It contains some basic concept of radiobiology like linear energy transfer , relative biologic effectiveness and oxygen enhancement ratio and their interrelationship
It describes relationship between radiation dose and the fraction of cells that “survive” that dose.
This is mainly used to assess biological effectiveness of radiation.
To understand it better, we need to know about a few basic things e.g.
Cell Death
Estimation of Survival / Plating Efficiency
Nature of Cell killing etc.
A cell survival curve is the relationship between the fraction of cells retaining their reproductive integrity and absorbed dose.
Conventionally, surviving fraction on a logarithmic scale is plotted on the Y-axis, the dose is on the X-axis . The shape of the survival curve is important.
The cell-survival curve for densely ionizing radiations (α-particles and low-energy neutrons) is a straight line on a log-linear plot, that is survival is an exponential function of dose.
The cell-survival curve for sparsely ionizing radiations (X-rays, gamma-rays has an initial slope, followed by a shoulder after which it tends to straighten again at higher doses.
describes relationship between radiation dose and the fraction of cells that “survive” that dose
model of cell killing
target model
linear quadratic model
It contains some basic concept of radiobiology like linear energy transfer , relative biologic effectiveness and oxygen enhancement ratio and their interrelationship
It describes relationship between radiation dose and the fraction of cells that “survive” that dose.
This is mainly used to assess biological effectiveness of radiation.
To understand it better, we need to know about a few basic things e.g.
Cell Death
Estimation of Survival / Plating Efficiency
Nature of Cell killing etc.
A cell survival curve is the relationship between the fraction of cells retaining their reproductive integrity and absorbed dose.
Conventionally, surviving fraction on a logarithmic scale is plotted on the Y-axis, the dose is on the X-axis . The shape of the survival curve is important.
The cell-survival curve for densely ionizing radiations (α-particles and low-energy neutrons) is a straight line on a log-linear plot, that is survival is an exponential function of dose.
The cell-survival curve for sparsely ionizing radiations (X-rays, gamma-rays has an initial slope, followed by a shoulder after which it tends to straighten again at higher doses.
describes relationship between radiation dose and the fraction of cells that “survive” that dose
model of cell killing
target model
linear quadratic model
This presentation on "Cell Cycle regulation" takes you to the cell cycle describing the stages and checkpoints involved providing some of the evidences of cell cycle regulation. Then we will move to cyclins and cyclin dependent kinases and the mechanism they follow.
This journey in regulation of cell cycle will take a halt after a general discussion of positive and negative cell cycle regulators.
Thankyou.
This presentation is regarding the normal cell cycle through which a cell passes throughout its life. It highlights each step in the formation of daughter cells from a mother cell. It puts light on the events in both the interphase and division (mitotic) phase and the resting (G0 phase).
You will also get knowledge about the cell cycle checkpoints and the cellular brakes, the proteins that keeps the cell to divide normally, and how the abnormalities in these proteins results in defects of cell cycle and subsequently leads to uncontrolled cell division and cancer formation.
The phenomenon of signal transduction, also known as cell signaling, pertains to the intricate mechanisms that facilitate the transfer of biological information between cells. The effective coordination of diverse specialized cell types in various tissues and organs is a prerequisite for the proper functioning of complex multicellular organisms, necessitating intercellular communication. This communication must be continuous and dynamic to maintain coordination. Additionally, cell signaling pathways play a crucial role in the mechanisms of action of numerous drugs, including both local and general anesthetics. Consequently, a fundamental understanding of cell signaling mechanisms is imperative for comprehending various pathophysiologic and pharmacologic mechanisms.
This presentation on "Cell Cycle regulation" takes you to the cell cycle describing the stages and checkpoints involved providing some of the evidences of cell cycle regulation. Then we will move to cyclins and cyclin dependent kinases and the mechanism they follow.
This journey in regulation of cell cycle will take a halt after a general discussion of positive and negative cell cycle regulators.
Thankyou.
Why do different cell types' rates of the cell cycle differ?
The cell cycle is swiftly completed by injured or lost cell types to produce replacements.
Adult skin and digestive tract cells go through the cell cycle quite fast, whereas nervous system cells divide very seldom.
Cells divide regularly during embryonic development, perhaps as frequently as once or twice an hour, moving through the cell cycle very quickly.
What is the cell cycle?
The regular sequence of activities that cells go through as they develop and divide is known as the cell cycle. Prokaryotic cells go through a rapid cycle of cell division, DNA replication, and expansion. In prokaryotes, cell division occurs in a single stage known as binary fission (shown right).Compared to prokaryotic cells, eukaryotic cells have a more complicated cell cycle.
How is the eukaryotic cell cycle divided?
Interphase is the period between cell divisions. Depending on the kind of cell, the interphase might be shorter or longer.
The three stages or phases of the eukaryotic interphase are G1, S, and G2.
The M phase of the cell cycle is when eukaryotic cells divide. Mitosis and cytokinesis are the two stages that make up the M phase.
What happens during each phase of eukaryotic interphase?
G1: Cells do most of their growing during this phase. It begins when mitosis is complete and ends when DNA replication begins.
S: DNA is synthesized as chromosomes are replicated.
G2: Many of the molecules and cell structures required for cell division are produced; usually the shortest phase of the cell cycle.
What happens during the M phase of the eukaryotic cell cycle?
The M phase is usually much shorter than interphase and results in two daughter cells.
The first step of the M phase is mitosis. The cell’s nucleus divides during mitosis.
The second step of the M phase is cytokinesis, during which the cell’s cytoplasm is divided.
What are the steps of mitosis?
Mitosis consists of four steps: prophase, metaphase, anaphase, and telophase.
Prophase: nuclear envelope breaks down, DNA condenses, spindle begins to form.
Metaphase: replicated chromosomes, which appear as paired sister chromatids, line up across the center of the cell and attach to spindle.
Anaphase: sister chromatids separate and move toward ends of the cell.
Telophase: chromosomes disperse, nuclear envelope reforms.
What completes the M phase of the cell cycle?
Cytokinesis completes the M phase of the cell cycle. It may begin while telophase is still taking place.
During cytokinesis, the cytoplasm (which includes all of the contents of a eukaryotic cell outside the nucleus) draws inward, eventually pinching off into two nearly equal parts. Each part contains a nucleus.
In plant cells and other eukaryotic cells that have a cell wall, a cell plate forms halfway between the divided nuclei. It gradually develops into cell membranes and forms a complete cell wall surrounding each daughter cell.
Upon the completion of cytokinesis and the M phase, a
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Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
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Send an interactive Slack channel message (using buttons)
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Cell cycle
1. CELL AND THE CELL CYCLE
BY DR. DEEPA GAUTAM
1st yr resident , Radiotherapy
2. • Cell is the basic structural, functional and
biological unit of all known living
organisms
• Often called as building blocks of life.
3.
4. Cell organelles
• Cell membrane: protects inner cell and
regulates entry and exit of substances
• Mitochondria: power house of cell, site for
cellular respiration and ATP generation
• Ribosome: site for protein synthesis
• Endoplasmic reticulum:
– Rough: contains ER so site for protein
synthesis
– Smooth: lipid synthesis and drug
detoxification
5. • Golgi apparatus: packages proteins inside
the cell before send to destination.
• Lysosome: k/a suicidal bags, responsible
for cellular digestion by hydrolysis
• Microtubules : maintain the cellular
structure
• Microfilaments: cell motility
9. • Purines and pyrimidines are held together
by hydrogen bonds
• Sugar and phosphate linked together by
phosphodiester bonds
10.
11. DNA
RNA
• Double stranded
• A=T, G= C
• Carries genetic
information in most of the
organisms
• Single stranded
• A=U, G=C
• Carries genetic
information in some
viruses
• Types:
– messenger RNA
– transfer RNA
– ribosomal RNA
12. Chromosome
•Organised structure
of DNA , protein and
RNA.
•Total 23 pairs of
chromosomes in
human beings with
21 somatic and 2
pairs of sex
chromosomes.
13. Gene
• The functional unit of inherited information
in DNA
• Represented by discrete section of
sequence that is necessary to encode a
particular protein structure
18. G1
• From end of previous M phase to
beginning of DNA synthesis
• Also k/a growth phase
• Biosynthesis of protein , enzymes required
for S phase needed for DNA replication
• Under control of p53 gene
19. S phase
• Starts when DNA replication starts
• Completes when all chromosomes have
been replicated and each chromosome
has sister chromatids
20. G2
• Gap between DNA synthesis and mitosis
• Cell grows
• Checked everything is ready to enter the
mitosis phase
21. Mitosis
• Divided into following phases:
– Prophase
– Prometaphase
– Metaphase
– Anaphase
– Telophase
22. Prophase
• Internal membranous compartments of
the cell including nucleus are
disassembled and dispersed
• Chromatids condense
• Protein synthesis ceases
26. Telophase
• Chromatids reach the opposite poles
• Nuclei and other membrane structures
reassemble
• Chromosomes recondense
• Karyokinesis is followed by cytokinesis
27. Regulation of cell cycle
• Regulation of entry and exit from
proliferation mode
• Co-ordination of cell cycle events
• Specialised responses that increase the
probability of environmental and internally
generated insults
30. Cell-Cycle Phase Transitions
• between G1 and S phase: cyclin A and E
dependent
• between G2 and M phase: Cyclin B and
CDK1 dependent
• within M phase that is between metaphase
and anaphase to preserve genomic
integrity
31.
32. Checkpoints in cell cycle
• Damaged molecules make necessary
repairs
• Harmful cell cycle progression delayed
35. DNA damage check points
• G1 and G2 checkpoints are p53
dependent while intra S phase DNA
damage checkpoint is not.
36. Replication checkpoints
• Functions like G2 DNA damage
checkpoint but through different pathway
• Mitotic entry blocked by inhibiting CDC25C
via action of chk1, preventing action of
CDK1
37. Spindle Integrity Checkpoint
• Mechanism of delay at prometaphase or
metaphase in response to spindle defects
or improper chromosome attachment
• Sensors of the defect are APC/C cofactor,
CDC20
• Cells are prevented from initiating
anaphase
38. Restriction point
• A point in mid G1
• Cells deprived of essential nutrients or
growth factor are blocked
39. Senescence
• Loss of capacity of proliferation
• Protective phenomenon against
malignancy
• Accumulation of high levels of CDK
inhibitors leading to permanent G1 arrest
40. • Lack of enzyme telomerase
Progressive shortening of telomere of
chromosome
Discontinuity of telomere
Chronic check point responses
Permanent cell cycle arrest
41. Cell Cycle and Cancer
• Cancer is a disease of uncontrolled
proliferation
42. Alterations in Pathways
• Growth and Proliferation Signaling
Pathways:
– Overexpression of receptors
– eg.Her-2/neu in ca breast
43. • Cell cycle machinery:
– Increased synthesis of cyclin D
– Increased degradation of CDK inhibitors
– Activation of CDK4/6
– Inactivation of tumour supression gene
44. • Senescence:
– mutations in gene encoding for DNA
checkpoints signaling elements most
commonly p53,
– Telomerase expression
45. Genetic and genomic instability
• Tumour supressor gene:
– mutation leading to loss of function gives rise
to cancer. Eg. p53, Rb , BRCA-1/2
– have recessive mutation i.e both alleles of
the chromosome need to be mutated
• Proto-oncogene:
– mutation leading to enhanced function gives
rise to cancer. Eg. RAS ,SRC kinase
– have dominant mutation i.e single allele
mutation.
46. • Stress Responses:
– Abnormal growth provokes stress response
leading to cell cycle arrest or cell death
– Eg. p53 required for DNA damage checkpoint
response as well as key effector of stress
response
– Mutation in p53 can lead to cancer by both
ways
47. Application of cell cycle in treatment
of cancer
• Radiotherapy
– Cells are most radiosensitive in mitotic phase
and least sensitive in S phase of cell cycle.