Mitose - Divisão Celular - Aula | Biologia com Samuel Cunha

What is Mitosis?

Introduction to Mitosis

• The speaker introduces the concept of mitosis, explaining that it is the process by which a cell divides into two identical cells.

• There are two types of cell division: mitosis (for somatic cells) and meiosis (for gametes), with a focus on mitosis in this discussion.

Importance of Mitosis

• Mitosis is crucial for growth and development; it has occurred trillions of times throughout an individual's life, replacing dying skin cells and producing new blood cells.

• Certain cells, like neurons and muscle cells, do not undergo mitosis regularly, while fibroblasts can enter a state of latency until stimulated to divide.

Functions of Mitosis

Key Functions

• Mitosis plays a vital role in tissue regeneration; for example, healing cuts relies on the division of skin cells.

• In multicellular organisms, differences in size between individuals arise from varying numbers of cells due to more frequent mitotic divisions.

Cancer Connection

• Uncontrolled cell division during mitosis can lead to cancer, highlighting the importance of regulated cellular cycles.

The Cell Cycle: Interphase and Mitosis

Overview of the Cell Cycle

• The cell cycle consists of interphase (the longer phase where the cell prepares for division) and mitosis (the actual division).

Phases of Interphase

• Interphase includes three phases: G1 (growth), S (DNA synthesis), and G2 (preparation for mitosis).

G1 Phase

• During G1 phase, the cell grows and synthesizes proteins necessary for DNA replication. A checkpoint ensures conditions are favorable for division.

S Phase

• In S phase, DNA is duplicated to ensure each daughter cell receives an identical set. This phase also involves duplicating centrioles essential for later stages.

Detailed Look at Interphase Phases

Growth and Preparation

• The G1 checkpoint assesses if the cell has grown sufficiently before proceeding. If not ready or if DNA damage is detected, it may delay or halt progression.

What Happens During the Cell Cycle?

Overview of the Cell Cycle

• The S phase is crucial for DNA duplication, where the cell checks if all DNA has been correctly replicated before proceeding to mitosis.

• If DNA replication is incorrect, the cell will not enter mitosis, highlighting the tightly controlled nature of the cell cycle to prevent errors that could lead to cancer.

Understanding Mitosis

• Mitosis consists of four main phases: prophase, metaphase, anaphase, and telophase. Familiarity with these terms is essential for understanding cellular division.

• In prophase, chromosomes condense and become visible as distinct structures; each chromosome consists of two sister chromatids connected at a centromere.

Chromosome Structure and Function

• Chromosomes are formed by DNA wrapping around proteins called histones, leading to their condensation into a more compact structure.

• Each chromosome carries two molecules of DNA (chromatids), which are linked by a thin region known as the centromere.

Key Events in Prophase

• The nuclear envelope disintegrates during prophase, allowing spindle fibers to form and attach to chromosomes.

• Spindle fibers are microtubules that extend from centrosomes at opposite poles of the cell to pull chromatids apart during later stages.

Transitioning Through Mitosis Phases

• Proper fragmentation of the nucleus is critical; without it, spindle fibers cannot effectively attach to chromosomes.

• Metaphase follows prophase; here, chromosomes align along the equatorial plate in preparation for separation.

Why Is Alignment Important in Metaphase?

Importance of Chromosome Alignment

• Chromosomes must be maximally condensed during metaphase to minimize entanglement risks when being pulled apart.

• All chromosomes should be attached to spindle fibers at this stage; improper attachment can lead to errors in chromatid separation.

Mechanism of Spindle Fiber Attachment

• The connection between spindle fibers and chromosomes occurs at kinetochores located on centromeres; this ensures proper pulling during anaphase.

Final Checks Before Anaphase

Cell Division Process

Overview of Chromosome Behavior During Cell Division

• The chaotic nature of chromosome visibility is due to their maximum condensation, allowing for better observation of individual chromosomes and identification of genetic characteristics such as sex.

• In the separation phase (anaphase), sister chromatids break apart, resulting in single DNA molecules. Spindle fibers pull these chromatids towards opposite sides of the cell.

• Anaphase concludes with each side receiving a copy of the DNA, marking a critical step in ensuring genetic material is evenly distributed.

Telophase and Cytokinesis

• Telophase involves the de-condensation of chromosomes; if not properly unwound, reading DNA for protein synthesis becomes impossible.