Directed Reading for Content Mastery Overview Cell Processes Answers

Learning Objectives

By the terminate of this section, you will be able to:

• Describe the 3 stages of interphase
• Talk over the behavior of chromosomes during karyokinesis
• Explain how the cytoplasmic content is divided during cytokinesis
• Ascertain the quiescent G₀ phase

The cell wheel is an ordered series of events involving prison cell growth and cell division that produces two new daughter cells. Cells on the path to cell division go on through a series of precisely timed and carefully regulated stages of growth, DNA replication, and sectionalization that produces two identical (clone) cells. The jail cell cycle has ii major phases: interphase and the mitotic phase (Figure 1). During interphase, the cell grows and DNA is replicated. During the mitotic stage, the replicated Deoxyribonucleic acid and cytoplasmic contents are separated, and the cell divides.

Figure 1. The cell cycle consists of interphase and the mitotic phase. During interphase, the cell grows and the nuclear Deoxyribonucleic acid is duplicated. Interphase is followed by the mitotic phase. During the mitotic phase, the duplicated chromosomes are segregated and distributed into daughter nuclei. The cytoplasm is usually divided as well, resulting in ii girl cells.

Interphase

During interphase, the cell undergoes normal growth processes while also preparing for cell division. In order for a cell to move from interphase into the mitotic phase, many internal and external weather must exist met. The three stages of interphase are called 1000₁, S, and G₂.

One thousand_one Phase (First Gap)

The first phase of interphase is chosen the G₁ stage (beginning gap) because, from a microscopic aspect, fiddling modify is visible. Nevertheless, during the Thou₁ stage, the cell is quite active at the biochemical level. The cell is accumulating the building blocks of chromosomal DNA and the associated proteins as well equally accumulating sufficient free energy reserves to complete the task of replicating each chromosome in the nucleus.

S Phase (Synthesis of DNA)

Throughout interphase, nuclear DNA remains in a semi-condensed chromatin configuration. In the S stage, Dna replication can proceed through the mechanisms that result in the germination of identical pairs of DNA molecules—sister chromatids—that are firmly attached to the centromeric region. The centrosome is duplicated during the Southward phase. The two centrosomes volition give ascent to the mitotic spindle, the apparatus that orchestrates the motion of chromosomes during mitosis. At the centre of each animal cell, the centrosomes of animate being cells are associated with a pair of rod-like objects, the centrioles, which are at right angles to each other. Centrioles assist organize jail cell division. Centrioles are not present in the centrosomes of other eukaryotic species, such as plants and most fungi.

G_ii Phase (Second Gap)

In the G₂ stage, the cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation. Some jail cell organelles are duplicated, and the cytoskeleton is dismantled to provide resources for the mitotic phase. There may be additional prison cell growth during 1000₂. The terminal preparations for the mitotic phase must exist completed before the jail cell is able to enter the first stage of mitosis.

The Mitotic Phase

The mitotic phase is a multistep process during which the duplicated chromosomes are aligned, separated, and move into 2 new, identical girl cells. The start portion of the mitotic phase is called karyokinesis, or nuclear partitioning. The 2d portion of the mitotic phase, called cytokinesis, is the physical separation of the cytoplasmic components into the two daughter cells.

Karyokinesis (Mitosis)

Karyokinesis, also known every bit mitosis, is divided into a series of phases—prophase, prometaphase, metaphase, anaphase, and telophase—that result in the division of the cell nucleus (Figure two). Karyokinesis is also called mitosis.

Art Connection

Effigy two. Karyokinesis (or mitosis) is divided into five stages—prophase, prometaphase, metaphase, anaphase, and telophase. The pictures at the bottom were taken by fluorescence microscopy (hence, the black background) of cells artificially stained by fluorescent dyes: blue fluorescence indicates Dna (chromosomes) and green fluorescence indicates microtubules (spindle apparatus). (credit "mitosis drawings": modification of work past Mariana Ruiz Villareal; credit "micrographs": modification of work past Roy van Heesbeen; credit "cytokinesis micrograph": Wadsworth Center/New York State Department of Health; calibration-bar data from Matt Russell)

Which of the following is the correct order of events in mitosis?

1. Sister chromatids line up at the metaphase plate. The kinetochore becomes fastened to the mitotic spindle. The nucleus reforms and the prison cell divides. Cohesin proteins intermission down and the sister chromatids separate.
2. The kinetochore becomes attached to the mitotic spindle. Cohesin proteins suspension down and the sister chromatids split. Sister chromatids line upwardly at the metaphase plate. The nucleus reforms and the cell divides.
3. The kinetochore becomes fastened to the cohesin proteins. Sister chromatids line up at the metaphase plate. The kinetochore breaks down and the sis chromatids separate. The nucleus reforms and the prison cell divides.
4. The kinetochore becomes attached to the mitotic spindle. Sister chromatids line up at the metaphase plate. Cohesin proteins suspension downwardly and the sis chromatids split. The nucleus reforms and the prison cell divides.

During prophase, the "first phase," the nuclear envelope starts to dissociate into small vesicles, and the membranous organelles (such as the Golgi complex or Golgi apparatus, and endoplasmic reticulum), fragment and disperse toward the periphery of the cell. The nucleolus disappears (disperses). The centrosomes begin to move to opposite poles of the prison cell. Microtubules that will form the mitotic spindle extend between the centrosomes, pushing them farther apart as the microtubule fibers lengthen. The sister chromatids begin to coil more tightly with the assistance of condensin proteins and become visible nether a light microscope.

Effigy 3. During prometaphase, mitotic spindle microtubules from opposite poles attach to each sister chromatid at the kinetochore. In anaphase, the connection between the sister chromatids breaks downwards, and the microtubules pull the chromosomes toward reverse poles.

During prometaphase, the "commencement change phase," many processes that were begun in prophase go along to advance. The remnants of the nuclear envelope fragment. The mitotic spindle continues to develop as more than microtubules get together and stretch across the length of the former nuclear area. Chromosomes become more condensed and discrete. Each sister chromatid develops a poly peptide structure called a kinetochore in the centromeric region (Figure iii). The proteins of the kinetochore attract and bind mitotic spindle microtubules. As the spindle microtubules extend from the centrosomes, some of these microtubules come into contact with and firmly bind to the kinetochores. In one case a mitotic fiber attaches to a chromosome, the chromosome volition be oriented until the kinetochores of sis chromatids face the opposite poles. Somewhen, all the sis chromatids will be attached via their kinetochores to microtubules from opposing poles. Spindle microtubules that do not appoint the chromosomes are called polar microtubules. These microtubules overlap each other midway betwixt the two poles and contribute to cell elongation. Astral microtubules are located almost the poles, help in spindle orientation, and are required for the regulation of mitosis.

During metaphase, the "modify phase," all the chromosomes are aligned in a aeroplane called the metaphase plate, or the equatorial aeroplane, midway between the two poles of the jail cell. The sister chromatids are still tightly attached to each other by cohesin proteins. At this time, the chromosomes are maximally condensed.

During anaphase, the "upwardly phase," the cohesin proteins dethrone, and the sister chromatids separate at the centromere. Each chromatid, now called a chromosome, is pulled rapidly toward the centrosome to which its microtubule is attached. The jail cell becomes visibly elongated (oval shaped) equally the polar microtubules slide against each other at the metaphase plate where they overlap.

During telophase, the "distance stage," the chromosomes reach the opposite poles and begin to decondense (unravel), relaxing into a chromatin configuration. The mitotic spindles are depolymerized into tubulin monomers that will exist used to get together cytoskeletal components for each daughter cell. Nuclear envelopes class effectually the chromosomes, and nucleosomes appear within the nuclear area.

Cytokinesis

Figure four. During cytokinesis in fauna cells, a band of actin filaments forms at the metaphase plate. The ring contracts, forming a cleavage furrow, which divides the cell in two. In institute cells, Golgi vesicles coalesce at the former metaphase plate, forming a phragmoplast. 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 fuse to form a plasma membrane that divides the cell in 2.

Cytokinesis, or "cell motion," is the second main stage of the mitotic phase during which jail cell division is completed via the physical separation of the cytoplasmic components into two daughter cells. Division is non complete until the cell components have been apportioned and completely separated into the ii daughter cells. Although the stages of mitosis are similar for most eukaryotes, the process of cytokinesis is quite different for eukaryotes that have jail cell walls, such equally establish cells.

In cells such as animal cells that lack jail cell walls, cytokinesis follows the onset of anaphase. A contractile ring equanimous of actin filaments forms simply within the plasma membrane at the former metaphase plate. The actin filaments pull the equator of the jail cell inward, forming a fissure. This fissure, or "scissure," is called the cleavage furrow. The furrow deepens as the actin ring contracts, and eventually the membrane is cleaved in 2 (Effigy 4).

In establish cells, a new jail cell wall must grade betwixt the daughter cells. During interphase, the Golgi apparatus accumulates enzymes, structural proteins, and glucose molecules prior to breaking into vesicles and dispersing throughout the dividing cell. During telophase, these Golgi vesicles are transported on microtubules to course a phragmoplast (a vesicular structure) at the metaphase plate. There, the vesicles fuse and coalesce from the center toward the cell walls; this structure is called a cell plate. As more than vesicles fuse, the cell plate enlarges until it merges with the prison cell walls at the periphery of the cell. Enzymes use the glucose that has accumulated between the membrane layers to build a new prison cell wall. The Golgi membranes go parts of the plasma membrane on either side of the new cell wall (Effigy four).

G₀ Phase

Not all cells attach to the classic cell cycle pattern in which a newly formed daughter jail cell immediately enters the preparatory phases of interphase, closely followed by the mitotic stage. Cells in Grand₀ phase are not actively preparing to divide. The cell is in a quiescent (inactive) stage that occurs when cells exit the prison cell wheel. Some cells enter G₀ temporarily until an external signal triggers the onset of G₁. Other cells that never or rarely separate, such as mature cardiac muscle and nerve cells, remain in Chiliad₀ permanently.

Scientific Method Connection

Determine the Time Spent in Prison cell Bicycle Stages

Trouble: How long does a prison cell spend in interphase compared to each stage of mitosis?

Background: A prepared microscope slide of blastula cross-sections will show cells arrested in various stages of the cell wheel. It is not visually possible to dissever the stages of interphase from each other, but the mitotic stages are readily identifiable. If 100 cells are examined, the number of cells in each identifiable cell cycle phase will give an estimate of the time it takes for the prison cell to complete that stage.

Trouble Statement: Given the events included in all of interphase and those that take place in each stage of mitosis, estimate the length of each stage based on a 24-hour cell bicycle. Before proceeding, land your hypothesis.

Test your hypothesis: Test your hypothesis by doing the following:

1. Place a fixed and stained microscope slide of whitefish blastula cross-sections under the scanning objective of a light microscope.
2. Locate and focus on ane of the sections using the scanning objective of your microscope. Notice that the section is a circle composed of dozens of closely packed private cells.
3. Switch to the low-power objective and refocus. With this objective, individual cells are visible.
4. Switch to the high-power objective and slowly motility the slide left to right, and up and down to view all the cells in the section (Figure 5). Equally you lot scan, you will detect that about of the cells are non undergoing mitosis but are in the interphase period of the cell cycle.

   

   Figure 5.  Slowly scan whitefish blastula cells with the loftier-power objective as illustrated in image (a) to identify their mitotic phase. (b) A microscopic image of the scanned cells is shown. (credit "micrograph": modification of work by Linda Flora; scale-bar information from Matt Russell)

5. Practice identifying the various stages of the cell cycle, using the drawings of the stages equally a guide (Figure 2).
6. Once you are confident most your identification, brainstorm to tape the phase of each prison cell you lot see as you scan left to correct, and acme to lesser across the blastula section.
7. Go along a tally of your observations and finish when yous reach 100 cells identified.
8. The larger the sample size (total number of cells counted), the more accurate the results. If possible, gather and tape group information prior to calculating percentages and making estimates.

Record your observations: Brand a table similar to Table i in which y'all record your observations.

Results of Cell Stage Identification
Phase or Stage	Individual Totals	Grouping Totals	Percent
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Totals	100	100	100 percentage

Tabular array 1

Analyze your information/study your results: To observe the length of fourth dimension whitefish blastula cells spend in each phase, multiply the pct (recorded as a decimal) by 24 hours. Brand a table similar to Table to illustrate your data.

Estimate of Prison cell Phase Length
Phase or Phase	Pct (as Decimal)	Time in Hours
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

Draw a conclusion: Did your results support your estimated times? Were any of the outcomes unexpected? If and then, hash out which events in that stage might contribute to the calculated time.

Section Summary

The cell cycle is an orderly sequence of events. Cells on the path to cell division proceed through a series of precisely timed and advisedly regulated stages. In eukaryotes, the cell cycle consists of a long preparatory menstruum, called interphase. Interphase is divided into G_i, S, and G₂ phases. The mitotic phase begins with karyokinesis (mitosis), which consists of v stages: prophase, prometaphase, metaphase, anaphase, and telophase. The last stage of the mitotic phase is cytokinesis, during which the cytoplasmic components of the daughter cells are separated either by an actin ring (creature cells) or past cell plate formation (plant cells).

Additional Cocky Check Questions

1. Which of the post-obit is the correct order of events in mitosis?

A. Sister chromatids line upwardly at the metaphase plate. The kinetochore becomes attached to the mitotic spindle. The nucleus reforms and the cell divides. Cohesin proteins interruption downwardly and the sister chromatids divide.
B. The kinetochore becomes attached to the mitotic spindle. Cohesin proteins suspension downwardly and the sister chromatids separate. Sister chromatids line up at the metaphase plate. The nucleus reforms and the cell divides.
C. The kinetochore becomes attached to the cohesin proteins. Sis chromatids line up at the metaphase plate. The kinetochore breaks downwardly and the sister chromatids separate. The nucleus reforms and the jail cell divides.
D. The kinetochore becomes attached to the mitotic spindle. Sister chromatids line upwardly at the metaphase plate. Cohesin proteins break downwardly and the sister chromatids separate. The nucleus reforms and the cell divides.

ii. Briefly describe the events that occur in each phase of interphase.

3. Chemotherapy drugs such as vincristine and colchicine disrupt mitosis by bounden to tubulin (the subunit of microtubules) and interfering with microtubule assembly and disassembly. Exactly what mitotic structure is targeted past these drugs and what effect would that take on cell sectionalisation?

four. Draw the similarities and differences between the cytokinesis mechanisms found in animate being cells versus those in constitute cells.

5. Listing some reasons why a cell that has just completed cytokinesis might enter the G₀ phase instead of the G_one phase.

6. What cell cycle events will exist affected in a prison cell that produces mutated (not-functional) cohesin protein?

Answers

1. D. The kinetochore becomes attached to the mitotic spindle. Sister chromatids line upward at the metaphase plate. Cohesin proteins break down and the sis chromatids separate. The nucleus reforms and the cell divides.

2.During G₁, the cell increases in size, the genomic DNA is assessed for damage, and the cell stockpiles energy reserves and the components to synthesize DNA. During the S phase, the chromosomes, the centrosomes, and the centrioles (animal cells) duplicate. During the G₂ phase, the prison cell recovers from the S phase, continues to abound, duplicates some organelles, and dismantles other organelles.

3. The mitotic spindle is formed of microtubules. Microtubules are polymers of the protein tubulin; therefore, it is the mitotic spindle that is disrupted past these drugs. Without a functional mitotic spindle, the chromosomes will not exist sorted or separated during mitosis. The jail cell volition arrest in mitosis and die.4. At that place are very few similarities between animal prison cell and plant cell cytokinesis. In animate being cells, a band of actin fibers is formed effectually the periphery of the jail cell at the former metaphase plate (cleavage furrow). The actin ring contracts inwards, pulling the plasma membrane toward the eye of the prison cell until the cell is pinched in two. In plant cells, a new cell wall must be formed betwixt the daughter cells. Due to the rigid prison cell walls of the parent cell, contraction of the middle of the cell is not possible. Instead, a phragmoplast outset forms. Subsequently, a cell plate is formed in the middle of the cell at the former metaphase plate. The prison cell plate is formed from Golgi vesicles that contain enzymes, proteins, and glucose. The vesicles fuse and the enzymes build a new cell wall from the proteins and glucose. The prison cell plate grows toward and somewhen fuses with the cell wall of the parent cell.5. Many cells temporarily enter G₀ until they reach maturity. Some cells are just triggered to enter G₁ when the organism needs to increment that particular cell type. Some cells only reproduce following an injury to the tissue. Some cells never split up in one case they attain maturity.6. If cohesion is not functional, chromosomes are not packaged subsequently Dna replication in the S phase of interphase. It is likely that the proteins of the centromeric region, such as the kinetochore, would not form. Even if the mitotic spindle fibers could attach to the chromatids without packing, the chromosomes would non exist sorted or separated during mitosis.

Glossary

anaphase: phase of mitosis during which sister chromatids are separated from each other

jail cell cycle: ordered series of events involving cell growth and prison cell division that produces 2 new daughter cells

cell plate: construction formed during constitute cell cytokinesis by Golgi vesicles, forming a temporary structure (phragmoplast) and fusing at the metaphase plate; ultimately leads to the formation of prison cell walls that divide the 2 daughter cells

centriole: rod-like structure constructed of microtubules at the center of each animal cell centrosome

cleavage furrow: constriction formed by an actin ring during cytokinesis in animal cells that leads to cytoplasmic partitioning

condensin: proteins that help sister chromatids coil during prophase

cytokinesis: division of the cytoplasm following mitosis that forms two daughter cells.

G₀ phase: singled-out from the G₁ phase of interphase; a cell in G₀ is non preparing to dissever

G₁ stage: (also, first gap) kickoff stage of interphase centered on cell growth during mitosis

Chiliad₂ phase: (also, second gap) third phase of interphase during which the cell undergoes final preparations for mitosis

interphase: menses of the jail cell cycle leading up to mitosis; includes G₁, South, and G₂ phases (the interim menstruum between two consecutive prison cell divisions

karyokinesis: mitotic nuclear division

kinetochore: protein structure associated with the centromere of each sister chromatid that attracts and binds spindle microtubules during prometaphase

metaphase plate: equatorial plane midway between the two poles of a cell where the chromosomes align during metaphase

metaphase: stage of mitosis during which chromosomes are aligned at the metaphase plate

mitosis: (as well, karyokinesis) flow of the jail cell cycle during which the duplicated chromosomes are separated into identical nuclei; includes prophase, prometaphase, metaphase, anaphase, and telophase

mitotic stage: period of the cell cycle during which duplicated chromosomes are distributed into two nuclei and cytoplasmic contents are divided; includes karyokinesis (mitosis) and cytokinesis

mitotic spindle: apparatus composed of microtubules that orchestrates the movement of chromosomes during mitosis

prometaphase: stage of mitosis during which the nuclear membrane breaks downwards and mitotic spindle fibers adhere to kinetochores

prophase: phase of mitosis during which chromosomes condense and the mitotic spindle begins to grade

quiescent: refers to a jail cell that is performing normal prison cell functions and has not initiated preparations for cell division

Due south stage: second, or synthesis, stage of interphase during which DNA replication occurs

telophase: phase of mitosis during which chromosomes arrive at opposite poles, decondense, and are surrounded by a new nuclear envelope

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Source: https://courses.lumenlearning.com/biology1/chapter/the-cell-cycle/

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