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Questions and Answers
What is the primary purpose of mitosis?
What is the primary purpose of mitosis?
Mitosis is used for both growth and asexual reproduction.
Mitosis is used for both growth and asexual reproduction.
True
What are gametes?
What are gametes?
Sex cells like eggs and sperm
Chromosomes are made of ______ wrapped tightly around proteins called histones.
Chromosomes are made of ______ wrapped tightly around proteins called histones.
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What role do histones play in the structure of chromosomes?
What role do histones play in the structure of chromosomes?
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Match the following processes with their purposes:
Match the following processes with their purposes:
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Chromosomes are visible when the cell is inactive.
Chromosomes are visible when the cell is inactive.
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What happens after fertilization in sexual reproduction?
What happens after fertilization in sexual reproduction?
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What role do cyclins play in the cell cycle?
What role do cyclins play in the cell cycle?
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CDKs are enzymes that work independently to activate the next phase of the cell cycle.
CDKs are enzymes that work independently to activate the next phase of the cell cycle.
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What phase are permanent cells sometimes known to be in?
What phase are permanent cells sometimes known to be in?
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The process of ensuring all new cells have the same DNA as the original is called _____ during mitosis.
The process of ensuring all new cells have the same DNA as the original is called _____ during mitosis.
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Match the following cell types with their characteristics:
Match the following cell types with their characteristics:
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Which of the following describes the function of checkpoints in the cell cycle?
Which of the following describes the function of checkpoints in the cell cycle?
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Mitosis is not necessary for growth and repair of tissues.
Mitosis is not necessary for growth and repair of tissues.
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What happens to chromosomes before a cell divides?
What happens to chromosomes before a cell divides?
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What are sister chromatids?
What are sister chromatids?
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Humans have 23 pairs of chromosomes, including sex chromosomes.
Humans have 23 pairs of chromosomes, including sex chromosomes.
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What is a karyotype?
What is a karyotype?
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The ______ is the phase when the cell is not dividing but preparing for division.
The ______ is the phase when the cell is not dividing but preparing for division.
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What happens during the S phase of the cell cycle?
What happens during the S phase of the cell cycle?
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Match the phase of the cell cycle with its description:
Match the phase of the cell cycle with its description:
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How many chromosomes do humans have?
How many chromosomes do humans have?
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Cytokinesis is the process of dividing the nucleus.
Cytokinesis is the process of dividing the nucleus.
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Study Notes
Cell Cycle
- The cell cycle is a process that helps cells divide to produce new, genetically identical daughter cells
- These new cells are essential for:
- Growth: Increasing the size of an organism
- Repair: Replacing old or damaged cells
- Reproduction (asexual): For some organisms, cell division creates entirely new organisms
Cell Division and Reproduction
Mitosis
- Purpose: A single cell divides into two cells with identical DNA
- Uses of Mitosis:
- Asexual reproduction: One parent creates offspring that are identical copies (e.g., Amoeba, Bougainvillea plants).
- Growth: Producing more cells to make an organism larger
- Repair: Replacing damaged tissues (e.g., healing wounds)
Sexual Reproduction
- Depends on meiosis, which creates gametes (sex cells like eggs and sperm).
- After fertilization (fusion of gametes), mitosis takes over producing many new cells for the developing organism
Chromosomes
Structure and Importance
- Chromosomes are like "instruction manuals" inside each cell, carrying genetic information (DNA)
- Chromosomes are made of DNA tightly wrapped around proteins called histones.
- Histones act like spools, condensing DNA into neat bundles called nucleosomes.
Visibility of Chromosomes
- Inactive cells: Chromosomes are thin, uncoiled, and hard to see
- Dividing cells: Chromosomes coil tightly and become dense, which makes them easier to observe under a microscope.
How Chromosomes Work During Mitosis
- Before a cell divides, each chromosome is copied to create two identical copies called sister chromatids.
- During cell division, the chromatids are split and shared equally between two new cells, ensuring each daughter cell has the identical DNA as the original.
Chromosome Count
- Humans have 46 chromosomes (23 pairs). One chromosome in each pair comes from the mother and the other from the father.
Karyotype
- A karyotype is a photograph of all the chromosomes in a cell, arranged in pairs
- Example: Humans have 22 pairs of autosomes (non-sex chromosomes) and one pair of sex chromosomes (XX for females, XY for males).
The Cell Cycle
- A repeating process where cells grow, divide, and form new cells
- Has specific steps to properly ensure division
Phases of the Cell Cycle: Interphase
- A period when the cell is not dividing, but is preparing for division by growing and duplicating its DNA.
- Has 3 stages:
- G1 (Gap 1): The cell grows in size and collects materials needed for the next steps.
- S (Synthesis): The cell makes exact copies of its DNA, turning single chromosomes into double-stranded chromatids.
- G2 (Gap 2): The cell gets ready for division by creating more organelles and materials.
Mitosis (Division of the nucleus) (karyokinesis)
- The cell divides its nucleus, ensuring that each new cell gets an identical set of chromosomes.
Cytokinesis (division of the cytoplasm)
- The cell's cytoplasm divides, forming two separate cells. Each cell gets its own nucleus and a full set of organelles.
Control of the Cell Cycle
- The cell cycle is tightly regulated to ensure cells divide only when ready
Cyclins and CDKs (Proteins That Control the Cycle)
- Cyclins: Proteins that control the timing of the cell cycle.
- CDKs (Cyclin-Dependent Kinases): Enzymes that work with cyclins to activate the next phase of the cell cycle.
Checkpoints
- The cell has built-in checkpoints to pause the cycle if something goes wrong (e.g., damaged DNA or incomplete replication).
Permanent Cells
- Some cells do not divide once formed. These are called permanent cells. Examples include nerve, retina, lens, and heart muscle cells.
Key Takeaways
- Mitosis is essential for ensuring all new cells have the same DNA as the original, and are necessary for growth, repair, and some types of reproduction
- Chromosomes must be duplicated before dividing to ensure each daughter cell has a complete set.
- The cell cycle is controlled by proteins like cyclins and CDKs, acting as "traffic lights" to ensure the cell only moves to the next step when ready.
- Cells divide at different rates.
Learning Tip
- DNA replicates, forming two separate DNA helices (chromatids), separating during mitosis, becoming individual chromosomes in a daughter cell.
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This is the Edexcel Unit 2 prep.
