Cell Division Flashcards
The 4 Phases of Mitosis
Prophase
Metaphase
Anaphase
Telophase
Prokaryotic and Eukaryotic Cells Division
Prokaryotic divides through binary fission
Eukaryotic divides through mitosis
Cell proliferation in Tissue Repair
Wounds to many prats of the body can heal by using cell division to replace lost cells. This depends on the presence of undifferentiated stem cells that can divide and then differentiate.
If there are basal cells present in the skin, they can regenerate outer layers of skin in a few days
If the damage in the skin is so severe that there’s no stem cells, then skin grafts may be needed
Mitosis VS Meiosis
Takes place in body cells
Takes place in germ cells
Produces body cells
Produces gametes
Has 1 division
Has 2 divisions
2 identical diploid daughter cells are formed
4 different haploid daughter cells are formed
No crossing over
Crossing over
No variation
Variation
Purpose of Control of Cell Division
Ensures that each daughter cell receives an exact copy of their parent’s DNA
Maintains proper cell numbers by preventing uncontrolled division
Allows for cell differentiation to create various cell types
Allows for organism growth, tissue repair, and wound healing
Meiosis
Reduction division in which the chromosome number is halved from diploid o haploid, resulting in genetically different cells
Telophase I Events
Spindle microtubules disintegrate, and each chromosome from the homologous pair is found at opposite poles
A nuclear membrane starts reforming around each daughter nucleus
The membrane divides through Cytokinesis I
Chromosomes uncondensed and uncoil
Crossing Over and Process
Exchange of alleles between non-sister chromatids of homologous chromosomes
In Prophase I, homologous chromosomes undergo synapsis thus forming a bivalent
A cut called SSB (Single Stranded Break) is made at the same part of DNA of each of the non-sister chromatids
Each non-sister chromatid re-joins with its homologous partner where they can then exchange genetic material through the chiasmata.
The chromatids formed after crossing over are called recombinant chromatids
Telophase Events
Microtubule spindle fibers disintegrate
The nuclear membrane reforms around the daughter chromosomes
Chromosomes uncondensed and coil back to become no longer visible
During the entire process of mitosis, the cell undergoes cytokinesis and ends in telophase
Prophase Events
Chromatin condense into chromosomes by supercoiling and becoming visible
The nuclear membrane starts disappearing
Centrosomes move to opposite poles of the cell and the microtubules start to form
Kinetochores start to appear on centromeres
Oogenesis Unequal Cytokinesis
Oogonia grows into primary oocyte
Primary oocyte undergoes Meiosis I which results in unequal cytokinesis
A large secondary oocyte forms which contains most of the cytoplasm which will become the mature egg, but the other daughter cell (polar body) has very little cytoplasm and eventually degenerates
Interphase Processes
DNA Replication
Organelle Duplication
Cell Growth
Transcription and Translation
Protein Synthesis
Cell Growth during Interphase
DNA Replication: DNA is doubled through replication
Cytoplasmic Growth: Volume of the cytoplasm increases
Organelle Duplication: Mitochondria and chloroplast divide, mb-bound bud off from existing ones, and non-mb bound are assembled from the beginning
Protein Synthesis Cell synthesizes more proteins for more cellular processes
Metaphase I Events
The nuclear membrane is fully broken down
The paired up homologous chromosomes line up at the equator randomly and independently of each other
The spindle microtubules attach to the centromeres of the homologous chromosomes
Importance of Centromere
Essential for the proper segregation of chromosomes during cell division
Condensation of Chromosomes
Nucleosomes wrap in a helical fashion to form a thick supercoil that stack over each other forming a single thick fiber named chromatin
Chromatin coils even further to form chromosomes which carries genetic information in the form of genes
Metaphase Events
Nuclear membrane disappears completely
Microtubules grow and attach to centromere’s kinetochores, and move them to align both sister chromatids towards the equator of the cell
Each sister chromatid faces a pole, and the spindle fibers are fully developed
Budding Unequal Cytokinesis
A small bud sticks out from the parent yeast cell
The cytoplasm and organelles are unequally distributed, with the bud receiving a smaller portion compared to the parent cell
Over time, the bud grows and separates from the parent cell and becomes a new independent yeast cell
Homologous Chromosomes
Pairs of non-identical chromosomes in a diploid cell that are inherited from parents. They have same length, gene sequence, centromere positions, and same gene locus. They only differ from each other by alleles
Mitotic Index
A measure of how fast cells are dividing
Formula is:
Cells in mitosis / total number of cells
Characteristics of Cancer Cells
Do not differentiate
Have abnormal nuclei
Form tumor
Undergo metastasis
Benign VS Malignant
Slow pace
Rapid and uncontrolled pace
Do not spread from site of origin
Detach and spread throughout the body
Unlikely to cause harm
Can cause harm and made of the same type of cell as the primary tumor
Not life-threatening
Life-threatening, known as cancer
Interphase Stages
G1: Where the cell grows and duplicates organelles and synthesizes proteins
S: Where DNA is replicated
G2: Where the cell continues to grow and make proteins needed for metabolic reactions in mitosis
Prophase I Events
Replicated chromosomes condense by supercoiling and becoming visible
Replicated homologous chromosomes pair up to form bivalent and undergo crossing over
Spindle fibers form and stretch out from each pole to the equator
The nuclear membrane starts to break down
Cytokinesis in Plant Cell
Vesicles that come from the Golgi move to the center of the cell, and fuse together to form a cell plate. The cell plate continues to develop until it joins with the cell’s plasma membrane which completes the division of the cytoplasm, then both daughters secrete cellulose to form their new cell walls.
Cell Proliferation in Growth
In animals, the zygote divides rapidly by mitosis and becomes and embryo. This continues until the animal reaches an adult size where growth and cell proliferation stops
In plants, meristems, unspecialized cells found at the tip of a shoot and a root, are where cell proliferation occurs.
Anaphase Events
Kinetochores use spindle fibers to split the centromere of each sister chromatid, thus pulling them to opposite poles
Each sister chromatid becomes a chromosome
Haploid and Diploid
Haploid: Contains one set of chromosomes and formed by meiosis
Diploid: Contains two sets of chromosomes and formed by mitosis
Cytokinesis in Animal Cell
A contractile protein ring forms around the equator of the cell and pulls the plasma membrane inwards. This inward pull is called the cleavage furrow, and when the cleavage furrow reaches the center of the cell it is pinched apart to form two daughter cells
Meiosis I VS Meiosis II
Synapsis and crossing over occurs in Prophase I
Synapsis and crossing over doesn’t occur in Prophase II
Homologous pairs of chromosomes line up in the equator
Sister chromatids line up in the equator
Homologous pairs of chromosomes separate and move to opposite poles of the cell
Sister chromatids separate and move to opposite poles of the cell
2 haploid cells are formed
4 haploid cells are formed
Down Syndrome and Non-disjunction
Non-disjunction is when chromosomes fail to separate during gamete formation
Can happen in Anaphase I or II
In Anaphase I, the chromosomes pair fail to separate properly which results in the formation of 4 abnormal cells
In Anaphase II, the sister chromatids fail to separate properly which results in the formation of 2 abnormal cells
How do Chromosomes Move
Kinetochores and Microtubules
Kinetochores are protein complexes that form on the centromere during cell division, and provide an attachment point for spindle fibers with the centromere region
Microtubules are hollow cylinders that can rapidly assemble and disassemble at the centrosome
Microtubules and Kinetochores work together by lengthening and shortening the microtubules to move chromosomes during cell division
Anaphase I Events
Homologous chromosomes pairs are pulled to opposite poles thus halving the chromosome number
Centromeres do not split
Independent Assortment
In Metaphase I, bivalents line up randomly and independently of each other on the equator
Since they line up in any orientation on the equator, they segregate randomly
The possible combination of gametes depends on the number of homologous pairs and is calculated using 2^n,where n is the haploid number of chromosomes
Cyclins
Proteins that control the progression of cells through the cycle, and act as checkpoints between two stages to ensure every task is performed
Cyclins bind to enzymes named CDK’s (cyclin dependent kinases) which phosphorylate specific proteins therefore making them become active and carry out tasks to continue the cell cycle. After the event occurred, the cyclin is degraded and the CDK is inactive
Cell Proliferation
A rapid increases in the number of cells, and happens when cell division happens at a faster rate than cell death
Used in multicellular organisms for growth, cell replacement and tissue repair
Cell Proliferation in Cell Replacement
When cells are lost from the epidermis of the skin, more cells are produced to replace them
Cell division happens in the basal later of the epidermis. The cells then get moved towards the skin surface by continued cell division. The continuous cell division allows for the production of a tough protein called keratin, which is hydrophobic and causes cells to dry out, and by the time the cells reach the skin surface they’re flattened and dead.
