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Questions and Answers
During which phase does the unreplicated DNA checkpoint occur, preventing entry into mitosis?
During which phase does the unreplicated DNA checkpoint occur, preventing entry into mitosis?
What is the main function of the DNA damage checkpoints in the cell cycle?
What is the main function of the DNA damage checkpoints in the cell cycle?
What does the spindle-assembly checkpoint ensure before allowing the cell to enter anaphase?
What does the spindle-assembly checkpoint ensure before allowing the cell to enter anaphase?
When does the chromosome-segregation checkpoint occur, and what is its primary function?
When does the chromosome-segregation checkpoint occur, and what is its primary function?
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How long does a typical dividing mammalian cell spend in the M phase of the cell cycle?
How long does a typical dividing mammalian cell spend in the M phase of the cell cycle?
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What percentage of the cell cycle does interphase occupy?
What percentage of the cell cycle does interphase occupy?
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Which phase of the cell cycle involves DNA replication?
Which phase of the cell cycle involves DNA replication?
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What is the primary focus of genetics?
What is the primary focus of genetics?
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Which of the following processes corresponds to nuclear division during the M Phase?
Which of the following processes corresponds to nuclear division during the M Phase?
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Which of the following is NOT a sub-discipline of genetics?
Which of the following is NOT a sub-discipline of genetics?
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What occurs during the G1 phase of the cell cycle?
What occurs during the G1 phase of the cell cycle?
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What is the quiescent stage of the cell cycle referred to as?
What is the quiescent stage of the cell cycle referred to as?
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During which phase does cell division occur?
During which phase does cell division occur?
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Which type of cells primarily remain in the G0 phase and do not divide?
Which type of cells primarily remain in the G0 phase and do not divide?
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What is the significance of the cell cycle in genetics?
What is the significance of the cell cycle in genetics?
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What are the two basic phases of the cell cycle?
What are the two basic phases of the cell cycle?
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What significant event occurs at the transition between G1 and S phase?
What significant event occurs at the transition between G1 and S phase?
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How do cells in the G0 phase respond to the need for division?
How do cells in the G0 phase respond to the need for division?
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Which industry does NOT rely heavily on genetics?
Which industry does NOT rely heavily on genetics?
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What occurs at the end of a cell's life cycle?
What occurs at the end of a cell's life cycle?
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How long does cell division last in the average 24-hour human cell cycle?
How long does cell division last in the average 24-hour human cell cycle?
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What happens to the amount of DNA in a cell during the S phase?
What happens to the amount of DNA in a cell during the S phase?
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How many chromatids does each chromosome consist of after the S phase is completed?
How many chromatids does each chromosome consist of after the S phase is completed?
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What is synthesized during the G2 phase in preparation for mitosis?
What is synthesized during the G2 phase in preparation for mitosis?
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Which checkpoint is considered the most important in the cell cycle?
Which checkpoint is considered the most important in the cell cycle?
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What occurs to the centrioles during the S phase?
What occurs to the centrioles during the S phase?
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What is formed from the DNA during the S phase?
What is formed from the DNA during the S phase?
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Which type of DNA replicates earlier in the S phase?
Which type of DNA replicates earlier in the S phase?
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What is a key function of growth factors in the cell cycle?
What is a key function of growth factors in the cell cycle?
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Study Notes
Introduction of Genetics
- Genetics is the study of inheritance, focusing on the molecular mechanisms at cellular level, generational trait transmission, and gene movement within and between populations.
- Three main branches of genetics: transmission genetics, molecular genetics, and population genetics.
Importance of Genetics
- Plays a crucial role in agriculture, pharmaceutical industry, biotechnology industry, and medicine.
Cell Cycle
- Represents the life story of a cell, encompassing stages from one division to the next.
- Essential for genetics because it transmits genetic instructions from parent to daughter cells.
- Involves cell growth, metabolism, and development.
- Ends with cell division, producing two daughter cells capable of undergoing further cycles.
Phases of Cell Cycle
- Divided into two main phases: Interphase and M Phase (Mitosis).
- M Phase represents the actual cell division or mitosis.
- Interphase is the period between two successive M phases.
- Interphase lasts longer than the M Phase, accounting for over 95% of the cell cycle duration.
- Interphase is further divided into three sub-phases: G1 phase, S phase, and G2 phase.
G1 Phase
- Longest phase of interphase, lasting about 9 hours.
- Cell grows, synthesizes proteins necessary for cell division, but does not replicate DNA.
- RNA and protein synthesis occur.
- Centrosomes duplicate near the transition between G1 and S phase.
Quiescent Stage (G0)
- A non-dividing phase cells enter before reaching the G1/S checkpoint.
- Cells may remain in G0 indefinitely, or they may reenter G1 and complete the cell cycle.
- Some cells, like heart cells, do not divide further and stay in G0 perpetually.
S Phase
- DNA synthesis or replication occurs.
- DNA amount doubles, but the chromosome number remains the same (2n).
- Centriole duplication in the cytoplasm occurs in animal cells.
- DNA synthesis lasts about 5 hours in mammalian cells.
- Early replicating DNA tends to contain more active genes than late replicating DNA.
G2 Phase
- Proteins are synthesized, preparing for mitosis.
- Biochemical events necessary for cell division take place.
- Centrosome duplication is completed.
- Lasts about 3 hours.
Regulation of the Cell Cycle
- Controlled by growth factors to coordinate cell proliferation with the organism's needs.
- Cell cycle transitions are regulated by biochemical circuits called checkpoints.
Checkpoints of the Cell Cycle
- Restriction Checkpoint (G1/S Checkpoint): Occurs in G1 phase, detecting cell size and environmental interactions. Cells failing to receive appropriate growth stimuli don't proceed past G1 and are eliminated by apoptosis. This is the most important checkpoint.
- DNA Damage Checkpoints (G1, S, and G2): Block cell cycle progression until damaged DNA is repaired, or apoptosis occurs.
- Unreplicated DNA Checkpoint (G2/M Checkpoint): Occurs in G2, preventing entry into mitosis before complete DNA synthesis.
- Spindle-Assembly Checkpoint (Metaphase Checkpoint): Occurs in mitosis, preventing entry into anaphase until all chromosomes are properly attached to the mitotic spindle.
- Chromosome-Segregation Checkpoint: Occurs in telophase, preventing cytokinesis until all chromosomes are correctly separated.
M Phase - The Division Phase
- Lasts about 1-2 hours in most mammalian cells.
- Includes the five stages of mitosis: Prophase, Prometaphase, Metaphase, Anaphase, and Telophase.
- Mitosis is followed by cytokinesis.
Key Facts
- Interphase length varies between cell types.
- During interphase, chromosomes are relaxed and visible only as diffuse chromatin, uncoiled.
- The cell cycle ensures replication and division of genetic material accurately.
- The M Phase is a continuous process, although its division into stages can be somewhat arbitrary.
Control of the Cell Cycle
- Important to ensure proper timing and completion of the cell cycle, preventing errors that can lead to mutations and diseases.
- Growth factors and checkpoints are crucial for this regulation.
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