The document discusses genetic recombination and site-specific recombination. It describes the Meselson-Radding model of genetic recombination, which involves a single-strand nick that allows DNA polymerase to extend the 3' end and displace the other strand, forming a D loop structure. Site-specific recombination involves recombinases cutting DNA at specific recognition sequences and rejoining the strands to form a Holliday junction intermediate. Examples discussed include bacteriophage lambda integration into E. coli DNA, which is mediated by lambda integrase recombining attP and attB sites.
One of the first plausible models to account for the preceding observations was
formulated by Robin Holliday.
The key features of the Holliday model are the formation of heteroduplex DNA; the
creation of a cross bridge; its migration along the two heteroduplex strands,
termed branch migration; the occurrence of mismatch repair; and the
subsequent resolution, or splicing, of the intermediate structure to yield different
typesof recombinant molecules.
One of the first plausible models to account for the preceding observations was
formulated by Robin Holliday.
The key features of the Holliday model are the formation of heteroduplex DNA; the
creation of a cross bridge; its migration along the two heteroduplex strands,
termed branch migration; the occurrence of mismatch repair; and the
subsequent resolution, or splicing, of the intermediate structure to yield different
typesof recombinant molecules.
DNA replication, repair and recombination NotesYi Fan Chen
DNA, replication, repair and recombination Notes based on Molecular biology of the cell. Biology Elite: biologyelite.weebly.com, please use together with the presentation
HGP was conceived in 1984 & officially begun in earnest in October 1990.
HGP is a large multicentric, international collaborative venture, the main aim of which is to determine the nucleotide sequence of the entire human nuclear genome.
In 1997, United States established the National Human Genome Research Institute (NHGRI).
The HGP was an international research groups from six countries- USA, UK, France, Germany, Japan and China, & several laboratories and a large no. of scientists and technicians from various disciplines.
Exchange of genes between two DNA molecules to form new combinations of genes on a chromosome
contributes to a population’s genetic diversity (source of variation in evolution)
Recombination is more likely than mutation to be beneficial
Less likely destroy a gene's function
May bring together combinations of genes
bacteriophages require bacterial host to complete its life-cycle, wherein site-specific genetic recombination occurs. furthermore, homologous recombination also occur in phages in case of multiple infection of the host cell.
Prokaryotic and eukaryotic dna replication with their clinical applicationsrohini sane
A comprehensive presentation on Prokaryotic and Eukaryotic DNA Replication with their clinical applications for MBBS , BDS, B Pharm & Biotechnology students to facilitate self- study.
Recombination in repair n damage of DNA.pptxANAKHA JACOB
• Maintaining a low mutation rate is essential for cell viability and health. It is estimated that both in prokaryotic and eukaryotic cells, DNA is replicated with very high fidelity with one wrong nucleotide incorporated once per 108–1010 nucleotides polymerized. The fidelity of DNA replication relies on nucleotide selectivity of replicative DNA polymerase, exonucleolytic proofreading, and post-replicative DNA repair systems.
• Mutations can occur due to errors in DNA replication as well as due to certain damages to the DNA. Errors in replication are corrected to a great extent by proofreading mechanisms. Maintaining the genetic stability that an organism needs for its survival requires not only an extremely accurate mechanism for replicating DNA but also mechanisms for repairing many accidental lesions that occur continually. Most such spontaneous changes in DNA are temporary because they are immediately corrected by a set of processes that are collectively called DNA repair.• Maintaining a low mutation rate is essential for cell viability and health. It is estimated that both in prokaryotic and eukaryotic cells, DNA is replicated with very high fidelity with one wrong nucleotide incorporated once per 108–1010 nucleotides polymerized. The fidelity of DNA replication relies on nucleotide selectivity of replicative DNA polymerase, exonucleolytic proofreading, and post-replicative DNA repair systems.
• Mutations can occur due to errors in DNA replication as well as due to certain damages to the DNA. Errors in replication are corrected to a great extent by proofreading mechanisms. Maintaining the genetic stability that an organism needs for its survival requires not only an extremely accurate mechanism for replicating DNA but also mechanisms for repairing many accidental lesions that occur continually. Most such spontaneous changes in DNA are temporary because they are immediately corrected by a set of processes that are collectively called DNA repair.• Maintaining a low mutation rate is essential for cell viability and health. It is estimated that both in prokaryotic and eukaryotic cells, DNA is replicated with very high fidelity with one wrong nucleotide incorporated once per 108–1010 nucleotides polymerized. The fidelity of DNA replication relies on nucleotide selectivity of replicative DNA polymerase, exonucleolytic proofreading, and post-replicative DNA repair systems.
• Mutations can occur due to errors in DNA replication as well as due to certain damages to the DNA. Errors in replication are corrected to a great extent by proofreading mechanisms. Maintaining the genetic stability that an organism needs for its survival requires not only an extremely accurate mechanism for replicating DNA but also mechanisms for repairing many accidental lesions that occur continually. Most such spontaneous changes in DNA are temporary because they are immediately corrected by a set of processes that are collectively called DNA repair.
Replication:
DNA replication is the biological process of producing two identical copies of DNA from the original/parentral DNA molecule.
This process occurs in all living organism.
Basis for biological inheritance
DNA Replication Is Semiconservative
Replication Begins at an Origin and Usually Proceeds Bidirectionally
DNA Synthesis Proceeds in a 5’-3’ Direction and Is semidiscontinuous
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
This pdf is about the Schizophrenia.
For more details visit on YouTube; @SELF-EXPLANATORY;
https://www.youtube.com/channel/UCAiarMZDNhe1A3Rnpr_WkzA/videos
Thanks...!
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
2. GENETIC RECOMBINATION
• Genetic recombination is the production of offspring with
combinations of traits that differ from those found in either
parent
• In eukaryotes, genetic recombination during meiosis can lead
to a novel set of genetic information that can be passed on
from the parents to the offspring
• Most recombination is naturally occurring
4. MESELSON RADDING MODEL
• It is a second recombination model that is based on one
single-strand nick for initiation
• The model retains some key features of the holliday model
namely,
1. Formation of heteroduplex DNA
2. Mismatch repair of the heteroduplex DNA to give 3:1 and 1:3
gene conversion events
3. The holliday junction intermediate that could be resolved as
non crossover or cross over
5. MECHANISM
• A single strand nick is introduced into a strand of one of the
duplexes
• DNA polymerase extends the newly created 3’ end causing
displacement of strand on the other side of the nick
• With the assistance of Rec A, the displaced strand with a 5’P
tail invades a homologous region in the second duplex to form
a D loop
• The D loop is cleaved forming a single strand links between
the two duplexes
6. MECHANISM(ctd)
• The strands are isomerised or rotated around the crossed
strand point to allow the free ends at the exchange site to be
ligated, forming a holliday junction
• The holliday junction can branch migrate.
• Branch migration form the initial site of strand invasion forms
symmetric heteroduplex DNA
7.
8. SITE-SPECIFIC RECOMBINATION
Viruses and transposable elements often integrate their
genomes into the host chromosome
Site-specific recombination, is a type of genetic
recombination in which DNA strand exchange takes place
between segments possessing at least a certain degree
of sequence homology
Site- specific recombination is used by both eukaryotes and
prokaryotes to regulate gene expression and to increase the
organisms genetic range
Each site- specific recombination involves:
• Recombinase
• A short (20-200bp) unique DNA sequence where
recombinase act
9. Site specific recombination
FIGURE 25–38 A site-specific
recombination reaction. (a) The reaction is
carried out within a tetramer of identical
subunits. Recombinase subunits bind to a
specific sequence, often called simply the
recombination site. 1 One strand in each
DNA is cleaved at particular points within
the sequence. The nucleophile is the OH
group of an active-site Tyr residue, and the
product is a covalent phosphotyrosine link
between protein and DNA. 2 The cleaved
strands join to new partners, producing
a Holliday intermediate. Steps 3 and 4
complete the reaction by a process similar
to the first two steps. The original sequence
of the recombination site is regenerated
after recombining the DNA flanking the
site. These steps occur within a complex of
multiple recombinase subunits that
sometimes includes other proteins.
10. MECHANSIM
• There are two general classes of site specific recombination
which rely on either Tyr or Ser residues in the active site.
• Recombinase is an important enzyme involved in the site
specific recombination
• The recombinase recognizes and binds to each of two
recombination sites on two different DNA molecules or within
the same DNA
11. MECHANISM(ctd)
• Step 1- One DNA strand in each site is cleaved at a specific
point within the site, and the recombinase becomes
covalently linked to DNA at the cleavage site through a
phosphotyrosine bond
• Step 2- The transient protein-DNA linkage preserves the
phosphodiester bond that is lost in cleaving the DNA. The
cleaved DNA strands are rejoined to new partners to form a
holliday intermediate, with new phosphodiester bond created
at the expense of the protein-DNA linkage
• Step -3 The process is repeated at the second point within
each of the two recombination sites in order to complete the
reaction
12. • In the systems that employ an active Ser or Tyr residue, both
strands of each recombination site are cut concurrently and
rejoined to new partners without the holliday intermediate
• In both the systems the, the exchange is always reciprocal and
precise, regenerating the recombination sites when the
reaction is complete
• The first site specific recombination system studied in vitro
was that encoded by bacteriophage ƛ. When ƛ phage DNA
enters an E.COLI cell, a complex series of regulatory events
commits the DNA to one of two fates.
• The ƛ DNA replicates and produces more bacteriophages or it
integrates into the host chromosome and replicates passively
along with the chromosome for many cell generations.
13. • Integration is accomplished by a phage –encoded tyrosine
class recombinase (ƛ integrase) that acts at recombination
sites on the phage and bacterial DNAs at the attachment sites
attP and attB, respectively
14. FIGURE 25–40 Integration and excision of bacteriophage DNA at the
chromosomal target site. The attachment site on the phage DNA (attP) shares only
15 bp of complete homology with the bacterial site (attB) in the region of the crossover.
The reaction generates two new attachment sites (attR and attL) flanking the integrated
phage DNA.
The recombinase is the integrase (or INT protein). Integration and excision use
different attachment sites and different auxiliary proteins. Excision uses the proteins
XIS, encoded by the bacteriophage, and FIS, encoded by the bacterium. Both reactions
require the protein IHF (integration host factor), encoded by the bacterium.
15. • The sequences of the recombination sites recognized by site-
specific recombinases are partially assymetric and the two
recombining sites align in the same orientation during the
recombinase reaction
• The outcome depends on the location and orientation of the
recombination sites
• If the two sites are on the same DNA molecule, the reaction
either inverts or deletes the intervening DNA ,determined by
whether the recombination sites have the opposite or the
same orientation, respectively
• If the same sites are on different DNAs the recombination is
intermolecular, if one or both DNAs are circular, the result is
an insertion