Microbial genetics involves the transmission of hereditary traits in microorganisms. It plays a role in developing fields like molecular and cell biology. Bacteria contain a single circular chromosome made of DNA that is compacted. Bacteria can also contain plasmids. DNA replication copies the parental DNA. Variability in microorganisms comes from changes in genotype and phenotype from factors like mutation and recombination. Mutation rates depend on type and can be increased by mutagens. Recombination involves processes like transformation, transduction, and conjugation. Plasmids can confer traits like antibiotic resistance and are transferred by conjugation. Gene expression in bacteria is regulated through mechanisms like induction and repression that control operons.
transduction is a process which that bacteriophage is transfer the genetic material to one to another bacterial cell .the transduction is have a two types that is generalized and specialized transduction .the two types of phage will be involve in the transduction process that is virulant and temptate pahge
Gene regulation in eukaryotes in a nutshell covering all the important stages of gene regulation in eukaryotes at transcriptional level, translation level and post-translational level.
REGULATION OF
GENE EXPRESSION
IN PROKARYOTES & EUKARYOTES .
This presentation is enriched with lots of information of gene expression with many pictures so that anyone can understand gene expression easily.
Gene expression is the process by which the information encoded in a gene is used to direct the assembly of a protein molecule.
Gene expression is explored through a study of protein structure and function, transcription and translation, differentiation and stem cells.
It is the process by which information from a gene is used in the synthesis of a functional gene product.
These products are often proteins, but in non-protein coding genes such as ribosomal RNA (rRNA), transfer RNA (tRNA) or small nuclear RNA (snRNA) genes, the product is a functional RNA.
The process of gene expression is used by all known life - eukaryotes (including multicellular organisms), prokaryotes (bacteria and archaea)
Regulation of gene expression:
Regulation of gene expression includes a wide range of mechanisms that are used by cells to increase or decrease the production of specific gene products (protein or RNA).
Gene regulation is essential for viruses, prokaryotes and eukaryotes as it increases the versatility and adaptability of an organism by allowing the cell to express protein when needed.
CLASSIFICATION OF GENE WITH RESPECT TO THEIR EXPRESSION:
Constitutive ( house keeping) genes:
Are expressed at a fixed rate, irrespective to the cell condition.
Their structure is simpler.
Controllable genes:
Are expressed only as needed. Their amount may increase or decrease with respect to their basal level in different condition.
Their structure is relatively complicated with some response elements.
TYPES OF REGULATION OF GENE:
positive & negative regulation.
Steps involving gene regulation of prokaryotes & eukaryotes.
Operon-structure,classification of mechanisms- lac operon,tryptophan operon ,
and many things related to gene expression.
This is a video slide so anyone can understand this topic easily by seeing pictures included in this slide.
transduction is a process which that bacteriophage is transfer the genetic material to one to another bacterial cell .the transduction is have a two types that is generalized and specialized transduction .the two types of phage will be involve in the transduction process that is virulant and temptate pahge
Gene regulation in eukaryotes in a nutshell covering all the important stages of gene regulation in eukaryotes at transcriptional level, translation level and post-translational level.
REGULATION OF
GENE EXPRESSION
IN PROKARYOTES & EUKARYOTES .
This presentation is enriched with lots of information of gene expression with many pictures so that anyone can understand gene expression easily.
Gene expression is the process by which the information encoded in a gene is used to direct the assembly of a protein molecule.
Gene expression is explored through a study of protein structure and function, transcription and translation, differentiation and stem cells.
It is the process by which information from a gene is used in the synthesis of a functional gene product.
These products are often proteins, but in non-protein coding genes such as ribosomal RNA (rRNA), transfer RNA (tRNA) or small nuclear RNA (snRNA) genes, the product is a functional RNA.
The process of gene expression is used by all known life - eukaryotes (including multicellular organisms), prokaryotes (bacteria and archaea)
Regulation of gene expression:
Regulation of gene expression includes a wide range of mechanisms that are used by cells to increase or decrease the production of specific gene products (protein or RNA).
Gene regulation is essential for viruses, prokaryotes and eukaryotes as it increases the versatility and adaptability of an organism by allowing the cell to express protein when needed.
CLASSIFICATION OF GENE WITH RESPECT TO THEIR EXPRESSION:
Constitutive ( house keeping) genes:
Are expressed at a fixed rate, irrespective to the cell condition.
Their structure is simpler.
Controllable genes:
Are expressed only as needed. Their amount may increase or decrease with respect to their basal level in different condition.
Their structure is relatively complicated with some response elements.
TYPES OF REGULATION OF GENE:
positive & negative regulation.
Steps involving gene regulation of prokaryotes & eukaryotes.
Operon-structure,classification of mechanisms- lac operon,tryptophan operon ,
and many things related to gene expression.
This is a video slide so anyone can understand this topic easily by seeing pictures included in this slide.
DNA as a Genetic Material - Dr. P. Saranraj, Assistant Professor, Department of Microbiology, Sacred Heart College (Autonomous), Tirupattur, Vellore District, Tamil Nadu, India.
DNA as a Genetic Material - Dr. P. Saranraj, Assistant Professor, Department of Microbiology, Sacred Heart College (Autonomous), Tirupattur, Vellore District, Tamil Nadu, India.
Functions of Operating Systems:
Types of Operating Systems:
Real-Time Operating Systems
Single-User/Single-Tasking Operating Systems
Single-User/Multitasking Operating Systems
Multi-User/Multitasking Operating Systems
User Interface
Graphical User Interface (GUI)
Command-Line Interface
Running Programs
Managing Hardware
Two hydrothermal vent fields have been described at the ultra-slow spreading ridge of the Mid-Cayman Rise (MRC), including the world’s deepest (Piccard ~4985m) and the nearby Von Damm vent field (~2300m). Both vent fields support a localized high-biomass. The food web has chemoautotrophic bacteria at the base and includes bacterivorous shrimp as well as carnivores: shrimp and anemones.
The alvinocaridid shrimp Rimicaris hybisae is abundant at both vent fields and shows spatial variability in population structure. So far it has been considered bacterivorous. Large variations in tissue δ13C values remained largely unexplained, and it has been argued that δ13C values are not a good food web tracer in hydrothermal vent ecosystems.
We observed that shrimp tended to be either in dense aggregations on active chimneys, or more sparsely distributed and peripheral in (near) ambient temperatures. With the hypotheses that varying δ13C values show real differences in food sources and that shrimp in different locales might have different diets, we collected shrimp from both environments at the Von Damm site during an Ocean Exploration Trust Expedition with E/V Nautilus (NA034, 08/2013) and examined their gut contents.
Gut contents of all shrimp from dense aggregations consisted of white, amorphous material that resembled bacteria. Sparsely distributed shrimp (~1m from dense aggregations) had guts filled with fragments of crustacean exoskeleton, a mixture of bacteria-like material and crustacean exoskeleton, or bacteria-like material only.
We analyzed stable isotope compositions of the shrimp and their gut contents. Shrimp δ13C, δ15N and δ34S values reflect those of their gut contents +1 trophic level. Sparse shrimp have dramatically lower δ13C and δ34S values, and slightly elevated δ15N values, in comparison to dense shrimp. Sparse and dense R. hybisae clearly have different diets. Ongoing work is determining what exactly is this crustacean food source, whether diet changes occur during life history, and if this is linked to the molting cycle.
Cell Biology and genetics paper - Mutation a basic touch to b.sc students with examples. DNA, genome, gene level mutation and chromosome level with examples. Touched some of the mutation types.
regeneration
Proliferative Capacities of Tissues
Stem Cells
REPAIR BY CONNECTIVE TISSUE
Angiogenesis
Migration of Fibroblasts and ECM Deposition (Scar Formation)
PATHOLOGIC ASPECTS OF REPAIR
What is wound healing?
Classification of Wounds
Classification of Wounds Closure
Risk Factors for Surgical Wound Infections
Antibiotic Use
Hypertrophic Scars and Keloids
25.1Digestion and Absorption of Lipids
25.2Triacylglycerol Storage and Mobilization
25.3 Glycerol Metabolism
25.4 Oxidation of Fatty Acids
25.5 ATP Production from Fatty Acid Oxidation
25.6 Ketone Bodies
25.7 Biosynthesis of Fatty Acids: Lipogenesis
25.8 Relationship Between Lipogenesis and Citric Acid Cycle Intermediates
25.9 Fate of Fatty-Acid Generated Acetyl CoA
25.10 Relationships Between Lipid and Carbohydrate Metabolism
25.11B Vitamins and Lipid Metabolism
24.1 Digestion and Absorption of Carbohydrates
24.2 Hormonal Control of Carbohydrate Metabolism
24.3 Glycogen Synthesis and Degradation
24.4 Gluconeogenesis
24.5 The Pentose Phosphate Pathway
24.6 Glycolysis
24.7 Terminology for Glucose Metabolic Pathways
24.8 The Citric Acid Cycle
24.9 The Electron Transport Chain
24.10 Oxidative Phosphorylation
24.11 ATP Production for the Complete Oxidation of Glucose
24.12 Importance of ATP
24.13 Non-ETC Oxygen-Consuming Reactions
24.14 B-Vitamins and Carbohydrate Metabolism
22.1 Types of Nucleic Acids
22.2 Nucleotide Building Blocks
22.3. Nucleotide Formation
22.4 Primary Nucleic Acid Structure
22.5 The DNA Double Helix
22.6 Replication of DNA Molecules
22.7 Overview of Protein Synthesis
22.8 Ribonucleic Acids
22.9 Transcription: RNA Synthesis
22.10 The Genetic Code
22.11 Anticodons and tRNA Molecules
22.12 Translation: Protein Synthesis
22.13 Mutations
22.14 Nucleic Acids and Viruses
22.15 Recombinant DNA and Genetic Engineering
22.16 The Polymerase Chain Reaction
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
2. Microbial genetics is concerned with the
transmission of hereditary characters in
microorganisms.
Microbial genetics has played a unique role
in developing the fields of molecular and cell
biology and also has found applications in
medicine, agriculture, and the food and
pharmaceutical industries.
3. Chromosome
- a dense structure inside cells that physically carries hereditary information
from one generation to the next.
Bacterial Cell - contains only one chromosome, consisting of a single molecule of
double-stranded deoxyribonucleic acid (DNA) in the form of closed circle.
*Procaryotic chromosome is:
1. Naked (lacking the nuclear membrane found in eucaryotic cell)
2. is twisted, coiled and packaged into a highly compact form (because
bacterial chromosome has length of about 1200 times of the entire
cell)
-in addition to its chromosome, a bacterial cell contains
one or more PLASMIDS (double-stranded DNA molecules
that are much smaller than the chromosome and can
replicate independently of the chromosome).
-most are circular but linear plasmids have been
found in few bacteria(e.g. Spirochete that cause
Lyme disease)
-have been used extensively in genetic engineering
techniques.
4.
5.
6. DNA REPLICATION
- process that copies the
nucleotide sequence of a double-
stranded parent DNA into two
double-stranded daughter molecules
7. Figure 5.14. Origin of replication in E. coli Replication initiates at a
unique site on the E. coli chromosome, designated the origin (ori)
8. Component Function
Initiator protein Binds to origin and separates strands of
DNA to initiate replication
DNA helicase Unwinds DNA at replication fork
Single-strand-binding proteins Attach to SS-DNA and prevent 20 structures
from forming
DNA gyrase Moves ahead of the replication fork ,
making and resealing breaks in the double-
helical DNA to release the torque that
builds up as a result of unwinding at the
replication fork
DNA primase Synthesizes a short RNA primer to provide
a 3’-OH group for the attachment of DNA
nucleotides
DNA polymerase III Elongates a new nucleotide strand from
the 3’-OH group provided by the primer
DNA polymerase I Removes RNA primers and replaces them
with DNA
Table 4.1 Components required for replication in bacterial cells
9. Component Function
DNA ligase Joins Okazaki fragments by sealing nicks in the sugar-phosphate
of newly synthesized DNA
10. Transcription Elongation in Eucaryotes Is Tightly Coupled To RNA Processing
Figure 6-21. Summary of the
steps leading from gene to
protein in eucaryotes and
bacteria. The final level of a
protein in the cell depends on the
efficiency of each step and on the
rates of degradation of the RNA
and protein molecules. (A) In
eucaryotic cells the RNA molecule
produced by transcription alone
(sometimes referred to as the
primary transcript) would contain
both coding (exon) and
noncoding (intron) sequences.
Before it can be translated into
protein, the two ends of the RNA
are modified, the introns are
removed by an enzymatically
catalyzed RNA splicing reaction,
and the resulting mRNA is
transported from the nucleus to
the cytoplasm.
11. Variability in Microorganisms
-associated with its genotype and its phenotype
Genotype
- represents the inheritable total potential of a cell
Phenotype
- represents the portion of the genetic potential that is actually
expressed by the cell under a given set of condition.(eg. May
be particular color or size of bacterial colony or presence of bacterial
capsules which may or may not formed by certain bacteria depending on their
environment)
12. Phenotypic changes
-both the genotype and the environment influence the phenotypeof
an organism
eg. Bacteria of the genus Azomonas form large, gummy colonies
when grown with the sugar sucrose and smaller, nongummy colonies in the
absence of this sugar
Genotypic changes
-although some phenotypic changes are the result of Environmental
influences, others are the result of changes in the DNA.
These can occur as the result of:
1. mutation – a change in the nucleotide
sequence of a gene or
2. recombination –a process that leads to new
combinations of genes on a chromosome
13. Mutation and Recombination
• Mutation is a heritable change in DNA
sequence that can lead to a change in phenotype.
By definition, a mutant differs from its parental
strain in genotype, the nucleotide sequence of
the genome.
14. • Selectable mutations are those that give the
mutant a growth advantage under certain
environmental conditions and are especially
useful in genetic research. If selection is not
possible, mutants must be identified by
screening.
15. • Although screening is always more tedious than
selection, methods are available for screening
large numbers of colonies in certain types of
mutations. For instance, nutritionally defective
mutants can be detected by the technique of
replica plating (Figure 8.2).
16. Molecular Basis of Mutation
• Mutations, which can be either
spontaneous or induced, arise because of
changes in the base sequence of the
nucleic acid of an organism's genome.
17. Mutations can be classified into various types based upon the kinds of changes
they produce in a gene.
Two common types are:
1. Point mutations –results from the substitution of 1 nucleotide for
another in a gene
a. Neutral mutation
eg. AAU to AAC still codes for
asparagine
b. missense mutation
eg. AAU become AAG asparagine
to lysine
c. nonsense mutation
eg. UAU to UAA premature
halting
2. Frameshift mutation –addition or loss of one or
more nucleotides in a gene
a. insertion
b. deletion
18. • A point mutation, which results from a
change in a single base pair, can lead to a
single amino acid change in a polypeptide
or to no change at all, depending on the
particular codon involved (Figure 8.3).
19.
20.
21. • Deletions and insertions cause more
dramatic changes in the DNA, including
frameshift mutations, and often result in
complete loss of gene function (Figure 8.4).
25. Mutation Rates
• Different types of mutations can occur at
different frequencies. For a typical bacterium,
mutation rates of 10–7 to 10–11 per base pair are
generally seen.
• Although RNA and DNA polymerases make errors
at about the same rate, RNA genomes typically
accumulate mutations at much higher
frequencies than DNA genomes.
26. Mutagenesis
• Mutagens are chemical, physical, or
biological agents that increase the
mutation rate. Mutagens can alter DNA in
many different ways, but such alterations
are not mutations unless they can be
inherited.
27. • Table 8.2 gives an overview of some of the
major chemical and physical mutagens and their
modes of action.
28. • There are several classes of chemical mutagens,
one being the nucleotide base analogs (Figure
8.5).
29. • Several forms of radiation are highly mutagenic
(Figure 8.6).
30. • Some DNA damage can lead to cell death if
not repaired. A complex cellular
mechanism called the SOS regulatory
system is activated as a result of some
types of DNA damage and initiates a
number of DNA repair processes, both
error-prone and high-fidelity (Figure 8.7).
31.
32.
33. Mutagenesis and Carcinogenesis: The Ames Test
• The Ames test employs a sensitive bacterial assay system
for detecting chemical mutagens in the environment.
34.
35. Recombination
•DNA rearrangements are caused by a set of mechanisms that are
collectively called genetic recombination.
•Two broad classes:
1. general recombination
2. site-specific recombination.
General recombination (also known as homologous recombination)
-genetic exchange takes place between a pair of homologous DNA sequence
The breaking and rejoining of two homologous DNA
double helices creates two DNA molecules that have
“crossed over.” In meiosis, this process causes each
chromosome in a germ cell to contain a mixture of
maternally and paternally inherited genes.
36. Homologous recombination arises when closely related DNA
sequences from two distinct genetic elements are combined in a
single element (Figure 10.9)
37. • Recombination is an important evolutionary process, and cells
have specific mechanisms for ensuring that recombination takes
place.
38. In bacteria, gene transfer that can lead to recombination may occur in any of
three different ways:
1. transformation- simplest type of gene transfer; a recipient
cell acquires genes from “free floating” DNA molecules in the
surrounding medium
2. transduction –gene transfer in which a virus serves as
vehicle for carrying DNA from a donor bacteriumto a recipient
bacterium.
3. conjugation- a process of gene transfer that requires
cell-to-cell contact and thus differs from
transformation and trasnduction.
44. • The discovery of transformation was one of the
seminal events in biology because it led to
experiments demonstrating that DNA is the
genetic material (Figure 8.13).
45. • Certain prokaryotes exhibit competence, a state in
which cells are able to take up free DNA released by
other bacteria.
• Incorporation of donor DNA into a recipient cell requires
the activity of single-stranded binding protein, RecA
protein, and several other enzymes. Only competent cells
are transformable (Figure 8.14).
46.
47. Transduction
• Transduction involves the transfer of host genes from
one bacterium to another by bacterial viruses.
• In generalized transduction (Figure 8.15), defective
virus particles incorporate fragments of the cell's
chromosomal DNA randomly, but the efficiency is low.
48.
49. • In specialized transduction (Figure 8.16), the DNA of a
temperate virus excises incorrectly and takes adjacent
host genes along with it; transducing efficiency in this
case may be very high.
50.
51. Plasmids: General Principles
• Plasmids are small circular or linear DNA molecules
that carry any of a variety of unessential genes.
Although a cell can contain more than one plasmid,
they cannot be closely related genetically.
52.
53. • Figure 10.18 shows a genetic map of the F (fertility)
plasmid, a very well characterized plasmid of
Escherichia coli.
54. • Lateral transfer in the process of conjugation can
transfer plasmids (Figure 8.19).
56. • The genetic information that plasmids carry is not
essential for cell function under all conditions but may
confer a selective growth advantage under certain
conditions.
57. • Examples include antibiotic resistance (Figure
8.20), enzymes for degradation of unusual
organic compounds, and special metabolic
pathways. Virulence factors of many
pathogenic bacteria are often plasmid-
encoded.
58. Types of plasmids
1. Conjugative plasmids: transmitted during
conjugation, carry a variety of information
2. R plasmids: resistance plasmids; protect against
environmental factors, MDR (multiple drug
resistance) plasmid
3. Hfr plasmids: promotes genomic recombination
4. Col-plasmids: codes for proteins that kill other
microbes
5. Degradative plasmids: contain sequencing that
allows host to digest uncommon substances (ex:
toluene, salicylic acid)
6. Virulence plasmids: codes for altering the microbe
into a pathogen
59.
60. • Table 10.3 lists some phenotypes that plasmids confer
on prokaryotes.
61.
62.
63.
64. Conjugation: Essential Features
• Conjugation is a mechanism of DNA transfer in
prokaryotes that requires cell-to-cell contact.
• Genes carried by certain plasmids (such as the F
plasmid) control conjugation, and the process
involves transfer of the plasmid from a donor cell to a
recipient cell (Figure 8.22). Plasmid DNA transfer
involves replication via the rolling circle mechanism.
65.
66. The Bacterial Chromosome
Genetic Map of the Escherichia coli Chromosome
• The Escherichia coli chromosome has been
mapped usingconjugation, transduction,
molecular cloning, and sequencing (Figure
8.42).
67.
68. • E. coli has been a useful model organism,
and a considerable amount of information
has been obtained from it, not only about
gene structure but also about gene
function and regulation.
69. Regulation of Gene Expression
Operon – in bacteria, the genes that code for the enzymes of a metabolic pathway are
usually arranged in a consecutive manner to form a functional unit.
*most transcriptional control mechanisms for operons involve either enzyme induction or
end-product repression
1. Induction –form of control of gene transcription, with the gene transcribed
only when appropriate substrate for the protein is present
-used mainly to control the synthesis of proteins that are used to
transport and breakdown nutrients.
2. End-product repression – transcription of an operon for a synthetic pathway is often
regulated by its end product, and not by the initial substrate of the
pathway.