Chapter 4: The Cell Cycle Flashcards
What is the purpose of cell replication?
It is essential for growth, repair and maintenance, and reproduction.
What is binary fission?
Binary fission is the method of reproduction bacteria use.
How does binary fission occur?
Its similar to mitosis as it is cell division but they have different purposes.
What is the purpose of binary fission in comparison to mitosis?
Binary fission is a way for bacteria to reproduce and increase population whereas mitosis is to replace old, worn-out cells and to increase the size of an organism.
Cytokinesis definition
Cytokinesis is when the cells enlarges in preparation for the division to be able to survive.
What does mitosis do?
Mitosis ensures that each cell is an exact replicate (daughter cell) prior to cytoplasmic division (cytokinesis).
What is the stage in between nuclear divisions (M)?
Interphase
What are the periods in interphase?
Active Growth (G1)
Synthesis of DNA (S)
Preparation for the next division (G2)
Order of periods in Interphase
G1, S, G2, M
What is G0?
G0 is an extended G1 phase which occurs in cells that have reached maturity and no longer need to replicate. This usually occurs in specialised cells.
G1 phase
The cell produces proteins, grows and carries out its usual tasks for the body
S phase
Exact duplicates of DNA are formed
G2 phase
Preparation for cell division
M phase
The cell divides into two daughter cells (mitosis)
What are the 4 stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
Prophase
Prophase is considered to be the first true stage of the mitotic process.
- The chromatin threads condense and become a visible pair of chromatids held together by the centromere.
- Centrioles then move to either end of the cell and microtubules begin to radiate from them.
- This then begins to form the framework for fibres as the nuclear membrane breaks down.
Metaphase
The chromatid pairs move along the metaphase plate towards the centre of the cell.
The centromere of each pair is attached to a spindle fibre.
Anaphase
The spindle fibres attached to the chromatids begin to pull them apart. They move to opposite poles of the cell and are now called chromosomes as they are now individual.
Telophase
- The two sets of chromosomes form tight clusters at either side of the cell.
- The chromosomes decondense as the chromatin unwinds and become less visible.
- A new nuclear envelope forms, nucleoli reforms and the spindle disassembles.
Apoptosis
The process for a cell to
self-destruct when necessary such as, structural damage, worn-out or internal altercations.
What is the process of apoptosis?
- Shrink and develop bubble-like protrusions on their surface
- The DNA breaks down as well as some organelles
- The entire cell splits into small fragments
- The chunks release signals that attract debris-eating immune cells
What is necrosis?
Necrosis is essentially when a cell “spills their guts” due to plasma membrane damages
Extrinsic apoptosis
This begins outside the cell when conditions in the extracellular environment determine the cell must die
Intrinsic apoptosis
This is a result of internal damages of a cell that cause stress activating the apoptotic pathway
What is a checkpoint?
A checkpoint is used to determine if a cell is ready to move into the next stage of the cell cycle
G1 Checkpoint
The cell can only pass onto the S phase if it is of adequate size and appropriate energy reserves. This phase is signalled by cyclins and cyclin dependent kinases
G2 Checkpoint
The G2 checkpoint’s most important role is to ensure the chromosome has been exactly replicated. When an issue is identified, the cell tries to repair it but when the cell is deemed okay it moves onto the mitotic phase
M checkpoint
This occurs at the end of the metaphase cycle where the cell is checked based on how the sister chromatids are attached to the spindles as the cell is ready to divide
Proto-oncogenes
Code for proteins to stimulate cell division, prevent cell differentiation and regulate programmed cell death
Tumour suppressor genes
This keeps the cell from dividing too quickly and allows repairs to the cell to occur and also tell cells when to die
p53 gene
This prevents tumours and codes for a protein that regulates the cell cycle
What signals may trigger p53 proteins? What are there major functions?
Internal damages may cause more p53 proteins which function growth arrest, DNA repair and apoptosis
Mutagens
A substance that affects an organism’s genetic system by altering hereditary materials
Are mutagens biological, physical or chemical?
All
What are chemical mutagens?
They alter DNA, by interrupting its structure, sequence or replication
Physical mutagens
UV light, nuclear radiation and X-rays are examples of physical mutagens which also alter DNA
What are biological mutagens?
These are viruses that impair cell cycle regulation, ultimately resulting in cancer
Stem cells
They are unspecialised cells that have the potential to become specialised cells
Totipotent stem cells
Can differentiate between all tissue types
Pluripotent stem cells
They are able to differentiate between most types of tissues but they are unable to produce all tissues of the body
Multipotent stem cells
Able to differentiate into a number of tissues
