Process of cell division, differentiation, and specialization

Phases of cell cycle: G0, G1, G2, M-Key Terms

interphase: the stage in the life cycle of a cell where the cell grows and DNA is replicated centrosome: an organelle near the nucleus of a cell that contains the centrioles (in animal cells) and from which the spindle fibers develop in cell division. mitotic spindle: the apparatus that orchestrates the movement of chromosomes during mitosis quiescent: in a state or period of inactivity or dormancy centrioles: the main centers that help in the formation of microtubule fiber

Loss of cell cycle controls in cancer cells-Key Terms

tumor suppressor gene: a segment of DNA that codes for regulator proteins that prevent the cell from undergoing uncontrolled division apoptosis: a process of programmed cell death G1 checkpoint: a point in the animal cell cycle at which the cell becomes "committed" to the cell cycle, which is determined by external factors and signals p53: cell cycle regulatory protein that regulates cell growth and monitors DNA damage; it halts the progression of the cell cycle in cases of DNA damage and may induce apoptosis

Mitotic Structures

Asters are star-shaped radial arrays that form around each pair of centrioles. Aster guides the chromosome to ensure that each daughter cell has the right complement chromosome. It helps to organize and position spindle apparatus during mitosis and also determines the site of cleavage furrow that splits the dividing cell in half during cytokinesis. Asters anchor the spindle fibers to the cell membrane.

Loss of cell cycle controls in cancer cells

A cell with an abnormal p53 protein cannot repair damaged DNA and thus cannot signal apoptosis. Without a fully functional p53, the G1 checkpoint of interphase is severely compromised and the cell proceeds directly from G1 to S; this creates two daughter cells that have inherited the mutated p53 gene. Mutated p53 genes are believed to be responsible for causing tumor growth because they turn off the regulatory mechanisms that keep cells from dividing out of control. Cells with abnormal p53 can become cancerous.

Control of cell cycle-Key Points

A checkpoint is one of several points in the eukaryotic cell cycle at which the progression of a cell to the next stage in the cycle can be stopped until conditions are favorable. The G1 checkpoint monitors adequate cell growth, the state of the genomic DNA, adequate stores of energy, and materials for S phase. At the G2 checkpoint, DNA is checked to ensure that all chromosomes were duplicated and that there are no mistakes in newly synthesized DNA. Additionally, cell size and energy reserves are evaluated.

Loss of cell cycle controls in cancer cells-Key Points

A tumor suppressor gene is a segment of DNA that codes for the negative cell-cycle regulators; if that gene becomes mutated to an underactive form, the cell cycle will run unchecked. Mutated p53 genes are responsible for causing tumor growth because they turn off the regulatory mechanisms that keep cells from dividing out of control.

Mitotic process:prophase, metaphase, anaphase, telophase, interphase

Anaphase During anaphase, proteins that bind the sister chromatids together break down. The connected sister chromatids, now called chromosomes, pull toward opposite poles and cause the chromosomes to split. The nonkinetochore spindle fibers from one pole also push on the other pole, which causes cell elongation. By the end of anaphase, each pole of the cell contains an identical set of chromosomes. The root "ana-" refers to "apart". See photo @jackwestin.com. In anaphase, cohesin proteins binding the sister chromatids together break down sister chromatids (now called chromosomes) pull toward opposite poles non-kinetochore spindle fibers lengthen, elongating the cell

Loss of cell cycle controls in cancer cells

Cancer comprises many different diseases caused by a common mechanism: uncontrolled cell growth. Cancer is the result of unchecked cell division caused by a breakdown of the mechanisms that regulate the cell cycle. The loss of cell cycle control begins with a DNA sequence change of a gene that codes for one of the regulatory molecules, known as a mutation. Faulty instructions lead to a protein that does not function normally. Each successive cell division will give rise to daughter cells with even more accumulated damage. Eventually, all checkpoints become non-functional, and rapidly reproducing cells that push out healthy cells, resulting in a tumor or leukemia (blood cancer).

Control of cell cycle-Key Points

Cdk must bind to a cyclin, and it must be phosphorylated in the correct position to become fully active. Rb and other negative regulatory proteins control cell division, so they prevent the formation of tumors.

Growth arrest-Key Points

Cells that are not actively preparing to divide enter an alternate phase called G0. G0 is a temporary condition until triggered to enter G1, while some remain in G0 permanently.

Mitotic Structures

Centrioles are the main centers that help in the formation of microtubule fiber, which makes up the spindles. Without centrioles, there are no spindles that assist the movement of the chromosome. Centrioles are found within centrosomes and migrate to the opposite ends of the cell to produce spindle fibers.

Mitotic Structures-Key Points

Centrioles, asters, and spindles are mitotic structures responsible for pulling apart the sister chromatids. Chromatids, centromeres, and kinetochores are For most eukaryotes, the nuclear membrane breaks down at the beginning of mitosis (prometaphase) and reorganizes around each of the two newly formed daughter cells at the end (telophase) Microtubules cause the chromosome movement; during anaphase, chromatids move apart by the spindle fibers.

Mitotic Structures

Centrioles, asters, spindles Mitotic structures responsible for pulling apart the sister chromatids are centrioles, asters, and spindles. These structures are a component of the spindle apparatus, which also includes motor proteins and chromosomes.

Mitotic Structures

Chromatids, centromeres, kinetochores In the absence of centromere, a kinetochore will not assemble on the replicated chromatids. And that chromosome will fail to segregate during mitosis.

Mitotic process:prophase, metaphase, anaphase, telophase, interphase

Cytokinesis Cytokinesis is the separation of the cytoplasm into two new daughter cells. Animal cells divide when proteins pinch in the center of the cell until it separates into two. This region is called the cleavage furrow.Plant cells divide when new cell wall components lay down in the center of the cell. This part is called the cell plate.

Phases of cell cycle: G0, G1, G2, M

During interphase, the cell grows, and DNA replicates. In the mitotic phase, the replicated DNA and cytoplasmic contents separate, and the cell divides. See photo @jackwestin.com.

Mitotic process:prophase, metaphase, anaphase, telophase, interphase-Key Points

During prophase, the nucleus disappears, spindle fibers form, and DNA condenses into chromosomes (sister chromatids). During metaphase, sister chromatids align along the middle of the cell by attaching their centromeres to the spindle fibers. During anaphase, sister chromatids physically separate at the centromere and pull towards opposite poles of the cell by the mitotic spindle.

Mitotic process:prophase, metaphase, anaphase, telophase, interphase-Key Points

During telophase, chromosomes arrive at opposite poles and unwind into thin strands of DNA, the spindle fibers disappear, and the nuclear membrane reappears. Cytokinesis is the actual splitting of the cell membrane; animal cells pinch apart, while plant cells form a cell plate that becomes the new cell wall. Cells enter the G0 (inactive) phase after they exit the cell cycle when they are not actively preparing to divide; some cells remain in G0 phase permanently.

Phases of cell cycle: G0, G1, G2, M

G0 Phase Not all cells undergo mitotic phase. Cells in the G0 phase are not actively preparing to divide. The cell is in a quiescent (inactive) stage that occurs when cells exit the cell cycle. Some cells enter G0 temporarily until an external signal triggers the onset of G1. No more DNA replication or cell division happens at this phase. The cells that never or rarely divide include mature cardiac muscle and nerve cells, and they remain in G0 permanently.

Phases of cell cycle: G0, G1, G2, M

G1 Phase (First Gap) The first stage of interphase is the G1 phase (first gap), the growing phase. All cells undergo G1. Here, the cell is quite active at the biochemical level. The cell grows and accumulates the building blocks of chromosomal DNA and the associated proteins as well as sufficient energy reserves to complete the task of replicating each chromosome in the nucleus. Cells increase in size and produce organelles. The cell has two choices at this point: to divide or not to divide. Between G1 and S phase, the cell decides if it wants to grow. Some cells that do not divide include bone cells and blood cells (they do not undergo mitosis). These cells do not go through S or G2. They stop at G1 or G0. The cell is creating organelles for energy and protein production (mitochondria, ribosomes, and endoplasmic reticulum), while increasing its size.

Control of cell cycle-Key Terms

G1 checkpoint: a point in the animal cell cycle at which the cell becomes "committed" to the cell cycle, which is determined by external factors and signals sister chromatid: either of the two identical strands of a chromosome (DNA material) that separate during mitosis M checkpoint: prevents separation of the duplicated chromosomes until each chromosome is properly attached to the spindle apparatus

Phases of cell cycle: G0, G1, G2, M

G2 Phase (Second Gap) In the G2 phase, the cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation. This phase is where the cell prepares for division. Here, the cell has double the DNA and again increase in size. Some cell organelles are duplicated, and the cytoskeleton is dismantled to provide resources for the mitotic phase. There may be additional cell growth during G2.

Growth arrest

Growth arrest or G0 is viewed as either an extended G1 phase, where the cell stops growing (in M phase) due to mutation/damage, due to contact inhibition (crowding), or lack of food.

Mitotic Structures

In addition to their kinetochore-related function, centromeres perform another essential role in mitosis by serving as the sites of sister chromatid attachment. A chromatid is one of two strands that form when a chromosome replicates. Sister chromatids join together. For accurate mitoses, sister chromatids must remain connected until the spindle checkpoint permits. See photo @jackwesti.com.

Mitotic Structures

Kinetochores appear as platelike structures composed of several layers. During anaphase, several microtubules appear to insert into the kinetochore which situates on the side of the chromosome facing the spindle pole to which the chromosome attaches. The purpose of the kinetochore is to pull the chromatids apart. Kinetochores also help during cell division by making sure that each new cell has one chromatid from each pair.

Phases of cell cycle: G0, G1, G2, M

M Phase Following the interphase, the cell enters the multistep mitotic phase, where cell nucleus divides, and the cell components split into two identical daughter cells.

Mitotic Structures

Mechanisms of chromosome movement During anaphase, the sister chromatids separate at the centromere. Each chromatid is pulled rapidly toward the centrosome by the spindle fibers. Meanwhile, changes in microtubule length(provide the mechanism for chromosome movement. In the first part of anaphase, the kinetochore microtubules shorten and draw the chromosomes toward the spindle poles. In the second part, the astral microtubules, which anchor to the cell membrane, pull the poles further apart. See photo @jackwestin.com.

Mitotic process:prophase, metaphase, anaphase, telophase, interphase

Metaphase Metaphase is so named because the chromosomes line up in the middle of the cell. The centromeres attach to the spindle fibers originating at opposite poles. The root "meta-" means "middle." See photo @jackwestin.com. In metaphase, mitotic spindle is fully developed, and centrosomes are at opposite poles of the cell chromosomes line up at the metaphase plate each sister chromatid is attached to a spindle fiber originating from opposite poles

Mitotic Structures

Microtubules are rope-like tubes made of protein in cells. They form the mitotic spindle, which is responsible for the capture of chromosomes and align them at the center during prometaphase.

Mitotic process:prophase, metaphase, anaphase, telophase, interphase

Mitosis steps consist of prophase, metaphase, anaphase, and telophase; the cell undergoes nucleus division and split into two identical daughter cells. The stages of mitosis occur in sequence with specific events in each one. By observing the chromosome, one can identify the mitotic process. Remember that the DNA is in the nucleus, which is surrounded by the nuclear membrane. The DNA needs to be free from the nucleus so it can evenly distribute to two daughter cells.

Mitotic Structures

Mitotic structures such as the spindle apparatus and motor proteins orchestrate the movement of chromosomes during mitosis. Mitotic structures such as spindle fibers and motor proteins assist in the process and mechanism that separate chromosomes during mitosis. To accurately separate the chromosomes, there is a need for a condense, small, compact object, and a way to move these objects around the cell. Thus, microtubules are essential structures that accomplish this significant step.

Control of cell cycle

Negative regulator molecules (Rb, p53, and p21) act primarily at the G1 checkpoint and prevent the cell from moving forward to division until damaged DNA is repaired. p53 halts the cell cycle and recruits enzymes to repair damaged DNA; if DNA cannot be repaired, p53 triggers apoptosis to prevent duplication. Production of p21 is triggered by p53; p21 prevents the cycle by binding to and inhibiting the activity of the Cdk/cyclin complex. Dephosphorylated Rb binds to E2F, which halts the cell cycle; when the cell grows, Rb is phosphorylated and releases E2F, which advances the cell cycle.

Growth arrest

Not all cells adhere to the normal cell cycle pattern in which a newly-formed daughter cell immediately enters the interphase, closely followed by the mitotic phase. Cells in G0 phase are not actively preparing to divide. The cell is in a quiescent (inactive) stage that occurs when cells exit the cell cycle. Some cells enter G0 temporarily until an external signal triggers the onset of G1. Other cells that never or rarely divide, such as mature cardiac muscle and nerve cells, remain in G0 permanently. See photo @jackwestin.com.

Mitotic Structures

Nuclear membrane breakdown and reorganization The nuclear membrane or envelope provides a selective barrier between the nuclear interior and the cytoplasm and constitutes a central component of the intracellular structure. It needs to breakdownthe nuclear membrane at the beginning of mitosis, or during the prometaphase stage, to allow the mitotic spindle fibers to access the chromosomes inside and mix with the nuclear content in the cytosol. At the end of mitosis or during telophase, nuclear envelope reorganizesaround decondensed chromatin. Then, the nuclear compartment reestablishes in each of the newly formed daughter cells.

Mitotic Structures

Spindles are microtubule fibers that arrange and move chromosomes. It is necessary to equally divide the chromosomes in a parental cell into two daughter cells during mitosis. Spindle fibers are also called the mitotic spindle.

Mitotic process:prophase, metaphase, anaphase, telophase, interphase

Prophase Mitosis begins in prophase, where the chromosome condenses into chromatids. A centromere connects each chromatid to its copy, making the linked pairs look like X's. The nuclear envelope starts to disintegrate, mitotic spindle begins to assemble, and centriole pairs move toward opposite poles of the cell. This stage is a preparatory stage. "Pro-" means "before;" "phase" means "stage." So, this is the stage before the process gets into full swing. See photo @jackwestin.com. In prophase, chromosomes condense and become visible spindle fibers emerge from the centrosomes nuclear envelope breaks down nucleolus disappears

Loss of cell cycle controls in cancer cells

Proto-oncogenes normally regulate cell division but can be changed into oncogenes through mutation, which may cause cancers to form. Proto-oncogenes positively regulate the cell cycle, whereas oncogenes disrupt normal cell division and cause cancers to form. Some mutations prevent the cell from reproducing, which keeps the mutations from being passed on. If a mutated cell is able to reproduce because the cell division regulators are damaged, then the mutation will be passed on, possibly accumulating more mutations with successive divisions.

Loss of cell cycle controls in cancer cells-Key Points

Proto-oncogenes positively regulate the cell cycle. Mutations may cause proto-oncogenes to become oncogenes, disrupting normal cell division and causing cancers to form. When genes that produce regulator proteins become mutated, it creates a malformed and non-functional, cell-cycle regulator that increases the chance of more mutations in the cell.

Phases of cell cycle: G0, G1, G2, M

S Phase (Synthesis of DNA) The synthesis phase of interphase takes the longest because of the complexity of the duplicated genetic material. The S phase is where DNA replication occurs, and centrioles replicate. The two centrosomes give rise to the mitotic spindle, the apparatus that orchestrates the movement of chromosomes during mitosis. At the center of each animal cell, the centrosomes of animal cells associate with a pair of rod-like objects, the centrioles, which are at right angles to each other. Centrioles help organize cell division. The ploidy of the cell does not change and each cell has 46 chromosomes or 92 chromatids. The word chromosome can be used to refer to a single chromatid before the S phase or a pair of chromatids attached at the centromere after S phase.

Mitotic process:prophase, metaphase, anaphase, telophase, interphase

Telophase In telophase, the nuclei at each pole form again. The chromosomes separate into two identical nuclei. That implies the end of mitosis. However, the two nuclei are still in a single cell. "Telo" comes from the Greek word for "end". See photo @jackwestin.com. In telophase, chromosomes arrive at opposite poles and begin to condense nuclear envelope material surrounds each set of chromosomes the mitotic spindle breaks down The next step will separate the cytoplasm into two compartments. Telophase is basically the reverse of prophase.

Control of cell cycle

The G2 checkpoint ensures all of the chromosomes are replicated and that the replicated DNA is not damaged before the cell enters mitosis. The M checkpoint determines whether all the sister chromatids are attached to the spindle microtubules. This is important before the cell enters anaphase. See photo @jackwestin.com.

Control of cell cycle-Key Points

The M checkpoint confirms the correct attachment of the mitotic spindle fibers to the kinetochores. Positive cell regulators such as cyclin and Cdk perform tasks that advance the cell cycle to the next stage. Negative regulators such as Rb, p53, and p21 block the progression of the cell cycle until certain events have occurred.

Phases of cell cycle: G0, G1, G2, M

The Stages of Interphase and the Cell Cycle: The cell cycle consists of interphase and the mitotic phase. During interphase, the cell grows and the nuclear DNA 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 two daughter cells

Phases of cell cycle: G0, G1, G2, M

The cell cycle has two major phases: interphase (G0, G1, S, G2) and the mitotic phase (M). During interphase, the DNA is not highly visible. It is in its less condensed form known as chromatin because the cell is not actively dividing. During mitosis, the cell will be actively dividing so it is not chromatin but becomes chromosomes which is a condensed version of chromatin.

Control of cell cycle

The cell cycle is also controlled by regulator molecules that either promote the process or stop it from progressing. Two groups of proteins, cyclins and cyclin-dependent kinases (Cdks), are responsible for promoting the cell cycle. Cyclins regulate the cell cycle only when they are bound to Cdks. To be activated, the Cdk/cyclin complex must be phosphorylated, which allows it to phosphorylate other proteins that advance the cell cycle.

Phases of cell cycle: G0, G1, G2, M

The cell cycle is an ordered series of events involving cell growth and cell division that produces two new daughter cells. Cells undergoing cell division proceed through a series of precisely timed and carefully regulated stages of growth, DNA replication, and division that produces two identical (clone) cells.

Control of cell cycle

The cell cycle is controlled by mechanisms both internal and external to the cell, and by regulator molecules. The cell cycle is controlled at three internal checkpoints. Damage to DNA and other external factors are evaluated at the G1 checkpoint; if conditions are inadequate, the cell will not be allowed to continue to the S phase of interphase.

Mitotic Structures

The centromere is a region of highly specialized chromatin. Without it, the cells cannot divide properly, and the overall process of mitosis fails. Its primary function is to provide the foundation for the assembly of the kinetochore, which is a patch of protein structure essential to proper chromosomal segregation.

Mitotic process:prophase, metaphase, anaphase, telophase, interphase

The events of mitosis describe the processes of splitting and moving nuclear DNA to opposite ends of the parent cell, where the nuclear membranes will reform. Then the cell membrane can split the cytoplasm and organelles (termed cytokinesis). The two daughter cells will each have the same genetic code. The significant mitosis stages are: 1.Prophase 2.Metaphase 3.Anaphase 4.Telophase

Phases of cell cycle: G0, G1, G2, M-Key Points

There are three stages of interphase: G1 (first gap), S (synthesis of new DNA ), and G2 (second gap). Cells spend most of their lives in interphase, specifically in the S phase where genetic material must be copied. Some cells that do not divide or replicate stops at G1 or G0; G0 and G1 are sometimes the same thing. The cell grows and carries out biochemical functions, such as protein synthesis, in the G1 phase. During the S phase, DNA as well as centrioles are replicated. In the G2 phase, energy is replenished, new proteins are synthesized, and additional growth occurs. After interphase, mitosis follows.

Loss of cell cycle controls in cancer cells

Tumor suppressor genes are segments of DNA that code for negative regulator proteins, which keep the cell from undergoing uncontrolled division. One of the most important tumor suppressors is tumor protein p53, which plays a vital role in the cellular response to DNA damage. The role of normal p53 is to monitor DNA and the supply of oxygen (hypoxia is a condition of reduced oxygen supply). If damage is detected, p53 triggers repair mechanisms. If repairs are unsuccessful, p53 signals apoptosis.

Mitotic process:prophase, metaphase, anaphase, telophase, interphase-Key Terms

cell plate: where plant cells divide when new cell wall are made mitotic spindle: the apparatus that orchestrates the movement of chromosomes during mitosis sister chromatid: the identical copies formed by the DNA replication of a chromosome centrosome: an organelle near the nucleus of a cell that contains the centrioles (in animal cells) and from which the spindle fibers develop in cell division.

Mitotic Structures-Key Terms

centrioles: the main centers that help in the formation of microtubule fiber asters: star-shaped radial arrays that form around each pair of centrioles cytokinesis: the physical process of cell division, which divides the cytoplasm

Mitotic Structures-Key Terms

centromere: the specialized DNA sequence of a chromosome that links a pair of sister chromatids kinetochore: a complex of proteins associated with the centromere of a chromosome during cell division, to which the microtubules of the spindle attach nuclear membrane: the membrane around the nucleus

Mitotic process:prophase, metaphase, anaphase, telophase, interphase-Key Terms

centrosome: an organelle near the nucleus in the cytoplasm of most organisms that control the organization of its microtubules and gives rise to the mitotic spindle cytokinesis: the second portion of the mitotic phase in which the cytoplasm of a cell divides following the division of the nucleus nuclear membrane: the membrane around the nucleus

Control of cell cycle-Key Terms

cyclin: any of a group of proteins that regulates the cell cycle by forming a complex with kinases cyclin-dependent kinase (Cdk): (CDK) a member of a family of protein kinases first discovered for its role in regulating the cell cycle through phosphorylation E2F: which is a transcription factor required for the transcription and eventual translation of molecules required for the G1/S transition.

Mitotic Structures-Key Terms

microtubules: small tubes that form part of the cytoskeleton and provide structure and shape to eukaryotic cells motor proteins: molecular motors that aids in the formation of the spindle apparatus and the separation of the chromosomes during mitosis spindle fibers: filaments that are chiefly involved in moving and segregating the chromosomes

Loss of cell cycle controls in cancer cells-Key Terms

mutation: any heritable change of the base-pair sequence of genetic material proto-oncogene: a normal gene that when mutated becomes an oncogene oncogene: a mutated version of a normal gene involved in the positive regulation of the cell cycle

Control of cell cycle-Key Terms

p21: cell cycle regulatory protein that inhibits the cell cycle; its levels are controlled by p53 p53: cell cycle regulatory protein that regulates cell growth and monitors DNA damage; it halts the progression of the cell cycle in cases of DNA damage and may induce apoptosis retinoblastoma protein (Rb): a group of tumor-suppressor proteins that regulates the cell cycle by monitoring cell size phosphorylate: the addition of a phosphate group as a modification

Growth arrest-Key Terms

quiescent: in a state or period of inactivity or dormancy