lecture 10: the cell cycle Flashcards
3 elements of Cell Theory?
- All organisms are made of one or more cells
- Cell is fundamental unit of structure and functions in organisms
- All cells come form pre-existing cells
What happens during cell division (generally) and it requires the division of… (2 elements)?
- 1 parent cell gives rise to 2 or more daughter cells
- Division of 1. The nucleus (or nucleoid region) and of 2. The cytoplasm
What are the two types of cell division in eukaryotes and what are they based on?
- Mitotic cell division (mitosis)
- Meiotic cell division (meiosis)
- Based on how the nucleus is divided
3 characteristics of mitosis?
- Daughter cells contain same number of chromosomes as parent cell
- Daughter cells are genetically identical
- Produce somatic (body) cells/clones of unicellular organisms
3 characteristics of meiosis?
- Daughter cells contain half the number of chromosomes in parent cell
- Daughter are genetically unique
- Produce gametes/spores for reproduction
Mitosis/meiosis divide the… and cytokinesis divides the…?
- nucleus
- cytoplasm
3 functions of mitosis?
- Asexual reproduction in unicellular and multicellular organisms
- Growth and development of multicellular organisms
- Tissue repair and renewal in multicellular organisms
What is the cell cycle?
Ordered sequence of events in the life of a cell (from origin to its division)
How and why are the steps in the cell cycle monitored?
- Monitored by a molecular regulatory system
- Not well-monitored = lose control = can lead to cancer
What are the 2 major phases in the cell cycle?
- Interphase (90%): G1, S (DNA synthesis), G2
2. Mitotic (M) phase (10%)
What is the mitotic spindle apparatus and what is it composed of?
Dynamic structure formed from cytoskeletal fibers called microtubules that are produced form the centrosome of the cell
What are the 2 functions of the mitotic spindle apparatus and what are used to accomplish those functions?
- Provides forces for moving chromosomes: Kinetochore microtubules –> attach to the kinetochore and pull chromosomes
- Provides forces for cell elongation: Polar microtubules –> interact with polar microtubules from opposite poles and push to elongate the cell
What needs to be done during G1 and G2? (3)
Cell need to make materials to grow
- Proteins
- Plasma membrane and cytoplasm components
- Replicate organelles, duplicate centrosomes
What is done during the S phase?
Replication of all chromosomes
What are the 8 things that are done during the mitotic (M) phase (cell division)?
- Chromosomes need to condense
- Microtubule machinery needs to be made
- Nuclear envelope needs to break down
- Spindle fibers need to contact chromosomes
- Spindle fibers need to pull sister chromosomes to opposite poles of cell
- Nuclear membrane needs to re-form
- Mitotic spindle needs to be dissembled
- Cytoplasm needs to be divided (cytokinesis)
STEPS OF CELL. DIVISION: What are the 6 phases of mitosis + 2 steps of cytokinesis + small description?
- Interphase: just after all chromosomes + centrosomes have been replicated
- Prophase: chromosomes condense + spindle apparatus is starting to form
- Prometaphase: chromosomes are in most compact form + nuclear membrane is broken down + kinetochore microtubules contact chromosomes at kinetochore
- Metaphase: chromosomes aligned in middle of cell
- Anaphase: sister chromatids are separated and pulled to opposite poles of cell
- Telophase: cleanup —> nuclear envelopes are reformed + spindle apparatus is dissembled + chromosomes are less compact
CYTOKINESIS: - Cell starts to divide into two: actin-myosin ring causes plasma membrane to begin pinching in —> cytoplasm is divided
- Cell division is completed: two daughter cells form
How does cytokinesis happen in ANIMAL cells? (3)
Cleavage Furrow Formation
- Appearance of a cleavage furrow: trench in the middle of the parent cell
- Contractile ring composed of cytoskeletal fiber called actin microfilaments + myosin (motor protein)
- Pinches cell into two daughter cells
How does cytokinesis happen in PLANT cells? (3)
Cell Plate Formation
- Vesicles from Golgi apparatus carry plasma membrane + cell wall materials to the center of the parent cell
- Cell plate forms in between the 2 daughter nuclei
- Cell plate grows to separate the cells: plasma membrane surround each new cell with immature cell walls between each daughter cell
Why can’t a plant cell use a cleavage furrow for cytokinesis?
Because of its cell wall
How do prokaryotic cell divide? (4 steps)
Using binary fission
- Chromosomes replicate & each is anchored to cell membrane
- Chromosomes move apart in 2 groups & ring of FtsZ protein forms
- FtsZ ring constricts: membrane and cell wall infold
- Fission complete as cell is split into two genetically identical cells
What (2) uses binary fission to replicate semi-autonomously?
- Mitochondria
- Plastids
—> Evidence that eukaryotic cells are related to prokaryotic cells (endosymbiont theory)
How does the cell cycle varies in length?
Caused by variation in the length of G1 (more or less cell growth)
- Some cells divide rapidly (hours; intestinal cells) or slowly (years; liver cells)
What is the cell cycle control system?
Monitors progression through the cell cycle and regulates the steps involved
—> Tightly regulated
What does the cell cycle control system ensure? (3)
- Ensures that cell initiates the cycle only when appropriate cues are present (ex: damaged cells)
- That each step is carried out in correct sequence (phases of mitosis)
- That each step has been properly completed before continuing
