Lecture 10: Cell Division Flashcards
What are the three possible destinies of a cell?
Live and function without dividing
Grow and divide
Die
Various signals tell a cell which path to take
What is homeostasis in the context of cell proliferation?
Balance between cell proliferation and cell death (Apoptosis)
What is mitosis?
The process in which the nucleus turns into two nuclei
What does the cell theory state?
All organisms are made of cells and all cells come from pre-existing cells
What is somatic cell division?
Mitosis – diploid (2n) to diploid (2n)
What is reproductive cell division?
Meiosis - diploid (2n) to haploid (1n)
What is the primary reason somatic cells divide?
Growth and development, tissue renewal
What is the result of somatic cell division?
Two daughter cells that are genetically and functionally identical to the parent cell.
Do all somatic cells divide?
Many, but not all; some divide more than others
What phase are somatic cells in most of the time?
Interphase
What is M Phase (Mitotic Phase)?
Mitosis + Cytokinesis
What is the length of interphase dependent on?
Cell type
What occurs during the G₁ phase of interphase?
Cell grows larger, metabolically active, duplicates organelles and cytosolic components
What happens during the S (Synthesis) phase of interphase?
DNA replication occurs, strands are separated at the hydrogen bonds holding the nucleotides together, new strand of DNA is synthesized opposite each of the old strands.
What happens during the G₂ phase of interphase?
Checks for correct DNA synthesis
Prepares for the Mitotic phase (synthesis of the proteins and enzymes required,
gathering of reactants)
Replication of centrosomes is completed
What is a sister chromatid?
Identical chromatids formed during DNA replication that are cross at the centromere
What checks occur at the G₁ checkpoint?
• Is the DNA undamaged?
• Is cell size and health/nutrition OK?
• Are appropriate signals present?
What happens if a cell does not pass the G₁ checkpoint?
May exit to G₀
What occurs during prophase of mitosis?
Nuclear membrane dissolves and DNA thickens; centrosomes move to opposite ends and form spindle fibers (microtubules)
What occurs during metaphase of mitosis?
Chromosomes “line” up in the center of the cell
Spindle Fibers grow towards the DNA chromosomes and the other centrosome
The Spindle Fibers attach to the centromeres on the chromosomes and pull/push them into the middle of the cell
What occurs during anaphase of mitosis?
Sister chromatids separate, each now considered an independent chromosome
Chromomeres are now called kinetochores
Chromosomes are pulled apart by spindle fiber, to opposite ends of the cell before the nuclear envelope reforms in telophase
What occurs during telophase in mitosis?
Two new nuclei form and chromosomes unwind
Cleavage furrow as the cells divide
What is cytokinesis?
Cell divides into two, happens in parallel to mitosis
Where does meiosis occur?
In the gonads (ovaries and testes)
What is produced during meiosis?
Gametes which are haploid (a single set of 23 chromosomes)
Cells genetically different from the parent cell
What is synapsis in meiosis?
Pairing of homologous chromosomes during prophase I
What occurs during crossing over in meiosis?
Non-sister chromatids exchange genetic material
How many haploid cells are produced at the end of meiosis II?
4
What is the difference between meiosis I and meiosis II?
Meiosis I separates homologous chromosomes; Meiosis II separates sister chromatids
What are homologous chromosomes?
Pairs of chromosomes that have the same genes in the same order, but may have different alleles
What is the number of divisions in mitosis?
One, including prophase, prometaphase, metaphase, anaphase, and telophase
What is the number of divisions in meiosis?
Two, each including prophase, metaphase, anaphase, and telophase
What are sources of genetic variation in meiosis?
- independent assortment at metaphase I (2²³ >8 million possible combinations)
- crossing over at prophase 1 (~1-3 crossover events per pair)
- fusion between two gametes (> 2²³ times 2²³ combinations!!!)
What are the steps of the eukaryotic cell cycle?
Mitotic phase -> G₁ phase -> S phase -> G₂ phase -> mitotic phase
What is interphase?
G₁ phase, S phase, and G₂ phase
Most cells of the body are performing there functions in interphase
What occurs in the G1 phase?
Most cellular activities - the duration varies from cell to cell
What occurs in the S phase?
DNA replication - 23 sets of chromosomes before exist as single chromatids, they become 23 sets of chromosomes which are formed from two sister chromatids pairing up
What occurs in the G2 phase?
Checks for correct DNA synthesis
Preparation for mitosis (synthesis of proteins and enzymes, gathering of reactants)
Replication of centrosomes (made up of centrioles which organise microtubules)
Crossover between homologous chromosomes occurs during…?
metaphase I
