Chapter 7 : The Cell Cycle and Cell Growth and Differentiation Flashcards
The Cell Cycle Phases
- Inter-phase G1 - primary growth S - synthesis = genome replicated G2 - secondary growth M - mitosis - Prophase - Metaphase - Anaphase - Telophase C - cytokinesis
Inter-phase
- Lots of activity happening in this phase
- Cells prepare for mitosis
- Protein synthesis
- DNA synthesis
- Replication of other cellular structures
- Longest part of cell cycle
The phase of mitosis in eukaryotic cells
- Division of nucleus into 2 nuclei
- Each nuclei has the same number of chromosomes
- Occurs in all somatic (body) cells
- Each new daughter cell has a nucleus complete set of chromosomes
Phases and what occurs in order
Prophase :
- Separates duplicated genetic material carried in -
- nucleus of a parent cell into 2 identical daughter cells
- Chromosomes coil up
- Nuclear envelope disappears
- Spindle fibres form
Metaphase :
- Chromosomes line up in middle of the cell
- Spindle fibres connect to chromosomes
Anaphase :
- Chromosome copies divide
- Spindle fibres pull chromosomes to opposite poles
Telophase :
- Chromosomes uncoil
- Nuclear envelopes form
- 2 new nuclei are formed
- Spindle fibres disappear
Cytokinesis in eukaryotic cells
Cytokinesis :
- Division of the rest of the cell after nucleus divides
- Cytoplasm in animal cells pinch in
- Cell plate forms in plant cells
- After mitosis and cytokinesis the cell returns to interphase
Binary fission / process
The division of a cell into 2 without mitosis; the process by which a prokaryotic cell splits to form 2 daughter cells.
Similar to mitosis but occurs in prokaryotic cells as there is only one chromosome and no centromere.
Process includes:
- DNA replication
- Chromosome segregation
- Cytokinesis
- Produces 2 daughter cells with identical DNA to parent cell
Occurs in eukaryotic cells but only for producing:
- Mitochondria
- Chloroplasts
Disruption of cell cycle regulation
Apoptosis :
- Programmed cell death
- Normal part of an organism’s function
- Important for development, shaping organs and tissues and removing cells that are old or no longer needed
- Almost all multicellular organisms have cells that are born to die
- Failure in Apoptosis can result in many problems, ranging from development defects to cancer
- Formation of cancer happens when apoptosis is avoided and cells do not die as they should
Example of apoptosis :
- Enables tadpole to lose its tail as it becomes a frog
- Allows human embryo to lose the webbing between its fingers and toes
Cell cycle checkpoints :
G0 - resting state
- Doesn’t divide or preparing for division
- Occurs outside of cell cycle
- Damaged cells are located here
G1 checkpoint : Check for: - Cell size - Nutrients - Growth factors - DNA damage
G2 checkpoint
Check for:
- Cell size
- DNA replication
Mitosis checkpoint - spindle assembly checkpoint
Check for:
- Chromosome attachment to spindle
Action of Mutagens in cell cycle
Chemical mutagens :
- Ability to interfere with DNA
- Interrupts its structure, sequence and replication
Physical mutagens :
- Ultraviolet light, X rays and nuclear radiation
- When UV light is absorbed DNA is damaged
- Mutations in tumor suppressor gene p53 play a critical - role in development of precancerous lesions and have - been implicated in all types of skin cancer
Biological mutagens :
- Viruses - take over cells
- Impair cell cycle regulation - results in cancer
- Cause uncontrolled cell growth
Types of stem cells
Stem cells :
Stem cells are undifferentiated cells that have the potential to replicate and to develop into many different kinds of cell
Pluripotent stem cells :
- Capable of giving rise to most but not all tissues of an organism
Example = the inner cell mass
Multipotent stem cells :
Able to give rise to cells that have a specific function
Example = blood stem cells
Adult stem cells
Multipotent :
- Form cells of different kinds of tissue
Advantage = patient’s own cells could be used for treatment
- Risks are lower because patient’s immune system won’t reject its own cells
Disadvantage = are pre-specialised
- Blood stem cells only make blood
- Brain stem cells only make brain cells
- Can replace dead or damaged cells
- Bone marrow has multipotent stem cells that give rise - to all cells of the blood
Embryonic stem cells
- Cultured from frozen embryos that are obtained from in-vitro fertilisation clinics (IVF clinics)
- Ethical issues related to the use of these cells
Obtaining them requires destruction of an embryo - Governments have strict regulations in place for controlling this type of technology
Advantage = pluripotent - Can become any of the cell types of the body
- More versatile than adult stem cells
Disadvantage = come from embryo that’s not derived from patient’s own cells - Patients immune system may reject them
Sources of stem cells for research and therapy - types
Umbilical cord blood and placental stem cells
- Present in blood in umbilical cord and placenta
- Once baby is born cells can be extracted from
- discarded tissue and used for the benefit of children and adults who suffer from bone marrow or blood diseases
- Stored in case baby requires replacement tissues or organs later in life
- Obtained after baby is born and there’s no harm to mother or baby
- Multipotent
Fission
- Single celled eukaryotic or prokaryotic organisms
- Divide into 2 new organisms
- Each is an exact copy of parent cell
- Nucleus is replicated and cytoplasm splits to form 2 new daughter cells
Budding
- New organism is grown on the outside of the parent organism
- Eventually detaches as its own complete organism
- Hydra, yeast
