BMB 251 1st Edition Lecture 13 Outline of Last Lecture I. Clicker QuestionsII. GTP/GDP moleculesIII. Protein p53IV. Watson/Crick Model of DNAV. Nucleotides and Base PairsOutline of Current Lecture VI. GenomeVII. Cell divisionVIII. DNA conservationIX. ReplicationX. HistonesXI. MutationsXII. DNA “proofreaders”Current Lecture- Composite base-pairing of purines (G, A) to pyrimidines (C,T,U) enables base pairs to be packed in energetically most favorable arrangement on interior of double helix (sugar-PO4 backbone is on the outside of the helix)o Base pairs only fit together when strands of double helix is antiparallel (polarity of one strand is oppositely oriented from the other)- Genome: complete set of info in organism’s DNA (carries info for ALL RNA and proteins)- Cell division: copies entire genome to give to each new daughter cell and uses each strand of double helix as a template for new strand- In eukaryotes, most DNA is stored in nucleus, delimited form the rest of cell via nuclear envelope(formed by two concentric lipid bilayer membranes) with holes punched into membrane (nuclear pores) to transport materials in/out of cello Nuclear envelope is directly connected to the ER- Although DNA is tightly folded, enzymes can still replicate, repair and use its genes to produce RNA and proteins- Human = 24 different chromosomes, 46 total  each is extremely long DNA associated with specific proteins that fold and pack fine DNA thread into a more compact structure o Complex of DNA and protein: chromatin- Each human cell contains two copes of each chromosome (one from mom and another from dad); copies in a pair from each parent are called homologous chromosomes (homologs)o Only nonhomologous chromosomes are the sex chromosomeso Pairs in a somatic cell: 22 = autosomes, 1 = gameteThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- DNA hybridization: technique in which nucleic acids are labeled and used as probes which can locate a composite strand- Karyotype: picture of 46 chromosomes lined up during mitosiso When part of the chromosomes are lost/switched, this can be detected through changesin the banding patterns or patterns in chromosome painting allows cytogeneticists to find chromosome abnormalities (mutations)- **Chromosome painting provides better resolution of chromosome translocations but Giemsa staining is easier to perform- How the genome is divided into chromosomes varies between eukaryotes; even closely related species with similar genome sizes can gave very different numbers and sizes of chromosomeso **No simple relationship between number of chromosomes, species complexity and total genome size- Average gene size = 27,000 nucleotideso Coding sequences = exons, noncoding sequences = introns o **Most of the gene = introns (concise genomes usually lack introns)o Regulatory DNA sequences: ensure that the gene is turned on/off at proper time, expressed at right level, and only in the proper type of cell- Sequences of DNA that have a function are normally conserved throughout evolution (those with no function are free to mutate)- Conserved regions: closely similar regions of DNA between organisms that include both functionally important exons and regulatory DNA sequences- Nonconserved regions: DNA that is not critical for a function- Conserved synteny: humans/mammals do not only share a majority of the same genes, but also in the same order  large blocks of our chromosomes can be recognized in other organisms- Cell cycle: ordered series of stages where chromosomes are separated (after replication) and divided into two daughter cellso Interphase: chromosomes are replicatedo Mitosis: chromosomes become highly condensed, separated and put into two daughter cellso Mitotic chromosomes: highly condensed forms; easy to see/distinguish- Replication/segregation is controlled by three types of specialized nucleotide sequenceso DNA replication origin: location where DNA duplication (replication) begins Contain many origins so that chromosome can be replicated quickly Two daughter chromosomes remain attached to one anothero Centromere: allows one cope of each duplicated and condensed chromosome to be polled into each daughter cell as cell is dividing Kinetochore: protein complex which forms at the centromere and attaches duplicated chromosomes to mitotic spindle  pulls them aparto Telomeres: ends of chromosomes; contain repeated nucleotide sequences that enable ends of chromosomes to be efficiently replicated Form structures that protect the ends of chromosomes from being mistaken by cell as broken DNA molecule in need of repairo Genome sequences of two species differ in proportion to amount of time they were separately evolving o Phylogenic tree: basic tool of comparative genetics Close similarity in genomes = less time for mutationso Purifying selection: selection that eliminates individuals carrying mutations which interfere with important genetic functions Protein-coding, RNA-coding, and regulatory sequences= usually conservedo Fossil record = important for absolute dating, but is hard to use when looking for protein divergence between specieso Molecular clocks = finer resolution than fossil record- Chromosome 22 should be 1.5 cm in length, but it is more like 2 um during mitosiso 10,000-fold difference via proteins that coil/fold DNA compactly- Histone: responsible for first and most basic level of chromosome packing nucleosome- “Beads on a string” where string = DNA (aka linkers) and each bead= nucleosome core particle (DNA wrapped around protein core of 8 histones)o 1 nucleosome = 8 histones (2 H2A, 2 H2B, 2 H3, and 2 H4) + 147 DNA nucleotide pairso **Formation of nucleosomes converts DNA chromatin thread into 1/3 its original lengtho All 4 histones are small proteins which share a common structural motif, aka histone fold(3 alpha helices connected by 2 loops)o **142 H-bonds form between amino acid backbone of histones and phosphodiester backbone of DNA and hydrophobic interactions/salt linkages help to hold structures together 1/5 amino acids are basic side chains lysine and arginine whose positively charged amino acids interact with negatively charged DNA - Histones are among the most highly conserved eukaryotic proteinso Change in the histone amino acid sequence = deleterious to cell- Two types of chromatin in interphase