Definition and Impact of Cancer
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Cancer is defined as a disease characterized by unregulated cell division, leading to the
formation of tumors.
It is the second leading cause of death in the United States, highlighting its significant
impact on public health.
Despite decades of research, cancer remains a major challenge due to its complexity
and the variety of forms it can take.
Cancer is not a single disease; it encompasses over 100 different types, each with
unique characteristics and behaviors.
Genetic mutations are a primary cause of cancer, but environmental factors and lifestyle
choices also contribute significantly to its development.
Understanding the mechanisms of cancer is crucial for developing effective treatments
and prevention strategies.
Risk Factors and Treatment
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Risk factors for cancer include genetic predisposition, exposure to carcinogens, lifestyle
choices (such as smoking and diet), and infections.
Treatments for cancer vary widely and may include surgery, radiation therapy,
chemotherapy, immunotherapy, and targeted therapies.
The choice of treatment depends on the type of cancer, its stage, and the overall health
of the patient.
Ongoing research is focused on personalized medicine, which tailors treatment based on
the individual characteristics of each patient's cancer.
Early detection through screening can significantly improve treatment outcomes and
survival rates.
Supportive care and palliative care are essential components of cancer treatment,
addressing the physical and emotional needs of patients.
Cell Division Mechanisms
Overview of Cell Division
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Cell division is a fundamental process that allows organisms to reproduce, grow, and
repair tissues.
It results in the formation of two daughter cells, each containing a complete set of
chromosomes.
The process requires the duplication of chromosomes, which are structures that house
the cell's DNA.
There are two primary methods of reproduction: asexual and sexual, each with distinct
mechanisms and outcomes.
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Asexual reproduction produces genetically identical offspring, while sexual reproduction
results in genetic variation among offspring.
Understanding these processes is essential for grasping how cancer can arise from
errors in cell division.
Types of Cell Division
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Asexual reproduction includes methods such as binary fission in prokaryotes and
fragmentation in certain eukaryotes.
In binary fission, a prokaryotic cell divides into two identical cells through a simple
process involving chromosome duplication and cell elongation.
Eukaryotic cell division is more complex, involving mitosis and cytokinesis, which ensure
accurate distribution of chromosomes to daughter cells.
Mitosis is divided into several phases: prophase, metaphase, anaphase, and telophase,
each with specific events that lead to chromosome separation.
Cytokinesis follows mitosis, physically separating the cytoplasm and organelles into two
distinct daughter cells.
Errors in these processes can lead to cancerous growths, as cells may divide
uncontrollably.
The Cell Cycle
Phases of the Cell Cycle
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The cell cycle is an ordered sequence of events that a cell undergoes from formation to
division.
It consists of two main stages: Interphase and the Mitotic phase (M phase).
Interphase is further divided into three subphases: G1 (growth), S (synthesis of DNA),
and G2 (preparation for division).
The Mitotic phase includes mitosis (nuclear division) and cytokinesis (cytoplasmic
division).
Cells spend the majority of their life in interphase, where they grow and prepare for
division.
The regulation of the cell cycle is critical; disruptions can lead to uncontrolled cell division
and cancer.
Regulation of the Cell Cycle
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The cell cycle is tightly regulated by a series of checkpoints that ensure proper division
and function.
Key proteins, such as cyclins and cyclin-dependent kinases (CDKs), play crucial roles in
regulating the progression through the cell cycle.
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Checkpoints occur at G1, G2, and during mitosis, allowing the cell to assess DNA
integrity and readiness for division.
If errors are detected, the cell may undergo apoptosis (programmed cell death) to
prevent the propagation of damaged DNA.
Mutations in genes that regulate the cell cycle can lead to cancer, as they may allow
cells to bypass these critical checkpoints.
Understanding these regulatory mechanisms is essential for developing targeted cancer
therapies.
Overview of Cell Division
Types of Cell Division
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Liver cells typically do not divide unless damaged, while adult nerve cells are
non-dividing.
This highlights the specialization of cell types and their regenerative capabilities.
Factors Affecting Cell Division
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Environmental factors significantly influence the rate of cell division, including nutrient
availability and growth factors.
Density-dependent inhibition prevents overcrowding by halting division when cells are
too dense.
Anchorage dependence requires cells to be attached to a solid surface to divide, which
is crucial for tissue integrity.
Mechanisms of Cell Cycle Control
Cell Cycle Control System
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The cell cycle control system consists of molecules that regulate key events in the cell
cycle, ensuring proper timing and sequence of events.
Checkpoints serve as critical control points where signals can either halt or allow
progression through the cycle.
Checkpoints in the Cell Cycle
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G1 checkpoint is crucial for many cells, determining whether to proceed to S phase or
enter a non-dividing G0 phase.
G2 checkpoint ensures DNA is replicated correctly before mitosis.
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M checkpoint verifies that all chromosomes are properly attached to the spindle before
anaphase begins.
Growth Factors and Their Role
Role of Growth Factors
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Growth factors are proteins that stimulate cell division and signal the cell cycle control
system.
They bind to receptors on the cell surface, initiating a signal transduction pathway that
influences cell cycle progression.
Consequences of Checkpoint Failures
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If checkpoints detect issues, the cell may pause to repair or undergo apoptosis if
damage is irreparable.
Accumulation of mutations can lead to cancer, as cells bypass normal regulatory
mechanisms.
Phases of Mitosis
Stages of Mitosis
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Mitosis consists of several stages: prophase, prometaphase, metaphase, anaphase, and
telophase, often summarized as IPPMAT.
Each stage has distinct events that ensure accurate chromosome segregation.
Cytokinesis
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Cytokinesis is the final step of cell division, differing between animal and plant cells.
In animal cells, a cleavage furrow forms, while in plant cells, a cell plate develops to
separate the two daughter cells.
Cell Division and Cytokinesis
Overview of Cell Division
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Cell division is essential for growth, development, and tissue repair in multicellular
organisms.
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The cell cycle consists of interphase, mitosis, and cytokinesis, each playing a critical role
in cell replication.
Mitosis ensures equal distribution of replicated chromosomes to daughter cells, while
cytokinesis physically divides the cytoplasm.
Cytokinesis in Animal Cells
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In animal cells, cytokinesis is characterized by the formation of a cleavage furrow, which
is a contractile ring of microfilaments.
The cleavage furrow deepens as the ring contracts, ultimately pinching the cell into two
daughter cells.
Electron microscopy (SEM) at 113× magnification reveals the structural details of the
cleavage furrow.
Cytokinesis in Plant Cells
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Plant cells undergo cytokinesis differently, forming a cell plate that develops from
vesicles containing cell wall materials.
The cell plate grows outward until it fuses with the existing cell wall, creating two distinct
daughter cells.
Light microscopy (LM) at 1,050× magnification shows the formation of the cell plate and
the new cell wall.
BRCA Mutations and Cancer Risk
Introduction to BRCA Genes
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BRCA1 and BRCA2 are genes located on chromosomes 17 and 13, respectively, and
are crucial for DNA repair.
Mutations in these genes significantly increase the risk of breast and ovarian cancer,
particularly in women.
BRCA stands for breast cancer susceptibility gene, highlighting its role in cancer
predisposition.
Inherited Cancer Risk
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Individuals with a mutated BRCA gene have a compromised DNA repair system,
increasing their cancer risk.
Women with one mutated copy of BRCA1 or BRCA2 have a higher lifetime risk of
developing breast and ovarian cancer.
Men with these mutations also face increased risks for breast and other cancers.
Prevalence of BRCA Mutations
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It is estimated that 5% to 10% of all cancers are attributed to inherited BRCA mutations.
The majority of cancers (90% to 95%) arise from mutations acquired during a person's
lifetime, indicating that most cancers are sporadic rather than inherited.
Types of Genes Linked to Cancer
Proto-oncogenes and Oncogenes
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Proto-oncogenes are normal genes that promote cell division; when mutated, they
become oncogenes, leading to uncontrolled cell growth.
An example is the HER2 gene, which, when mutated, results in overexpression of the
HER2 protein, contributing to breast cancer.
Oncogenes act as accelerators in the cell cycle, promoting rapid cell division even
without growth signals.
Tumor Suppressor Genes
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Tumor suppressor genes, such as BRCA1, BRCA2, and p53, normally function to inhibit
cell division and repair DNA.
Mutations that inactivate these genes can lead to cancer, as they fail to control cell
growth and repair damaged DNA.
More than 50% of cancers involve mutations in the p53 gene, which is critical for cell
cycle regulation and apoptosis.
Cancer Progression and Treatment
Cancer Development
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Cancer typically arises from multiple mutations in genes regulating the cell cycle, leading
to uncontrolled cell division.
The progression from a normal cell to a cancerous cell involves evasion of the immune
system and potential metastasis.
Tumors can be benign (localized) or malignant (capable of spreading), with metastasis
referring to the spread of cancer cells to other body parts.
Conventional Cancer Treatments
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Surgery is effective for early-stage solid tumors but less so for widespread cancer.
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Chemotherapy uses toxic agents to target rapidly dividing cells, affecting both cancerous
and healthy cells, leading to significant side effects.
Radiation therapy damages DNA in targeted cells, killing them but also posing risks to
surrounding healthy tissue.
Emerging Cancer Treatments
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Targeted therapy aims to exploit specific weaknesses in cancer cells caused by genetic
mutations, sparing normal cells.
Immunotherapy enhances the body's immune response against cancer cells, though it
can lead to serious immune-related side effects.
Preventive measures include lifestyle changes, regular screenings, and genetic testing
for hereditary cancer risks.