Microbiology Chapter 8 Flashcards
Theory that says one gene one protein
DNA Polymerase makes RNA polymerase in transcription to Mrna to Translation in the ribosome to make protein.
flow of central dogma theory
Flow of Genetic Material in Expression?
Genetic information is used within a cell to produce the proteins needed for the cell to function.
Flow of Genetic Material in Recombination?
Genetic information can be
transferred between cells
of the same generation.
Flow of Genetic Material in Replication?
Genetic information can
be transferred between
generations of cells.
Monocystronic vs Polycistronic
An mRNA molecule is said to be monocistronic when it contains the genetic information to translate only a single protein. This is the case for most of the eukaryotic mRNAs. On the other hand, polycistronic mRNA carries the information of several genes, which are translated into several proteins. These proteins usually have a related function and are grouped and regulated together in an operon. Most of the mRNA found in bacteria and archea are polycistronic.
Why is it important to regulate the expression of genes?
Prokaryotes: environmental conditions
Adapt and Survive
Growth and Division
Eukaryotes: multicellular organisms = homeostasis
Embryological development
Tissue and organ differentiation
Constitutive genes are expressed at a fixed rate Other genes are expressed only as needed Inducible genes Repressible genes so whats the difference?
nducible operons are used to produce proteins only under specific conditions. Most bacteria use glucose as their main energy source. Therefore, the unusual arrival of the milk sugar lactose in the cell turns the operator switch to the “on” position, which allows transcription to occur. Repressible operons have operators that are always on (transcription occurring) unless a signal (for example, too much product) turns them off.
Cluster of adjacent genes oriented in the same direction
Co-transcribed into a single polycistronic mRNA
Coordinately regulated
operon
One type of signal (i.e. lactose) can regulate expression of several genes that are clustered together on a chromosome
Empirical evidence has shown many bacterial genes are clustered and transcribed together as single mRNA (co-transcribed)
The gene clusters are termed operons
The mRNA transcript is called polycistronic
jacob and manod :operon theory
Lac operon, trp operon is inducible or repressible
inducible = lac and repressible trp
structure of inducible lac operon
Structure of the operon. The operon consists of the promoter (P) and operator (O) sites and structural genes that code for the protein. The operon is regulated by the product of the regulatory gene
The lacI gene coding for the repressor lies nearby the lac operon and is always expressed (constitutive)
mechanism of inducible gene
Repressor active, operon off. The repressor protein binds with the operator, preventing transcription from the operon. which means when no lactose is present repressor binds tightly, inhibits transcription
Repressor inactive, operon on. When the inducer allolactose binds to the repressor protein, the inactivated repressor can no longer block transcription. The structural genes are transcribed, ultimately resulting in the production of the enzymes needed for lactose catabolism.
Lactose induces further induction of lacZYA gene cluster expression
Induction of Gene Expression
scenarios: no lactose or with lactose
No lactose in medium:
lacI produces repressor which binds to operator => no gene expression
Lactose in medium:
Lactose (inducer) binds to repressor => repressor cannot bind to operator anymore => gene expression can start
Repressible operons structure?
Structure of the operon. The operon consists of the promoter (P) and operator (O) sites and structural genes that code for the protein. The operon is regulated by the product of the regulatory gene (I ).
In repressible operons, the structural genes are transcribed until that are turned off.
Repressible operon mechanism?
Repressor inactive, operon on. The repressor is inactive, and transcription and translation proceed, leading to the synthesis of tryptophan.
Repressor active, operon off. When the corepressor
tryptophan binds to the repressor protein, the activated
repressor binds with the operator, preventing transcription
from the operon.
positive vs negative regulation
(a) Negative Regulation:
Turning off of the structural gene expression by a repressor protein is known as negative regulation. In an inducible system, the repressor protein alone binds to the operator and inhibits transcription in the absence of an inducer.
However, in the presence of an inducer, the repressor protein binds to it and undergoes a conformational change. The resultant repressor-inducer complex can not bind to the operator ancKhereby, initiates transcription. (Example: lac-operon)
(b) POSITIVE REGULATION:
Turning on of the structural gene expression by the active repressor protein is known as positive regulation.
In a repressible system, the repressor protein alone can not bind to the operator and thus, facilitates the binding of the RNA polymerase and transcription. The repressor-co-repressor complex undergoes a conformational change in the structure. This complex can bind to the site and inhibit transcription
Mecahnism of epigenetic control Methylating nucleotides Methylated (off) genes are passed to offspring cells Not permanent May explain biofilm behavior
1.Transcription of miRNA occurs. 2.miRNA binds to target mRNA that has at least six complementary bases. 3.mRNA is degraded
mutations terms?
Mutagen: agent that causes mutations
Spontaneous mutations: occur in the absence of a mutagen
X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone
UV radiation causes thymine dimers
ionizing radiation
Positive (direct) selection detects mutant cells because they grow or appear different
Negative (indirect) selection detects mutant cells because they do not grow
Replica plating
modes of selection based on mutation
Kinds of Horizontal Gene Transfer
the transfer of genes between cells of the same generation Transformation Conjugation Transduction Generalized Specialized Transposons
Vertical gene transfer
occurs during reproduction between generations of cell(cell division)
Exchange of genes between two DNA molecules
Crossing over occurs when two chromosomes break and rejoin
Genetic recombination
modes of conjugation
sex pillus and mating bridge
Kinds of Plasmids
Conjugative plasmid: carries genes for sex pili and transfer of the plasmid
Dissimilation plasmids: encode enzymes for catabolism of unusual compounds
R factors: encode antibiotic resistance
Transposons
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
