Cell cycle and Cell growth, Death and Differentiating Flashcards
(29 cards)
What is embryological development?
All human life begins at the point of conception. A zygote is a diploid cell formed when the sperm of a male fertilises an ovum (egg).
The embryological development is the period from fertilisation to the development of the foetus.
What are stem cells?
A stem cell is a type of cell that is capable of giving rise to any type of specialized cell in the body of a multicellular organism. It does not have a specific function within the organism, instead differentiating into almost any type of cell when the body needs it.
Difference between totipotent and pluripotent
toti potent cells can differentiate into all possible cell types while pluripotent cells can differentiate into almost any type of cell.
Purpose of cell division
growth, repair and reproduction
What is binary fission and what is its process?
Binary fission is an asexual process of cell division carried out by bacteria.
Process:
1. The bacterial DNA replicates to form two identical circular chromosomes.
2. The parent cell elongates.
3. The two chromosomes move to opposite sides of the cell. A septum forms along the middle of the cell, forming new cell walls and the parent cell is split into two, creating two daughter cells.
Interphase
Cells spend most of their time in interphase. It consists of the G1, S, G2 and, in some cells, G0 phase of the cell cycle. In interphase, chromosomes are not visible and the nucleus appears as a dark mass of chromatin (uncondensed).
what happens in G1 phase?
Cell grows larger and doubles in size.
Organelles are copied so that daughter cells will be equipped with the necessary ‘machinery’ to sustain their own survival.
what happens in S phase?
DNA within the nucleus is replicated, creating two identical copies of DNA.
Centromere duplicates
what happens in G2 phase?
Cell enters a period of growth (again).
Increases its energy store in preparation for division.
What happens in prophase?
Chromatin condenses into chromosomes
Centrosomes move to opposite poles of the cell, spindle fibers form between poles
Nuclear membrane breaks down
what happens in metaphase?
Chromosomes line up in the centre of the cell by the attachment of spindle fibers
Chromosomes most visible now
what happens in anaphase?
Sister chromatids split apart at centromere
The two sister chromatids move towards opposite poles
Spindle fibres from centrosome retract pulling the chromatids to the poles
what happens in telophase?
Single chromosomes arrive at opposite poles
Chromosomes revert back to chromatin
spindle fibres disappear
New nuclear membrane forms around the two groups of chromosomes
what happens in cytokineses?
Cytokinesis is the final stage of the cell cycle, which is the splitting of the cytoplasm. It restores the original size of the cell and maintains the SA:V ratio.
Animal cells:
Plasma membrane moves inwards, giving rise to cleavage furrow
Daughter cells are pinched apart
what are cell cycle checkpoints?
Cell cycle checkpoints are the controlling factors that process internal and external signals before determining whether a cell can proceed to the next stage of division. The checkpoints ensure that a compromised cell does not continue to divide and pass on its defects (damage or mutated DNA) to the next generation.
Where does the G1 checkpoint occur and what is its role?
The G1 checkpoint occurs at the transition of G1 into S phase.
Checks for:
Cell size and growth patterns are normal
nutrients/energy is sufficient
DNA damage
If the cell fails to meet these requirements, it will not progress to S phase. It will either attempt to rectify the errors or pass into the G0 state temporarily or permanently.
Where does the G2 checkpoint occur and what is its role?
The G2 checkpoint occurs before the cell enters mitosis.
Checks for:
DNA damage
DNA replication accuracy
If damage or errors are detected, then the checkpoint will halt the cell’s progression through the cell cycle until DNA replication is completed or the damaged DNA is repaired. If DNA damage cannot be fixed, apoptosis will occur.
Where does the M checkpoint occur and what is its role?
The M checkpoint occurs between metaphase and anaphase.
Checks:
Chromosomes are attached to the spindle fibers correctly before anaphase occurs
Chromosomes are aligned correctly
What are regulatory proteins?
Inside each cell is a set of regulatory proteins that form the cell cycle control system. Regulatory proteins are a group of proteins that operate at cell cycle checkpoints to allow healthy cells to progress in the cycle by responding to internal and external environmental signals.
Define Apoptosis
Apoptosis, or programmed cell death, is a highly controlled process that results in a eukaryotic cell committing ‘cellular suicide’.
Purposes of Apoptosis
Protection - removes cells that cannot be repaired (have damaged DNA)
Balance - regulates the number of cells in an organism
Development - part of the regular growth and development of an organism
when is the Intrinsic pathway activated?
When intracellular stress signals are received by the mitochondria. These stress signals could be the result of DNA or protein damage or lack of growth factors.
when is the extrinsic pathway activated?
In response to external signals that bind to ‘death’ receptors on the plasma membrane of the target cell that is to be destroyed. The death signal may be the result of extreme heat exposure, but usually the cell is deceased.
what is the p53 protein and what is its role?
The p53 protein is a regulatory protein that operates in the G1 and G2 cell cycle checkpoints. Its role is to detect damaged DNA within a cell prior to the cell reaching mitosis. In a healthy cell, p53 protein levels are low but in cells with damaged DNA, p53 protein levels increase.
