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Halotolerant pathogens are an important source of foodborne illnesses because they contaminate foods preserved in salt. | https://openstax.org/books/microbiology/pages/9-summary |
Photosynthetic bacteria depend on visible light for energy. | https://openstax.org/books/microbiology/pages/9-summary |
Most bacteria, with few exceptions, require high moisture to grow. | https://openstax.org/books/microbiology/pages/9-summary |
Chemically defined mediacontain only chemically known components. | https://openstax.org/books/microbiology/pages/9-summary |
Selective mediafavor the growth of some microorganisms while inhibiting others. | https://openstax.org/books/microbiology/pages/9-summary |
Enriched mediacontain added essential nutrients a specific organism needs to grow | https://openstax.org/books/microbiology/pages/9-summary |
Differential mediahelp distinguish bacteria by the color of the colonies or the change in the medium. | https://openstax.org/books/microbiology/pages/9-summary |
DNAwas discovered and characterized long before its role in heredity was understood. Microbiologists played significant roles in demonstrating that DNA is the hereditary information found within cells. | https://openstax.org/books/microbiology/pages/10-summary |
In the 1850s and 1860s, Gregor Mendel experimented with true-breeding garden peas to demonstrate theheritabilityof specific observable traits. | https://openstax.org/books/microbiology/pages/10-summary |
In 1869, Friedrich Miescher isolated and purified a compound rich in phosphorus from the nuclei of white blood cells; he named the compound nuclein. Miescherâs student Richard Altmann discovered its acidic nature, renaming itnucleic acid. Albrecht Kossell characterized thenucleotide basesfound within nucleic acids. | https://openstax.org/books/microbiology/pages/10-summary |
Although Walter Sutton and Theodor Boveri proposed theChromosomal Theory of Inheritancein 1902, it was not scientifically demonstrated until the 1915 publication of the work of Thomas Hunt Morgan and his colleagues. | https://openstax.org/books/microbiology/pages/10-summary |
UsingAcetabularia,a large algal cell, as his model system, Joachim Hämmerling demonstrated in the 1930s and 1940s that the nucleus was the location of hereditary information in these cells. | https://openstax.org/books/microbiology/pages/10-summary |
In the 1940s, George Beadle and Edward Tatum used the moldNeurospora crassato show that each proteinâs production was under the control of a single gene, demonstrating theâone geneâone enzymeâ hypothesis. | https://openstax.org/books/microbiology/pages/10-summary |
In 1928, Frederick Griffith showed that dead encapsulated bacteria could pass genetic information to live nonencapsulated bacteria and transform them into harmful strains. In 1944, Oswald Avery, Colin McLeod, and Maclyn McCarty identified the compound as DNA. | https://openstax.org/books/microbiology/pages/10-summary |
The nature of DNA as the molecule that stores genetic information was unequivocally demonstrated in the experiment of Alfred Hershey and Martha Chase published in 1952. Labeled DNA from bacterial viruses entered and infected bacterial cells, giving rise to more viral particles. The labeled protein coats did not partici... | https://openstax.org/books/microbiology/pages/10-summary |
Nucleic acidsare composed ofnucleotides, each of which contains a pentose sugar, a phosphate group, and anitrogenous base.Deoxyribonucleotideswithin DNA containdeoxyriboseas the pentose sugar. | https://openstax.org/books/microbiology/pages/10-summary |
DNA contains thepyrimidines cytosineandthymine, and thepurinesadenineandguanine. | https://openstax.org/books/microbiology/pages/10-summary |
Nucleotidesare linked together by phosphodiester bonds between the 5ʹ phosphate group of one nucleotide and the 3ʹ hydroxyl group of another. Anucleic acid strandhas a free phosphate group at the 5ʹ end and a free hydroxyl group at the 3ʹ end. | https://openstax.org/books/microbiology/pages/10-summary |
Chargaff discovered that the amount ofadenineis approximately equal to the amount ofthyminein DNA, and that the amount of theguanineis approximately equal tocytosine. These relationships were later determined to be due to complementary base pairing. | https://openstax.org/books/microbiology/pages/10-summary |
Watson and Crick, building on the work of Chargaff, Franklin and Gosling, and Wilkins, proposed the double helix model and base pairing for DNA structure. | https://openstax.org/books/microbiology/pages/10-summary |
DNA is composed of two complementary strands orientedantiparallelto each other with thephosphodiester backboneson the exterior of the molecule. The nitrogenous bases of each strand face each other and complementary bases hydrogen bond to each other, stabilizing the double helix. | https://openstax.org/books/microbiology/pages/10-summary |
Heat or chemicals can break the hydrogen bonds between complementary bases, denaturing DNA. Cooling or removing chemicals can lead to renaturation or reannealing of DNA by allowing hydrogen bonds to reform between complementary bases. | https://openstax.org/books/microbiology/pages/10-summary |
DNA stores the instructions needed to build and control the cell. This information is transmitted from parent to offspring throughvertical gene transfer. | https://openstax.org/books/microbiology/pages/10-summary |
Ribonucleic acid (RNA)is typically single stranded and contains ribose as its pentose sugar and the pyrimidine uracil instead of thymine. An RNA strand can undergo significant intramolecular base pairing to take on a three-dimensional structure. | https://openstax.org/books/microbiology/pages/10-summary |
There are three main types of RNA, all involved in protein synthesis. | https://openstax.org/books/microbiology/pages/10-summary |
Messenger RNA (mRNA) serves as the intermediary between DNA and the synthesis of protein products during translation. | https://openstax.org/books/microbiology/pages/10-summary |
Ribosomal RNA (rRNA) is a type of stable RNA that is a major constituent of ribosomes. It ensures the proper alignment of the mRNA and the ribosomes during protein synthesis and catalyzes the formation of the peptide bonds between two aligned amino acids during protein synthesis. | https://openstax.org/books/microbiology/pages/10-summary |
Transfer RNA (tRNA) is a small type of stable RNA that carries an amino acid to the corresponding site of protein synthesis in the ribosome. It is the base pairing between the tRNA and mRNA that allows for the correct amino acid to be inserted in the polypeptide chain being synthesized. | https://openstax.org/books/microbiology/pages/10-summary |
Although RNA is not used for long-term genetic information in cells, many viruses do use RNA as their genetic material. | https://openstax.org/books/microbiology/pages/10-summary |
The entire genetic content of a cell is itsgenome. | https://openstax.org/books/microbiology/pages/10-summary |
Genescode for proteins, or stable RNA molecules, each of which carries out a specific function in the cell. | https://openstax.org/books/microbiology/pages/10-summary |
Although thegenotypethat a cell possesses remains constant, expression of genes is dependent on environmental conditions. | https://openstax.org/books/microbiology/pages/10-summary |
Aphenotypeis the observable characteristics of a cell (or organism) at a given point in time and results from the complement of genes currently being used. | https://openstax.org/books/microbiology/pages/10-summary |
The majority of genetic material is organized intochromosomesthat contain the DNA that controls cellular activities. | https://openstax.org/books/microbiology/pages/10-summary |
Prokaryotes are typically haploid, usually having a single circular chromosome found in the nucleoid. Eukaryotes are diploid; DNA is organized into multiple linear chromosomes found in the nucleus. | https://openstax.org/books/microbiology/pages/10-summary |
Supercoiling and DNA packaging using DNA binding proteins allows lengthy molecules to fit inside a cell. Eukaryotes and archaea use histone proteins, and bacteria use different proteins with similar function. | https://openstax.org/books/microbiology/pages/10-summary |
Prokaryotic and eukaryotic genomes both containnoncoding DNA, the function of which is not well understood. Some noncoding DNA appears to participate in the formation of small noncoding RNA molecules that influence gene expression; some appears to play a role in maintaining chromosomal structure and in DNA packaging. | https://openstax.org/books/microbiology/pages/10-summary |
Extrachromosomal DNAin eukaryotes includes the chromosomes found within organelles of prokaryotic origin (mitochondria and chloroplasts) that evolved by endosymbiosis. Some viruses may also maintain themselves extrachromosomally. | https://openstax.org/books/microbiology/pages/10-summary |
Extrachromosomal DNA in prokaryotes is commonly maintained asplasmidsthat encode a few nonessential genes that may be helpful under specific conditions. Plasmids can be spread through a bacterial community by horizontal gene transfer. | https://openstax.org/books/microbiology/pages/10-summary |
Viral genomes show extensive variation and may be composed of either RNA or DNA, and may be either double or single stranded. | https://openstax.org/books/microbiology/pages/10-summary |
DNA serves two important cellular functions: It is the genetic material passed from parent to offspring and it serves as the information to direct and regulate the construction of the proteins necessary for the cell to perform all of its functions. | https://openstax.org/books/microbiology/pages/11-summary |
Thecentral dogmastates that DNA organized into genes specifies the sequences of messenger RNA (mRNA), which, in turn, specifies the amino acid sequence of proteins. | https://openstax.org/books/microbiology/pages/11-summary |
The genotype of a cell is the full collection of genes a cell contains. Not all genes are used to make proteins simultaneously. The phenotype is a cellâs observable characteristics resulting from the proteins it is producing at a given time under specific environmental conditions. | https://openstax.org/books/microbiology/pages/11-summary |
The DNA replication process issemiconservative, which results in two DNA molecules, each having one parental strand of DNA and one newly synthesized strand. | https://openstax.org/books/microbiology/pages/11-summary |
In bacteria, theinitiation of replicationoccurs at theorigin of replication, wheresupercoiledDNA is unwound byDNA gyrase, made single-stranded byhelicase, and bound bysingle-stranded binding proteinto maintain its single-stranded state.Primasesynthesizes a short RNAprimer, providing a free 3â-OH group to whichDNA pol... | https://openstax.org/books/microbiology/pages/11-summary |
Duringelongation, theleading strandof DNA is synthesized continuously from a single primer. Thelagging strandis synthesized discontinuously in shortOkazaki fragments, each requiring its own primer. The RNA primers are removed and replaced with DNA nucleotides by bacterialDNA polymerase I, andDNA ligaseseals the gaps be... | https://openstax.org/books/microbiology/pages/11-summary |
Terminationof replication in bacteria involves the resolution of circular DNA concatemers by topoisomerase IV to release the two copies of the circular chromosome. | https://openstax.org/books/microbiology/pages/11-summary |
Eukaryotes typically have multiple linear chromosomes, each with multiple origins of replication. Overall, replication in eukaryotes is similar to that in prokaryotes. | https://openstax.org/books/microbiology/pages/11-summary |
The linear nature of eukaryotic chromosomes necessitatestelomeresto protect genes near the end of the chromosomes.Telomeraseextends telomeres, preventing their degradation, in some cell types. | https://openstax.org/books/microbiology/pages/11-summary |
Rolling circle replicationis a type of rapid unidirectional DNA synthesis of a circular DNA molecule used for the replication of some plasmids. | https://openstax.org/books/microbiology/pages/11-summary |
Duringtranscription, the information encoded in DNA is used to make RNA. | https://openstax.org/books/microbiology/pages/11-summary |
RNA polymerasesynthesizes RNA, using the antisense strand of the DNA as template by adding complementary RNA nucleotides to the 3â end of the growing strand. | https://openstax.org/books/microbiology/pages/11-summary |
RNA polymerase binds to DNA at a sequence called apromoterduring theinitiation of transcription. | https://openstax.org/books/microbiology/pages/11-summary |
Genes encoding proteins of related functions are frequently transcribed under the control of a single promoter in prokaryotes, resulting in the formation of apolycistronic mRNAmolecule that encodes multiple polypeptides. | https://openstax.org/books/microbiology/pages/11-summary |
Unlike DNA polymerase, RNA polymerase does not require a 3â-OH group to add nucleotides, so aprimeris not needed during initiation. | https://openstax.org/books/microbiology/pages/11-summary |
Termination of transcriptionin bacteria occurs when the RNA polymerase encounters specific DNA sequences that lead to stalling of the polymerase. This results in release of RNA polymerase from the DNA template strand, freeing theRNA transcript. | https://openstax.org/books/microbiology/pages/11-summary |
Eukaryotes have three different RNA polymerases. Eukaryotes also have monocistronic mRNA, each encoding only a single polypeptide. | https://openstax.org/books/microbiology/pages/11-summary |
Eukaryotic primary transcripts are processed in several ways, including the addition of a5â capand a 3â²-poly-A tail, as well assplicing, to generate a mature mRNA molecule that can be transported out of the nucleus and that is protected from degradation. | https://openstax.org/books/microbiology/pages/11-summary |
Intranslation, polypeptides are synthesized using mRNA sequences and cellular machinery, including tRNAs that match mRNAcodonsto specific amino acids and ribosomes composed of RNA and proteins that catalyze the reaction. | https://openstax.org/books/microbiology/pages/11-summary |
Thegenetic codeisdegeneratein that several mRNA codons code for the same amino acids. The genetic code is almost universal among living organisms. | https://openstax.org/books/microbiology/pages/11-summary |
Prokaryotic (70S) and cytoplasmic eukaryotic (80S) ribosomes are each composed of a large subunit and a small subunit of differing sizes between the two groups. Each subunit is composed of rRNA and protein. Organelle ribosomes in eukaryotic cells resemble prokaryotic ribosomes. | https://openstax.org/books/microbiology/pages/11-summary |
Some 60 to 90 species of tRNA exist in bacteria. Each tRNA has a three-nucleotideanticodonas well as a binding site for acognate amino acid. All tRNAs with a specific anticodon will carry the same amino acid. | https://openstax.org/books/microbiology/pages/11-summary |
Initiationof translation occurs when the small ribosomal subunit binds withinitiation factorsand an initiator tRNA at thestart codonof an mRNA, followed by the binding to the initiation complex of the large ribosomal subunit. | https://openstax.org/books/microbiology/pages/11-summary |
In prokaryotic cells, the start codon codes for N-formyl-methionine carried by a special initiator tRNA. In eukaryotic cells, the start codon codes for methionine carried by a special initiator tRNA. In addition, whereas ribosomal binding of the mRNA in prokaryotes is facilitated by the Shine-Dalgarno sequence within t... | https://openstax.org/books/microbiology/pages/11-summary |
During theelongationstage of translation, acharged tRNAbinds to mRNA in theA siteof the ribosome; a peptide bond is catalyzed between the two adjacent amino acids, breaking the bond between the first amino acid and its tRNA; the ribosome moves one codon along the mRNA; and the first tRNA is moved from theP siteof the r... | https://openstax.org/books/microbiology/pages/11-summary |
Terminationof translation occurs when the ribosome encounters astop codon, which does not code for a tRNA. Release factors cause the polypeptide to be released, and the ribosomal complex dissociates. | https://openstax.org/books/microbiology/pages/11-summary |
In prokaryotes, transcription and translation may be coupled, with translation of an mRNA molecule beginning as soon as transcription allows enough mRNA exposure for the binding of a ribosome, prior to transcription termination. Transcription and translation are not coupled in eukaryotes because transcription occurs in... | https://openstax.org/books/microbiology/pages/11-summary |
Polypeptides often require one or morepost-translational modificationsto become biologically active. | https://openstax.org/books/microbiology/pages/11-summary |
Amutationis a heritable change in DNA. A mutation may lead to a change in the amino-acid sequence of a protein, possibly affecting its function. | https://openstax.org/books/microbiology/pages/11-summary |
Apoint mutationaffects a single base pair. A point mutation may cause asilent mutationif the mRNA codon codes for the same amino acid, amissense mutationif the mRNA codon codes for a different amino acid, or anonsense mutationif the mRNA codon becomes a stop codon. | https://openstax.org/books/microbiology/pages/11-summary |
Missense mutations may retain function, depending on the chemistry of the new amino acid and its location in the protein. Nonsense mutations produce truncated and frequently nonfunctional proteins. | https://openstax.org/books/microbiology/pages/11-summary |
Aframeshift mutationresults from an insertion or deletion of a number of nucleotides that is not a multiple of three. The change in reading frame alters every amino acid after the point of the mutation and results in a nonfunctional protein. | https://openstax.org/books/microbiology/pages/11-summary |
Spontaneous mutationsoccur through DNA replication errors, whereasinduced mutationsoccur through exposure to amutagen. | https://openstax.org/books/microbiology/pages/11-summary |
Mutagenic agents are frequently carcinogenic but not always. However, nearly all carcinogens are mutagenic. | https://openstax.org/books/microbiology/pages/11-summary |
Chemical mutagens include base analogs and chemicals that modify existing bases. In both cases, mutations are introduced after several rounds of DNA replication. | https://openstax.org/books/microbiology/pages/11-summary |
Ionizing radiation,such as X-rays and γ-rays, leads to breakage of the phosphodiester backbone of DNA and can also chemically modify bases to alter their base-pairing rules. | https://openstax.org/books/microbiology/pages/11-summary |
Nonionizing radiationlike ultraviolet light may introduce pyrimidine (thymine) dimers, which, during DNA replication and transcription, may introduce frameshift or point mutations. | https://openstax.org/books/microbiology/pages/11-summary |
Cells have mechanisms to repair naturally occurring mutations. DNA polymerase has proofreading activity. Mismatch repair is a process to repair incorrectly incorporated bases after DNA replication has been completed. | https://openstax.org/books/microbiology/pages/11-summary |
Pyrimidine dimers can also be repaired. Innucleotide excision repair (dark repair), enzymes recognize the distortion introduced by the pyrimidine dimer and replace the damaged strand with the correct bases, using the undamaged DNA strand as a template. Bacteria and other organisms may also usedirect repair, in which th... | https://openstax.org/books/microbiology/pages/11-summary |
Through comparison of growth on the complete plate and lack of growth on media lacking specific nutrients, specific loss-of-function mutants calledauxotrophscan be identified. | https://openstax.org/books/microbiology/pages/11-summary |
TheAmes testis an inexpensive method that uses auxotrophic bacteria to measure mutagenicity of a chemical compound. Mutagenicity is an indicator of carcinogenic potential. | https://openstax.org/books/microbiology/pages/11-summary |
Horizontal gene transferis an important way for asexually reproducing organisms like prokaryotes to acquire new traits. | https://openstax.org/books/microbiology/pages/11-summary |
There are three mechanisms of horizontal gene transfer typically used by bacteria:transformation,transduction, andconjugation. | https://openstax.org/books/microbiology/pages/11-summary |
Transformation allows for competent cells to take up naked DNA, released from other cells on their death, into their cytoplasm, where it may recombine with the host genome. | https://openstax.org/books/microbiology/pages/11-summary |
Ingeneralized transduction, any piece of chromosomal DNA may be transferred by accidental packaging of the degraded host chromosome into a phage head. Inspecialized transduction, only chromosomal DNA adjacent to the integration site of a lysogenic phage may be transferred as a result of imprecise excision of the propha... | https://openstax.org/books/microbiology/pages/11-summary |
Conjugation is mediated by theF plasmid,which encodes aconjugation pilusthat brings an F plasmid-containingF+cellinto contact with anF-cell. | https://openstax.org/books/microbiology/pages/11-summary |
The rare integration of the F plasmid into the bacterial chromosome, generating anHfr cell, allows for transfer of chromosomal DNA from the donor to the recipient. Additionally, imprecise excision of the F plasmid from the chromosome may generate an Fâ plasmid that may be transferred to a recipient by conjugation. | https://openstax.org/books/microbiology/pages/11-summary |
Conjugation transfer ofR plasmidsis an important mechanism for the spread of antibiotic resistance in bacterial communities. | https://openstax.org/books/microbiology/pages/11-summary |
Transposonsare molecules of DNA with inverted repeats at their ends that also encode the enzyme transposase, allowing for their movement from one location in DNA to another. Although found in both prokaryotes and eukaryotes, transposons are clinically relevant in bacterial pathogens for the movement of virulence factor... | https://openstax.org/books/microbiology/pages/11-summary |
Gene expressionis a tightly regulated process. | https://openstax.org/books/microbiology/pages/11-summary |
Gene expression in prokaryotes is largely regulated at the point of transcription. Gene expression in eukaryotes is additionally regulated post-transcriptionally. | https://openstax.org/books/microbiology/pages/11-summary |
Prokaryotic structural genes of related function are often organized intooperons, all controlled by transcription from a single promoter. The regulatory region of an operon includes the promoter itself and the region surrounding the promoter to which transcription factors can bind to influence transcription. | https://openstax.org/books/microbiology/pages/11-summary |
Although some operons areconstitutively expressed, most are subject to regulation through the use oftranscription factors(repressors and activators). Arepressorbinds to anoperator, a DNA sequence within the regulatory region between the RNA polymerase binding site in the promoter and first structural gene, thereby phys... | https://openstax.org/books/microbiology/pages/11-summary |
Thetrpoperon is a classic example of arepressible operon. When tryptophan accumulates, tryptophan binds to a repressor, which then binds to the operator, preventing further transcription. | https://openstax.org/books/microbiology/pages/11-summary |
Thelacoperon is a classic example aninducible operon. When lactose is present in the cell, it is converted to allolactose. Allolactose acts as an inducer, binding to the repressor and preventing the repressor from binding to the operator. This allows transcription of the structural genes. | https://openstax.org/books/microbiology/pages/11-summary |
Thelacoperon is also subject to activation. When glucose levels are depleted, some cellular ATP is converted into cAMP, which binds to thecatabolite activator protein (CAP). The cAMP-CAP complex activates transcription of thelacoperon. When glucose levels are high, its presence prevents transcription of thelacoperon an... | https://openstax.org/books/microbiology/pages/11-summary |
Small intracellular molecules calledalarmonesare made in response to various environmental stresses, allowing bacteria to control the transcription of a group of operons, called a regulon. | https://openstax.org/books/microbiology/pages/11-summary |
Bacteria have the ability to change whichÏ factorof RNA polymerase they use in response to environmental conditions to quickly and globally change which regulons are transcribed. | https://openstax.org/books/microbiology/pages/11-summary |
Prokaryotes have regulatory mechanisms, includingattenuationand the use ofriboswitches, to simultaneously control the completion of transcription and translation from that transcript. These mechanisms work through the formation of stem loops in the 5â end of an mRNA molecule currently being synthesized. | https://openstax.org/books/microbiology/pages/11-summary |
There are additional points of regulation of gene expression in prokaryotes and eukaryotes. In eukaryotes,epigenetic regulationby chemical modification of DNA or histones, and regulation of RNA processing are two methods. | https://openstax.org/books/microbiology/pages/11-summary |
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