Human Microbiology Final
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- The science of heredity.
- What genes are
- how they carry information
Genetic information in a cell
structures containing DNA that physically carry hereditary information.
- segements of DNA (except in viruses in which they are ade up of RNA) that code for functional products.
- macromolecule composed of repeating units called nucleotides.
- nucleobase- adenine, thymine, cytosine, guanine.
- Always occur in a specific way
- Adenine - thymine
- Cytosine - guanine
- base sequence of one DNA strand determines the base sequence of the other strand.
- The two strands are complimentary.
Structure of DNA
- two primary features of biological information
- 1. Linear sequence - provides the actual information
- genetic information encoded by the sequence of bases along the DNA strand
- 2. Complimentary structure allows for the precise duplication of DNA during cell division
- genetic make-up
- codes for all the particular characteristics of an organism
- potential properties not properties themselves
- refers to the actual expressed characteristics.
- organisms ability to perform a particular chemical reaction
- most studied of bacterial species
- found in human large intestine 4.6 million base pairs
- produces Shiga toxin through virus infecting bacteria through bacteriophages.
the sequencing and molecular characterization of genomes
- Any bases that are improperly base paired are removed and replaced by replication enzymes. Once aligned the newly added nucleotide is joined to the growing DNA strand by an enzyme called DNA polymerase.
- Proofreads- As each new base is added enzyme evaluates whether it forms the proper complementary base-pairing structure.
semi conservative replication
one original (conserved) strand and one new strand
- supercoiling is relaxed by topoisomerase or gyrase
- two strands of parental DNA are unwound by helicase
- separated from each other in one small DNA segment.
- free nucleotides present are matched up with to the exposed bases of the single-stranded parental DNA.
the process of synthesizing RNA from a DNA template
The use of mRNA as a template in the synthesis of a protein
RNA and Protein Synthesis
- Ribonucleic acid single stranded template of DNA
- three types of RNA in bacterial cells mRNA, rRNA, and tRNA
- ribosomal RNA forms integral part of ribosomes, cellular machinery for protein synthesis.
- tRNA also involved in protein synthesis.
- carries coded information for making specific proteins from DNA to ribosomes, where are proteins are synthesized.
- mRNA synthesized during transcription.
- uses specific portion of cell's DNA as a template.
- DNA template sequence is rewritten so that the same information appears at the base sequence of mRNA
- The process of transcription requires both an enzyme called RNA polymerase and a supply of RNA nucleotides.
- Transcription begins when RNA polymerase binds to the DNA at a site called the promoter.
- Transcription ends when RNA polymerase reaches a site on the DNA called the terminator.
Process of transcription
- Allows the cell to produce short-term copies of genes that can be used as the direct source of information for protein synthesis.
- mRNA acts as an intermediate between the permanent storage form, DNA, and the process that uses the information, translation.
- mRNA as source of information for the synthesis of proteins
- Involves decoding the "language" of nucleic acids and converting that information into the language of proteins
- Codons- groups of three nucleotides, codons of mRNA molecule determines the sequence of amino acids. Codons code for a particular amino acids This is the genetic code.
- groups of three nucleotides
- mRNA molecule groups determine sequence of amino acids
- 64 possible codons
- 61 are sense codons - code for amino acids
- 3 nonsense codons - also called stop codons do not code signal the end of protein molecule synthesis.
- 64 possible codons
- only 20 amino acids
- most amino acids are signaled by several alternative codons
- allows for a certain amount of change or mutation, in the DNA without affecting the protein ultimately produced.
- The site of translation is the ribosome and transfer RNA molecules both recognize the specific codons and transport the required amino acids
- Each tRNA have an anticodon a sequence of three base that is complementary to a codon
- tRNA - mRNA- ribsomes come apart into its two subunits and are available for use again.
A set of operator and promoter sites and the structural genes they control
regulation of gene expression in bacteria by induction
- The process that turns on the transcription of a gene or genes is induction.
- Inducers - substance that acts to induce transcription of a gene
The regulatory mechanism that inhibits gene expression and decreases the synthesis of enzymes
- Inhibition of the metabolism of alternative carbon sources by glucose also called the glucose effect.
- When glucose is available, the level of cAMP in the cell is low, and CAP (catabolic activator protein) is not bound.
are expressed at a fixed rate
Genes expressed on as needed
- Repressible genes
- Inducible genes
- catabolite repression
- A change in the base sequence of DNA.
- most neutral
- base substitutions- also called point mutations; most common type of mutation involving single base pairs. single base at one point in the DNA sequence is replaced with a different base.
- missense mutation- when base substitution results in an amino acid substitution in the synthesized protein this change in the DNA is known as a missense mutation.
- frameshift mutation - one in which one or a few nucleotidepairs are deleted or inserted in the DNA...Huntington's disease.
- nonsense mutations- stop the coding
- spontaneous mutations- occur in the absence of any mutation-causing agents. 1 in 109 replicated base pairs or 1 in 106 replicated genes.
- Mutagens- agents in the enviroment, chemicals, radiation that directly or indirectly bring about mutations. Increase to 10-5 or 10-3 per replicated gene.
effects of mutagen on the mutation rate
increases the mutation rate by the factor of 10 to 1000 times. mutagens are used experimentally to enhance the production of mutant cells for research.
methods of Positive (direct) and negative (indirect) selection of mutants.
Positive selection involves the dection of mutant cells by the rejection of the unmutated parents cells. example- bacteria that have mutated and are resistant to penicillin will be identified when plated mutants will grow and form colonies. Parent cells cannot grow.
Negative selection - selects a cell that cannot perform a certain function using the techique of replica plating. A colony that grows on the plate with histidine cannot on the medium without is auxotrophic. (histidine requiring mutant). has a nutrient requirement absent in the parent.
- faster and less expensive procedure for the preliminary screening of potential carcinogens.
- Based on the observation that exposure of mutant bacteria to mutagenic substances may cause new mutations that reverse the effect (change in the phenotype) of the original mutations.
- 90% of the substances found by the Ames test to be mutagenic have also been shown to be carcinogenic in animals
Photolyases-separate thymine dimers
- vertical gene transfer-occurs during reproduction between generations of cells
- Horizontal gene transfer- The transfer of genes betweeen cells of the same generation.
- segments of DNA that can move from one region of DNA to another
- Contain insertion sequences for cutting and resealing DNA(transposase)
- Complex transposons carry other genes
- resistant factors are plasmids that have significant medical importance.
- infectious agent was resistant to usual antibiotics
Kenya 71% closeness of strain
- DNA Gyrase-relaxes supercoiling
- DNA Ligase-makes covalent bonds to join DNA strands; joins Okazaki fragments and new segments in excision repair.
- DNA Polymerase-Synthesizes DNA proofreads and repairs DNA
- Topoisomerase- relaxes supercoiling ahead of the replication fork; separates DNA circles at the end of DNA replication.
viruses that infect bacteria.
- contain a single type of nucleic acis, either DNA or RNA
- Contain a protein coat that surround the nucleic acid
- Multiply inside living cells
- Some have spikes
- infect specific types of cells in one host
is determined by specific host attachment sites and cellular factors.
- nucleic acid- DNA or RNA
- capsid- capsomeres/polyhedral virus
- Envelope-surrounds nucleic acid
- has either DNA or RNA
- can replicate in arthropods that transmit them
- Hep C
- Ebola an Marburg virus
- Envelope helical virus
parainfluenza, mumps -disease in chickens
- RNA tumor viruses, Oncoviruses cause leukemia
- Lentivirus- HIV
SARS upper respiratory tract infection
hemorrhagic fever pulmonary syndrome. associated with rodents
Influenza A, B, C
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