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What is the primary function of telomeres?
DNA molecules in sister chromatids are genetically different.
False
What is a gene?
A section of DNA that codes for one protein.
The size of a DNA molecule is approximately _______ nm.
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Match the following components with their functions.
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What is the primary function of nucleosomes?
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Telomeres are found in the middle of chromosomes.
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What are chromosomes made of?
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The protective sequence of nucleotides at the ends of chromosomes is known as __________.
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Match the following terms with their definitions:
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How long is the total length of DNA in 46 human chromosomes?
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Histone proteins are acidic in nature.
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What is the width of a centromere?
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What is the role of centromeres during mitosis?
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In plant cells, daughter cells are separated by a cleavage furrow.
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What is the term used to describe the ability of a stem cell to produce different cell types?
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A __________ is an agent that causes cancer, such as UV radiation or nuclear fallout.
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Match the following terms related to cancer with their definitions:
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What structure forms across the equator of a plant cell during cytokinesis?
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Cytokinesis in animal cells involves the formation of a cell plate.
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What is the primary function of centrioles during cell division?
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During mitosis, the __________ ensures chromosome stability by moving chromosomes to the poles of the cell.
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Match the following cell division processes with their characteristics:
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Which of the following statements is true about stem cells?
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Animal cells contain both centrioles and centrosomes.
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What is the role of the contractile ring during animal cell cytokinesis?
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What is the primary purpose of mitosis?
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Interphase is the shortest phase in the cell cycle.
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During which phase do centrosomes migrate to opposite poles?
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The process by which DNA is duplicated is called the ______ phase.
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Match each phase of mitosis with its description:
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Which of the following statements about the G1 phase is true?
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In anaphase, chromosomes line up at the equator of the spindle.
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What occurs during the G2 phase?
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The mitotic spindle is made up of ______ required for chromosome movement.
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What is formed at the end of the M phase?
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Study Notes
The Structure Of A Chromosome
- Chromosomes are thread-like structures made of DNA
- The total length of DNA in a human cell is about 1.8m
- DNA is wound around proteins called histones.
- Histone proteins associate with DNA to form nucleosomes.
- Nucleosomes condense DNA into chromatin.
- Chromatin is a complex of DNA and RNA, as well as proteins that compress DNA.
Structure of a Chromosome
- A chromatid is one half of a replicated chromosome
- The centromere is the region of a chromosome where microtubules attach during cell division.
- Telomeres are protective sequences of nucleotides found at the ends of chromosomes.
Structure of a Nucleosome
- 11nm wide and 6nm long.
- Made up of 8 histone molecules.
Structure of Telomeres
- Cap the ends of chromosomes.
- Are required for successful cell division.
- Allow continued replication.
- Prevent the loss of genes.
- Made of DNA with short base sequences repeated multiple times.
The Cell Cycle
- The cell cycle is a series of events that take place in a cell leading up to its division.
Interphase
- The longest phase of the cycle
- The cell grows to its normal size.
- When the cell performs its normal functions
- The time spent between cell division
G1 Phase
- Cells make RNA, enzymes, and other proteins needed for growth.
- At the end of G1, the cell becomes committed to either dividing or not.
S Phase
- DNA synthesis takes place
- The DNA in the nucleus replicates, so each chromosome consists of 2 identical chromatids.
- This is known as DNA replication.
G2 Phase
- The cell continues to grow.
- New DNA is checked, and any errors are repaired.
- Preparations are made to start cell division.
M Phase (Mitosis)
- Nuclear division that produces 2 genetically identical daughter cells.
- Maintains genetic stability.
- Ensures cells retain function
- Maintains chromosome number
Functions of Mitosis
- Growth
- Cell replacement
- Repair of tissues
- Asexual reproduction
- Immune response (clonal selection of B and T-lymphocytes)
The Stages of Mitosis
- Prophase, metaphase, anaphase, telophase
Prophase
- Centrosomes migrate to opposite poles of the cell.
- Chromatin begins to condense.
- The nuclear envelope and nucleolus begin to disappear.
- Centrosomes and migrate to opposite poles of the cell.
- Asters and spindle fibers form.
Metaphase
- Centrosomes are at the poles of the cell and organize the production of spindle microtubules.
- Chromosomes line up across the equator of the spindle.
- Each chromosome splits at its centromere.
- Chromosomes start to be pulled apart by microtubules.
Anaphase
- Chromatids move to opposite poles.
- Centromeres are first pulled by microtubules.
- Spindle fibers contract and chromosomes are pulled to opposite ends.
Telophase
- Nuclear envelope and nucleolus reforms.
- Nucleus divides.
- Chromosomes are at the poles of the cell.
Cytokinesis
- The division of cytoplasm
- Cytoplasm is divided into two cells.
Cytokinesis In Plant Cells
- Cell plate forms across the equator of the cell, cellulose, and cell wall laid down.
Cytokinesis In Animal Cells
- A contractile ring forms.
- The contractile ring pushes the equator of the cell inwards, forming a cleavage furrow.
- The cleavage furrow deepens as active filaments in the ring contract.
- Eventually, the cell splits into two cells.
Differences in Plant and Animal Cell Mitosis
- Plant cells have no visible centriole or aster.
- Daughter cells get separated by a cell plate, there is no cleavage furrow formation.
Centromeres, Centrosome, Centrioles
Centromere
- Needed for separation of chromatids during mitosis
- Site of attachment of spindle microtubules
- Each metaphase chromosome has 2 kinetochores at its centromere and microtubules
- Kinetochore is a protein molecular complex that binds to DNA and microtubules.
- Bundles of microtubules called spindle fibers extend from the kinetochores to the poles of the spindle during mitosis.
Centrosome
- Found in animal cells.
- Acts as the microtubule organizing center for the construction of the spindle.
- Located at the poles of the cells.
Centrioles
- Act as microtubule organizing centers.
- Assemble and form spindle fibers during prophase.
- Contraction of spindle fibers during anaphase separates sister chromatids.
Stem Cells
- Can divide an unlimited number of times by mitosis.
- The extent of the power that a cell has to produce different types of cells is called its potency.
- Stem cell therapy is the introduction of new adult stem cells into damaged tissue to treat disease or injury.
Cancer
- Results from uncontrolled mitosis.
- Cancer cells divide repeatedly and form a tumor.
- Carcinogens are agents that cause cancer.
Cellular Changes that Occur in the Development of Cancer
- A mutation occurs in a gene responsible for cell division.
- This leads to the formation of an oncogene from a proto-oncogene.
- This causes uncontrolled cell division.
- The coordination of the cell cycle is lost. The signal to stop dividing is not received by the cell.
- Loss of function and lack of specialization occurs.
- A tumor is formed, an irregular mass of cells that show an abnormal change in shape.
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Description
Explore the intricate structure of chromosomes, including their composition of DNA and histones. Learn about the roles of nucleosomes, centromeres, and telomeres in cell division and genetic stability. This quiz covers key components of chromosome structure essential for understanding cellular biology.
