THE CELL CYCLE 12 APUSH

Key roles of cell division.

Best characteristic that differintiates non-living things from living things.

MOST CELL DIVISION RESULTS IN GENETICALLY IDENTICAL DAUGHTER CELLS.

distributuiin of indentical genetic material.

CELLULAR ORGANIZATION OF THE GENETIC MATERIA

a cells endownment of DNA is called a genome

a typical human cell has about 2m of DNA

DNA molecules are pacaged into chromosomes.

The DNA molecule carries several hundred to a few thousand genes

the entire complex of DNA is referred to chromatin.

Somatic cells each contain 46 chromosomes made up of 23 .

exception are the gametes which only have 23 chromosomes each.

DISTRIBUTION OF CHROMOSOMES DURING EUKARYOTIC CELL DIVISON.

each crhomosme is in the from of a long thin chromatin fiber

EACH duplicated chromosomes has two sister chromatids

coheins

are proteins that hold the sister chromatids together until they are separated during anaphase of mitosis. .

centromere a region of the crhromosomal dna where the chromatid is attached

MEIOSIS only ocurrs inly in special cell sin the ovaries or testes.

THE MITOTIC PHASE ALTERNATES WITH INTERPHASE IN THE CELL CYCLE.

PHASES OF THE CELL CYCLE

Mitotic phase includes both mitosis and cytokenises.

Interphase includes h phase s phase and g phase 2.

Mitosis is subdivided in

to several stages: prophase, metaphase, anaphase, and telophase, each playing a crucial role in the accurate distribution of chromosomes to the daughter cells.

THE MITOTIC SPINDLE: A CLOSER LOOK

it begins to for in the prophase.

G2 of interphase

During this phase, the cell prepares for mitosis by synthesizing proteins and organelles necessary for cell division.

prophase

During prophase, the chromatin condenses into visible chromosomes, and the nuclear envelope begins to break down, allowing the spindle fibers to form and attach to the centromeres.

Prometaphase

During prometaphase, the chromosomes become even more condensed, and the spindle fibers connect to the kinetochores of the chromosomes, facilitating their movement toward the metaphase plate.

Metaphase

During metaphase, the chromosomes align at the metaphase plate, ensuring that each sister chromatid is attached to spindle fibers from opposite poles, which is crucial for accurate segregation during the next phase.

Anaphase

During anaphase, the sister chromatids are pulled apart towards opposite poles of the cell, ensuring that each new daughter cell will receive an identical set of chromosomes.

Telophase and Cytokinesis

During telophase, the chromosomes begin to de-condense back into chromatin, and the nuclear envelope re-forms around each set of chromosomes, while cytokinesis follows, dividing the cytoplasm and resulting in two separate daughter cells. This entire process is crucial for maintaining genetic stability and ensuring that each daughter cell has the necessary components to function properly.

the assembly of microtuibules atarts at the centrosome

Aster→

The aster is a star-shaped structure formed around the centrosome during cell division, which helps in organizing the microtubules that will pull the chromosomes apart during mitosis.

kinetochore→

The kinetochore is a protein structure on the chromosome that assembles on the centromere, serving as the attachment point for spindle fibers during cell division, ensuring accurate segregation of sister chromatids to the daughter cells.

• spindle fibers → Spindle fibers are dynamic structures that emerge from the centrosomes, facilitating the movement of chromosomes by attaching to the kinetochores and pulling them toward opposite poles of the cell during anaphase.

metaphase plate→

The metaphase plate is an imaginary plane equidistant from the two spindle poles, where chromosomes align during metaphase, ensuring that each daughter cell will receive an equal and accurate distribution of genetic material.

Anaphase begins when cohesins are cleave by an enzyme called separase.

CYTOKINESIS: A CLOSER LOOK

cleavage→

the process where the cytoplasm of a parental cell is divided into two daughter cells, which is essential for the completion of cell division.

Cleavage furrow→

The indentation that begins to form on the surface of the cell as it undergoes cytokinesis, signaling the separation of the two daughter cells.

cytokinesis in plant cell ocurr because of vesicle which go an forma cellular wall in the middle of the cell.

In contrast, during cytokinesis in animal cells, the cleavage furrow deepens until the cell membrane pinches off, ultimately dividing the cytoplasm and completing the cell division process.

BINARY FISSION IN BACTERIA

asexual reproductiion of a single-celled organism

origin of replication→

the point where DNA replication begins, allowing the cell to duplicate its genetic material before division.

THE EVOLUTION OF MITOSIS

The fast that some of the proteins involved iin bacerial binary fission are related to eukaryotic prtoeins.

The Eukaryotic cell cylce is regulated by a molecular control system.

THE CELL CYCLE CONTROL SYSTEM

Checkpoitns G1, G2 AND M

These checkpoints ensure that the cell is ready to proceed to the next phase, allowing for the repair of any DNA damage and the proper completion of cellular processes. Furthermore, the proteins involved in these checkpoints, such as cyclins and cyclin-dependent kinases (CDKs), play crucial roles in signaling the cell to move forward or halt the cycle based on internal and external conditions.

THE CELL CYCLE CLOCK: CYCLINS AND CYCLIN-DEPENDENT KINASES

protein kinases are enzykes that activate or inactivate other proteins by phosphorylating them.

Cyclin a protein that gets its name from its cyclically fluctuating concentraiton in the cell.

Cyclin dependen kinases risses and fall with changes in concentration of cdk

MPF→

Maturation Promoting Factor (MPF) is a complex of cyclin and cyclin-dependent kinase (CDK) that triggers the cell's transition from the G2 phase to the M phase, thereby initiating mitosis.

MPF conrolls passagfe through checkpoint g2

STOP AND GO SIGNS INTERNAL AND EXTERNAL SIGNALS AT THE CHECKPOINTS

G1 or restriction point→

cells assess whether conditions are favorable for division, checking for sufficient nutrients, growth factors, and DNA integrity before proceeding to the S phase.

• G2 checkpoint: Ensures all DNA is replicated accurately before proceeding to mitosis.

G0→

cells enter a quiescent state where they are metabolically active but do not actively divide, allowing them to conserve energy and resources until conditions are suitable for re-entry into the cell cycle.

growth factor→ is a protein released by certai cells that stimulates other cells to divide.

density-dependent inhibition a phenomenon in which crowded cells stop dividing.

density-dependent inhibition→

is crucial for maintaining tissue architecture and preventing overgrowth, as it ensures that cells only proliferate when there is sufficient space to do so.

M checkpoint→

the point in the cell cycle where the cell checks for DNA damage and ensures that all chromosomes are properly aligned before proceeding to anaphase.

ANCHORAGE DEPENDENCE→

the requirement that cells must be attached to a solid surface or substrate in order to grow and divide, which helps prevent uncontrolled cell proliferation.

LOSS OF CELL CYCLE CONTROLS IN CANCER CELLS

cancer cell do not stop dividng and become essentially inmortal

• This uncontrolled division is often a result of mutations in genes that regulate the cell cycle, leading to the bypass of normal checkpoints that would typically halt division in response to errors.

transformation→

the process by which a normal cell becomes a cancer cell, characterized by its ability to grow and proliferate uncontrollably.

benign tumor→

A non-cancerous growth that does not invade surrounding tissues or spread to other parts of the body, typically considered less dangerous than malignant tumors.

malignant tumors→

Cancerous growths that can invade nearby tissues and spread to other parts of the body through the bloodstream or lymphatic system, often requiring more aggressive treatment.

Metastasis→

The process by which cancer cells spread from the original tumor to distant sites in the body, forming secondary tumors that can complicate treatment and prognosis.

.Checkpoint