Enduring Understanding The processing of genetic information is imperfect and is a source of genetic variation.
Objective: You will be able to create a visual representation to illustrate how changes in a DNA nucleotide sequence can result in a change in the polypeptide produced. Do Now: Read the enduring understanding
Mutations are the primary source of genetic variation. External factors, including radiation and reactive chemicals, can cause random changes, e.g., mutations in the DNA Mutagens are physical or chemical agents that can cause mutations Describe the basic process by which a change in the DNA sequence results in a change in a peptide sequence
First mrna base (5 end of codon) Third mrna base (3 end of codon) Figure 14.6 Second mrna base U C A G U UUU UUC UUA UUG Phe Leu UCU UCC UCA UCG Ser UAU UAC UAA UAG Tyr Stop Stop UGU UGC UGA UGG Cys Stop Trp U C A G C CUU CUC CUA CUG Leu CCU CCC CCA CCG Pro CAU CAC CAA CAG His Gln CGU CGC CGA CGG Arg U C A G A AUU AUC AUA AUG IIe Met or start ACU ACC ACA ACG Thr AAU AAC AAA AAG Asn Lys AGU AGC AGA AGG Ser Arg U C A G G GUU GUC GUA GUG Val GCU GCC GCA GCG Ala GAU GAC GAA GAG Asp Glu GGU GGC GGA GGG Gly U C A G
Essential knowledge: Changes in genotype can result in changes in phenotype. Alterations in a DNA sequence can lead to changes in the type or amount of the protein produced and the consequent phenotype.
DNA mutations can be positive, negative or neutral This depends on the on the effect or the lack of effect they have on the resulting protein and the phenotypes that are conferred by the protein. Whether or not a mutation is detrimental, beneficial or neutral depends on the environmental context.
Types of Small-Scale Mutations Point mutations within a gene can be divided into two general categories Nucleotide-pair substitutions Insertions or Deletions
Figure 14.26 3 T 5 5 3 T 5 5 Met DNA template strand 3 T 5 mrna 5 Protein Amino end (a) Nucleotide-pair substitution Lys Phe Gly A C T T C A A A C C G A T T A T G A A G T T T G G C T A A A U G A A G U U U G G C U A A Met A C T T C A A A C C A A T T A T G A A G T T T G G T T A A A U G A A G U U U G G U U A A Stop Silent (no effect on amino acid sequence) A C T T C A A A T C G A T T A T G A A G T T T A G C T A A A U G A A G U U U A G C U A A Met Missense Lys 3 T A C 5 T U instead of A 5 U G G Met Nonsense A instead of T Phe Ser A T C A A A C C G A T T A G T A G T T T G G C T A A A U A U U U G G U U A A Stop A instead of G U instead of C T instead of C A instead of G Stop 5 3 3 5 3 3 5 3 3 Wild type Lys Phe 3 T 5 5 3 T 5 5 3 T 5 5 Gly A Met C 5 3 3 Stop Carboxyl end (b) Nucleotide-pair insertion or deletion Extra A A T T C A A A C C G A T A T G T A A G T T T G G C T A A U G U A A G U U U G G U U A A C T T C A A C C G A T T A T G A A G T T G G C T A A A U G A A G U U G G G U A A Met A Met Extra U Stop Frameshift causing immediate nonsense (1 nucleotide-pair insertion) T T C A C Lys A Phe A A U Leu C C G Gly A Ala Frameshift causing extensive missense (1 nucleotide-pair deletion) A T G T T T G G C T A A A A G missing missing missing missing A U G U U U G G C U A T T A 5 3 3 5 3 Stop No frameshift, but one amino acid missing (3 nucleotide-pair deletion) T A A 3 5 3 3
Example of a nucleotide-pair Substitution Silent mutations Would this mutation be positive, negative or neutral?
Example of a nucleotide-pair Substitution Missense mutations Would this mutation be positive, negative or neutral?
Example of a Nucleotide-Pair Substitution Nonsense mutations When would this mutation be positive?
Frameshift mutations can create whole new genes!! Or they can make them useless (deleted)
Real World Examples Sickle cell anemia Base pair substitution Cystic Fibrosis (CF)- deletion of three nucleotides that results in the loss of the amino acid phenylalanine and causes an incorrectly folded membrane protein. CF is associated with thick, sticky mucus in the lungs and trouble breathing, salty sweat, infertility in certain individuals, and a shortened life expectancy Cancer
Objective: You will be able to describe processes that increase genetic variation. Do Now: Take out your Molecular Evolution of Gene Birth and Death packet
Errors in DNA replication or DNA repair mechanisms can cause random changes, e.g., mutations in the DNA.
Errors in mitosis or meiosis can result in changes in phenotype. Changes in chromosome number often result in: New phenotypes, including sterility caused by triploidy and increased vigor of other polyploids. Human disorders with developmental limitations Trisomy 21 (Down syndrome) XO (Turner syndrome).
Finish Birth and Death of Genes case study Finish packet for homework
Objective: You will be able to compare and contrast processes by which genetic variation is produced and maintained in organisms from multiple domains. Do Now:
The horizontal acquisitions of genetic information primarily in prokaryotes via: Transformation (uptake of naked DNA), Transduction (viral transmission of genetic information) Conjugation (cell-to-cell transfer) Transposition (movement of DNA segments within and between DNA molecules) All of these increase variation.
Figure 13.2 Experiment Living S cells (control) Living R cells (control) Heat-killed S cells (control) Mixture of heat-killed S cells and living R cells Results Mouse dies Mouse healthy Mouse healthy Mouse dies Living S cells
Figure 24.15-5 1 Phage infects bacterial donor cell with A + and B + alleles. Transduction Phage DNA A + B + 2 Phage DNA is replicated and proteins synthesized. A + B + Donor cell 3 Fragment of DNA with A + allele is packaged within a phage capsid. A + 4 5 Phage with A + allele infects bacterial recipient cell. Incorporation of phage DNA creates recombinant cell with genotype A + B +. Crossing over Recombinant cell A + A A + B B Recipient cell
Figure 24.16 1 m Sex pilus
Figure 18.7 DNA of genome Transposon is copied Transposon New copy of transposon Insertion Mobile transposon
Sexual reproduction in eukaryotes involves Gamete formation, including crossing-over during meiosis The random assortment of chromosomes during meiosis Fertilization
Figure 10.10-3 Independent Assortment Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Combination 1 Combination 2 Combination 3 Combination 4
Figure 10.11-5 Prophase I of meiosis Pair of homologs Chiasma Nonsister chromatids held together during synapsis Synapsis and crossing over Centromere TEM Anaphase I Breakdown of proteins holding sister chromatid arms together Anaphase II Daughter cells Recombinant chromosomes
Random Fertilization Each person can make 8.4 million different sex cells from independent assortment That means parents can produce a zygote with about 70 trillion diploid combinations That s without accounting for crossing over
Objective: You will be able to construct an explanation of how viruses introduce genetic variation in host organisms. Do Now:
Essential knowledge: Viral replication results in genetic variation, and viral infection can introduce genetic variation into the hosts. Viral replication differs from other reproductive strategies and generates genetic variation via various mechanisms.
Viral replication differs from other reproductive strategies and generates genetic variation via various mechanisms. Viruses have highly efficient replicative capabilities that allow for rapid evolution and acquisition of new phenotypes Viruses replicate via a component assembly model allowing one virus to produce many progeny simultaneously via the lytic cycle Virus replication allows for mutations to occur through usual host pathways Related viruses can combine/recombine information if they infect the same host cell.
Figure 17.3 1 2 Entry and uncoating Replication DNA Capsid HOST CELL VIRUS 3 Transcription and manufacture of capsid proteins Viral DNA mrna Viral DNA Capsid proteins 4 Self-assembly of new virus particles and their exit from the cell
Figure 17.4-5 This is called the lytic cycle 5 Release 1 Attachment 2 Entry of phage DNA and degradation of host DNA Phage assembly Head Tail Tail fibers 4 Assembly 3 Synthesis of viral genomes and proteins
Some viruses are able to integrate into the host DNA and establish a latent (lysogenic) infection.
Figure 17.5 Phage Phage DNA The phage injects its DNA. Bacterial chromosome Phage DNA circularizes. Prophage exits chromosome. Daughter cell with prophage Many cell divisions create many infected bacteria. Lytic cycle The cell lyses, releasing phages. Lysogenic cycle Prophage Prophage is copied with bacterial chromosome. Phage DNA and proteins are synthesized and assembled. Phage DNA integrates into bacterial chromosome.
Viruses Can increase genetic variation of their hosts Transduction Recombination of Bacterial and viral DNA can create a new gene for the bacteria Latent viral genomes can result in new properties for the host such as increased pathogenicity in bacteria. Example, a virus can leave behind genes making the bacteria resistant or toxic
RNA viruses lack replication error-checking mechanisms, and thus have higher rates of mutation.
HIV is a well-studied system where the rapid evolution of a virus within the host contributes to the pathogenicity of viral infection. The rapid mutation rates of retroviruses results from the inaccuracy of the enzyme reverse transcriptase
Figure 17.7 Glycoprotein Viral envelope HIV Membrane of white blood cell Capsid Reverse HIV transcriptase RNA (two identical strands) Viral RNA RNA-DNA hybrid DNA HOST CELL Reverse transcriptase 0.25 m HIV entering a cell Chromosomal DNA RNA genome for the next viral generation mrna NUCLEUS Provirus New virus New HIV leaving a cell