DNA replication is the process by which DNA copies itself for cell division. It is semiconservative, meaning each new DNA molecule contains one old and one new strand. Replication occurs through the unwinding of the DNA double helix at an origin of replication by helicase. DNA polymerase then adds complementary nucleotides to each strand, while ligase seals the DNA. Replication of the leading strand is continuous while the lagging strand occurs discontinuously in fragments called Okazaki fragments. Various enzymes and mechanisms ensure replication occurs with high fidelity and accuracy.
Reverse transcription of RNA, which refers to the conversion of the RNA template into its complimentary DNA strand (cDNA) is an essential step in the analysis of gene transcripts.
cDNA can be sequenced, cloned and applied to estimate the copy number of specific genes in order to characterize and to validate gene expression.
it describes transcription with simple diagram and animation. its steps and inhibitors are described for both eukaryotes and prokaryotes. it will be easily understood by UG students . post transcriptional modification of all the RNA are also described with diagrams.
An Overview...
Definition of Translation.
Def. of Eukaryotes.
Translation: An Overview.
Components of Translation.
Some Enzymes .
Ribosome Role.
Mechanism of Translation.
Initiation.
Scanning Model of Initiation.
Initiation Factors.
Animation.
Elongation.
Chain Elongation: Translocation.
Animation.
Termination.
Animation....
It's not perfect still... what are your views friends?
De novo and salvage pathway of nucleotides synthesis.pptx✨M.A kawish Ⓜ️
This slides explains Metabolism topic "De novo and salvage pathway of nucleotides synthesis. In which synthesis of Purines and pyrimidines synthesis has been occurred. In last there is a difference between these two pathways.
Reverse transcription of RNA, which refers to the conversion of the RNA template into its complimentary DNA strand (cDNA) is an essential step in the analysis of gene transcripts.
cDNA can be sequenced, cloned and applied to estimate the copy number of specific genes in order to characterize and to validate gene expression.
it describes transcription with simple diagram and animation. its steps and inhibitors are described for both eukaryotes and prokaryotes. it will be easily understood by UG students . post transcriptional modification of all the RNA are also described with diagrams.
An Overview...
Definition of Translation.
Def. of Eukaryotes.
Translation: An Overview.
Components of Translation.
Some Enzymes .
Ribosome Role.
Mechanism of Translation.
Initiation.
Scanning Model of Initiation.
Initiation Factors.
Animation.
Elongation.
Chain Elongation: Translocation.
Animation.
Termination.
Animation....
It's not perfect still... what are your views friends?
De novo and salvage pathway of nucleotides synthesis.pptx✨M.A kawish Ⓜ️
This slides explains Metabolism topic "De novo and salvage pathway of nucleotides synthesis. In which synthesis of Purines and pyrimidines synthesis has been occurred. In last there is a difference between these two pathways.
I have tried to make a precise presentation on protein transport, targeting and sorting into organelle's other than nucleus. Hope this might help you. Comments are welcome.
Transcription and post-transcriptional modification.Abhishek Dahal
A slide about Transcription and Post-transcription modification prepared for undergraduates understanding but PG levels may find it good for revision and handy for exams.
User Interface Prototyping - Low- and High-Fidelity Prototyping TodayThomas Memmel
Zühlke offers various usability engineering services – get in touch at www.zuehlke.com/usability
User Studies, User Profiling & User Modeling (e.g. Personas), User-Centered Requirements Engineering, Usability Concepts & Modeling (e.g. Scenarios, Storyboards), Agile Development & User Experience (e.g. User Stories combined with elements of Interaction Design), User Interface Prototyping (Low- & High-Fidelity), User Interface Engineering (Integration of Usability Methodology in the Software Development Process), Usability Testing (e.g. with Mobile Usability Lab), User Interface Specification.
Eukaryotic DNA replication is a conserved mechanism that restricts DNA replication to once per cell cycle. Eukaryotic DNA replication of chromosomal DNA is central for the duplication of a cell and is necessary for the maintenance of the eukaryotic genome.
DNA replication in eukaryotes occurs in three stages: initiation, elongation, and termination, which are aided by several enzymes. Because eukaryotic genomes are quite
complex, DNA replication is a very complicated process that involves several enzymes and other proteins. It occurs in three main stages: initiation, elongation, and termination.
New Directions in Targeted Therapeutic Approaches for Older Adults With Mantl...i3 Health
i3 Health is pleased to make the speaker slides from this activity available for use as a non-accredited self-study or teaching resource.
This slide deck presented by Dr. Kami Maddocks, Professor-Clinical in the Division of Hematology and
Associate Division Director for Ambulatory Operations
The Ohio State University Comprehensive Cancer Center, will provide insight into new directions in targeted therapeutic approaches for older adults with mantle cell lymphoma.
STATEMENT OF NEED
Mantle cell lymphoma (MCL) is a rare, aggressive B-cell non-Hodgkin lymphoma (NHL) accounting for 5% to 7% of all lymphomas. Its prognosis ranges from indolent disease that does not require treatment for years to very aggressive disease, which is associated with poor survival (Silkenstedt et al, 2021). Typically, MCL is diagnosed at advanced stage and in older patients who cannot tolerate intensive therapy (NCCN, 2022). Although recent advances have slightly increased remission rates, recurrence and relapse remain very common, leading to a median overall survival between 3 and 6 years (LLS, 2021). Though there are several effective options, progress is still needed towards establishing an accepted frontline approach for MCL (Castellino et al, 2022). Treatment selection and management of MCL are complicated by the heterogeneity of prognosis, advanced age and comorbidities of patients, and lack of an established standard approach for treatment, making it vital that clinicians be familiar with the latest research and advances in this area. In this activity chaired by Michael Wang, MD, Professor in the Department of Lymphoma & Myeloma at MD Anderson Cancer Center, expert faculty will discuss prognostic factors informing treatment, the promising results of recent trials in new therapeutic approaches, and the implications of treatment resistance in therapeutic selection for MCL.
Target Audience
Hematology/oncology fellows, attending faculty, and other health care professionals involved in the treatment of patients with mantle cell lymphoma (MCL).
Learning Objectives
1.) Identify clinical and biological prognostic factors that can guide treatment decision making for older adults with MCL
2.) Evaluate emerging data on targeted therapeutic approaches for treatment-naive and relapsed/refractory MCL and their applicability to older adults
3.) Assess mechanisms of resistance to targeted therapies for MCL and their implications for treatment selection
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Couples presenting to the infertility clinic- Do they really have infertility...Sujoy Dasgupta
Dr Sujoy Dasgupta presented the study on "Couples presenting to the infertility clinic- Do they really have infertility? – The unexplored stories of non-consummation" in the 13th Congress of the Asia Pacific Initiative on Reproduction (ASPIRE 2024) at Manila on 24 May, 2024.
Ozempic: Preoperative Management of Patients on GLP-1 Receptor Agonists Saeid Safari
Preoperative Management of Patients on GLP-1 Receptor Agonists like Ozempic and Semiglutide
ASA GUIDELINE
NYSORA Guideline
2 Case Reports of Gastric Ultrasound
Acute scrotum is a general term referring to an emergency condition affecting the contents or the wall of the scrotum.
There are a number of conditions that present acutely, predominantly with pain and/or swelling
A careful and detailed history and examination, and in some cases, investigations allow differentiation between these diagnoses. A prompt diagnosis is essential as the patient may require urgent surgical intervention
Testicular torsion refers to twisting of the spermatic cord, causing ischaemia of the testicle.
Testicular torsion results from inadequate fixation of the testis to the tunica vaginalis producing ischemia from reduced arterial inflow and venous outflow obstruction.
The prevalence of testicular torsion in adult patients hospitalized with acute scrotal pain is approximately 25 to 50 percent
Title: Sense of Smell
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the primary categories of smells and the concept of odor blindness.
Explain the structure and location of the olfactory membrane and mucosa, including the types and roles of cells involved in olfaction.
Describe the pathway and mechanisms of olfactory signal transmission from the olfactory receptors to the brain.
Illustrate the biochemical cascade triggered by odorant binding to olfactory receptors, including the role of G-proteins and second messengers in generating an action potential.
Identify different types of olfactory disorders such as anosmia, hyposmia, hyperosmia, and dysosmia, including their potential causes.
Key Topics:
Olfactory Genes:
3% of the human genome accounts for olfactory genes.
400 genes for odorant receptors.
Olfactory Membrane:
Located in the superior part of the nasal cavity.
Medially: Folds downward along the superior septum.
Laterally: Folds over the superior turbinate and upper surface of the middle turbinate.
Total surface area: 5-10 square centimeters.
Olfactory Mucosa:
Olfactory Cells: Bipolar nerve cells derived from the CNS (100 million), with 4-25 olfactory cilia per cell.
Sustentacular Cells: Produce mucus and maintain ionic and molecular environment.
Basal Cells: Replace worn-out olfactory cells with an average lifespan of 1-2 months.
Bowman’s Gland: Secretes mucus.
Stimulation of Olfactory Cells:
Odorant dissolves in mucus and attaches to receptors on olfactory cilia.
Involves a cascade effect through G-proteins and second messengers, leading to depolarization and action potential generation in the olfactory nerve.
Quality of a Good Odorant:
Small (3-20 Carbon atoms), volatile, water-soluble, and lipid-soluble.
Facilitated by odorant-binding proteins in mucus.
Membrane Potential and Action Potential:
Resting membrane potential: -55mV.
Action potential frequency in the olfactory nerve increases with odorant strength.
Adaptation Towards the Sense of Smell:
Rapid adaptation within the first second, with further slow adaptation.
Psychological adaptation greater than receptor adaptation, involving feedback inhibition from the central nervous system.
Primary Sensations of Smell:
Camphoraceous, Musky, Floral, Pepperminty, Ethereal, Pungent, Putrid.
Odor Detection Threshold:
Examples: Hydrogen sulfide (0.0005 ppm), Methyl-mercaptan (0.002 ppm).
Some toxic substances are odorless at lethal concentrations.
Characteristics of Smell:
Odor blindness for single substances due to lack of appropriate receptor protein.
Behavioral and emotional influences of smell.
Transmission of Olfactory Signals:
From olfactory cells to glomeruli in the olfactory bulb, involving lateral inhibition.
Primitive, less old, and new olfactory systems with different path
Flu Vaccine Alert in Bangalore Karnatakaaddon Scans
As flu season approaches, health officials in Bangalore, Karnataka, are urging residents to get their flu vaccinations. The seasonal flu, while common, can lead to severe health complications, particularly for vulnerable populations such as young children, the elderly, and those with underlying health conditions.
Dr. Vidisha Kumari, a leading epidemiologist in Bangalore, emphasizes the importance of getting vaccinated. "The flu vaccine is our best defense against the influenza virus. It not only protects individuals but also helps prevent the spread of the virus in our communities," he says.
This year, the flu season is expected to coincide with a potential increase in other respiratory illnesses. The Karnataka Health Department has launched an awareness campaign highlighting the significance of flu vaccinations. They have set up multiple vaccination centers across Bangalore, making it convenient for residents to receive their shots.
To encourage widespread vaccination, the government is also collaborating with local schools, workplaces, and community centers to facilitate vaccination drives. Special attention is being given to ensuring that the vaccine is accessible to all, including marginalized communities who may have limited access to healthcare.
Residents are reminded that the flu vaccine is safe and effective. Common side effects are mild and may include soreness at the injection site, mild fever, or muscle aches. These side effects are generally short-lived and far less severe than the flu itself.
Healthcare providers are also stressing the importance of continuing COVID-19 precautions. Wearing masks, practicing good hand hygiene, and maintaining social distancing are still crucial, especially in crowded places.
Protect yourself and your loved ones by getting vaccinated. Together, we can help keep Bangalore healthy and safe this flu season. For more information on vaccination centers and schedules, residents can visit the Karnataka Health Department’s official website or follow their social media pages.
Stay informed, stay safe, and get your flu shot today!
ARTIFICIAL INTELLIGENCE IN HEALTHCARE.pdfAnujkumaranit
Artificial intelligence (AI) refers to the simulation of human intelligence processes by machines, especially computer systems. It encompasses tasks such as learning, reasoning, problem-solving, perception, and language understanding. AI technologies are revolutionizing various fields, from healthcare to finance, by enabling machines to perform tasks that typically require human intelligence.
Lung Cancer: Artificial Intelligence, Synergetics, Complex System Analysis, S...Oleg Kshivets
RESULTS: Overall life span (LS) was 2252.1±1742.5 days and cumulative 5-year survival (5YS) reached 73.2%, 10 years – 64.8%, 20 years – 42.5%. 513 LCP lived more than 5 years (LS=3124.6±1525.6 days), 148 LCP – more than 10 years (LS=5054.4±1504.1 days).199 LCP died because of LC (LS=562.7±374.5 days). 5YS of LCP after bi/lobectomies was significantly superior in comparison with LCP after pneumonectomies (78.1% vs.63.7%, P=0.00001 by log-rank test). AT significantly improved 5YS (66.3% vs. 34.8%) (P=0.00000 by log-rank test) only for LCP with N1-2. Cox modeling displayed that 5YS of LCP significantly depended on: phase transition (PT) early-invasive LC in terms of synergetics, PT N0—N12, cell ratio factors (ratio between cancer cells- CC and blood cells subpopulations), G1-3, histology, glucose, AT, blood cell circuit, prothrombin index, heparin tolerance, recalcification time (P=0.000-0.038). Neural networks, genetic algorithm selection and bootstrap simulation revealed relationships between 5YS and PT early-invasive LC (rank=1), PT N0—N12 (rank=2), thrombocytes/CC (3), erythrocytes/CC (4), eosinophils/CC (5), healthy cells/CC (6), lymphocytes/CC (7), segmented neutrophils/CC (8), stick neutrophils/CC (9), monocytes/CC (10); leucocytes/CC (11). Correct prediction of 5YS was 100% by neural networks computing (area under ROC curve=1.0; error=0.0).
CONCLUSIONS: 5YS of LCP after radical procedures significantly depended on: 1) PT early-invasive cancer; 2) PT N0--N12; 3) cell ratio factors; 4) blood cell circuit; 5) biochemical factors; 6) hemostasis system; 7) AT; 8) LC characteristics; 9) LC cell dynamics; 10) surgery type: lobectomy/pneumonectomy; 11) anthropometric data. Optimal diagnosis and treatment strategies for LC are: 1) screening and early detection of LC; 2) availability of experienced thoracic surgeons because of complexity of radical procedures; 3) aggressive en block surgery and adequate lymph node dissection for completeness; 4) precise prediction; 5) adjuvant chemoimmunoradiotherapy for LCP with unfavorable prognosis.
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New Drug Discovery and Development .....NEHA GUPTA
The "New Drug Discovery and Development" process involves the identification, design, testing, and manufacturing of novel pharmaceutical compounds with the aim of introducing new and improved treatments for various medical conditions. This comprehensive endeavor encompasses various stages, including target identification, preclinical studies, clinical trials, regulatory approval, and post-market surveillance. It involves multidisciplinary collaboration among scientists, researchers, clinicians, regulatory experts, and pharmaceutical companies to bring innovative therapies to market and address unmet medical needs.
Title: Sense of Taste
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the structure and function of taste buds.
Describe the relationship between the taste threshold and taste index of common substances.
Explain the chemical basis and signal transduction of taste perception for each type of primary taste sensation.
Recognize different abnormalities of taste perception and their causes.
Key Topics:
Significance of Taste Sensation:
Differentiation between pleasant and harmful food
Influence on behavior
Selection of food based on metabolic needs
Receptors of Taste:
Taste buds on the tongue
Influence of sense of smell, texture of food, and pain stimulation (e.g., by pepper)
Primary and Secondary Taste Sensations:
Primary taste sensations: Sweet, Sour, Salty, Bitter, Umami
Chemical basis and signal transduction mechanisms for each taste
Taste Threshold and Index:
Taste threshold values for Sweet (sucrose), Salty (NaCl), Sour (HCl), and Bitter (Quinine)
Taste index relationship: Inversely proportional to taste threshold
Taste Blindness:
Inability to taste certain substances, particularly thiourea compounds
Example: Phenylthiocarbamide
Structure and Function of Taste Buds:
Composition: Epithelial cells, Sustentacular/Supporting cells, Taste cells, Basal cells
Features: Taste pores, Taste hairs/microvilli, and Taste nerve fibers
Location of Taste Buds:
Found in papillae of the tongue (Fungiform, Circumvallate, Foliate)
Also present on the palate, tonsillar pillars, epiglottis, and proximal esophagus
Mechanism of Taste Stimulation:
Interaction of taste substances with receptors on microvilli
Signal transduction pathways for Umami, Sweet, Bitter, Sour, and Salty tastes
Taste Sensitivity and Adaptation:
Decrease in sensitivity with age
Rapid adaptation of taste sensation
Role of Saliva in Taste:
Dissolution of tastants to reach receptors
Washing away the stimulus
Taste Preferences and Aversions:
Mechanisms behind taste preference and aversion
Influence of receptors and neural pathways
Impact of Sensory Nerve Damage:
Degeneration of taste buds if the sensory nerve fiber is cut
Abnormalities of Taste Detection:
Conditions: Ageusia, Hypogeusia, Dysgeusia (parageusia)
Causes: Nerve damage, neurological disorders, infections, poor oral hygiene, adverse drug effects, deficiencies, aging, tobacco use, altered neurotransmitter levels
Neurotransmitters and Taste Threshold:
Effects of serotonin (5-HT) and norepinephrine (NE) on taste sensitivity
Supertasters:
25% of the population with heightened sensitivity to taste, especially bitterness
Increased number of fungiform papillae
2. DNA carries genetic information from
generation to generation.
Responsible to preserve the identity of the
species over millions of years.
DNA may be regarded as Reserve bank of
genetic information or memory bank.
3. Some viruses contain RNA as the genetic
material
DNA is more stable than RNA.
DNA is more suitable molecule for long-term
repository of genetic information.
4. The biological information flows from DNA to RNA,
& from there to proteins.
This is central dogma of life.
DNA in a cell must be duplicated (replicated),
maintained & passed down accurately to the
daughter cells.
DNA RNA Protein
Replication
Transcription Translation
5. DNA is the genetic material.
When the cell divides, the daughter cells
receive an identical copy of genetic
information from the parent cell.
Definition:
Replication is a process in which DNA copies
itself to produce identical daughter molecules
of DNA with high fidelity.
6. Replication is semiconservative:
The parent DNA has two strands
complementary to each other.
Both the strands undergo simultaneous
replication to produce two daughter
molecules.
7. Each one of the newly synthesized DNA has
one-half of the parental DNA (one strand
from original) & one half of new DNA.
This is known as semiconservative
replication - “half of the original DNA is
conserved in the daughter DNA”.
Experimental evidence was provided by
Meselson & Stahl (1958)
8.
9. The initiation of DNA synthesis occurs at a
site called origin of replication.
In prokaryotes, only one site, where as in
eukaryotes, there are multiple sites of origin.
These sites mostly consist of a short sequence
of A-T base pairs.
10.
11. A specific protein called dna A(20-50
monomers) binds with the site of origin for
replication.
This causes the double-stranded DNA to
separate.
12. Two complementary strands of DNA
separate at the site of replication to form a
bubble.
Multiple replication bubbles are in
eukaryotic DNA molecules, which is essential
for a rapid replication process.
13.
14. For the synthesis of new DNA, a short
fragment of RNA (5-50 nucleotides, variable
with species) is required as a primer.
The enzyme primase (a specific RNA
polymerase) in association with single-
stranded binding proteins (SSBP) forms a
complex called primosome & produces RNA
primers.
15. A constant synthesis & supply of RNA
primers should occur on the lagging strand
of DNA
On leading strand only one RNA primer is
required.
16. The replication of DNA occurs in 5' to 3'
direction, simultaneously, on both strands of
DNA.
Leading strand (continuous or forward):
The DNA synthesis is continuous.
17. Lagging strand (discontinuous or retrograde):
The DNA synthesis is discontinuous, short
pieces of DNA (15-250 nucleotides) are
produced on lagging strand.
Replication occurs in both direction from
replication bubble.
18. The separation of two strands of parent DNA
results in the formation of replication fork.
The active synthesis of DNA occurs in this
region.
The replication fork moves along the parent
DNA as the daughter DNA molecules are
synthesized.
19. DNA helicases bind to both the DNA strands
at the replication fork.
Helicases move along the DNA helix &
separate the strands.
Their function is comparable with a zip
opener.
Helicases are dependent on ATP for energy
supply.
20. Also called helix-destabilizing proteins.
SSB proteins bind only to single-stranded DNA.
They bind cooperatively the binding of one
molecule of SSB protein makes it easier for
additional molecules of SSB protein to bind
tightly to the DNA strand.
21. These are not enzymes.
These will provide single-stranded template
required by polymerases & also protects the
DNA from nucleases that degrades single-
stranded DNA.
22. The DNA polymerases responsible for copying the
DNA templates are only able to "read" the parental
nucleotide sequences in the 3' to 5' direction & they
synthesize the new DNA strands in the 5' to 3' (anti
parallel) direction.
The two newly synthesized nucleotide chains must
grow in opposite in the directions one in the 5' to 3'
direction toward the replication fork & one in the 5' to
3' direction away from the replication fork.
23.
24. Leading strand:
The strand that is being copied in the direction
of the advancing replication fork is called the
leading strand & is synthesized continuously.
Lagging strand:
The strand that is being copied in the direction
away from the replication fork is synthesized
discontinuously, with small fragments of DNA
being copied near the replication fork.
25. These short stretches of discontinuous DNA,
termed Okazaki fragments & are joined to
become a single, continuous strand.
This is called as lagging strand.
26.
27.
28. Synthesis of a new DNA strand, catalysed by
DNA polymerase lll, occurs in 5'-3' direction.
This is antiparallel to the parent template DNA
strand.
The presence of all the four
deoxyribonucleoside triphosphates (dATP,
dGTP, dCTP & dTTP) is an essential prerequisite
for replication to take place.
29. The synthesis of two new DNA strands,
simultaneously, takes place in the opposite
direction - one is in a direction (5'-3') towards
the replication fork which is continuous
(Leading strand)
The other in a direction (5'- 3') away from the
replication fork which is discontinuous
(Lagging strand).
30. The incoming deoxyribonucleotides are
added one after another, to 3' end of the
growing DNA chain.
A molecule of pyrophosphate (PPi) is
removed with the addition of each nucleotide.
The template DNA strand (the parent)
determines the base sequence of the newly
synthesized complementary DNA.
31. Prokaryotic & eukaryotic DNA polymerases
elongate a new DNA strand by adding deoxy
ribonucleotides, one at a time, to the 3'-end of
the growing chain.
The sequence of nucleotides that are added is
dictated by the base sequence of the template
strand, with which the incoming nucleotides
are paired.
32.
33. The DNA strand (leading strand) with its 3'-
end (3'-OH) oriented towards the fork can be
elongated by sequential addition of new
nucleotides.
The other DNA strand (lagging strand) with 5'-
end presents some problem,
34. There is no DNA polymerase enzyme (in any
organism) that can catalyse the addition of
nucleotides to the 5‘ end (3'- 5' direction) of the
growing chain.
This problem is solved by synthesizing this
strand as a series of small fragments.
These pieces are made in the normal 5'-3'
direction & later joined together.
35. The small fragments of the discontinuously
synthesized DNA are called Okazaki pieces.
These are produced on the lagging strand of
the parent DNA.
Okazaki pieces are later joined to form a
continuous strand of DNA.
DNA polymerase I & DNA ligase are
responsible for this process.
36. Fidelity of replication is the most important
for the very existence of an organism.
Besides its 5'-3' directed catalytic function,
DNA polymerase III also has a proof-reading
activity.
37. It checks the incoming nucleotides & allows
only the correctly matched bases (i.e.
complementary bases) to be added to the
growing DNA strand.
DNA polymerase edits its mistakes (if any) &
removes the wrongly placed nucleotide
bases.
38. For example, if the template base is cytosine
& the enzyme mistakenly inserts an adenine
instead a guanine into the new chain, the 3' to
5' exonuclease removes the misplaced
nucleotide.
The 5' to 3' polymerase replaces it with the
correct nucleotide containing guanine.
39.
40. The synthesis of new DNA strand continues
till it is in close proximity to RNA primer.
DNA polymerase I removes the RNA primer
& takes its position.
DNA polymerase I catalyses the synthesis (5'-
3' direction) of a fragment of DNA that
replaces RNA primer.
41.
42. The enzyme DNA ligase catalyses the
formation of a phosphodiester linkage
between the DNA synthesized by DNA
polymerase III & the small fragments of DNA
produced by DNA polymerase l.
This process-nick sealing-requires energy,
provided by the breakdown of ATP.
DNA polymerase II participates in the DNA
repair process.
43.
44. The double helix of DNA separates from one
side & replication proceeds, supercoils are
formed at the other side.
The problem of supercoils in DNA replication
is solved by a group of enzymes called DNA
topoisomerases.
45.
46.
47. Reversibly cut a single strand of the double
helix.
They have both nuclease (strand-cutting) &
ligase (strand-resealing) activities.
They do not require ATP, but rather appear to
store the energy from the phosphodiester
bond they cleave, reusing the energy to reseal
the strand.
48.
49. Bind tightly to the DNA double helix & make
transient breaks in both strands.
The enzyme then causes a second stretch of
the DNA double helix to pass through the
break & finally reseals the break.
Supercoils can be relieved.
50.
51. Replication of DNA in eukaryotes closely
resembles that of prokaryotes.
Certain differences exist.
Multiple origins of replication is a
characteristic feature of eukaryotic cell.
Five distinct DNA polymerases are known in
eukaryotes.
52. DNA polymerase α is responsible for the
synthesis of RNA primer for both the leading
& lagging strands of DNA.
DNA polymerase β is involved in the repair
of DNA.
Its function is comparable with DNA
polymerasIe found in prokaryotes.
53. DNA polymerase γ participates in the
replication of mitochondrial DNA.
DNA polymerase δ is responsible for the
replication on the leading strand of DNA.
It also possesses proof-reading activity.
DNA polymerase ε is involved in DNA
synthesis on the lagging strand & proof-
reading function.
54. The events surrounding eukaryotic DNA
replication & cell division (mitosis) are
coordinated to produce the cell cycle.
The period preceding replication is called the
G1 phase (Gap1).
DNA replication occurs during the S
(synthesis) phase.
55. Following DNA synthesis, there is another
period (G2 phase, Gap2) before mitosis (M).
Cells that have stopped dividing, such as
mature neurons, are said to have gone out of
the cell cycle into the GO phase.
56.
57. Bacteria contain a specific type II
topoisomerase namely gyrase.
This enzyme cuts & reseals the circular DNA
(of bacteria) & thus overcomes the problem of
supercoils.
Bacterial gyrase is inhibited by the antibiotics
ciprofloxacin, novobiocin & nalidixic acid.
58. Certain compounds that inhibit human
topoisomerases are used as anticancer
agents e.g. adriamycin, etoposide,
doxorubicin.
The nucleotide analogs that inhibit DNA
replication are also used as anticancer drugs
e.g. 6-mercaptopurnie , 5-fluorouracil.
59. The leading strand is completely synthesized
On lagging strand, removal of the RNA
primer leaves a small gap which cannot be
filled.
The daughter chromosomes will have
shortened DNA molecule.
Over a period of time, chromosomes may
lose certain essential genes & cell dies.
60. Telomeres are the special structures that
prevent the continuous loss of DNA at the
end of the chromosomes during replication.
Protect the ends of the chromosomes &
prevent the chromosomes from fusing with
each other.
Human telomeres contain thousands of
repeat TTAGGG sequences, which can be up
to a length of 1500 bp.
61. Telomerase is an unusual enzyme, it is composed of
both protein & RNA.
In humans, RNA component is 450 nucleotides in
length, & at 5'-terminal & it contains the sequence 5‘-
CUAACCCUAAC-3'.
Central region of this sequence is complementary to
the telomere repeat sequence 5'-TTAGGG-3'.
Telomerase RNA sequence can be used as a
template for extension of telomere.
62.
63. Eukaryotic DNA is associated with tightly bound
basic proteins, called histones.
These serve to order the DNA into basic structural
units, called nucleosomes.
Nucleosomes are further arranged into increasingly
more complex structures that organize & condense
the long DNA molecules into chromosomes that can
be segregated during cell division.
64. Five classes of histones -H1, H2A, H2B, H3 & H4.
These small proteins are positively charged at
physiologic pH & contain high content of lysine
& arginine.
They form ionic bonds with negatively
charged DNA.
65.
66. Two molecules each of H2A, H2B, H3 & H4 form
the structural core of the individual
nucleosome "beads.“
Around this core, a segment of the DNA
double helix is wound nearly twice, forming
a negatively super twisted helix.
Neighboring nucleosomes are joined by
"linker" DNA approximately fifty base pairs
long.
67. Histone H1 of which there are several related
species, is not found in the nucleosome core,
but instead binds to the linker DNA chain
between the nucleosome beads.
H1 is the most tissue-specific & species-specific
of the histones.
It facilitates the packing of nucleosomes into
the more compact structures.
68. Nucleosomes can be packed more tightly to form a
polynucleosome (also called a nucleofilament),
This structure assumes the shape of a coil, often
referred to as a 30-nm fiber.
The fiber is organized into loops that are anchored
by a nuclear scaffold containing several proteins.
Additional levels of organization lead to the final
chromosomal structure.
69.
70. Textbook of Biochemistry - U Satyanarayana
Textbook of Biochemistry - Lippincott’s