Microbiology 201 10/3 to 10/7
Microbiology 201 10/3 to 10/7 MICRB 201
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This 5 page Class Notes was uploaded by Julianna Sickafus on Sunday October 9, 2016. The Class Notes belongs to MICRB 201 at Pennsylvania State University taught by Dr. Steven Keating in Spring 2016. Since its upload, it has received 14 views. For similar materials see Introductory Microbiology in Microbiology at Pennsylvania State University.
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Date Created: 10/09/16
Microbiology 201 10/3/16 – 10/7/16 Biosynthesis II Phosphorus Assimilation -major component of -nucleic acids -proteins -phospholipids -ATP, FAD, NAD, NADP -phosphorus is donated to other macromolecules from ATP -ATP formed by: -oxidative phosphorylation -substrate-level phosphorylation -photophosphorylation Sulfur Assimilation -essential component of amino acids -methionine (start codon), cysteine (disulfide bond), coenzymes -acquired from recycled methionine and cysteine from the environment and intracellular breakdown of proteins -acquired by assimilatory sulfate reduction -formation of cysteine from sulfates Nitrogen Assimilation -major component of proteins, amino acids, and coenzymes + -to be assimilated into cells, N2must be reduced to NH (NH 3 4 -acquired from -atmospheric N (2itrogen fixation) + -NH 4 (or NH 3 -nitrates Nitrogen Fixation -anaerobic process -occurs in only a few prokaryotes -does not occur in eukaryotes -requires specialized structures -called heterocyst -non photosynthetic -very energy intensive -about 40 ATP per reduced N 2 compare with industrial N f2xation via Haber-Bosch process -catalyzed by nitrogenase + -reduces atmospheric nitrogen to NH and 3H 4 NH /NH incorporation 4 3 + -most common route of NH 4 incorporation is via condensation reaction between NH 4+and -KG (from TCA cycle) -amine group of glutamic acid can be transferred to other carbon skeletons to generate other amino acids -catalyzed by transaminases NO A3similation -due to heavy demand on catabolic pathways for carbon skeletons used in biosynthesis, intermediates need to be replenished -reactions that generate such intermediates are known as anaplerotic reactions -major anaplerotic pathway: -glyoxylate cycle/bypass -modified TCA cycle that bypasses decarboxylation steps: therefore, no loss of carbon as CO 2 -key enzymes: -isocitrate lyase -malate synthase Nucleic Acids Discovery of DNA as genetic material a) Griffiths (1928) -discovery of transmitting principle -“lucky” experiment -strep are naturally competent -ability of cells to take up naked DNA -cellular component from virulent step transforms avirulent to virulent b) Avery, McLeod, McCarthy (1944) -transforming principle is DNA -nucleotides are building blocks of nucleic acids a) nitrogenous base -purines or pyrimidines b) 5 C sugar -ribose or deoxyribose c) phosphate -nucleoside: nitrogenous base + sugar -nucleotide: nucleoside + phosphate -nucleic acid -polymer of nucleotides -DNA consists of deoxyribonucleotides of: -adenine, guanine, cytosine, thymine -RNA consists of: -same bases except uracil (U) replaces thymine (T) -nucleotides are linked together via phosphodiester bonds -sugar phosphate backbone of nucleic acids DNA Structure -generally 2 polynucleotide chains wound around each other to form double helix -bases attach to 1’C of sugar and extends into center of helix -consecutive bases separated by 0.34nm -strands in double helix are complementary and connected via H-bonds -A with T (2 H bonds) -C with G (3 H bonds) -purine pairs with pyrimidine -2 ring with 1 ring -3 ring across -10 base pairs per turn of helix -each base pair rotated 36 relative to it immediate neighbor -each base pair is separated by 0.34nm -1 complete turn of helix= 3.4nm -strands run in antiparallel directions -5’ to 3’ -3’ to 5’ -enzymes can read strands -know where to start transcription/translation -5’ end -> phosphate group -3’ end -> OH group RNA Structure -usually single stranded -folds over to form intra molecular H bonds -main forms: -mRNA (messenger) -tRNA (transfer) -rRNA (ribosomal) -sRNA (small) Organization of DNA in Cells -genome -all genetic material within a cell -depending on organism may include: -plasmids -chloroplast genome -mitochondrial genome -structural gene -string of nucleotides that can be converted into RNA -collection of genes constitutes chromosomes -collection of chromosomes constitutes genome Chromosomes in Most Prokaryotes -single, circular, supercoiled, confined to nucleoid, associated with basic proteins to aid packaging Chromosomes in Eukaryotes -more than 1, linear, associated with basic proteins known as histones -DNA wrapped around histones to form nucleosomes -collection of nucleosomes make up chromatin DNA Replication -process of copying genetic information in parental DNA -objective is to transmit genetic information to offspring -semi conservative process -each strand contains 1 parent strand and 1 new strand Mechanism of DNA Replication -enzyme -DNA polymerase -synthesized in 5’ to 3’ direction -nucleotides added to 3’ end -template strand read from 3’ to 5’ -helicase used to unzip double helix by breaking H bonds to allow DNA polymerase to read bases -uses energy -once strands are separate, they need to be kept apart -single stranded DNA binding proteins (SSBs) -keep strands apart -do not cover up bases -binds to backbone -helicase introduces over winding (tension) -topoisomerase relieve tension by cutting and ligating backbone -DNA polymerase does not initiate replication spontaneously -requires and RNA oligonucleotide primer (about 10 base pairs) on which to add new nucleotides -made by DNA primase (an RNA polymerase) -RNA eventually removed and replaced by DNA -the process of replicating both strands involves a leading strand and a lagging strand -leading strand synthesized continuously -lagging strand synthesis is discontinuous -made in short fragments known as Okazaki fragments -eventually joined together by DNA ligase -DNA polymerase is an extremely accurate enzyme -possesses proofreading activity due to exonuclease activity -allows depolymerization from a free end