10.2 The Cell Cycle

10.2 The Cell Cycle

• The chromatin fiber is coiled into the nucleosomes.
• The chromosomes condense even more when a cell undergoes a mitosis.

• The S phase of interphase is the part of DNA that replicates and must always precede it.
• When fully compact, the pairs of identically packed chromosomes are bound to each other.
• The sister chromatids are visible under a light microscope.
• The centromeric region is very small and will look like a constricted area.

• The animation shows the different levels of packing.

• Cells on the path to cell division go through a series of timed and carefully regulated stages of growth, which eventually leads to the creation of two identical (clone) cells.
• There are two major phases in the cell cycle.
• In which case cells with multiple nuclei are produced, interphase and mitosis may take place without cytokinesis.

• The nuclear DNA is duplicated when the cell grows.
• The Interphase is followed by the mitotic phase.
• The duplicated chromosomes are divided into daughter nuclei.
• The cytoplasm is usually divided by cytokinesis, resulting in two genetically identical daughter cells.

• During interphase, the cell undergoes normal growth processes.
• Many internal and external conditions must be met in order for a cell to move.
• Three stages of interphase are called G1, S, and G2.

• The cell is active at the biochemical level during the G1 stage.
• The cell has enough energy to complete the task of replicating each chromosomes in the nucleus.

• Nuclear DNA is in a semi-condensed configuration.
• During the S phase, the centrosome is duplicated.
• Centrioles help organize cells.

• Some cells are duplicated and the cytoskeleton is dismantled.

• During G2, there may be additional cell growth.
• Before the cell can enter the first stage of mitosis, final preparations need to be completed.

• The process of aligning the duplicated chromosomes and moving them into two new daughter cells is called the mitotic phase.
• The physical separation of the cytoplasmic components into the two daughter cells is called cytokinesis and is part of the second portion of the mitotic phase.

• You can revisit the stages at this site.

• The five stages of Karyokinesis are prophase, prometaphase, metaphase, anaphase, and telophase.
• The black background of the cells artificially stained by fluorescent dyes was used to take the pictures at the bottom.

• The kinetochore is attached to the spindle.
• The sister chromatids separate.

• The kinetochore is attached to the spindle.
• The sister chromatids separate.

• The sister chromatids separate from the kinetochore.

• The sister chromatids separate.

• The centrosomes move to opposite poles of the cell when the nucleolus disappears.

• The remnants of the nuclear envelope fragment continue to grow as more microtubules form and stretch across the former nuclear area.
• The chymosomes are even more dense.

• Some of the microtubules come into contact with the kinetochores as they extend from the centrosomes.
• The chromosomes will be oriented until the kinetochores of sister chromatids face the opposite poles.
• All the sister chromatids will be attached via their kinetochores.
• The microtubules overlap each other midway between the two poles.
• The sarcophagus are located near the poles and aid in spindle orientation.

• Microtubules from opposite poles attach to each sister at the kinetochore.
• The chromosomes are pulled toward the opposite poles when the connection between the sisters breaks down.

• The chromatid's are tightly attached to each other.
• The chromosomes are very small.

• The centrosome is where the microtubule is attached.
• As the polar microtubules slide against each other at the metaphase plate, the cell becomes omb shaped.

• tubulin monomers are used to assemble the components for each daughter cell.
• Nuclear envelopes form around the chromosomes.

• Cell division isn't complete until the cell components are separated from the two daughter cells.
• The process of cytokinesis is different for plants that have cell walls than it is for other eukaryotes.

• Late anaphase is when cytokinesis starts in animal cells.

• The actin filaments pull the equator of the cell inward.

• The actin ring contracts as the furrow deepens, and then the membrane is cleaved in two.

• A new cell wall is formed between the daughter cells.
• During interphase, the Golgi apparatus breaks into vesicles and distributes its contents throughout the dividing cell.

• Golgi vesicles are transported on microtubules to form a vesicular structure at the metaphase plate.
• The cell plate enlarges as more vesicles are added to the cell.
• A new cell wall is built by using the glucose that has accumulated between the layers.
• The Golgi membranes are on either side of the cell wall.

• The ring splits the cell in two.
• Golgi vesicles coalesce at the former metaphase plate in plant cells.
• A cell plate formed by the fusion of the vesicles of the phragmoplast grows from the center toward the cell walls, and the membranes of the vesicles form a plasma membrane that divides the cell in two.

• Not all cells follow the classic cell-cycle pattern in which a newly formed daughter cell immediately enters the interphase, followed by the mitotic phase and cytokinesis.
• Some cells enter G0 temporarily due to environmental conditions.
• The cell will remain in this phase until conditions improve or an external signal causes G1 to start.
• The mature cardiac muscle and nerve cells are in G0 permanently.

• The number of cells in each identifiable cell-cycle stage will give an estimate of the time it takes for the cell to complete that stage if 100 cells are examined.

• Under the scanning objective of a light microscope, place a fixed and stained microscope slide of whitefish blastula cross-sections.

• Use the low-power objective of your microscope to locate one of the sections.
• There are dozens of closely packed individual cells in the section.

• The cells are visible, but the chromosomes are small.

• If you want to see all the cells in the section, you have to switch to the high-power objective.
• Most of the cells are in the interphase period of the cell cycle, which means they aren't going through the process of mitosis.

• Scan the whitefish blastula cells with the high-power objective illustrated in the image.

• Use the drawings of the stages as a guide to identify the various stages of the cell cycle.

• Once you are confident about your identification, begin to record the stage of each cell you encounter as you go across the blastula section.

• When you reach 100 cells, stop and keep a tally of your observations.

• The bigger the sample size, the more accurate the results will be.
• Before calculating percentages and making estimates, gather and record group data.