CH 12 BIO MO2A

why cell division is needed for unicellular organisms

crucial for unicellular organisms because it is their primary method of reproduction, meaning each time a cell divides, it creates a new, identical organism, effectively allowing the population to increase and spread; essentially, cell division in a unicellular organism is equivalent to reproduction itself

how cell division contributes to growth and differentiation

creating new cells, which increases the overall number of cells in an organism, leading to an increase in size, while differentiation allows these new cells to specialize into different types of cells, forming tissues and organs with specific functions, thus enabling the development of a complex organism from a single fertilized egg

why cell division is needed to maintain tissue

allows for the continuous replacement of old or damaged cells within a tissue, ensuring its proper function and structure; without cell division, tissues would eventually deteriorate as cells die off and are not replenished.

genome

the complete set of DNA within a cell, meaning all the genetic information that is precisely replicated and distributed to each daughter cell during cell division, ensuring each new cell receives an identical copy of the original genome

all of the genes in a organism

Chromatin

the complex of DNA and proteins that makes up chromosomes, which becomes highly condensed during cell division, allowing for the organized separation of replicated DNA strands into two daughter cells

chromosome

a highly condensed structure made up of DNA, visible during cell division, that carries genetic information and is duplicated before mitosis to ensure each daughter cell receives an identical copy of the parent cell's genome

discrete piece of DNA and associated proteins

Somatic cell

any cell in a multicellular organism that makes up the body, excluding reproductive cells (gametes), and these somatic cells divide through the process called mitosis to create identical copies of themselves; essentially, they are the "body cells" that undergo mitosis for growth and repair

Germline

the lineage of cells within an organism that are destined to develop into gametes (sperm or egg cells)

gamate

a cell specifically designed for sexual reproduction, formed by a separate cell division process that halves the chromosome number to create haploid cells, unlike the diploid cells produced by mitosis

how many chromosomes are present in a human somatic cell

46

how many chromosomes are present in a human gamete

23

Sister chromatid

one of the two identical copies of a chromosome created during DNA replication, joined together at the centromere, which are eventually separated during cell division to ensure each new cell receives a complete set of chromosomes

centromere

a specialized region on a chromosome that acts as the attachment point for spindle fibers during cell division, essentially holding together the two sister chromatids and allowing them to be separated evenly during mitosis and meiosis

arm

one of the two sections of a chromosome, separated by the centromere

part of the chromosome on either side of the centromere

mitosis

the process where a cell duplicates its chromosomes and then separates them equally into two new nuclei, resulting in two genetically identical daughter cells, each with the same number of chromosomes as the parent cell; essentially, it's a type of cell division that ensures each new cell receives a complete set of replicated chromosomes

division of the nucleus

Cytokinesis

the final stage of cell division where the cytoplasm of a cell physically divides into two separate daughter cells, ensuring that each new cell receives a complete set of segregated chromosomes from the original cell during mitosis or meiosis; essentially, it is the process of "splitting the cytoplasm" after the chromosomes have been separated and pulled to opposite poles of the cell

cohesion

the process of holding sister chromatids together during cell division

the attraction of molecules for other molecules of the same kind

how and why sister chromatids are attached to one another

by a protein complex called "cohesin," which forms a ring-like structure that encircles the two identical DNA strands created during DNA replication, holding them together most tightly at the centromere region; this attachment is crucial to ensure proper chromosome segregation during cell division, allowing each new daughter cell to receive one copy of each chromosome.

when and why DNA is replicated

DNA replication occurs during the Synthesis (S) phase of interphase, which is the stage before mitosis, so that each new daughter cell created during mitosis receives a complete copy of the genetic material from the parent cell, ensuring identical genetic information in both daughter cells

G0

a cell enters a resting state, meaning it is not actively preparing to divide and is essentially paused outside of the normal cell cycle

G1

a cell primarily grows in size, synthesizes proteins and RNA, and accumulates the necessary building blocks to prepare for DNA replication

G2

the cell actively prepares for cell division by synthesizing proteins necessary for mitosis, replicating organelles, and essentially ensuring all the necessary components are ready to enter the M (mitotic) phase, where the actual division of the cell occurs

what happens during mitosis

a cell's duplicated chromosomes are separated into two identical sets, with each set moving to opposite poles of the cell, effectively dividing the genetic material into two identical daughter nuclei, which will eventually become two separate daughter cells

the sister chromatids of replicated chromosomes are separated

what happens during cytokinesis

final stage of cell division where the cytoplasm of a single cell physically splits into two separate daughter cells, effectively dividing the cell into two distinct entities, each with its own nucleus, by the formation of a cleavage furrow in animal cells or a cell plate in plant cells

stages of mitosis

what happens to chromosomes in g1 phase

chromosomes remain in their normal, uncondensed state, meaning they are not actively being replicated and simply exist as single chromatids within the nucleus; the cell primarily focuses on growing and accumulating necessary materials for DNA replication which will occur in the subsequent S phase

what happens to Nuclear envelope in g1 phase

The nuclear envelope flattens at the end of the G1 phase. This flattening activates transcription factors that promote the transition from G1 to S phase

what happens to Centrosomes in g1 phase

a cell has one centrosome that is close to the nuclear envelope. During this phase, the cell grows, makes proteins and organelles, and synthesizes the centromere and other centrosome components

there is one centrosome per cell, consisting of two centrioles and the associated pericentriolar material

what happens to chromosomes in prophase

chromosomes condense and become visible under a microscope, appearing as distinct, X-shaped structures due to the presence of two identical sister chromatids joined at the centromere

what happens to nuclear envelope in prophase

still intact

what happens to centrosome in prophase

duplicated and separating

what happens to spindle in prophase

forming, not yet attach to chromosomes

what happens to chromosomes in Prometaphase

more condensed

what happens to nuclear envelope in Prometaphase

broken down

what happens to centrosome in Prometaphase

migrate to opposite poles of the cell, forming the bipolar spindle

what happens to kinetochore in prometaphase

becomes attached to microtubules from the spindle poles, allowing the chromosomes to be actively pulled and moved towards the center of the cell by the forces exerted by these microtubules

what happens to kinetochore microtubules in prometaphase

attach to the kinetochores (protein structures on the centromeres of chromosomes), pulling the chromosomes towards the center of the cell and setting the stage for proper alignment at the metaphase plate

what happens to non-kinetochore microtubules in prometaphase

extend between the poles of the cell without attaching to chromosomes, effectively pushing the centrosomes further apart and contributing to the elongation of the spindle apparatus

what happens to Chromosomes in metaphase

chromosomes line up in the middle of the cell, at the "metaphase plate," becoming highly condensed and visible under a microscope, with their centromeres precisely aligned, ready to be separated into individual sister chromatids

what happens to Nuclear envelope in metaphase

there is no longer a nuclear envelope

what happens to Centrosomes in metaphase

the centrosomes are positioned at opposite poles of the cell, having migrated there during prophase, and are actively involved in forming the spindle fibers that attach to the chromosomes

what happens to Chromosomes in anaphase

the sister chromatids of each chromosome separate at the centromere and are pulled apart by the spindle fibers, moving to opposite poles of the cell, effectively becoming individual chromosomes

what happens to Nuclear envelope in anaphase

the nuclear envelope is already broken down and remains disassembled

what happens to separase in anaphase

Separase is a protease that regulates chromatid cohesion during mitosis. Its activation leads to the cleavage of cohesin, which links replicated chromatids, and the subsequent separation of chromatids.

Separase is tightly regulated, and its malfunction can lead to genome instability and aneuploidy, which can cause cancers in higher vertebrates

what happens to Centrosomes in anaphase

centrosomes move further apart from each other as the spindle poles separate due to the elongation of interpolar microtubules, essentially "pushing" the centrosomes to opposite ends of the dividing cell

what happens to kinetochore microtubules in anaphase

shorten at the kinetochore end, effectively pulling the attached chromosomes towards the spindle poles by depolymerizing and releasing tubulin subunits, thus facilitating the separation of sister chromatids and their movement to opposite ends of the cell

what happens to non-kinetochore microtubules in anaphase

elongate, pushing the spindle poles further apart, contributing to the overall cell elongation as the chromosomes are pulled to opposite ends of the cell; essentially, they help "stretch" the cell during the separation of sister chromatids

what happens to chromosomes in telophase and cytokinesis

chromosomes reach opposite poles of the cell, begin to decondense (uncoil) back into chromatin, and new nuclear membranes form around each set of chromosomes, essentially reversing the condensation process that occurred earlier in mitosis; in cytokinesis, which follows telophase, the cytoplasm physically divides, separating the two sets of chromosomes into distinct daughter cells, while the chromosomes themselves remain in their decondensed state and are not actively changing

what happens to Nuclear envelope in telophase and cytokinesis

During telophase, the nuclear envelope reforms around each set of separated chromosomes, effectively reappearing after breaking down in earlier stages of mitosis, while in cytokinesis, the nuclear envelope remains fully formed and undergoes no significant change as the cytoplasm divides to create two separate daughter cells

what happens to spindle in telophase and cytokinesis

Completely disassemble and break down, essentially disappearing as the chromosomes reach the poles of the cell and new nuclear membranes form around each set of daughter chromosomes

what happens to centrosome in telophase and cytokinesis

begin to disassemble as the mitotic spindle breaks down, and each daughter cell inherits one centrosome

how chromosomes move during anaphase

chromosomes move towards opposite poles of the cell by being pulled apart at their centromeres by spindle fibers, specifically the kinetochore microtubules

Contrast cytokinesis in animal cells and plant cells

In plants, cytokinesis takes place by the cell plate method, while in animals, it occurs by cell cleavage. The new cell membrane is usually derived from the Golgi Body in the case of plant cytokinesis, while in animals, it is derived from the endoplasmic reticulum

how cell division is different in bacteria, dinoflagellates, diatoms and yeast

in bacteria occurs primarily through binary fission, a simple splitting process, while dinoflagellates undergo a unique form of closed mitosis with a complex nuclear structure, diatoms divide with a specialized cell wall formation, and yeast typically reproduces by budding, where a smaller daughter cell grows from the parent cell

In humans, describe which cells continuously divide, which divide as needed, and which do not divide

skin cells (epidermis) and blood cells (produced in the bone marrow), which need constant replacement due to wear and tear; cells that divide as needed include liver cells, which can regenerate after injury; and cells that do not divide include most mature nerve cells (neurons) and cardiac muscle cells

Explain what happened in Johnson and Rao’s 1970 experiment when they fused mammalian cells from S phase with ones from G

the G1 nucleus began to replicate its DNA immediately, indicating that the cytoplasm of the S phase cell contained factors that could trigger DNA synthesis in a G1 nucleus, demonstrating that cell cycle progression is regulated by cytoplasmic signals and not solely controlled by the nucleus itself

Explain what happened in Johnson and Rao’s 1970 experiment when they fused mammalian cells from M phase with ones from G1

the G1 nucleus prematurely entered mitosis, indicating that the cytoplasm of the M phase cell contained factors that could trigger mitosis in a G1 nucleus, demonstrating that cell cycle progression is controlled by cytoplasmic signals that can influence the state of a nucleus even when it is in a different cell cycle phase

growth factor necessary for cell cycle progression

they act as extracellular signals that trigger a cell to enter the cell cycle from a resting state (G0 phase), essentially giving the "go-ahead" to proceed through the G1 phase and initiate DNA replication in the S phase

Attachment to proper surface/substrate

cells that are removed from a substrate being unable to proliferate

Absence of DNA damage necessary for cell cycle progression

damaged DNA can lead to mutations being passed on to daughter cells, compromising genomic integrity, and potentially causing cell death or cancer development

why is Attachment of kinetochore microtubule during transition from metaphase to anaphase necessary for cell cycle progression

it allows for the proper segregation of chromosomes to opposite poles of the dividing cell, ensuring that each daughter cell receives the correct number of chromosomes

what MPF is and how it was discovered

"Maturation Promoting Factor," is a protein complex that plays a crucial role in initiating the M phase (mitosis) of the cell cycle by activating various proteins necessary for cell division.

it was discovered by researchers Yoshio Masui and Clement Markert in the 1970s through experiments with frog eggs.

consist of cyclin-dependent protein kinase 1

Explain what the relation between cyclin level and MPF activity. How is cyclin-dependent kinase

regulated?

as cyclin levels rise, so does MPF activity; essentially, cyclin acts as the regulatory subunit that activates the catalytic activity of the cyclin-dependent kinase (CDK) to form the active MPF complex

CDK inhibitors regulate cyclin-dependent kinase

cancer

a disease that occurs when cells divide without control and spread into surrounding tissues. Cancer is caused by DNA changes, most often in genes, which are like a cell's instruction manual

Tumor formation in cancer progression

Tumor initiation; a genetic alteration causes a single cell to proliferate abnormally, which leads to the growth of a tumor.

Tumor progression; As clonal selection continues, the tumor becomes more malignant and grows faster

Invasion into neighboring tissue in cancer progression

Cancer cell invasion is the process by which cancer cells break through the basement membrane and extracellular matrix to penetrate surrounding tissues. This is an early step in the process of metastasis, which is when cancer cells spread to other parts of the body to form new tumors.

Spread via lymphatic and blood vessels in cancer progression

Cancer cells spread through the body via the lymphatic system and bloodstream in a process called metastasis

Metastasis in cancer progression

when cancer cells spread from the primary tumor to other parts of the body, forming new tumors

Radiation

to target and destroy cancer cells while minimizing damage to healthy tissues, primarily by disrupting their ability to replicate through mechanisms like DNA damage, which can be achieved through radiation therapy by delivering high-energy beams that directly damage the genetic material (DNA) of cancer cells, preventing them from dividing and causing them to die off

taxol

its ability to stabilize and prevent microtubules depolymerization, leading to cell cycle arrest at the G2/M phase and cell death

stopping cancer cells from separating into two new cells

Herceptin

by attaching to HER2 receptors on the surface of breast cancer cells and blocking signals that tell the cells to grow and divide

Tamoxifen

blocking estrogen receptors and preventing estrogen from telling cancer cells to grow

interphase

prophase

metaphase

anaphase

telephase