Bio 251 Ch 4A

Summary

This video explains the cell cycle, starting with interphase, where cells perform their normal functions and decide whether to divide. It delves into DNA replication during the S phase, using key enzymes like helicase, polymerase, and ligase. The process of mitosis, including prophase, metaphase, anaphase, telophase, and cytokinesis, is also discussed. The video highlights the role of tumor suppressor genes and oncogenes in cancer, explaining how mutations in these genes can lead to uncontrolled cell division and cancer. The video emphasizes the importance of genetic mutations and multiple steps in the development of cancer.

Takeaways

• 😀 Interphase is the longest phase of the cell cycle, where cells grow and perform their regular functions before deciding to divide.
• 😀 The G1 phase is when a cell carries out its cellular job, like a hepatocyte synthesizing bile and detoxifying blood.
• 😀 DNA replication occurs during the S phase, where DNA is copied semi-conservatively, with each new DNA molecule having one old and one new strand.
• 😀 DNA structure consists of a sugar-phosphate backbone (rails) and nitrogenous base pairs (stairs), following specific base pairing rules (A with T, C with G).
• 😀 DNA is usually in a chromatin form in non-dividing cells and condenses into chromosomes during cell division.
• 😀 DNA replication involves enzymes like helicase (to unzip DNA), polymerase (to synthesize new strands), and ligase (to join fragments).
• 😀 Mitosis involves four stages: prophase, metaphase, anaphase, and telophase, followed by cytokinesis to separate the cytoplasm into two daughter cells.
• 😀 In prophase, chromosomes condense, spindle fibers form, and the nuclear envelope begins to disintegrate.
• 😀 In metaphase, duplicated chromosomes align on the metaphase plate, and microtubules attach to the sister chromatids.
• 😀 Mutations in proto-oncogenes and tumor suppressor genes (like p53) are key factors in the development of cancer, often requiring multiple mutations.

Q & A

What is the role of interphase in the cell cycle?

Interphase is the longest phase in the cell cycle, during which the cell performs its normal functions and prepares for cell division. It consists of three stages: G1, S, and G2 phases. In G1, the cell performs its regular activities. In S phase, DNA replication occurs. In G2, the cell prepares for mitosis.

What happens during the S phase of the cell cycle?

During the S phase, the cell replicates its DNA. The process involves using the enzyme DNA helicase to unzip the DNA strands and DNA polymerase to synthesize a new strand, creating two identical DNA molecules, each containing one old and one new strand (semi-conservative replication).

How does DNA structure support its function?

DNA has a double helix structure composed of two strands that form a spiral staircase. The sugar-phosphate backbone forms the rails, while nitrogenous bases (adenine, thymine, cytosine, and guanine) form the 'steps.' These bases pair according to base pairing rules (A with T, C with G), which ensures accurate DNA replication.

What is chromatin, and how does it differ from chromosomes?

Chromatin is the relaxed form of DNA that exists when the cell is not dividing. It consists of DNA wrapped around histone proteins to form nucleosomes. When the cell prepares for mitosis, chromatin condenses into chromosomes to facilitate easier distribution of genetic material during cell division.

What is the role of DNA helicase during DNA replication?

DNA helicase is responsible for unwinding the DNA double helix by breaking the hydrogen bonds between the paired nitrogenous bases, allowing the two strands to separate and become templates for replication.

What are proto-oncogenes and how do they contribute to cancer?

Proto-oncogenes are normal genes that promote cell division. When mutated, they become oncogenes, causing uncontrolled cell division, which is a key factor in the development of cancer.

How does the mutation of tumor suppressor genes contribute to cancer?

Tumor suppressor genes act as brakes on the cell cycle, slowing down or stopping cell division when necessary. Mutations in these genes, such as p53, can result in the loss of these 'brakes,' leading to unregulated cell growth and contributing to cancer development.

What is the difference between benign and malignant tumors?

Benign tumors are non-invasive and well-encapsulated, meaning they do not spread to surrounding tissues. Malignant tumors are cancerous, poorly encapsulated, and have the ability to invade neighboring tissues and spread to other parts of the body (metastasis).

What is the significance of checkpoints in the cell cycle?

Checkpoints are crucial regulatory mechanisms in the cell cycle that ensure proper progression through the cycle. They monitor DNA integrity and cell conditions, preventing the cycle from continuing if errors are detected, which helps prevent abnormal cell division and cancer.

Why do some cells divide rapidly while others do not?

The rate of cell division depends on the type of cell and its function. Some cells, like those in the skin or the lining of the stomach, divide rapidly because they have a short lifespan. Other cells, like neurons or muscle cells, divide infrequently or not at all once fully developed.