNA is composed of individual units called nucleotides. Three of these units form a code. The order, or sequence, of a code and the type of code determine the meaning of the message. 1. On a sheet of paper, write the word cats. List the letters or units that make up the word cats. 2. Try rearranging the units to form other words. Remember that each new word can have only three units. Write each word on your paper, and then add a definition for each word. 3. Did any of the codes you formed have the same meaning? 4. How do you think changing the order of the nucleotides in the DNA codon changes the codon s message?
DNA Video on DNA and Genes
DNA The Components and Structure of DNA DNA (Deoxyribonucleic acid) is made of units called nucleotides Nucleotides 3 basic components Deoxyribose 5-carbon sugar Phosphate group Nitrogen bases Adenine (a purine) Guanine (a purine) Cytosine (a pyrimidine) Thymine (a pyrimidine) Complementary Pairing Base Pairing rules: Adenine Thymine Cytosine Guanine Sequence of one strand determines sequence of other Adenine Guanine Cytosine Thymine Phosphate group Deoxyribose
DNA The Components and Structure of DNA The backbone of DNA is the sugar and phosphate groups (deoxyribose and the phosphate group) of each nucleotide. The nitrogenous bases stick out like a staircase tread (sideways) from this backbone Nucleotides can be joined in any sequence Several nucleotides together make a gene But scientists were still puzzled about how this string could carry genetic information (weren t there other molecules that were strung together?) So there had to be more to DNA s structure Adenine Guanine Cytosine Thymine Phosphate group Deoxyribose
DNA The Components and Structure of DNA Chargaff s Rules Erwin Chargaff noted that regardless of species, or even kingdom, DNA bases always appeared in the same proportions as each other Concluded that bases are paired: [A = T] [G = C] But why? X-Ray evidence Rosalind Franklin used x-rays to study the structure of DNA Looked at how the x-rays scattered on the film From the X shaped pattern, she concluded that DNA was twisted in Adenine Guanine Cytosine Thymine Phosphate group Deoxyribose a coil-like shape (a helix), that there may be two strands, and that the nitrogenous bases were near the center
DNA The Components and Structure of DNA The Double Helix Francis Crick and James Watson also working on DNA structure Saw work of Rosalind Franklin and used it to build a structural model of DNA A double helix Hydrogen bonds hold strands together at nitrogenous bases Sugarphosphate backbone Nucleotide Hydrogen bonds
Section 12-2 CHROMOSOMES AND DNA DUPLICATION
Chromosomes and DNA Replication Chromosome Structure Chromosome Nucleosome Supercoils Coils Histones DNA double helix 4 million base-pairs per cell (in both prokaryotic and eukaryotic cells) More than a meter long in humans Chromatin Consists of DNA tightly coiled around proteins called Histones Histones forms nucleosome (believed to help in separating chromosomes in mitosis) Coiled and super-coiled to form chromosomes
DNA Replication DNA Replication the process in which DNA strands and duplicate strands are produced Results in two DNA Molecules each with one new strand and one original strand The DNA strands separate at areas along the chromosome called replication forks In most prokaryotes this is a single point In larger eukaryotic chromosomes, this may be hundreds of points DNA polymerase an enzyme that joins DNA nucleotides to the opened parent strands Two complimentary strands are produced according to base-pairing rules A DNA strand that has the bases CTAGGT produces a strand with the bases?
DNA Replication New strand Original strand DNA polymerase DNA polymerase Growth Growth Replication fork Replication fork Nitrogenous bases New strand Original strand
DNA Replication Enzymes (DNA polymerase) unzip the DNA strand by breaking the hydrogen bonds Also allows for proofreading what has been produced so that DNA is replicated with near 100% accuracy
DNA Replication Short videos on DNA Replication DNA replication animation by interact Medical YouTube http://www.youtube.com/watch?v=zddkirw1pdu&featur e=related DNA replication (6 10) YouTube http://www.youtube.com/watch?v=z685ffqmrpo&featur e=channel
DNA Replication relating to Cell Reproduction
Section 12-3 RNA AND PROTEIN SYNTHESIS
RNA and Protein Synthesis Structure of RNA Similarities: Made up of a chain of nucleotides (like DNA) Has a phosphate group, a 5-carbon sugar and a nitrogenous base Differences Sugar is ribose (not deoxyribose) RNA is single stranded (not a double helix) Contains uracil instead of thymine Often just a segment that corresponds to a segment of DNA often a single gene
RNA and Protein Synthesis General Functions of RNA It can be varied but is generally protein synthesis Types and functions of RNA Messenger RNA (mrna) Carries copies of the genetic instructions for assembling amino acids into proteins Serve as messengers from DNA to the rest of the cell Ribosomal RNA (rrna) Part of the structure of ribosomes (where proteins are actually made) Transfer RNA (trna) Transfers each amino acid to the ribosomes as it is specified in the instructions provided by mrna
RNA and Protein Synthesis Transcription The process of producing RNA from a sequence of DNA molecule Requires an enzyme called RNA polymerase (very similar to DNA polymerase) Separates the DNA strands then uses one strand of DNA to assemble nucleotides to form the single stranded RNA molecule which separates and then DNA is rejoined.
RNA and Protein Synthesis Transcription Process RNA polymerase only binds to specific regions called promoters (have specific base sequences) also provides signals for when to stop RNA polymerase separates DNA by breaking the hydrogen bonds RNA nucleotides are assembled according to base pairing rules: (G C) Guanine to Cytosine (A U) Adenine to Uracil
RNA and Protein Synthesis Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) Transcription Process Begins at a promoter region (a section of DNA with a specific sequence Similar process to end RNA RNA polymerase DNA
RNA and Protein Synthesis RNA Editing Makes RNA molecule functional Most DNA are not involved in coding for proteins but get transcribed anyway Non-coding segments of RNA must be removed Introns non-coding regions Coding segments of RNA are spliced together Exons coding regions; instructions to make proteins All this editing takes place inside the nucleus before the mrna heads out for the ribosomes
RNA and Protein Synthesis The Genetic Code Translates mrna language into proteins (amino acids) Codon 3 nucleotide sequence that specifies for a single amino acid Sample RNA sequence: AUG UCG CAC GGU UAG What amino acid sequence will the above RNA sequence produce?
RNA and Protein Synthesis The Genetic Code Sample RNA sequence: AUG UCG CAC GGU UAG What 5-protein sequence will the above RNA sequence produce? ANSWER: Methionine-Serine- Histidine-Glycine-Stop **NOTE AUG can be a start sequence or Methionine; most proteins begin with the amino acid Methionine
RNA and Protein Synthesis Translation The process of decoding an mrna message into a protein (a polypeptide chain) Takes place on the ribosomes Process Begins when mrna attaches to a ribosome As each codon moves through the ribosome, the correct amino acid is brought by trna trna only carries one amino acid (corresponding to one codon) trna also has 3 unpaired bases called an anticodon (corresponding to the codon that the trna is supposed to attach to) Amino acids are joined together into long chains in the ribosome Continues until a stop codon is reached (there are several)
RNA and Protein Synthesis - Translation
RNA and Protein Synthesis Translation (continued)
RNA and Protein Synthesis
RNA Concept Map RNA can be Messenger RNA Ribosomal RNA Transfer RNA also called which functions to also called which functions to also called which functions to mrna Carry instructions rrna Combine with proteins trna Bring amino acids to ribosome from to to make up DNA Ribosome Ribosomes
Section 12-4 MUTATIONS
Mutations - Activity 1. Copy the following information about Protein X: Methionine Phenylalanine Tryptophan Asparagine Isoleucine STOP. 2. Use Figure 12 17 on page 303 in your textbook to determine one possible sequence of RNA to code for this information. Write this code below the description of Protein X. Below this, write the DNA code that would produce this RNA sequence. 3. Now, cause a mutation in the gene sequence that you just determined by deleting the fourth base in the DNA sequence. Write this new sequence. 4. Write the new RNA sequence that would be produced. Below that, write the amino acid sequence that would result from this mutation in your gene. Call this Protein Y. 5. Did this single deletion cause much change in your protein? Explain your answer.
Mutations DNA contains the code of instructions for cells. Sometimes, an error occurs when the code is copied. Such errors are called mutations. Two main types Gene mutations Changes in one or just a few nucleotides at a single point in the DNA sequence Chromosomal mutations Changes in the number or structure of chromosomes May even change the location of genes on the chromosomes or the number of copies of the genes
Mutations Gene Mutations Caused by errors in replication Changes in DNA affect the amino acid sequence Point mutations occur at a single point in the DNA sequence Substitutions one base is changed into another Usually affects one amino acid in the protein Insertions and Deletions a base is inserted or removed from the DNA sequence Causes frameshift mutations The reading frame of the genetic message is shifted and chances every amino acid that follows the point of the mutation
Mutations
Gene Mutations: Substitution, Insertion, Section 12-4 and Deletion Substitution Insertion Deletion
Mutations
Mutations Chromosomal Mutations Changes the structure of chromosomes by changing the location or the number of genes on a chromosome Deletions 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 part of one chromosome breaks off and attaches to another
Chromosomal Mutations Section 12-4 Deletion Duplication Inversion Translocation
Chromosomal Mutations
Mutations Significance of Mutations Most mutations are neutral have little or no effect on the expression of genes or the coding of proteins Dramatic changes can cause harmful results Genetic disorders (Chapter 14) Disruption of normal biological activities Cancer (many kinds) Some may even be incompatible with life! Also the source of genetic variability and adaptation to new or changing environments Galapagos Island finches and beak size
Section 12-5 GENE REGULATION
Gene Regulation If a specific kind of protein is not continually used the gene for that protein can be turned off Repressor Proteins bind to the chromosome to block transcription from occurring (common in prokaryotic cells) Operon a group of genes that operate together Example: Lac operon in E. coli group of genes that code for proteins that breakdown lactose (lactase) Lac repressor Protein that bind to chromosome to block transcription of lac operon turn off the lac genes when lactose isn t present
Gene Regulation Eukaryotic Gene Regulation Operons are not usually found in eukaryotic cells Most genes are controlled individually with more complex regulatory sequences than operons Many eukaryotic genes have a sequence of TATATA or TATAAA before the start of transcription Called a TATA box Promoters are usually found just before this spot Many different proteins can bind to these enhancer sequences resulting in very complex gene regulation for eukaryotes
Gene Regulation Eukaryotic Gene Regulation (continued) Allows for cell specialization All cells have a specific function for the body Nerve cell genes are not expressed in liver cells Specialized cells: regulate the expression of its genes only need to express genes it uses to function Areas of chromosome that help to regulate gene expression in Eukaryotes: Enhancer Sequence Opening tightly packed chromatin Attract RNA polymerase Can act as a repressor to block transcription Promoter Sequence a spot for RNA polymerase to bind to start transcription TATA Box - helps position RNA polymerase for transcription
Gene Regulation Development and Differentiation All cells in developing embryo undergo differentiation Cells become specialized in structure and function Hox Genes control the development and differentiation by telling cells how they should differentiate as the body develops Determine an animal s basic body plan Hox genes expressed like cascade affect Genes for head formation toward one end of chromosome Genes for posterior body parts at other end of chromosome Hox genes are turned on in precise order Genes for anterior formation get turned on first and then genes for development of posterior formations are turned on
Gene Regulation Development and Differentiation No mutations normally occur on Hox Genes Often lethal When mutations do occur Change the organs and body segments during development
Gene Regulation Development and Differentiation No mutations normally occur on Hox Genes Often lethal When mutations do occur Change the organs and body segments during development