Mitosis and Chromosome Duplication

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Questions and Answers

What is the role of the G1 checkpoint in the cell cycle?

Assesses DNA integrity and triggers apoptosis if necessary (correct)

Stimulates the cell to enter G0 stage

Checks that DNA has been copied

Ensures chromosomes are attached to the spindle

Which signal is known to stimulate skin cells during injury repair?

Estrogen

Cyclins

Epidermal growth factor (EGF) (correct)

Platelet Derived Growth Factor (PDGF)

What happens at the G2 checkpoint?

Cells are stimulated to divide by estrogen

DNA replication is verified to ensure it has occurred (correct)

Chromosomes are attached to the microtubule spindle

DNA is assessed for damage and integrity

Which of the following statements about cyclins is true?

Cyclins activate other proteins to advance the cell cycle Signup and view all the answers

What is the purpose of contact inhibition in cell division?

To prevent cells from dividing when they touch each other Signup and view all the answers

What happens during prophase of mitosis?

Chromosomes condense and spindle fibers form Signup and view all the answers

What is the main event during metaphase?

Chromosomes line up in the middle of the cell Signup and view all the answers

In which phase do sister chromatids separate?

Anaphase Signup and view all the answers

What process follows the separation of chromosomes?

Cytokinesis Signup and view all the answers

Which type of cells use actin and myosin filaments to divide?

Animal cells Signup and view all the answers

What is the primary function during the G1 phase of interphase?

Cell doubles its organelles Signup and view all the answers

What occurs during the S phase of the cell cycle?

DNA synthesis occurs, forming sister chromatids Signup and view all the answers

In what condition do some cells remain when they are unlikely to divide?

Go phase Signup and view all the answers

What happens to each chromosome before division?

Each chromosome duplicates to form sister chromatids. Signup and view all the answers

What is the term used for the chromosomes after sister chromatids are separated?

Daughter chromosomes Signup and view all the answers

How many chromosomes do human cells typically have?

46 Signup and view all the answers

During which phase of mitosis do chromosomes align at the equatorial plate?

Metaphase Signup and view all the answers

What is the main function of the microtubule spindle during mitosis?

To pull chromosomes apart. Signup and view all the answers

Which phase of mitosis involves the visibility of two distinct cells under a microscope?

Telophase and Cytokinesis Signup and view all the answers

What structure attaches microtubules to the chromosomes?

Kinetochore Signup and view all the answers

What characteristic of DNA allows for the formation of sister chromatids?

They are organized into a double helix. Signup and view all the answers

What is the role of apoptosis in multicellular organisms?

To maintain the correct number of cells Signup and view all the answers

Which of the following best describes the signals affecting cell cycling?

Some signals inhibit cell cycling while others activate it Signup and view all the answers

What is the process called that involves programmed cell death?

Apoptosis Signup and view all the answers

In multicellular organisms, how do they reproduce?

By producing gametes Signup and view all the answers

What happens to the final fragments of a cell undergoing apoptosis?

They are engulfed by white blood cells Signup and view all the answers

How does the concentration of cyclins change during the cell cycle?

It changes, being broken down in the next phase Signup and view all the answers

What triggers apoptosis in cells?

Internal or external signals Signup and view all the answers

What distinguishes reproduction in multicellular organisms from single-celled ones?

Multicellular organisms produce gametes while single-celled organisms often divide independently Signup and view all the answers

What occurs during anaphase II of meiosis?

Sister chromatids separate Signup and view all the answers

What is the chromosome composition of all gametes from female mammals?

They always have X chromosomes Signup and view all the answers

What is one difference between meiosis and mitosis during anaphase?

Meiosis involves separation of homologous chromosomes Signup and view all the answers

Which statement about the result of meiosis is correct?

Daughter nuclei have only half the chromosomes Signup and view all the answers

How can genetic variation be created during meiosis?

By crossing-over of homologous chromosomes Signup and view all the answers

What happens to the daughter nuclei after meiosis?

They are genetically different from the parent nucleus Signup and view all the answers

What is a defining characteristic of meiosis compared to mitosis?

Meiosis includes two rounds of cell division Signup and view all the answers

What is produced during the second meiotic division?

Four haploid gametes Signup and view all the answers

Study Notes

Chromosome duplication and sister chromatids

Before division, each chromosome duplicates itself to create two sister chromatids
Sister chromatids are joined at the centromere
Each sister chromatid carries identical DNA
During division, sister chromatids separate to become daughter chromosomes
All genes in the parent cell are passed to the daughter cells

Human cells

Each human cell contains 46 chromosomes
When arranged by size, condensed chromosomes form a karyotype

Mitosis: Cell division for growth

Mitosis is divided into four phases: prophase, metaphase, anaphase, and telophase/cytokinesis
During prophase, chromosomes are visible under a microscope as condensed pairs
During metaphase, chromosomes line up along the equatorial plate (middle of the cell)
During anaphase, chromatids are pulled to opposite poles of the cell
During telophase and cytokinesis, two distinct cells are formed

Microtubule spindle

The microtubule spindle pulls apart chromosomes (or chromatids)
Microtubules shorten by depolymerization and are pulled by motor proteins
These microtubules attach to opposite ends of the cell

Cytokinesis

During cytokinesis, the cell divides
Animal cells use actin and myosin filaments to contract and pinch off two new cells
Plant cells build a new cell wall to separate the daughter cells

Cell cycle: Interphase

Interphase is the majority of the cell cycle
During interphase, cells perform their usual functions
Interphase consists of three stages: G1, S, and G2
During G1, cells grow, double theirorganelles, and accumulate materials for DNA synthesis
G1 is also when cells decide whether to divide or not, they can enter G0, a state where they don't divide
Nerve cells are permanently in G0
During S, DNA synthesis occurs, resulting in each chromosome being composed of two sister chromatids
During G2, cells grow and synthesize proteins needed for cell division

Cell division rates

The rate of cell division varies depending on the type of cell
Some cells, such as nerve cells, are unlikely to divide (in G0)
The speed of cell division depends on the needs of those cell types

Cell cycle control system

The cell cycle must be controlled to ensure that stages occur in order and the cycle only continues when the previous stage is successfully completed
There are three main checkpoints: G1 checkpoint, G2 checkpoint, and mitotic stage checkpoint (M)
The G1 checkpoint checks for DNA integrity, if repair is not possible, apoptosis occurs or the cell goes into G0
The G2 checkpoint checks that DNA has been copied
The mitotic stage checkpoint (M) occurs between metaphase and anaphase, ensuring chromosomes are attached to the microtubule spindle

Control of cell cycling

Signals, molecules that stimulate or inhibit an event, can push cells through the cell cycle or block it
External signals come from outside the cell
- Epidermal growth factor (EGF) stimulates skin near injuries to divide and repair damage
- Platelets in blood clots secrete PDGF (Platelet Derived Growth Factor)
- Estrogen stimulates the uterine lining to divide and prepare for egg implantation
- Contact inhibition prevents cells from dividing when they touch
Internal signals come from inside the cell
- Cyclins are proteins present only during specific stages of the cell cycle
  - A cyclin activated in one stage of the cycle will help the cell pass into the next stage

Apoptosis (programmed cell death)

Apoptosis is caused by internal or external signals
Apoptosis helps maintain the correct number of cells
Apoptosis plays a part in growth and development
Final cell fragments are engulfed by white blood cells

Reproduction in single-cell organisms

Reproduction is simple for single-cell organisms

Reproduction in multicellular organisms

Multicellular organisms produce gametes through meiosis
Meiosis I: homologous chromosomes separate
Meiosis II: sister chromatids separate
Four haploid daughter nuclei (gametes) are produced
All gametes from female mammals have X chromosomes
If a gamete has a Y chromosome, it will produce a male offspring (XY)
If a gamete has an X chromosome, it will produce a female offspring (XX)

Meiosis compared to mitosis

During meiosis I, homologous chromosomes separate while in mitosis, they do not pair up
During meiosis II, sister chromatids separate
There is no proper interphase between meiosis I and meiosis II
In meiosis, daughter nuclei are different from the parent and are haploid (half the number of chromosomes)
In mitosis, daughter nuclei are genetically identical to the parent and are diploid

Meiosis function

Meiosis creates genetic variation in three ways:
- Fusing gametes from two parents mixes their DNA
- Shuffling chromosomes in a cell to produce genetically different gametes
- Crossing-over (exchanging genetic material between homologous chromosomes)

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Description

Explore the fascinating process of mitosis and chromosome duplication in human cells. This quiz covers the key phases of mitosis, the role of sister chromatids, and how human chromosomes are organized into a karyotype. Test your understanding of cell division and its importance for growth!