Name: cell cycle, mitosis, and meiosis
Uploaded: 2019-01-29T11:04:45.000Z
Duration: 5 min 44 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Life Science

LS.2

LS.2.d

Cell Division

The cell cycle refers to the sequence of events throughout a typical cell&#39;s life - involving growth, DNA replication, and preparation for cell division. For sexually-reproducing organisms, life begins as a zygote, a fertilized egg. Over time, that original single cell grows and divides in a controlled manner to produce a multicellular, complex individual. Cells continue this process, especially to maintain and repair tissues during aging. 
Now let&#39;s take a closer look. In eukaryotes, double-stranded DNA is specially organized within a membrane-bound nucleus to accommodate the cell&#39;s limited space. At the first level of compaction, DNA is wrapped tightly around specific proteins called histones. This combination of DNA protein particles is then repeated and packed into arrays known as nucleosomes, which, along with linker DNA, form coiled chromatin fibers. Finally, additional fibrous proteins compact the chromatin even further, packing long lengths of DNA into tightly-condensed units. Recognized as chromosomes, depending on the phase of cell division. 
To prepare for division, cells must go through interphase, which is divided into three stages. G1, S, and G2. In G1, the first gap phase, a newly-generated daughter cell grows in size and prepares for DNA duplication in the next phase. Now in S, the synthesis phase, cells duplicate their nuclear DNA, which remains packaged as chromatin. Cells also duplicate the centrosomes, the microtubule-organizing structures which form the mitotic spindle apparatus. Finally, in G2, the second gap phase, cells continue to grow, multiply organelles and proteins that are required for mitosis, and replenish their energy stores. The cell is now ready to enter the first stage of mitosis. 
Comprised of five unique stages, mitosis is a form of division where a cell&#39;s genetic material is partitioned between two daughter cells. First during prophase in humans, nucleic chromatin condenses into X-shaped chromosomes, composed of sister chromatid pairs attached at centromere junctions. Concurrently outside the nucleus, centrosomes migrate to opposite sides of the cell. As they do so, microtubule rods begin to grow from each. Either towards the cell&#39;s interior or exterior, forming a web-like spindle apparatus. Next, the nuclear envelope dissolves during prometaphase, exposing the chromosomes to the cell&#39;s other contents. Protein structures also appear on both sides of the centromeres, one for every chromatid. Once these kinetochores form, extending interior microtubules fasten to them, with each sister chromatid being tethered to a different pole. 
Mitosis then progresses to metaphase, where the spindle apparatus rearranges the chromosomes so that they are similarly oriented in a fixed row along the cell&#39;s equator. During anaphase, kinetochore-affixed microtubules shorten. And sister chromatids, now individually referred to as chromosomes, are dragged apart. These and other microtubule dynamics also elongate the cell. Finally, the chromosomes land at opposite cell sides during telophase. And the spindle apparatus disbands. The genetic material loosens, and two nuclear envelopes, one around each chromosome set, arise. During telophase, a distinct process, not technically a stage of mitosis, called cytokinesis, also divides the cell. Thus, the end result of mitosis is a cell pair genetically identical to their precursor. 
Unfortunately, mutations can cause damage to genes controlling cell cycle regulation, which leads to cell division proceeding unchecked. In this case, each successive cell division produces daughter cells with even more damage&#8230;and the faulty growth regulation ultimately leads to the formation of cell masses called tumors.
In this lab, you will examine the different stages of mitosis using onion root tip cells. And then examine what happens when cell cycle control is lost.

cell division

Cell division is fundamental to all living organisms and required for growth and development. As an essential means of reproduction for all living things, cell division allows organisms to transfer their genetic material to their offspring. For a unicellular organism, cellular division generates a completely new organism. For multicellular organisms, cellular division produces new cells for the general development of the organism, as well as produces healthy cells to replace damaged cells from injury. Reproduction of multicellular organisms requires cell division to create reproductive cells.
In order to divide, a cell first needs to duplicate and divide its genetic content into two daughter cells. This series of duplication and division is called the cell cycle. The details of the cell cycle vary from one organism to the next, but fundamental stages of cell division are universal.
<h4>Cell cycle</h4>
About 78% of a cell&#8217;s life is spent in Interphase, growing and preparing itself for cell division. Interphase itself contains three subphases. Immediately after cell division, a newly-formed cell enters the Gap 1 or G1 portion of Interphase. During G1, cells actively grow and, in many cases, differentiate to perform specific functions. At this stage, the cell is sensitive to internal and external signals to determine whether to divide or not. Some cells, such as neurons do not proceed to cell division after differentiation and remain in G1 until they die. Once the cell meets criteria to proceed to cell division, it enters the synthesis or S stage of Interphase, during which the cell replicates its entire genome. Next, the cell enters the Gap 2 or G2 phase to synthesize all the necessary proteins for cell division. This is followed by the cell division phase.
<h4>Types of Cell Division in Eukaryotes</h4>
There are two types of cell division in eukaryotic cells&#8212;mitosis and meiosis. Somatic or non-reproductive cells produce daughter cells via mitotic division. Mitosis is the nuclear division and consists of five stages: prophase, prometaphase, metaphase, anaphase, and telophase During prophase, duplicated DNA molecules condense into tightly-packed chromosomes, while microtubules form spindles. The nuclear envelope dissolves in prometaphase. During metaphase, chromosomes that are connected to spindles line up along the equator of the cells. During anaphase, sister chromatids are pulled to opposite poles of the cell. Finally, during telophase, new nuclear envelopes are formed around both groups of chromosomes. After nuclear division is completed, cytoplasm around each nucleus separates from one another via cytokinesis, resulting in two identical daughter cells.
The other type of eukaryotic cell division is called meiosis, which is specific to reproductive cells. Meiosis produces four daughter cells each with only half the genetic content of the parent cell. In this process the cell duplicates its DNA during Interphase and then completes two successive cell divisions splitting cells from two into four cells, respectively. These successive cell divisions are called meiosis I and meiosis II, both of which consist of all the stages from prophase to telophase. Exchange of genetic material between the sets of non-sister chromatids happens during prophase I in a process called crossing over. Homologous chromosome pairs are aligned along the equator of the cell during metaphase I and pulled away from each other during anaphase I. Haploid daughter nuclei are formed during telophase I. Cytokinesis commonly occurs before meiosis II, however, interphase almost never happens between the two successive divisions. Meiosis II is very similar to mitosis and separates sister chromatids. At the end of meiosis, four haploid daughter cells are formed. These cells daughter cells are called gametes and form the sperm or egg cells.
<h4>Regulation of Cell Division</h4>
Cell division is tightly regulated externally and internally. External regulation assures the necessity of the division. For example, cells of the stomach lining divide frequently to meet the ongoing need for new cells to replace damaged cells. Similarly, injured tissues may experience higher rates of cell division to replace damaged cells but only for a certain period of time as long as the external signals to direct cell division are present. Internal regulation of cell division ensures the health of daughter cells. There are many checkpoints within phases of the cell cycle that regulate the transition of the cell from one phase to the next. For instance, quality control mechanisms let the cell proceed from G1 to S phase only if the DNA is intact and suitable for replication. Similarly, a checkpoint at G2 allows cells to proceed to mitosis (M phase) only if the DNA has been completely and accurately replicated. Also, a metaphase checkpoint assures that the chromosomes are attached to the spindles and aligned correctly before anaphase can start. A cell that fails at a checkpoint may be targeted for apoptosis if the cell is unable to correct the mistake.
Some mutations allow cells to divide even when there is no signal directing cell division. For example, tumor-suppressor genes prevent cells from uncontrolled division and mutation in these genes relieves this inhibition. This aberrant cell division, if left unchecked, can cause tumor formation and in some cases lead to cancer. As one of the leading causes of death in the United States, cancer no doubt has a major impact on society. The lifetime risk of cancer increases with age as mutations in DNA accumulate over time, especially for breast, lung, prostate, and colon cancers1. Thus, ongoing research on cell division is essential for improving cancer detection, treatment, and eventually for prevention. In fact, current therapies to treat cancer take advantage of the knowledge of cell division mechanisms, such as targeting mechanisms involved in cell division. For example, platinum-drugs such as cisplatin bind to DNA and arrest DNA replication, while taxanes such as paclitaxel bind to microtubules and inhibit spindle disassembly thus arresting cell division2.
An understanding of cell cycle and cell division mechanisms is also important to understand and develop treatments for conditions that affect nondividing cells. Currently, injuries to the nervous system or the heart can have debilitating effects since damaged neuron and muscle cells cannot be replaced. However, injury to the nervous tissue is associated with activation of cell cycle pathways in neurons and supporting glial cells. Interestingly, inhibition of these cell cycle pathways reduces the glial scar formation and secondary damage after injury. Therefore, understanding the regulation of cell cycle and cell division is imperative to understand the healthy and diseased conditions of all organ systems3.
<h4>References</h4>
<ol class="references">
	<li>Kennedy, BJ. Aging and Cancer. Oncology. 2000, Vol. 14, 12 (1731-40).</li>
	<li>Mahotra, V and Perry, MC. Classical Chemotherapy: Mechanisms, Toxicities and the Therapeutc Window. Cancer Biology &#38; Therapy . 2003, Vol. 2, 1 (1-3).</li>
	<li>Byrnes, KR, et al. Cell cycle activation contributes to post-mitotic cell death and secondary damage after spinal cord injury. Brain. . 2007 , 130(Pt 11):2977-92.</li>
</ol>

Cell division is fundamental to all living organisms and required for growth and development. As an essential means of reproduction for all living things, ...

Education

JoVE Lab Manual

Biology

Cellular Processes

cell cycle, mitosis, and meiosis

Cell division is essential for growth, repair, and reproduction in living organisms. It lets single-celled organisms create a new organism and helps multicellular organisms make new cells for development and for replacing damaged cells. In multicellular species, cell division also makes reproductive cells needed for reproduction.

Before a cell divides, it must copy its genetic material and split it into two daughter cells. This process is called the cell cycle. Although the timing can vary among organisms, the main stages of cell division are the same.

Most of a cell’s life is spent in interphase, which is the growth and preparation period before division. Interphase has three parts: G1, S, and G2. During G1, the new cell grows and may differentiate, or specialize, for a specific function. Some cells, such as neurons, stop the cycle after differentiation and remain in G1 until they die. In S phase, the cell copies its entire genome. In G2, the cell makes the proteins needed for division.

Eukaryotic cells have two main types of division: mitosis and meiosis. Somatic, or non-reproductive, cells divide by mitosis to make daughter cells. Mitosis has five stages: prophase, prometaphase, metaphase, anaphase, and telophase. During prophase, duplicated DNA condenses into chromosomes and microtubules form spindle fibers. In prometaphase, the nuclear envelope breaks down. In metaphase, the chromosomes line up at the cell’s equator. In anaphase, sister chromatids move to opposite poles. In telophase, new nuclear envelopes form around both sets of chromosomes. Cytokinesis then divides the cytoplasm and produces two identical daughter cells.

Meiosis is used by reproductive cells. It produces four daughter cells, each with half the genetic content of the parent cell. After DNA is copied during interphase, the cell goes through two rounds of division called meiosis I and meiosis II. Each round includes the stages from prophase to telophase. During prophase I, non-sister chromatids exchange genetic material in crossing over. In metaphase I, homologous chromosome pairs line up at the equator, and in anaphase I they separate. Haploid daughter nuclei form in telophase I. Cytokinesis often occurs before meiosis II, but interphase almost never occurs between the two divisions. Meiosis II is similar to mitosis and separates sister chromatids. The final products are four haploid daughter cells called gametes, which become sperm or egg cells.

Cell division is tightly controlled by signals inside and outside the cell. External signals make sure division happens only when needed. For example, stomach lining cells divide often to replace damaged cells. Injured tissues may also increase cell division for a time, as long as the signals are present. Internal controls protect the health of daughter cells.

Checkpoints act as quality control during the cell cycle. A G1 checkpoint allows the cell to enter S phase only if the DNA is intact and ready for replication. A G2 checkpoint allows the cell to enter mitosis only if DNA has been fully and accurately copied. A metaphase checkpoint checks that chromosomes are attached to the spindle fibers and lined up correctly before anaphase begins. If a cell cannot fix a problem, it may undergo apoptosis, or programmed cell death.

When mutations disrupt normal control, cells may divide without the proper signal. Tumor-suppressor genes normally prevent uncontrolled division, and mutations in these genes remove that brake. This abnormal division can lead to tumors and, in some cases, cancer. Because cancer risk rises with age as DNA mutations build up, cell division research is important for better detection, treatment, and prevention. Some therapies use this knowledge directly. Cisplatin binds to DNA and stops DNA replication. Paclitaxel binds to microtubules and prevents spindle disassembly, which arrests cell division.

Understanding the cell cycle also matters for tissues that do not easily replace damaged cells. Injuries to the nervous system or the heart can have serious effects because damaged neurons and muscle cells cannot be replaced well. Nervous tissue injury can activate cell cycle pathways in neurons and supporting glial cells. Inhibiting these pathways can reduce glial scar formation and secondary damage after injury. For this reason, cell cycle control is important in healthy tissues and in disease across organ systems.

Cell Cycle, Mitosis, and Meiosis

photosynthesis

Photosynthesis: Light, Sugars, and Carbon

Photosynthesis turns sunlight into chemical energy in the form of glucose. This process powers most life on Earth by helping autotrophs, or primary producers, make food. The glucose they make can provide quick energy or be stored as starch for later use. Consumers depend on these producers for energy. Photosynthesis happens in many kinds of organisms. Cyanobacteria, some protists such as algae, and plants can all carry out this process. In eukaryotic cells, it takes place in the chloroplast.

cellular respiration

Cellular Energy From Glucose Breakdown

Cellular respiration is the process cells use to release usable energy from biomolecules such as sugars and lipids. Living things need a steady energy supply for growth, repair, movement, defense, and reproduction. Cells use that energy mainly by converting adenosine diphosphate (ADP) to adenosine triphosphate (ATP). Autotrophs and heterotrophs get the molecules for respiration in different ways. Autotrophs, such as plants, algae, and photosynthetic and chemosynthetic bacteria, build...

Cell division is essential for growth, repair, and reproduction in living organisms. It lets single-celled organisms create a new organism and helps multicellular organisms make new cells for development and for replacing damaged cells. In multicellular species, cell division also makes reproductive cells needed for reproduction. Before a cell divides, it must copy its genetic material and split it into two daughter cells. This process is called the cell cycle. Although the timing can vary...

transpiration

Water Movement in Plants

Water movement in plants depends on transpiration and the vascular system. Plants must move water and dissolved nutrients from the roots to the leaves. They also exchange materials with the environment as part of normal life processes. Vascular plants use bundles of tissues that run from the roots to the tips of the plant. Root hairs absorb water and nutrients, and osmosis moves water into the xylem, the main water-conducting tissue. Water then travels to the tallest parts of the plant and...

enzyme activity

Factors That Shape Enzyme Function

Enzymes are biological catalysts that help living things run biochemical reactions faster. They lower activation energy, which is the energy needed to start a reaction. Enzymes are not used up in the process, so they can keep working again and again. Most enzymes are proteins, although some ribonucleic acid molecules also have catalytic activity. Each enzyme usually binds only one or a few specific substrates. This selectivity depends on the enzyme’s active site, which fits its substrate like...

cellular processes

Learn how the cell cycle, mitosis, and meiosis support growth, repair, and reproduction, and how checkpoints help control cell division.

Cell Cycle, Mitosis, and Meiosis | JoVE K12

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

High School

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

HS-LS1-4

Next Generation Science Standards

new-york-state-science-learning-standards

New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS1-4.

Georgia Standards of Excellence

9-12

SB1.b

Prepare onion root tips, clean the roots, and make a nocodazole in DMSO solution for a cell cycle lab. Set out materials for each student bench.

Onion Root Tip Lab Setup | JoVE K12

Compare nocodazole-treated and untreated onion root tips to see mitosis stages, DAPI-stained DNA, and how cell cycle control is studied in root cells.

Root Tip Cell Cycle Lab | JoVE K12

Cell Structure

Background
Cells represent the most basic biological units of all organisms, whether it be simple, single-celled organisms like bacteria, or large, ...

What are Cells?

Cells are the smallest and basic units of life, whether it is a single cell that forms the entire organism, e.g., in a bacterium, or trillions of them, ...

Animal and Plant Cell Structure

Animal and plant cells not only differ in their structure, function, and mode of nutrition but also in how they reproduce, specialize, and organize into ...

Cell Diversity

The concept of a cell started with microscopic observations of dead cork tissue by Robert Hooke in 1665. Hooke coined the term &#34;cell&#34; based on the ...

An Introduction to Cell Division

Cell division is the process by which a parent cell divides and gives rise to two or more daughter cells. It is a means of reproduction for single-cell ...

The student will investigate and understand that all living things are composed of one or more cells that support life processes, as described by the cell theory. Key ideas include the development of the cell theory demonstrates the nature of science;

LS.2.a

Cytoplasm

The Nucleus

The Nucleosome

Human DNA is almost two meters long. However, it is compressed inside a tiny nucleus measuring only a few microns in diameter. To make this degree of ...

The Nucleosome Core Particle

Nucleosomes are the DNA-histone complex, where the DNA strand is wound around the histone core. The histone core is an octamer containing two copies of ...

Chromatin Packaging

Each human somatic cell contains 6 billion base pairs of DNA. Each base pair is 0.34 nm long, meaning each diploid cell contains a staggering 2 meters of ...

The Endoplasmic Reticulum

Golgi Apparatus

Lysosomes

Mitochondria

Mitochondrial Membranes

Peroxisomes

Ribosomes

Introduction to Cytoskeleton

Centrioles and Centrosomes

Most animal cells comprise a pair of centrioles together called a centrosome. The cell duplicates its centrosome and contains two centrosomes ...

Functions of Life

Human life is characterized by a variety of functions that are essential for survival and well-being. These functions include metabolism, movement, ...

Requirements for Human Life

The Earth and its atmosphere have provided humans with air, water, and food, but these are not the only requirements for survival. Humans also require a ...

The student will investigate and understand that all living things are composed of one or more cells that support life processes, as described by the cell theory. Key ideas include cell structure and organelles support life processes;

LS.2.b

Visualizing Onion and Cheek Cells
ExpandImmediately before the experiment, wash and peel onion bulbs for the class.
Remove the entire brown outer skin and ...

Visualizing Onion and Human Cells
ExpandIn this experiment you will prepare different types of cells from a plant and animal, onion and human ...

Prokaryotic vs. Eukaryotic Cells

Prokaryotic and eukaryotic cells represent two fundamental types of cellular organization, differing significantly in structure, complexity, and function. ...

Plant Cells and Tissues

Plant tissues are collections of similar cells performing related functions. Different plant tissues will have their own specialized roles and can be ...

Tissues

Cells with similar structure and function are grouped into tissues. A group of tissues with a specialized function is called an organ. There are four main ...

The student will investigate and understand that all living things are composed of one or more cells that support life processes, as described by the cell theory. Key ideas include similarities and differences between plant and animal cells determine how they support life processes;

LS.2.c

Mitosis and Cytokinesis

In eukaryotes, the cell division cycle is divided into distinct, coordinated cellular processes that include cell growth, DNA replication/chromosome ...

What is the Cell Cycle?

The cell cycle refers to the sequence of events occurring throughout a typical cell&#8217;s life. In eukaryotic cells, the somatic cell cycle has two ...

Binary Fission

Fission is the division of a single entity into two or more parts, which regenerate into separate entities that resemble the original. Organisms in the ...

Live Cell Imaging of Mitosis

Mitosis is a form of cell division in which a cell&#8217;s genetic material is divided equally between two daughter cells. Mitosis can be broken down into ...

The Cell Cycle Control System

The cell cycle is an organized set of events that leads the cell to divide into two daughter cells, each containing chromosomes identical to the parent ...

Preparation of Onion Root Tips and Solutions
ExpandFor the cell cycle experiment using root tips, first, leave an onion suspended over a beaker of water ...

Observing the Cell Cycle in a Root Tip
ExpandHypotheses: The experimental hypothesis is that in root tips slices that have been treated with nocodazole, a ...

The student will investigate and understand that all living things are composed of one or more cells that support life processes, as described by the cell theory. Key ideas include cell division is the mechanism for growth and reproduction; and

What are Membranes?

A key characteristic of life is the ability to separate the external environment from the internal space. To do this, cells have evolved semi-permeable ...

Membrane Fluidity

Cell membranes are composed of phospholipids, proteins, and carbohydrates loosely attached to one another through chemical interactions. Molecules are ...

Fluid Mosaic Model

The fluid mosaic model was first proposed as a visual representation of research observations. The model comprises the composition and dynamics of ...

What is an Electrochemical Gradient?

Adenosine triphosphate, or ATP, is considered the primary energy source in cells. However, energy can also be stored in the electrochemical gradient of an ...

Diffusion

Diffusion is the passive movement of substances down their concentration gradients&#x2014;requiring no expenditure of cellular energy. Substances, such as ...

Osmosis

Approximately 60% to 95% of the weight of living organisms is attributed to water. Therefore, maintaining appropriate water balance within cells is of ...

Tonicity in Animals

The tonicity of a solution determines if a cell gains or loses water in that solution. The tonicity depends on the permeability of the cell membrane for ...

Tonicity in Plants

Tonicity describes the capacity of a cell to lose or gain water. It depends on the quantity of solute that does not penetrate the membrane. Tonicity ...

Introduction to Membrane Proteins

The cell membrane, or plasma membrane, is an ever-changing landscape. It is described as a fluid mosaic where various macromolecules are embedded in the ...

Facilitated Transport

The chemical and physical properties of plasma membranes cause them to be selectively permeable. Since plasma membranes have both hydrophobic and ...

Primary Active Transport

In contrast to passive transport, active transport involves a substance being moved through membranes in a direction against its concentration or ...

Secondary Active Transport

One example of how cells use the energy contained in electrochemical gradients is demonstrated by glucose transport into cells. The ion vital to this ...

Receptor-mediated Endocytosis

Overview

Receptor-mediated endocytosis is a process through which bulk amounts of specific molecules can be imported into a cell after binding to cell ...

Pinocytosis

Cells use energy-requiring bulk transport mechanisms to transfer large particles, or large amounts of small particles, into or out of the cell. The cells ...

Phagocytosis

Cells pull particles inward and engulf them in spherical vesicles in an energy-requiring process called endocytosis. Phagocytosis (&#x201C;cellular ...

Exocytosis

Exocytosis is used to release material from cells. Like other bulk transport mechanisms, exocytosis requires energy.

While endocytosis takes particles ...

The student will investigate and understand that all living things are composed of one or more cells that support life processes, as described by the cell theory. Key ideas include cellular transport (osmosis and diffusion) is important for life processes.

LS.2.e

Cell Cycle, Mitosis, and Meiosis

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