Post on 10-May-2015
description
Genetic of microorganisms
Advantages of bacteria and viruses as objects for genetic researches
Simplicity of genome structure Universality of gene codeLack of diploid set of chromosomes and dominant genes Відносна легкість культивуванняGrate rapid of reproduction and plurality of population Genetic heterogeneity of population Accessibility modern methods of genetic analysis as sequencing of DNA, polymerase chain reaction (PCR)
Competitive structure genome of E.coli and human cell
Properties E.coli Human cellPlace in cell Nucleoid Nucleus
Quantity of chromosomes 1 46
Quantity of genes 4000 100000
Molecular weight of DNA 2х109 2х1012
DNA length 0,1 см 183 см
DNA shape Supercoiled Linear
Introns Present Absent
Time existence of mRNA Minutes Hours
Genome type Haploid Diploid
Plasmid Present Absent
DNA combined in cell with Polyamines Histones
The genome
is the some total of genetic material of a cell
Semiconservative replication of DNA. Simplified steps
a. A helicase unwinds the double helix into 2 parent strands (P1 and P2).
b. The replication of new complementary strands proceeds though the action of an enzyme that attaches nucleotides, using the exposed strands as templates.
c. Each completed daughter molecule contains one strand that is newly synthesized and one of the original parent strands.
Replication of bacterial DNA
a. The theta stage of replication, in which one strand loops down as it grown in length.
b. Nicking, separation, repair, and release of two completed molecules that will be separated into daughter cells during binary fission.
Definitions
Together the structural and regulatory genes constitute the genotype
Phenotype is determined by genotype and is the actual appearance and activities of the organism.
Exons are coding regions that will be translated into product – proteins, enzymes
Introns are sequences of bases that do not code for product
Structure of bacterial genome
Structural genes are genes that code for proteins
Regulatory genes are genes that have regulatory function and act to control the expression of the structural genes
Operon is a specific unit of DNA that regulates genetic function in procaryotes
The lac operon
Regulator – composed of the gene that codes for a protein capable of repressing the operon (a repressor)
Control lorus - composed of two genes, the promoter (recognized by RNA polymerase) and the operator, a sequence where transcription of the structural genes is initiated
Structural locus – made up of 3 genes, each coding for a different enzyme (b-galactosidase, permease, and transacetylase) needed to catabolize lactose
Regulator Control locus Structural locus
Two possible ways work of operon
Inducible. The operon can be turned on (induced) by the substrate of the enzyme for which the structural genes code
Repressible. The operon can be turned off (repressed) by the product its enzymes synthesize
A model of inducible regulation. Lac operon
A model of repressible regulation. Arg operon
Types of changes in the genetic code
Mutation is a change in the nucleotide sequence of DNA that result is a recognizable change in the organism
Recombination means the addition of genes from an outside source, such as a virus or another cell
Categories based on causes of mutations
A spontaneous mutation is a random change in the DNA arising from mistakes in replication of the detrimental effects of natural background radiation on DNA
An induced mutations result from exposure of the cell to exogenous DNA modifiers such as radiation or chemical substances
Categories of mutation based in alteration of base sequence in DNA
A base substitution mutation occurs when one pair of nucleotide bases in the DNA is replaced by another that results in change in codon and synthesis different protein.
Transitions involves the raplacement of a purine by a different purine or pyrimidine by a different pyrimidine
Transversions occurs when purines replace pyrimidines and pyrimidines replace purines.
A deletion mutation involves the removal of one or more nucleotide base pairs from the DNA
An insertion mutation involves the addition of one or more pairs to the DNA
A frameshift mutation are addition or loss of one or two bases in a gene. It can result in the misreading of large numbers of codons
Categories based in overall effect of mutation
A silent mutation alters a base but not change the amino acid and has no effect
A missense mutation is a change in the code that leads to placement of a different amino acid. It can do one of the following:
create a faulty, nonfunctional protein
produce a different but functional protein
cause no significant alteration in protein function
A nonsense mutation changes a normal codon into a stop codon that does not code for an amino acid and stops the production of the protein wherever it occurs. It almost always results in a nonfunctional protein
A back-mutation (reversion mutation) occurs when a gene that has undergone mutation reverse (mutates back) to its original base composition
Selected mutagenic agents and their effects
Agent EffectChemical
Nitrous acid, disulfite
Removes an amino group from some bases
Mustard gas Causes cross-linkage of DNA strands
Acridine dyes Cause frameshifts due to insertion between base pairs
Notrogen base analogs
Compete with natural bases for sites on replicating DNA
Radiation
Ionizing (gamma rays)
Form free radicals that cause single or double breaks in DNA
Ultraviolet Causes cross-links between adjacent pyrimidines
Transposable genetic elements
Insertion sequences (IS elements) Transposons Plasmids
Competitive characteristic IS, transposons, and plasmids
Genetic element
DNA size Quantity of genes
Self-dependent replication
IS 800-1400 pair nucleic bases
Only genes for transposase
No
Transposon 2000-2500 pair nucleic bases
Only few genes for transposase and resistance to antibiotics
No
Plasmid 3000-5000 pair nucleic bases
40-50 different genes
Yes
Transposable genetic elements
Plasmid
Chromosomal and plasmid DNA leaking out of a cell.
Cell functions coded for by some plasmids
Group Function Fertility plasmids (F)
Transfer of DNA from one cell to another via conjugation (F-pili)
Resistance plasmids (R)
Resistance to various antibiotics
Resistance to cadmium and mercury
Resistance to ultraviolet radiation
Col plasmids Bacteriocin production
Virulence factor plasmids
Enterotoxin production
Fimbriae production
Metabolic plasmids
Utilization of camphor
Formation of spores in streptomycetes
Intermicrobial DNA transfer and recombination
Transformation
Transduction
Conjugation
Plasmid transfer
Types of intermicrobial exchange
Mode Requirement Direct of indirect
Genes transferred
Conjuga-tion
Sex pilus on donorFertility plasmid in donorBoth donor and recipient Gram-negative cells
Direct Drug resistance, resistance to metal; enzymes; degradation of toxic substrate
Transfor-mation
Free donor DNA (fragment)Live, competent recipient cell
Indirect Polysaccharide capsule
Transduc-tion
Donor is lysed bacteriumDefective bacteriophage is carrier of donor DNALive, competent recipient cell of came species as donor
Indirect Toxins; enzymes for fermentation; drug resistance
Conjugation
Conjugation is mode of sexual process mating in which a plasmid or other genetic material is transferred by a donor to a recipient cell via a specialized appendage
Conjugation process
Sex, or F, pilus holding together donor and recipient cell of E.coli during DNA transfer
Participants of conjugation process
Gram-negative bacterium that produce F pili act as donors during conjugation. Donor strains are designated F+ if the F plasmid is independent
Bacteria lacking the F plasmid are recipients and designated
F-
If the F plasmid DNA incorporated into the bacterial chromosome the donor cell designated Hfr (high frequency recombination)
Cojugation – transfer of the F plasmid
Transformation F+ to Hfr cell
The F plasmid integrates at specific locations into the chromosome and F+ cell is transformed to Hfr cell.
The process is reversible.
Conjugation – transfer of chromosomal DNA
Transformation
In transformation a free DNA molecule is transferred from a donor to a recipient bacterium
Infecting mouse with virulent encapsulated streptococci
Infecting mouse with nonvirulent streptococci without capsule
Infecting mouse with killed virulent streptococci
Infecting mouse with mix killed virulent streptococci and alive nonvirulent
Transduction
is a process by which a bacteriophage serve a the carrier of DNA from a donor cell to a recipient cell.
There are 2 version of transduction:
Generalized
Specialized
Generalized transduction
Specialized transduction
In specialized transduction, a highly specific part of the host genome is regularly incorporated into the virus. It occurs only during infection caused by temperate phage
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