BIOL 3451 1st Edition Lecture 15 Outline of Last Lecture I. 11.3 Many Complex Issues Must Be Resolved during DNA ReplicationII. 11.4 A Coherent Model Summarizes DNA ReplicationIII. 11.5 Replication Is Controlled by a Variety of GenesIV. 11.6 Eukaryotic DNA Replication Is Similar to Replication in Prokaryotes, but Is More ComplexV. 11.7 The Ends of Linear Chromosome Are Problematic during ReplicationVI. 11.8 DNA Recombination, Like DNA Replication, Is Directed by Specific EnzymesVII. 12.1 Viral and Bacterial Chromosomes Are Relatively Simple DNA MoleculesVIII. 12.2 Supercoiling Facilitates Compaction of the DNA of Viral and Bacterial ChromosomesIX. 12.3 Specialized Chromosomes Reveal Variations in the Organization of DNAOutline of Current Lecture I. 12.3 Specialized Chromosomes Reveal Variations in the Organization of DNAII. 12.4 DNA Is Organized into Chromatin in EukaryotesIII. 12.5 Chromosome Banding Differentiates Regions along the Mitotic ChromosomeIV. 12.6 Eukaryotic Genomes Demonstrate Complex Sequence Organization Characterized by Repetitive DNAV. 12.7 The Vast Majority of a Eukaryotic Genome Does Not Encode Functional GenesVI. 13.1 The Genetic Code Uses Ribonulcleotide Bases as “Letters”VII. 13.2 Early Studies Established the Basic Operational Patterns of the CodeCurrent LectureI. 12.3 Specialized Chromosomes Reveal Variations in the Organization of DNA- Lampbrush Chromosomes Not really too important Chromosomes are large and have extensive DNA looping (Figure 12.7) Found mostly in vertebrate oocytes as well as spermatocytes of some insects Found in diplotene stage of prophase I of meiosis Lampbrush loops are similar to puffs in polytene chromosomes and are sites of gene activityII. 12.4 DNA Is Organized into Chromatin in Eukaryotes- Chromatin is important when looking at eukaryotic DNA Interphase: chromatin dispersed throughout nucleus, but still an organization Condenses during cell divisionThese 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. Bound up in nucleosomes with positive charged proteins called histones or less positively charged nonhistones Five main types histones: H1, H2A, H3, H4 (Table 12.2)1. Based on how much lysine and arginine they have (amino acids)2. These are pretty small in size3. Can’t really mess with these amino acids because they are the building blocks of DNA, so you’re dead if you do- Electron microscope observations show Chromatin fibers composed of linear array of spherical particles called nucleosomes “beads on a string” (Figure 12.8) Nucleosomes are condensed several times to form intact chromatids (Fig 12.9)- The Solenoid in chromatin is so wrapped up, you can’t get to it with proteins So: need to remodel to allow parts f structure to be exposed to regulatory proteins Twists and turns of superhelix of DNA encircle histones, and important packaging unit of DNA in eukaryotic nucleus (called building blocks)1. Can be altered chemically some There are unstructured histone tails that aren’t packed into folded histone domains with the nucleosome but protrude from them (modifications of theseis what controls accessibility to correct proteins)1. Found “histone code” that tells whether genes will be turned on or offa. 3 kinds: on that can be turned off, off that can be turned on, off that won’t be turned on without extreme effort 2. Histone tails provide potential targets along chromatin fiber for chemical modifications that may include:a. Acetylationb. Methylationc. phosphorylation- Euchromatin: uncoiled and active- Heterochromatin: condensed areas are inactive because they either lack genes or contain genes that are repressed (essential to organism but not to that specific cell) Telomere maintains chromosome integrity Centromere is involved in chromosome movementIII. 12.5 Chromosome Banding Differentiates Regions along the Mitotic Chromosome- Mitotic chromosomes have banding patterns: C-banding: only centromeres (heterochromatin) are stained (Fig 12.11) G-banding: differential staining along length of each chromosomes (Fig 12.12)1. Reflects heterogeneity and complexity of chromosome2. Allows identify identical-sized chromosomes and centromere placement3. Allows homologs to be distinguished from one another, including translocated segmentsIV. 12.6 Eukaryotic Genomes Demonstrate Complex Sequence Organization Characterized by Repetitive DNA- Different types of repetitions (fig 12.14) Highly repetitive can be a million or more times repeated Middle repetitive: interspersed means spread out; tandem: right next to each other1. Tandem: used in identity; they are hypervariable 2. Interspersed: can be short or long- Repetitve DNA: can sometimes make up half of DNA, characteristic in eukaryotic- “single copy” or “unique sequence”: only found once and it is right there!- Satellite DNA: highly repetitive and has short repeated sequences Found in heterochromatic centromeric regions of chromosomes; a lot of it is scattered all over Not found in prokaryotes (very tight, but no repetitions; they recycled some nucleotides- Centromeres: attachment point of spindle fibers (kinetochore) Primary constriction along eukaryotic chromosomes Mediate chromosomal migration during mitosis and meiosis Kinetochore proteins are the regions that bind to the spindle fibers during cell division- Telomeric DNA sequences (terminal heterochromatic caps): consist of short tandem repeats that contribute to the stability and integrity of the chromosome- Moderately repetitive DNA: Variable number tandem repeats (VNTRs)) Minisatellites Mircosatellites (short tandem repeats, STRs)- Short interspersed elements (SINES) and long interspersed elements (LINES) Dispersed throughout genome rather than tandemly repeated and constitutes over 1/3 of the human genome These transposable elements are generated via an RNA intermediate and are referred to as retrotransposons (reverse transcriptase)V. 12.7 The Vast Majority of a Eukaryotic Genome Does Not Encode Functional Genes- *Yeast (eukaryote) is e coli that got stuck following eukaryotic rules*- Only small portion eukaryotic genome constitutes protein-encoding genes- Large number of single-copy noncoding regions, some of which are pseudogenes (look like a gene, but doesn’t