This document provides an outline and overview of chapter 10 on cell division. It discusses bacterial cell division through binary fission and the replication of the bacterial chromosome. It then summarizes eukaryotic cell division, including the stages of mitosis (prophase, prometaphase, metaphase, anaphase, telophase) and cytokinesis. It also discusses the structure and compaction of eukaryotic chromosomes, the key events of the cell cycle including checkpoints, and the role of cyclin-dependent kinases in regulating the cell cycle. The document is accompanied by figures and tables to illustrate the concepts discussed.
CELL CYCLE
CELL CYCLE CHECK POINT
PHASES IN CELL CYCLE CHECK POINT
ROLE OF CYLINE AND CDKS
MUTURATIONAL PROMOTING FACTOR
FUNCTION OF MPR
CONCLUSION
REFRENCE
General overview of Plasma/ Cell membrane.
Definition of Plasma/ Cell membrane
Structure of Plasma membrane
1. Sandwitch model ORDanielli- Davson Model
2. Fluid mosaic model
Plasma Membrane Proteins
Chemical Composition of Plasma/ Cell Membrane
Movement across the Cell Membrane
Channels through cell membrane
CELL CYCLE
CELL CYCLE CHECK POINT
PHASES IN CELL CYCLE CHECK POINT
ROLE OF CYLINE AND CDKS
MUTURATIONAL PROMOTING FACTOR
FUNCTION OF MPR
CONCLUSION
REFRENCE
General overview of Plasma/ Cell membrane.
Definition of Plasma/ Cell membrane
Structure of Plasma membrane
1. Sandwitch model ORDanielli- Davson Model
2. Fluid mosaic model
Plasma Membrane Proteins
Chemical Composition of Plasma/ Cell Membrane
Movement across the Cell Membrane
Channels through cell membrane
INTRODUCTION TO CELLS
INTRODUCTION TO CELL THEORY
HISTORY
FORMULATION OF CELL THEORY
CLASSICAL CELL THEORY
DRAWBACKS OF CLASSICAL THEORY
MORDEN CELL THEORY
EXCEPTION OF CELL THEORY
SIGNIFICANCE OF CELL THEORY
HOW HAS THE CELL THEORY BEEN USED
CONCLUSION
INTRODUCTION TO CELLS
INTRODUCTION TO CELL THEORY
HISTORY
FORMULATION OF CELL THEORY
CLASSICAL CELL THEORY
DRAWBACKS OF CLASSICAL THEORY
MORDEN CELL THEORY
EXCEPTION OF CELL THEORY
SIGNIFICANCE OF CELL THEORY
HOW HAS THE CELL THEORY BEEN USED
CONCLUSION
This presentation include the process of cell division. It hope it will helpful for all the medical students. Cell division is the series of events of equally dividing of one single mother cell into two identical daughter cell. Cell cycle and cell division terms are alternately used. Cell division is an important part of the all living processes.
At the time of cell division, RNA replication is a natural process.
The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells.
These events include the duplication of its DNA (DNA replication) and some of its organelles, and subsequently the partitioning of its cytoplasm and other components into two daughter cells in a process called cell division.
There are two types of cell division
A) Mitosis and Binary fission – (Asexual reproduction) and B) Meiosis – (Sexual reproduction)
In prokaryotic cell, the cell division occurs via a process termed as Binary fission.
• In eukaryotic cell, the cell cycle can be divided in two periods i.e Interphase and Mitosis.
• During Interphase, the cell grows and DNA is replicated.
During Mitotic phase, the replicated DNA and cytoplasmic contents are separated, and cell divides.
The duration of cycle varies from hours to years. A typical human cell cycle has duration of 24 hours.
Some cells, such as skin cells, are constantly going through cell cycle, while other cells may divide rarely.
Some cells don’t grow and divide once they mature for ex. Neuron
Eukaryotic cell have a more complex cell cycle than prokaryotic cell.
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3. 3
Bacterial Cell Division
• Bacteria divide by binary fission
– No sexual life cycle
– Reproduction is clonal
• Single, circular bacterial chromosome is
replicated
• Replication begins at the origin of replication and
proceeds in two directions to site of termination
• New chromosomes are partitioned to opposite
ends of the cell
• Septum forms to divide the cell into 2 cells
7. 7
FtsZ protein has a structure similar to
eukaryotic tubulin
•Cell division in different organisms involves
protein assemblies
– Prokaryote protein assemblies involve FtsZ
– Eukaryotic protein assemblies involve microtubules
formed from tubulin
10. Chromosomes
• Composed of chromatin – complex of DNA and
protein
• DNA of a single chromosome is one long
continuous double-stranded fiber
• RNA associated with chromosomes during RNA
synthesis
• Typical human chromosome 140 million
nucleotides long
• In the nondividing nucleus
– Heterochromatin – not expressed
– Euchromatin – expressed 10
11. Chromosome Structure
• Nucleosome
– Complex of DNA and histone proteins
– Promote and guide coiling of DNA
– DNA duplex coiled around 8 histone proteins
every 200 nucleotides
– Histones are positively charged and strongly
attracted to negatively charged phosphate
groups of DNA
11
13. • Nucleosomes wrapped into higher order
coils called solenoids
– Leads to a fiber 30 nm in diameter
– Usual state of nondividing (interphase)
chromatin
• During mitosis, chromatin in solenoid
arranged around scaffold of protein to
achieve maximum compaction
– Radial looping aided by condensin proteins
13
15. Karyotype
• Particular array of chromosomes in an individual
organism
– Arranged according to size, staining properties,
location of centromere, etc.
• Humans are diploid (2n)
– 2 complete sets of chromosomes
– 46 total chromosomes
• Haploid (n) – 1 set of chromosomes
– 23 in humans
• Pair of chromosomes are homologous
– Each one is a homologue 15
17. Replication
• Prior to replication, each chromosome
composed of a single DNA molecule
• After replication, each chromosome
composed of 2 identical DNA molecules
– Held together by cohesin proteins
• Visible as 2 strands held together as
chromosome becomes more condensed
– One chromosome composed of 2 sister
chromatids
17
19. Eukaryotic Cell Cycle
1. G1 (gap phase 1)
– Primary growth phase, longest phase
2. S (synthesis)
– Replication of DNA
3. G2 (gap phase 2)
– Organelles replicate, microtubules
organize
4. M (mitosis)
– Subdivided into 5 phases
5. C (cytokinesis)
– Separation of 2 new cells 19
Interphase
20. 20
Duration
• Time it takes to complete a cell cycle varies
greatly
• Fruit fly embryos = 8 minutes
• Mature cells take longer to grow
– Typical mammalian cell takes 24 hours
– Liver cell takes more than a year
• Growth occurs during G1, G2, and S phases
– M phase takes only about an hour
• Most variation in length of G1
– Resting phase G0 – cells spend more or less time here
22. 22
Interphase
• G1, S, and G2 phases
– G1 – cells undergo major portion of growth
– S – replicate DNA
– G2 – chromosomes coil more tightly using motor
proteins; centrioles replicate; tubulin synthesis
• Centromere – point of constriction
– Kinetochore – attachment site for microtubules
– Each sister chromatid has a centromere
– Chromatids stay attached at centromere by cohesin
• Replaced by condensin in metazoans
25. 25
M phase
Mitosis is divided into 5 phases:
1. Prophase
2. Prometaphase
3. Metaphase
4. Anaphase
5. Telophase
26. 26
Prophase
• Individual condensed chromosomes first
become visible with the light microscope
– Condensation continues throughout prophase
• Spindle apparatus assembles
– 2 centrioles move to opposite poles forming spindle
apparatus (no centrioles in plants)
– Asters – radial array of microtubules in animals (not
plants)
• Nuclear envelope breaks down
28. 28
Prometaphase
• Transition occurs after disassembly of nuclear
envelope
• Microtubule attachment
– 2nd
group grows from poles and attaches to
kinetochores
– Each sister chromatid connected to opposite poles
• Chromosomes begin to move to center of cell –
congression
– Assembly and disassembly of microtubules
– Motor proteins at kinetochores
32. 32
Anaphase
• Begins when centromeres split
• Key event is removal of cohesin proteins
from all chromosomes
• Sister chromatids pulled to opposite poles
• 2 forms of movements
– Anaphase A – kinetochores pulled toward
poles
– Anaphase B – poles move apart
34. 34
Telophase
• Spindle apparatus disassembles
• Nuclear envelope forms around each set
of sister chromatids
– Now called chromosomes
• Chromosomes begin to uncoil
• Nucleolus reappears in each new nucleus
36. 36
Cytokinesis
• Cleavage of the cell into equal halves
• Animal cells – constriction of actin
filaments produces a cleavage furrow
• Plant cells – cell plate forms between the
nuclei
• Fungi and some protists – nuclear
membrane does not dissolve; mitosis
occurs within the nucleus; division of the
nucleus occurs with cytokinesis
39. 39
Control of the Cell Cycle
Current view integrates 2 concepts
1.Cell cycle has two irreversible points
– Replication of genetic material
– Separation of the sister chromatids
2.Cell cycle can be put on hold at specific points
called checkpoints
– Process is checked for accuracy and can be halted if
there are errors
– Allows cell to respond to internal and external signals
40. 3 Checkpoints
1. G1/S checkpoint
– Cell “decides” to divide
– Primary point for external signal influence
2. G2/M checkpoint
– Cell makes a commitment to mitosis
– Assesses success of DNA replication
3. Late metaphase (spindle) checkpoint
– Cell ensures that all chromosomes are
attached to the spindle 40
42. 42
Cyclin-dependent kinases (Cdks)
• Enzymes that phosphorylate proteins
• Primary mechanism of cell cycle control
• Cdks partner with different cyclins at different
points in the cell cycle
• For many years, a common view was that
cyclins drove the cell cycle – that is, the periodic
synthesis and destruction of cyclins acted as a
clock
• Now clear that Cdk itself is also controlled by
phosphorylation
45. 45
MPF
• Once thought that MPF was controlled solely by
the level of the M phase-specific cyclins
• Although M phase cyclin is necessary for MPF
function, activity is controlled by inhibitory
phosphorylation of the kinase component, Cdc2
• Damage to DNA acts through a complex
pathway to tip the balance toward the inhibitory
phosphorylation of MPF
46. 46
Anaphase-promoting complex (APC)
• Also called cyclosome (APC/C)
• At the spindle checkpoint, presence of all
chromosomes at the metaphase plate and
the tension on the microtubules between
opposite poles are both important
• Function of the APC/C is to trigger
anaphase itself
• Marks securin for destruction; no inhibition
of separase; separase destroys cohesin
47. 47
Control in multicellular eukaryotes
• Multiple Cdks control the cycle as
opposed to the single Cdk in yeasts
• Animal cells respond to a greater variety
of external signals than do yeasts, which
primarily respond to signals necessary for
mating
• More complex controls allow the
integration of more input into control of the
cycle
49. Growth factors
• Act by triggering intracellular signaling
systems
• Platelet-derived growth factor (PDGF) one
of the first growth factors to be identified
• PDGF receptor is a receptor tyrosine
kinase (RTK) that initiates a MAP kinase
cascade to stimulate cell division
• Growth factors can override cellular
controls that otherwise inhibit cell division
49
51. 51
Cancer
Unrestrained, uncontrolled growth of cells
•Failure of cell cycle control
•Two kinds of genes can disturb the cell
cycle when they are mutated
1. Tumor-suppressor genes
2. Proto-oncogenes
52. 52
Tumor-suppressor genes
• p53 plays a key role in G1 checkpoint
• p53 protein monitors integrity of DNA
– If DNA damaged, cell division halted and repair
enzymes stimulated
– If DNA damage is irreparable, p53 directs cell to kill
itself
• Prevent the development of mutated cells
containing mutations
• p53 is absent or damaged in many cancerous
cells
54. 54
Proto-oncogenes
• Normal cellular genes that become oncogenes
when mutated
– Oncogenes can cause cancer
• Some encode receptors for growth factors
– If receptor is mutated in “on,” cell no longer depends
on growth factors
• Some encode signal transduction proteins
• Only one copy of a proto-oncogene needs to
undergo this mutation for uncontrolled division to
take place
55. Tumor-suppressor genes
• p53 gene and many others
• Both copies of a tumor-suppressor gene
must lose function for the cancerous
phenotype to develop
• First tumor-suppressor identified was the
retinoblastoma susceptibility gene (Rb)
– Predisposes individuals for a rare form of
cancer that affects the retina of the eye
55
56. • Inheriting a single mutant copy of Rb means the
individual has only one “good” copy left
– During the hundreds of thousands of divisions that
occur to produce the retina, any error that damages
the remaining good copy leads to a cancerous cell
– Single cancerous cell in the retina then leads to the
formation of a retinoblastoma tumor
• Rb protein integrates signals from growth factors
– Role to bind important regulatory proteins and prevent
stimulation of cyclin or Cdk production
56
58. 58
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