Topic 2 - Cell Life Cycle Flashcards
Why do cells need to divide/reproduce?
To allow for the continuity of life, cells grow and repair. Cells reproduce to replace damaged cells.
Define Cell Cycle
the life cycle of a cell
2 Main stages of the cell cycle
- Mitosis (1-2hrs)
- Interphase (23 hrs)
What is mitosis?
- the division of the nucleus (the separation of chromosomes into two new cells)
- all somatic cells reproduce mitosis, not neurons and muscle cells OR GAMETES (sex-cells)
- happens every 24 hours
What is interphase?
the phase in which the cell spends 23 out of the 24 hrs - the cell grows, duplicates its DNA and gets ready for the next cell division by mitosis
What is cytokinesis?
- the cytoplasm pinches in half, and each new cell formed has an identical set of duplicated chromosomes.
3 parts of Interphase
- G1 Phase
- S Phase
- G2 Phase
What occurs in the G1 Phase
The cell prepares for cell division by:
- making proteins
- the cell getting bigger in mass/size
- growing in size.
It is the growth period before the replication of DNA
What occurs during the S Phase?
The period after G1 where all genetic material (DNA) is synthesized/replicated. The chromosomes are doubled.
What occurs during the G2 Phase?
The period after DNA synthesis has occurred but prior to the start of mitosis.
- The cell continues to grow by making more organelles (ribosomes and mitochondria)
What is a karyotype?
shows a complete set of chromosomes found in a body cell - organised in pairs and according to size
What is a duplicated chromosome?
when each chromosome is made up of two sister chromatids that are held together by a centromere.
What happens in Prophase?
The nuclear membrane starts to disappear and the centrioles start to move to different poles of the cell.
- Chromosomes coil up and are seen as strands.
What happens in Metaphase?
- The chromosomes line up in the middle and are attached to a fibre in the spindle (web).
- They attach across the middle called the equator and get ready to divide.
What happens in anaphase?
- The chromosomes pull apart, the centromeres split and each sister chromatid moves to the opposite end of the cell.
What happens in Telophase?
The nuclear membrane starts to form around the separate chromosomes, creating 2 new daughter cells.
- Cytokinesis pinches cytoplasm
What is checked at Checkpoint G1/S
- Checks the cell for any DNA damage before being duplicated in the S Phase.
- Makes sure cell is of a proper size and has enough energy to prepare for mitosis
- Cannot progress if damaged or too small
What is checked at Checkpoint G2/M
- Makes sure DNA is duplicated correctly before mitosis
- There should be no mistakes or damages to progress into mitosis
What is checked at Checkpoint M (metaphase)
Ensures that chromosomes are separating correctly in mitosis and that they divide evenly into the two new cells.
What is the G0 phase in the life cycle
- Cells that are sent to G0 after G1 as they do not get the signal to continue further in the cell cycle. They stay there resting, and functioning but do not divide any further.
- Quiscence
Why do cells need to balance cell reproduction and cell apoptosis?
to maintain healthy tissues and overall organism functioning. If too much cell reproduction without undergoing apoptosis, may lead to uncontrolled growth = cancer.
If too much apoptosis, can result in tissue damage or degenerative diseases
Why don’t all cells go through the cell-cycle at the same rate?
Because some cells receive more wear and tear than others and are more active than other cells. Eg Skin cells are constantly replaced, whereas neurons are not replaced at all.
What is being monitored at each stage?
Check if they are abnormal in any way:
- DNA Damage, extra chromosome, grown to correct size
