Questions and Answers
What is the primary focus of Lesson 1?
Foundations to set the stage
What does the cell cycle refer to?
The ordered series of processes of DNA replication and mitosis, or cell division.
What are the two major phases that produce two identical cells during cell division?
Interphase and Mitotic Phase
What happens during interphase?
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What occurs during the synthesis phase (S phase)?
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What is the mitotic phase (M phase)?
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Major points of cell regulation are entry and exit from the ______.
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What is the restriction point?
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What happens to most cells in the human body after mitosis?
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The exceptions to cells in G0 phase are those that are metabolically active, such as ______.
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What does cell cycling time refer to?
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What is the purpose of checkpoints in the cell cycle?
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What controls the progression through the cell cycle?
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Inhibitory proteins prevent ______ of the cycle when DNA damage is detected.
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What happens if DNA damage is present?
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What are M Phase checkpoints responsible for?
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What initiates the immune system's cellular components?
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Study Notes
Foundations of Cell Cycle and Immunity
- Cell cycle consists of DNA replication and mitosis, essential for growth and repair.
- Cell nucleus plays a critical role by managing molecular information necessary for these processes.
Phases of Cell Division
- Cell division occurs in two main phases: interphase and mitotic phase.
- During interphase, the cell grows and duplicates its DNA.
Interphase Steps
- First Growth Phase (G1): Cells increase in size and undergo RNA synthesis. Timing can vary significantly.
- Synthesis Phase (S): DNA replication results in identical pairs of chromosomes (chromatids) bonded at centromeres; typically lasts 2-10 hours.
- Mitotic Phase (M): Duplicate chromosomes align and separate into two new daughter cells; this phase takes about 30-60 minutes.
Cell Regulation Mechanisms
- Major checkpoints include G1 checkpoint, S phase, G2 checkpoint, and M phase to ensure proper cell cycle progression.
- The restriction point marks a critical transition where cells can commit to division; requires extracellular growth factors to proceed.
G0 Phase (Resting Phase)
- Many cells enter G0 post-mitosis, remaining in a non-dividing state; most cells in the body reside here.
Active Exceptions
- Cells like granulocytes and GI tract epithelium remain metabolically active even in G0, illustrating exceptions to typical resting behavior.
Time Management in Cell Cycling
- Cell cycling time measures the duration from one mitosis to the next, critical for understanding growth rates.
Cell Cycle Control and Checkpoints
- The cell cycle is tightly regulated with checkpoints preventing genetic anomalies that could lead to dysfunction or cancer.
- Checkpoints monitor DNA integrity, influencing progression through mitosis.
Role of Proteins in Cell Cycle Progression
- Two key protein groups involved: cyclins (D, E, A, B) and cyclin-dependent kinases (CDKs), forming complexes that enable phase progression.
Protein Distribution in Cell Cycle
- Cyclins and CDKs are located at distinct phases:
- G0-G1: Cyclin D and CDK 4/6
- Early S: Cyclin E and CDK 1/2
- Late S: Cyclin A and CDK 1/2
- G2: CDK 1/2 and cyclin A
- Before M: CDK 1 and Cyclin B
Inhibitory Proteins
- Inhibitory proteins, like p53, halt the cell cycle upon DNA damage, allowing for repair or inducing apoptosis.
DNA Damage Response
- In response to DNA damage, cells may cease dividing or initiate programmed cell death.
- Key regulatory proteins include retinoblastoma protein (Rb), p53, and p21.
Function of p53 as an Inhibitory Protein
- p53 levels rise in response to DNA damage, enhancing protective measures against uncontrolled cell proliferation. Known as the "suicide gene" for its role in programmed cell death.
M Phase Checkpoints
- Chromosomes must properly align on the mitotic spindle before cell division can proceed; misalignment triggers checkpoint mechanisms that halt division.
Overview of Immunity
- The immune system is essential for protecting against pathogens; composed of various cell types produced in the bone marrow.
Cells of the Immune System
- Immune cells originate from pluripotent stem cells in the bone marrow, highlighting the developmental aspect of immunity.
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