Topic 10 - The Cell Cycle Flashcards
Why do cells reproduce?
GROWTH: Multicellular organisms grow in size by increasing their cell number through replication.
REPAIR AND MAINTENANCE: Cells that become damaged or die resultant of injury or normal functioning (wearing out) must be repaired and replaced by replication.
REPRODUCTION: In unicellular organisms
DIFFERENTIATION: Cells that divide by mitosis may become differentiated (root tip of plants, mammalian embryo)
What is the cell cycle?
An exact mechanism to ensure that genetic info can be passed WITHOUT ERROR from one cell to two daughter cells of the next generation.
Why is DNA replication referred to as semi-conservative?
The outcome of DNA replication is the production of 2 new double helix molecules in the Synthesis stage of Interphase.
Single stranded chromosomes (1 molecule of DNA) become double stranded (2 molecules of DNA).
Each new double strand consists of 1 parental strand (from original DNA helix) and 1 daughter strand (formed from free floating nucleotides attaching to complementary bases).
Thus, semi conservative as one strand is conserved/retained from the previous generation.
What is mitosis?
Division of nucleus into 2 new identical nuclei. Process involved in production of new cell genetically identical to original cell.
What is the purpose of mitosis?
To separate the replicated DNA into two identical daughter cells. Grow, repair, replace, differentiate.
What is cytokinesis?
The division of the cytoplasm occurring after mitosis. The cytosol and organelles distribute around the new nuclei and become enclosed within an entire plasma membrane.
Plant vs Animal cell in cytokinesis?
Cytokinesis
(Cytokinesis is a process distinct from telophase and mitosis) ANIMAL CELLS: Pinching in of cell membrane between newly formed nuclei by contracting ring of microfilaments
PLANT CELLS: Cell plate forms between the groups of chromosomes giving rise to new cell wall for each cell
Describe interphase.
Interphase
(cell spends majority of life in this phase, distinct from mitosis)
GAP 1
• Growth – cell cytosol increases
• Mitochondria and chloroplasts (if present) divide
• Proteins synthesised for DNA replication
SYNTHESIS S STAGE
• DNA replication occurs
• Chromosome duplication
GAP 2
• Further cell growth preparing for division (mitosis)
• Synthesis of proteins forming the microtubules of the spindle
Describe prophase of mitosis.
- Nuclear membrane disappears
- Chromosomes appear and condense to form double stranded ‘X’
- Nuclear membrane gone
Describe metaphase of mitosis
- Chromosomes line up on spindle equator
- Mitotic spindle fully formed
- Centromeres attach to the spindle
Describe anaphase of mitosis.
- Centromere divides double stranded chromosomes separated into sister chromatids
- Sister chromatids move to opposite poles as microtubules shorten
Describe telophase of mitosis.
- Chromosomes decondense
* New nuclear membranes form around chromosomes at opposite ends of the cell
What occurs at the G1 checkpoint of Mitosis?
DNA is checked for damage or uncompletedness. If so, may enter GO quiescent non-dividing stage or is targeted for destruction.
Occurs at Gap 1 of Interphase.
What occurs at the G2 checkpoint of mitosis?
Replicated DNA is checked for completeness and lack of damage. Can then advance to the first stage of mitosis, prophase.
Occurs at Gap 2 of Interphase.
What occurs at the M checkpoint of Mitosis?
Sister chromatids are checked to be attached to correct microtubules of spindle so sister chromatids are pulled in opposite directions to correct spindle pole.
Occurs at the Metaphase stage of Mitosis.
