Ciclo Celular: Interfase - Aula 31 - Módulo I: Biologia Celular | Prof. Gui

What is Cancer?

Understanding Cancer

• Cancer is not a single disease but encompasses over 200 different types characterized by uncontrolled cell multiplication due to genetic material damage.

• Genetic damage can arise from chemical exposure or errors during the cell cycle, leading to failures in cellular repair mechanisms.

• When cells begin to multiply uncontrollably, they can detach from their original tissue and spread throughout the body.

Cell Cycle and Interphase

Overview of Cell Division

• The lecture introduces the concept of the cell cycle, focusing on interphase and its significance in cellular processes.

• A graphical representation illustrates that interphase (in blue) occupies more time than mitosis (in yellow), indicating normal cellular behavior.

Importance of Interphase

• If interphase duration decreases significantly compared to mitosis, it suggests potential issues with cell control, leading to neoplasia.

• Neoplasia refers to immature cells dividing before reaching full maturity, which is synonymous with cancer.

Phases of Interphase

Breakdown of Interphase Stages

• Interphase consists of three stages: G1 (Gap 1), S (Synthesis), and G2 (Gap 2).

• During G1, cells grow significantly while maintaining high metabolic activity; this phase involves synthesizing RNA and proteins essential for growth.

S Phase Dynamics

• In the S phase, DNA synthesis occurs as cells prepare for division. The law of Spencer indicates that as a cell grows larger, its volume increases faster than its surface area, creating metabolic instability.

Cell Growth Challenges

Implications of Cell Size

Understanding Chromosome Duplication and Cell Cycle Phases

The Basics of Chromosome Structure

• Cells must contain 46 chromosomes, which necessitates the duplication of genetic material during the S phase. This process involves the replication of DNA, although initially, it exists in chromatin form rather than as distinct chromosomes.

• A common misconception is that duplicating a chromosome results in two separate chromosomes; however, biologically, one chromosome can exist in both simple (single chromatid) and duplicated (two chromatids) forms.

• The term "chromatid" refers to the condensed structure of DNA within a duplicated chromosome. Thus, one chromosome may consist of one chromatid or two chromatids depending on its state.

Key Processes During the S Phase

• During the S phase, while chromosomes are said to duplicate, it is actually the quantity of DNA that doubles. Each chromosome remains singular but transitions from having one chromatid to two.

• Additionally, centriole duplication occurs during this phase. Centrioles play a crucial role in cell division by forming structures like cilia and flagella.

Insights into G2 Phase Activities

• In G2 phase, cells prepare for division by growing further and synthesizing RNA and proteins while maintaining high metabolic activity. Energy reserves are built up to support upcoming cellular processes.

• The cell's metabolism remains active but not as intense as during G1 phase. This energy reserve is critical since metabolic rates will drop significantly once division begins.

Visual Representation of Cell Cycle Phases

• Graphically representing cell phases shows how cells transition through G1, S, and G2 stages while duplicating their genetic material and centrioles effectively preparing for mitosis.

• Some cells enter a resting state known as G0 after reaching maturity where they cease to divide despite having grown sufficiently—this includes muscle cells and neurons which do not undergo further division.

Importance of Checkpoints in Cell Division

• The G0 phase represents an indefinite interphase where certain cells opt out of dividing entirely until conditions change or repair mechanisms allow them to re-enter the cycle.

• Checkpoints throughout the cell cycle ensure that any damage or issues with DNA are addressed before proceeding with replication or division. If irreparable damage is detected at these checkpoints, affected cells may be directed towards apoptosis instead of continuing through the cycle.

Apoptosis and Cell Cycle Checkpoints

Understanding Apoptosis

• Apoptosis is a phenomenon where cells are instructed to self-destruct when they have problems, preventing further multiplication of potential issues. This process is referred to as programmed cell death.

Cell Cycle Checkpoints

• Before entering mitosis, there is a checkpoint that ensures DNA duplication has occurred correctly and that the cell has grown sufficiently. If any issues are detected, the cell can either repair them or undergo apoptosis.

Autolysis Process

• If lysosomes within the cell rupture, it leads to autolysis, which is a self-destruction process of the cell. This mechanism highlights how cells can eliminate themselves if they become dysfunctional.

Key Checkpoints in Mitosis

• There are several checkpoints during the cell cycle: G1/S checkpoint, G2/M checkpoint, and metaphase/anaphase checkpoint. While specific names may not be crucial for exams, understanding their existence is beneficial.

Role of p53 Protein

• The p53 protein acts as a tumor suppressor by checking for errors in DNA. If it detects an issue that cannot be repaired, it signals for the destruction of defective cells. Mutations in p53 can lead to continued progression through the cycle despite genetic defects.

Cyclins and CDKs Interaction

• When functioning properly, p53 inhibits cyclins and cyclin-dependent kinases (CDKs), which control the progression of the cell cycle. If these proteins are active without proper checks from p53, it could result in tumor formation.

Conclusion on Cell Cycle Regulation

• The interaction between p53 and cyclins/CDKs is critical for regulating whether a cell continues through its cycle or undergoes apoptosis due to defects. Proper functioning of this system prevents potential tumor development.

Final Thoughts on Learning Resources

• The speaker emphasizes the value of structured learning resources available on their platform, highlighting organized materials and well-selected exercises designed to enhance understanding effectively.