The Cell Cycle Flashcards
What is the cell cycle
Highly ordered sequence of events that takes place in a cell, resulting in a division of the cell, and the formation of two genetically identical daughter cells.
Interphase intro
Cells don’t divide continuously-long periods of growth and normal working separate divisions. These periods are called interphase and a cell spends the majority of its time in this phase.
Interphase is sometimes referred to as the resting phase as cells are not actively dividing. However, this is not an accurate description-interphase is actually a very active phase of the cell cycle, when the cell is carrying out all its major functions such as producing enzymes or hormones, while also actively preparing for cell division.
During interphase:
-DNA is replicated and checked for errors in the nucleus.
-Protein synthesis occurs in the cytoplasm
-mitochondria grow and divide, increasing in number in the cytoplasm.
-chloroplasts grow and divide in plant and algal cell cytoplasm, increasing in number.
-The normal metabolic processes of cells occur
The three stages of interphase:
-G1- the first growth phase:proteins from which organelles are synthesised are produced and organelles replicate. The cell increases in size. (Cellular contents, apart from the chromosomes are duplicated)
-S-synthesis phase:DNA is replicated in the nucleus.
-G2-the second growth phase:the cell continued to increase in size, energy stores are increased and the duplicated DNA is checked for errors.
Mitotic phase
The mitotic phase is the period of cell division. Cell division involves two stages:
-Mitosis-the nucleus divides
-Cytokinesis-the cytoplasm divides and two cells are produced.
What is G0
G0 is the name given to the phase when the cell leaves the cycle, either temporarily or permanently.
Reasons why the cell leaves the cycle, either temporarily or permanently
-Differentiation-A cell that becomes specialised to carry out a particular function (differentiated) is no longer able to divide. It will carry out this function indefinitely and not enter the cell cycle again.
-The DNA of a cell may be damaged, in which case it is no longer viable. A damaged cell can no longer divide and enters a period of permanent cell arrest (G0). The majority of normal cells only divide a limited number of times and eventually become senescent.
-As you age, the number of these cells in your body increases. Growing numbers of senescent cells have been linked with many age related diseases, like Cancer and Arthritis.
A few types of cells that enter G0 can be stimulated to go back into the cell cycle and starts dividing again, eg lymphocytes (WBC) in an immune response.
Control of the cell cycle
It is vital to ensure a cell only divides when it has grown to the right size, the replicated DNA is error free (or is repaired) and the chromosomes are in their correct positions during mitosis. This is to ensure the fidelity of cell division- that two identical daughter cells are created from the parent cell.
What are checkpoints
The control mechanisms of the cell cycle. They monitor and verify whether the processes at each phase of the cell cycle have been accurately completed before the cell is allowed to progress into the next phase.
Where do checkpoints occur in the cell cycle
-G1 checkpoint-this checkpoint is at the end of the G1 phase, before entry into S phase. If the cell satisfies the requirements of this checkpoint it is triggered to begin DNA replication. If not, it enters a resting state (G0).
-G2 checkpoint-this checkpoint is at the end of G2 phase, before the start of the mitotic phase. In order for this checkpoint to be passed, the cell has to check a number of factors, including whether the DNA has been replicated without error. If this checkpoint is passed, the cell initiated the molecular processes that signal the beginning of mitosis.
-Spindle assembly checkpoint (also called metaphase checkpoint):This checkpoint is at the point in mitosis where all the chromosomes should be attached to spindles and have aligned (metaphase). Mitosis cannon proceed until this checkpoint is passed.
