DNA degraded by enzymes called nucleases DNA nucleases or DNases o Two major

Dna degraded by enzymes called nucleases dna

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DNA degraded by enzymes called nucleases (DNA nucleases or DNases) o Two major classes: Exonucleases —nibble in from end; may be 5’ OR 3’ (not both) Endonucleases start somewhere in the middle Restriction Enzymes endonucleases that attack specific sequences Restriction Enzymes/Restriction Endonucleases (RE) o Produced by bacteria; protect against infection by bacteriophages o Work on all DNA regardless of source o “Molecular Scissors”— cut double stranded DNA o Over 3000 different restriction enzymes known o RE Types: Type I: Randomly cuts DNA Type II: Cuts DNA at specific sequences Most useful for molecular techniques! Type III: Non-specific cuts
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13 Naming of Restriction Enzymes o Based on bacterial genus, species, strain, & enzyme number o Example: Eco RI Genus: Escherichia Species: coli Strain: RY13 Enzyme #: 1 (first RE isolated from strain) Cutting the DNA o Restriction site: specific DNA sequence where the enzyme cuts o Palindromic restriction sites: read the same forwards and backwards Madam I’m Adam Double- stranded DNA palindromic sequence reads the same 5’ to 3’ on both strands: 5’ -GAATTC- 3’ 3’ -CTTAAG- 5’ Blunt Ends vs. Sticky Ends o Blunt Ends some RE leave a blunt end: Sma I ( Serratia marcesens I) o Sticky Ends —some RE leave overhangs, known as “sticky ends” Eco RI and Pst I ( Providencia stuartii I) Images: Copyright © F.A. Davis Company, 2012
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14 Lecture 3, Part II: Nucleic Acid & Chromosome Structure RNA Types & Structure, & Chromosome Structure Objectives Following the lecture the student will be able to: 1. List and describe types of RNA and relate how it is synthesized compared with DNA. 2. Explain how and when a chromosome is formed. 3. Discuss the structure of a chromosome. 4. Define the following terms: genome, gene, allele, genotype, phenotype, locus. I. RNA Structure & Function Function: intermediate molecules translating DNA code into proteins Location: typically in cytoplasm RNA is transcribed from DNA Types of RNA: o Messenger RNA (mRNA): carries the information in DNA to the ribosomes o Ribosomal RNA (rRNA): part of ribosomal machinery used to make protein o Transfer RNA (tRNA): carries amino acids to ribosome where protein formed Structure of RNA: o Pentose sugar is ribose o Contains uracil (instead of thymine) o Most RNA is single-stranded o Smaller than DNA (10-1000 nucleotides) o Transient: easily degraded (part of regulation) Images:
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15 II. Chromosome Formation Chromosome: a DNA double helix that carries genes Formation of chromosomes: o Chromosomes consist of a chain of DNA with a group of stabilizing proteins o DNA is wrapped around proteins known as histones to form a nucleosome “beads on a string” formation o Nucleosomes are linked together with the help of a linker DNA to form chromatin Chromatin = DNA + structural proteins coiled up o Chromatin further condenses, coils, supercoils then condenses into a chromosome structure Image:
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16 III. Chromosome Structure
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