Unit 2 : Chapter 9 Flashcards
The cell cycle
The complete series of events from one cell division to the next, it ensures that genetic information can be passed without error from one cell to two daughter cells of the next generation.
Key events in the cell cycle
Interphase
Mitosis
Cytokinesis
Interphase
In the mitotic cell cycle, the period of cell growth and DNA synthesis
During interphase are chromosomes visible with a light microscope?
No
Stages of interphase
G1
Synthesis
G2
Gap 1
- the cell undergoes growth
- synthesises proteins required for DNA replication
- mitochondria/chloroplasts divide
- either continues into G0 stage or into synthesis
G0
Is the stage where the cell is just existing carrying out its daily functions
Quiescence (not dividing) stage
Synthesis
- The parent cell replicates or synthesises its DNA
- In the end, there are 2 identical copies of DNA
Gap 2
- Further growth in preparation for division
- Synthesis of proteins for spindle fibres
- By the end, the cell has doubled in size
How long does a typical human cell take to complete the cell cycle?
24 hours
Mitosis phases
Prophase
Metaphase
Anaphase
Telophase
Prophase
Chromosomes gradually condense - becoming shorter and thicker - and become visible as double-stranded structures.
The spindle forms and the nuclear membrane breaks down
Metaphase
The double-stranded chromosomes, dyads, lines up around the equator of the cell
Anaphase
The sister chromatids separate and are pulled to opposite ends of the spindle by the contraction of the spindle fibres
Telophase
A nuclear membrane forms around each separate group of single-stranded chromosomes and the chromosomes gradually decondense.
Chromatid
Visible as a double, thread-like structures held together in a constricted region and are held together by a centromere
Cytokinesis
Division of cytoplasm occurring after mitosis
Animals - The bridge of the cytoplasm pinches and separates the nuclei
Plant - A cell plate forms between the 2 groups of chromosomes to form a new cell wall
Differences in mitosis in animal and plant cells
Only occurs in plants meristems
Plants lack a centriole
Plants have a cell plate
Animals cleavage furrows
Binary fission
The process of cell multiplication in bacteria and other unicellular organisms in which there is no formation of spindle fibres and no chromosomal condensation
Steps of binary fission
DNA copies itself
Prokaryotic cell elongates and DNA separates
The cell begins to contract in the middle, dividing its contents (cytokinesis)
Cells separate and 2 identical daughter cells are produced
Checkpoints in the cell cycle
G1 checkpoint
G2 checkpoint
M checkpoint
G1 checkpoint
Occurs at Gap 1
Check if the DNA is damaged or incomplete and enters the quiescent stage and it may be fixed or kill itself
G2 checkpoint
Occurs at Gap 2
Replicated DNA is checked for damage if cleared it can then undergo mitosis
M checkpoint
Occurs at metaphase
Check that the sister chromatids are attached to the correct microtubules of the spindle
Mitotic spindle
Made up of centrioles and microtubules for the chromatids to be separated into the two parts
Why is the cell cycle important?
Growth - to increase the number of cells
Repair and maintenence - replacing dead or damaged cells
Reproduction - to make way for the new generation of cells
Cells that go through cell division constantly
Basal stem cells of the epidermis
Intestinal stem cells of the gut
Haematopoietic stem cells
What happens when cell division goes wrong?
Psoriasis
Cancer
