Cell division Flashcards
What are the three main stages on the cell cycle?
- Interphase, Mitosis, Cytokinesis
What is the interphase?
- First stage, the most active and longest phase of the cell cycle
- It involves many processes that occur both in the nucleus and cytoplasm
- With in this stage there are three stages: the G1 (Gap 1), S (synthesis), and G2 (Gap 2 )
- DNA exists as chromatin
What processes are involved in interphase?
The processes include (DOCTOR):
- DNA replication (during the S phase) and RNA synthesis
- Organelle duplication (twin daughter cells)
- Cell growth (size must increase before division)
- Transcription/translation (synthesis of proteins)
- Obtain nutrients (cellular materials)
- Respiration (ATP production
Explain where and what happens in the G1 phase of the interphase.
- In the cytoplasm
- Rapid protein synthesis, cells increases in size
- The proteins that are required for DNA synthesis (the next phase) are made
- Mitochondria and chloroplasts (in plants) are replicated
Explain where and what happens in the S phase of the interphase.
- In the nucleus
- The amount of DNA doubles as DNA replication takes place
- Genetic material in the form of chromosomes are duplicated
- Mitochondria and chloroplasts (in plants) continue to be replicated
Explain where and what happens in the G2 phase of the interphase.
- In the cytoplasm
- Protein synthesis occurs to produce the proteins needed for cell division, such as microtubule proteins that will make up a mitotic spindle
- The cell has more mitochondria than the cell in the G1 phase
- The cell prepares for cell division
When a cell is dividing too rapidly may have lost the ability to enter which phase?
G1 phase
What are cyclins?
- Cyclins are a family of proteins that control the progression of cells though the cell cycle
- The cyclin needs to reach a certain concentration so that the cell can progress to the next stage
- Cyclins bind to enzymes called cyclin-dependent kinases (CDKs) which are activated
- In order to activate proteins, the CDKs attach a phosphate group to the proteins
- The CDKs attach phosphate groups to other proteins in the cell, which causes the proteins to become active and carry out tasks
- Cyclins and CDKs regulate the cell cycle, the speed can be controlled and the cycle can be stopped completely
What type of cyclins have an effect on which stage in the interphase stages and in mitosis?
- In the G1 phase, the cyclin D levels gradually increase
- In the S phase, the cyclin E is important for DNA replication and also promotes centromere duplication
- In the G2 phase, the cyclin A helps promote DNA replication
- In Mitosis, the cyclin B helps in the formation of mitotic spindles and the alignment of chromatids
- Order: D, E, A, B
What is mitosis?
- The division of the nucleus into two genetically identical daughter nuclei
- The sister chromatids are separated into individual chromosomes which are then distributed among the daughter nuclei
What factors are involved in mitosis? What are histones and chromatin?
- The DNA which was replicated in the S phase is used
- In eukaryotic cells, DNA replication requires chromosomes, the DNA is tightly wound around proteins called histones
- Histones: are alkaline proteins that form part of nucleosomes, which are coiled together in a specific pattern to form a chromosome
- The DNA that is packed by histones, forms chromatin which undergo condensation to form the chromosomes
- Chromatin is a lower order of DNA organization
- The order of DNA organization changes throughout the stages of mitosis
What are the four phases of mitosis?
- Prophase, Metaphase, Anaphase, Telophase
Diagrams of each phase in book. Be able to identify these stages on a micrograph.
What happens in the prophase? Give 6 details.
- DNA supercoils causing the chromatin to condense
- The nucleolus disappears
- Nuclear membrane breaks up
- Spindle fibers (made of microtubules) form
- Centrioles (only present in animals) move to opposite poles
- DNA exists as a pair of sister chromatids that are identical to each other
What happens in metaphase?
- Spindle fibers bind to the centromere of sister chromatides and cause their movement towards the equatorial plate
- Sister chromatides are aligned at the equatorial plate at the end of the phase
- DNA present as Sister chromatides
What happens in anaphase?
- Shortest phase of mitosis
- Sister chromatides are separated and pulled to opposite poles by the spindle fibers
- DNA present in the form of chromosomes
What happens in telophase?
- The chromosomes have reached the poles
- A nuclear membrane starts to form at each pole
- A nucleolus appears in each new nucleus
- The spindle fibers disintegrate (break up)
- The cell elongates in preparation for cytokinesis
- DNA is present as chromosomes
How do you calculate the mitotic index?
- The ratio= the number of cells in a population undergoing mitosis (all phases): to the total number of visible cells
- mitotic index= P+M+A+T/Total cells
- Important to know because in a tumor the mitotic index is higher than in normal tissue.
- The index predicts how quickly a cancer could spread
What is cytokinesis?
- The cytoplasm of a parental cell is divided between the two daughter cells
- This process occurs after mitosis and often starts in telophase
- It is different for animals and plant cells due to the presence of a cell wall in plant cells
What are the differences between animal and plants cells during cytokinesis?
Animal
- Microfilaments (rings of proteins), which are beneath the plasma membrane at the equator, pull the plasma membrane inward
- This inward pull produces a cleavage furrow
- When the cleavage furrow reaches the center of the cell it is pinched apart to form two daughter cells
Plants
- In the Golgi apparatus, vesicles form that consist of material to build a cell plate
- The vesicles merge and form a new cell wall, which grows and divides into two daughter cells
Diagrams in book
What is tumorigenesis?
- The formation of a tumor (or multiple) which is defined as a mass of cells that divide uncontrollably
- The 2 types of tumors: benign and malignant tumors
- Cancer is caused by malignant tumour
What is a benign tumor and what is a malignant tumor?
- Usually localized and does not spread to other parts of the body, they respond well to treatment
- A cancerous growth that is often resistant to treatment and may spread to other parts of the body and may recur after being removed.
What causes tumors?
- When the cell cycle is disrupted because of a mutation in one of the cyclins, CDKs or a protein associated with the cell cycle
- Over 50% of all tumors have a mutation in the p53 gene
- The cells loses its ability to enter the G1 phase and continues to divide rapidly, uncontrolled growth
- Cancer can occur is any organ or cell
What are mutations, mutagens and oncogene?
- Mutations: a change in an organism’s genetic code (base sequence) may lead to a tumor
- Not all gene mutations lead to uncontrolled cell division
- Anything that causes a mutation has the potential to cause a cancer
- Mutagens: agents that cause gene mutation
- E.g. chemicals that are carcinogens such as dioxin, high-energy radiation (x-rays), short wave ultraviolet light, some viruses (hepatitis B)
- Oncogene: a mutated gene that contributes to the development of a tumor. When not mutated they are called proto-oncogenes
How do primary tumors develop into secondary tumors?
- Cancerous cells detach from the primary tumor and may end up in the blood circulation which may lead them to invade tissues at different locations and develop into secondary
- The development occurs due to uncontrolled cell division. The tumor has metastasized.
- Metastasis: movement of cells from primary tumor to other parts of the body where they develop into secondary tumors
