M Phase of the Cell Cycle

Summary

This lesson covers the M phase of the cell cycle, focusing on mitosis and cytokinesis. It reviews the cell cycle phases: G1, S, G2 (interphase), and M (cell division). Mitosis is divided into four stages: prophase (chromosomes form, nuclear membrane disappears), metaphase (chromosomes align at the cell equator), anaphase (sister chromatids separate and move to poles), and telophase (nuclear membranes reform). Cytokinesis follows, dividing the cytoplasm to form two identical daughter cells. In animal cells, this occurs by pinching the cell membrane; in plant cells, a cell plate forms. The M phase results in two identical daughter cells.

Takeaways

• 🔬 The M phase of the cell cycle includes mitosis and cytokinesis, representing cell division.
• 📅 The G1, S, and G2 phases make up interphase, while the M phase follows as the final phase.
• 🔄 Mitosis, the division of the nucleus, is broken down into four phases: prophase, metaphase, anaphase, and telophase.
• 🧬 During prophase, chromatin condenses into chromosomes, and the nucleolus and nuclear membrane disappear.
• 📏 In metaphase, spindle fibers align the chromosomes along the cell's equator, creating an end-to-end alignment.
• 🔗 Anaphase involves spindle fibers separating sister chromatids at their centromeres, pulling them to opposite poles.
• 🎯 Telophase sees the reformation of the nuclear membrane around each set of chromosomes and the nucleolus becoming visible again.
• 🧩 Cytokinesis, the division of the cytoplasm, completes the M phase, resulting in two identical daughter cells.
• 🌱 In animal cells, cytokinesis occurs through the inward pinching of the cell membrane, while in plant cells, a cell plate forms due to the rigid cell wall.
• 📚 Key points: The M phase ends with two daughter cells identical to each other and the original cell, comprising mitosis (nucleus division) and cytokinesis (cytoplasm division).

Q & A

What are the phases of the cell cycle mentioned in the script?

The phases of the cell cycle mentioned are G1, S, G2 (collectively known as interphase), and the M phase (mitosis and cytokinesis).

What occurs during the M phase of the cell cycle?

During the M phase, cell division occurs through two processes: mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm).

What happens during prophase in mitosis?

During prophase, chromatin condenses into chromosomes, the nucleolus disappears, spindle fibers begin to form, and the nuclear membrane dissolves.

How are chromosomes arranged during metaphase?

During metaphase, spindle fibers align the chromosomes along the equator of the cell, with each sister chromatid on opposite sides.

What is the role of spindle fibers in anaphase?

In anaphase, spindle fibers shorten and separate the sister chromatids at their centromeres, pulling them toward opposite poles of the cell.

How does telophase differ from the other phases of mitosis?

In telophase, a nuclear membrane reforms around each set of chromosomes, which then disperse into chromatin. The nucleolus also becomes visible again, marking the end of mitosis.

What is cytokinesis, and how does it differ between animal and plant cells?

Cytokinesis is the division of the cytoplasm. In animal cells, it occurs through the inward pinching of the cell membrane, while in plant cells, a cell plate forms along the equator, eventually developing into a new cell wall.

Why can't plant cells undergo cytokinesis through the same mechanism as animal cells?

Plant cells have a rigid cell wall that prevents the inward pinching of the cell membrane, so they form a cell plate to divide the cytoplasm.

What are centrioles, and how do they differ from centromeres?

Centrioles are structures at the poles of the cell where spindle fibers originate. Centromeres are the regions on chromosomes where sister chromatids are attached.

What is the end result of the M phase of the cell cycle?

The M phase results in the formation of two identical daughter cells, each with a complete set of chromosomes, identical to the original cell.

Outlines

00:00

📚 Overview of the M Phase in the Cell Cycle

This paragraph introduces the M phase of the cell cycle, which includes mitosis and cytokinesis. It provides a brief review of the cell cycle, highlighting that the G1, S, and G2 phases constitute interphase, while the M phase is dedicated to cell division. Mitosis, the division of the nucleus, is broken down into four phases: prophase, metaphase, anaphase, and telophase. This sets the stage for the detailed exploration of these phases and their significance in cell division.

05:04

🔬 Prophase: Initiation of Chromosome Formation and Spindle Apparatus

This paragraph delves into prophase, the first and longest phase of mitosis. During prophase, chromatin condenses into visible chromosomes, and the nucleolus disappears. Each chromosome consists of two sister chromatids connected by a centromere. In the cytoplasm, spindle fibers begin to form from centrioles, which move to opposite poles of the cell. The nuclear membrane disintegrates, allowing the spindle fibers to attach to the centromeres of the chromosomes.

📏 Metaphase: Chromosome Alignment at the Cell Equator

In this paragraph, metaphase is described as the phase where the centrioles reach the poles of the cell, and the spindle fibers align the chromosomes along the cell’s equator. This alignment ensures that each sister chromatid is positioned on either side of the equator, preparing the cell for the next phase of mitosis.

⚖️ Anaphase: Separation of Sister Chromatids

This section explains anaphase, where the spindle fibers pull the sister chromatids apart at their centromeres. Once separated, each chromatid is considered an individual chromosome. These chromosomes are dragged toward opposite poles of the cell by the shortening spindle fibers. The paragraph also clarifies the difference between centrioles and centromeres.

🏁 Telophase: Nuclear Reformation and Chromosome Dispersal

Telophase, the final stage of mitosis, is discussed here. During telophase, a nuclear membrane reforms around each set of chromosomes, which then disperse into chromatin. The nucleolus becomes visible again, marking the end of mitosis. This phase completes the division of the nucleus, preparing the cell for the final step of cytokinesis.

🌱 Cytokinesis: Formation of Daughter Cells

This paragraph focuses on cytokinesis, the process of cytoplasmic division that follows mitosis. In animal cells, the cell membrane pinches inward, dividing the cytoplasm and forming two identical daughter cells. In plant cells, a cell plate forms along the equator, gradually developing into a new cell wall that separates the two daughter cells. The paragraph highlights that the M phase concludes with the formation of two genetically identical daughter cells.

📝 Key Takeaways: Summary) of the M Phase

The final paragraph summarizes the key points of the M phase. It reiterates that the M phase is the fourth and final phase of the cell cycle, encompassing both mitosis and cytokinesis. Mitosis is broken down into four phases—prophase, metaphase, anaphase, and telophase—each with distinct processes leading to the division of the nucleus. Cytokinesis, the division of the cytoplasm, follows, resulting in two identical daughter cells. The paragraph emphasizes that these daughter cells are identical to each other and to the original parent cell.

Keywords

💡M phase

The M phase is the fourth and final phase of the cell cycle, during which cell division occurs. It includes two main processes: mitosis, the division of the nucleus, and cytokinesis, the division of the cytoplasm. In the script, the M phase is explained as the phase where the actual splitting of the cell into two daughter cells happens.

💡Mitosis

Mitosis is the process of nuclear division in eukaryotic cells that results in two identical daughter nuclei. It consists of four phases: prophase, metaphase, anaphase, and telophase. In the script, mitosis is described as the stage where the nucleus divides, leading to the formation of two separate sets of chromosomes.

💡Cytokinesis

Cytokinesis is the process during cell division in which the cytoplasm of a single eukaryotic cell divides to form two daughter cells. It follows mitosis. In animal cells, this involves the inward pinching of the cell membrane, while in plant cells, a cell plate forms to separate the new cells. The script highlights cytokinesis as the final step of the M phase.

💡Interphase

Interphase is the phase of the cell cycle during which the cell prepares for division by growing and replicating its DNA. It includes the G1, S, and G2 phases. In the script, interphase is mentioned as the preparatory phase that precedes the M phase.

💡Prophase

Prophase is the first phase of mitosis, characterized by the condensation of chromatin into visible chromosomes, the disappearance of the nucleolus, and the formation of the spindle fibers. The script describes prophase as the longest phase where significant structural changes occur in preparation for chromosome separation.

💡Metaphase

Metaphase is the second phase of mitosis, where chromosomes align at the cell's equator. Spindle fibers attach to the centromeres of the chromosomes, ensuring that each new cell will receive one copy of each chromosome. The script explains metaphase as the stage where chromosomes are lined up in the center of the cell.

💡Anaphase

Anaphase is the third phase of mitosis, during which sister chromatids are pulled apart by spindle fibers towards opposite poles of the cell. The script details anaphase as the phase where chromatids are separated into individual chromosomes and moved to the cell poles.

💡Telophase

Telophase is the final phase of mitosis, where new nuclear membranes form around each set of separated chromosomes, and the chromosomes begin to uncoil back into chromatin. The script describes telophase as the stage where the nucleus reforms, marking the end of nuclear division.

💡Spindle fibers

Spindle fibers are structures made of microtubules that help separate the chromosomes during mitosis. They extend from the centrioles and attach to the centromeres of chromosomes. The script mentions spindle fibers forming during prophase and playing a crucial role in chromosome movement during mitosis.

💡Centromere

A centromere is the region of a chromosome where the sister chromatids are joined together and where the spindle fibers attach during mitosis. The script highlights the centromere as the point of attachment for spindle fibers, which is essential for the proper separation of chromatids during anaphase.

💡Chromatin

Chromatin is the material that makes up chromosomes, consisting of DNA and proteins. During prophase, chromatin condenses into visible chromosomes. The script describes chromatin as spreading out into chromosomes during prophase and reverting to a dispersed state during telophase.

Highlights

Exploring the M phase of the cell cycle, including mitosis and cytokinesis.

Review of the cell cycle: G1, S, and G2 phases make up interphase, and M phase represents cell division.

Cell division includes division of the nucleus (mitosis) and division of the cytoplasm (cytokinesis).

Mitosis is further broken down into four phases: prophase, metaphase, anaphase, and telophase.

Prophase: chromatin condenses into chromosomes, nucleolus disappears, and spindle fibers begin to form.

Chromosomes become visible as individual entities for the first time during prophase.

Centromeres attach sister chromatids together.

Spindle fibers fan out from centrioles, which move to opposite poles of the cell during prophase.

Nuclear membrane disappears, allowing spindle fibers to attach to centromeres.

Metaphase: centrioles complete their movement to poles, and spindle fibers line up chromosomes along the equator of the cell.

Anaphase: spindle fibers separate sister chromatids at their centromeres, forming individual chromosomes.

Chromosomes move to opposite poles of the cell during anaphase.

Telophase: nuclear membrane reforms around chromosomes, which spread out into chromatin.

Cytokinesis: division of the cytoplasm resulting in two identical daughter cells.

In animal cells, cytokinesis occurs through inward movement of the cell membrane.

In plant cells, cytokinesis involves formation of a cell plate along the equator.

New cell walls form between the two daughter cells in plant cells.

Mitosis and cytokinesis ensure that each daughter cell is identical to the original cell.

Transcripts

in this lesson we'll be exploring the m

phase of the cell cycle including

mitosis and cytokinesis

let's do a quick review of the cell

cycle to see where they fit in

the g1

s and g2 phases make up interphase

and the m phase represents cell division

cell division includes division of the

nucleus called mitosis

and division of the cytoplasm called

cytokinesis

mitosis is further broken down into four

phases

prophase

metaphase

anaphase

and telophase

prophase is the longest phase of mitosis

prophase is when chromatin begins to

condense into the shape of chromosomes

and the nucleolus disappears

the previously replicated dna coils

tightly into sister chromatids

for the first time you see individual

chromosomes

in the center of each chromosome a

centromere

attaches the sister chromatids together

meanwhile in the cytoplasm microtubules

known as spindle fibers begin to fan out

from two sets of paired structures

called centrioles

the spindle fibers elongate as the

centrioles begin moving to opposite

sides or poles of the cell

while this is happening the nuclear

membrane surrounding the nucleus

disappears

now that chromosomes are no longer

separated from the cytoplasm the

opposite ends of the spindle fibers can

attach to the centromeres

next the cell enters metaphase

the centrioles complete their movement

to the poles of the cell while the

spindle fibers line up the chromosomes

along the equator of the cell

the end-to-end alignment of chromosomes

results in a sister chromatid on either

side of the equator

anaphase follows metaphase

during anaphase spindle fibers separate

the sister chromatids at their

centromere

once separated from each other each

chromatid is called a chromosome

the single-stranded chromosomes form a

v-shape as the spindle fibers shorten

and drag them through the gel-like

cytoplasm

the chromosomes move to opposite poles

of the cell toward their centrioles

it's common to confuse centrioles with

centromeres which connect chromatids

remember

centrioles are at the poles

telophase is the final stage of mitosis

in telophase a nuclear membrane reforms

around each set of chromosomes

then the chromosomes spread out into

chromatin and the nucleolus becomes

visible once again

mitosis the division of the nucleus is

now complete

the final step of the m phase is

cytokinesis the division of the

cytoplasm

in animal cells cytokinesis occurs

through the inward movement of the cell

membrane

this progressively pinches the cytoplasm

until two identical daughter cells form

in contrast plant cells can't pinch into

because they have a rigid cell wall

surrounding their cell membrane

instead cell wall material assembles

along the equator forming a structure

called the cell plate

the cell plate grows until it joins with

the existing cell membrane separating

the two halves of the cell into daughter

cells

over time new cell walls form between

the two daughter cells

here are the key points to remember

the m phase is the fourth and final

phase of the cell cycle

during the m phase cell division occurs

through two processes

mitosis when the nucleus divides

and cytokinesis when the cytoplasm

divides

mitosis has four phases

during prophase chromatin condenses into

chromosomes

spindle fibers form and the nucleolus

and nuclear membrane disappear

during metaphase spindle fibers align

the chromosomes along the cell equator

in anaphase the spindle fibers separate

sister chromatids into two separate

groups of chromosomes pulling them

toward the poles

and in telophase the nucleolus and

nuclear membrane reform

the chromosomes disperse into

chromatin cytokinesis is division of the

cytoplasm

the m phase is complete after

cytokinesis occurs

the m phase of the cell cycle always

results in two daughter cells

both of these daughter cells are

identical to each other and identical to

the original cell that underwent mitosis

[Music]

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