Cell Division & Mitosis: Key Concepts ad Stages

What are the main stages of cell division?

Cell growth and activity (Interphase), nuclear division (mitosis), and division of the cytoplasm (cytokinesis).

What process do prokaryotic cells use to reproduce?

Binary fission.

How is genetic information organized in eukaryotic cells?

It is distributed among individual, linear DNA molecules within the nucleus.

What is a chromosome composed of?

One DNA molecule and its associated proteins.

What is the simplest structure of DNA?

The double-helical structure.

What is a nucleosome?

A core particle consisting of DNA wrapped around an octamer of eight histone proteins.

What are sister chromatids?

Two identical copies of a chromosome produced during duplication before cell division.

What role do cohesins play in cell division?

They hold sister chromatids together until they are removed during mitosis.

What is ploidy?

The number of chromosome sets in a cell or species (e.g., haploidy, diploidy, polyploidy).

What type of cells are diploid?

Somatic cells.

What type of cells are haploid?

Germ cells.

What is the purpose of mitosis?

To divide replicated DNA equally and precisely, generating daughter cells that are exact genetic copies of the parent cell.

What are the three phases of Interphase?

G1 phase (cell growth), S phase (DNA replication), and G2 phase (preparation for mitosis).

What are the five stages of mitosis?

Prophase, Prometaphase, Metaphase, Anaphase, and Telophase.

What is cytokinesis?

The division of the cytoplasm to form two new cells after mitosis.

How does cytokinesis occur in plant cells?

Vacuoles join at the center to form a cell plate, which develops into a new cell wall.

How does cytokinesis occur in animal cells?

Microfilaments form contractile rings that cleave the cell into two new cells.

What is the primary function of cell division in single-celled organisms?

To reproduce and give rise to new organisms.

What role does cell division play in multicellular organisms?

It is crucial for growth, development, and the replacement of worn-out or damaged cells.

How is DNA packaged during interphase?

DNA is loosely packaged in chromatin form, allowing for replication and transcription.

What happens to DNA during chromosome condensation?

DNA is tightly packed into distinct chromosomes, making it easier to segregate during cell division.

List the phases of the cell cycle.

G1 phase (cell growth), S phase (DNA replication), G2 phase (preparation for mitosis), M phase (mitosis and cytokinesis).

What is accomplished during the G1 phase of the cell cycle?

Cell growth and preparation for DNA replication.

What occurs during the S phase of the cell cycle?

DNA replication takes place, resulting in two copies of each chromosome.

What is the main event during the G2 phase of the cell cycle?

Preparation for mitosis, including the synthesis of proteins necessary for cell division.

What are the key events of prophase in mitosis?

Chromosomes condense, the nuclear envelope breaks down, and spindle fibers begin to form.

What happens during metaphase in mitosis?

Chromosomes align at the metaphase plate, and spindle fibers attach to the centromeres.

Describe the events of anaphase in mitosis.

Sister chromatids are pulled apart toward opposite poles of the cell.

What occurs during telophase in mitosis?

Chromosomes de-condense, the nuclear envelope re-forms, and the cell prepares for cytokinesis.

How does mitosis ensure genetic continuity?

It accurately distributes identical copies of DNA to each daughter cell.

What are the three checkpoints that regulate the cell cycle?

G1 checkpoint, G2 checkpoint, and M checkpoint.

What can happen if cell cycle regulation fails?

It can lead to uncontrolled cell division and cancer.

What is binary fission?

A method of asexual reproduction in prokaryotic cells where the cell divides into two identical cells.

What is the role of the origin of replication (ORI) in prokaryotic cell division?

It is the specific site where DNA replication begins on the bacterial chromosome.

How does the prokaryotic cell cycle differ from the eukaryotic cell cycle?

Prokaryotic cells have a simpler cycle, primarily involving binary fission, while eukaryotic cells undergo more complex processes including mitosis and cytokinesis.

What is the significance of accurate DNA replication in cell division?

It ensures that each daughter cell receives a complete and identical set of genetic information.

What distinguishes living organisms from nonliving matter in terms of cell division?

The ability to reproduce and produce more of their own kind through cell division.

What is the function of actin-like proteins in bacterial cell division?

Their exact role is not well understood, but they are thought to assist in chromosome segregation.

What is the typical duration of the cell division cycle in E. coli?

Approximately 20 minutes, with DNA replication occupying 19 minutes of that time.

What happens to the cell during binary fission after DNA replication is complete?

The cell elongates and the plasma membrane begins to pinch inward, leading to division.

What is the genome of a cell?

All the DNA contained within a cell, which can consist of a single DNA molecule in prokaryotes or multiple DNA molecules in eukaryotes.

How are chromosomes formed from DNA?

DNA molecules are packaged into chromosomes for easier segregation during cell division.

What are chromosomes composed of?

Chromosomes are composed of DNA molecules and associated proteins.

How many genes can a DNA molecule in a chromosome carry?

A DNA molecule in a chromosome can carry several hundred to a few thousand genes.

What is the structure of chromosomes in eukaryotes?

In eukaryotes, hereditary information is distributed among individual, linear DNA molecules.

What is the haploid human genome composed of?

The haploid human genome contains approximately 3 billion base pairs of DNA packaged into 23 chromosomes.

What is the total number of base pairs in a diploid human cell?

A diploid human cell contains about 6 billion base pairs of DNA.

How long is the DNA in a diploid human cell?

Each diploid cell contains about 2 meters of DNA.

How many cells are estimated to be in the human body?

The human body is estimated to contain about 50 trillion cells.

What is the significance of histones in DNA packaging?

Histones provide the energy to fold DNA and help package it into a smaller volume.

What is chromatin?

Chromatin is the complex of DNA and all its associated proteins.

What is the simplest level of DNA structure?

The simplest level is the double-helical structure of DNA.

What forms a nucleosome?

A nucleosome forms when DNA winds around the histones H2A, H2B, H3, and H4.

What do nucleosomes and linkers resemble under an electron microscope?

Nucleosomes and linkers appear as beads on a string.

What is the diameter of the 10-nm chromatin fiber?

The 10-nm chromatin fiber has a diameter of about 10 nanometers.

What is the solenoid model in chromatin structure?

The solenoid model predicts that nucleosomes spiral helically with about six nucleosomes per turn.

What are the two proposed models for the 30-nm fiber?

The two proposed models are the solenoid model and the helix model.

What is a functional chromosome composed of?

A functional chromosome has a centromere, a pair of telomeres, and origins of replication.

What is the role of the centromere?

The centromere is the attachment point for spindle microtubules during cell division.

What assembles on the centromere before cell division?

A multiprotein complex called the kinetochore assembles on the centromere.

What are telomeres?

Telomeres are the natural ends, or tips, of a linear chromosome.

How does DNA fit into the nucleus?

DNA fits into the nucleus because it is packed into a shorter length by histone proteins.

What is the estimated length of DNA in a human body compared to the distance to the Sun?

The DNA in a human body could stretch to the Sun and back more than 300 times.

What happens to chromosomes before cell division?

Before cell division, chromosomes condense into thick, readily observed structures.

What is the length of DNA in direct contact with the histone octamer in a nucleosome?

The DNA in direct contact with the histone octamer is between 145 and 147 base pairs in length.

What is the role of nonhistone proteins in DNA packaging?

Nonhistone proteins also associate with DNA and assist in its packaging.

What do adjacent nucleosomes form in the 30-nm fiber?

Adjacent nucleosomes fold on themselves to form a dense, tightly packed structure.

What is the difference between euchromatin and heterochromatin?

Euchromatin is loosely packed, while heterochromatin shows dense packing.

What is the estimated amount of DNA per human body?

There is approximately 100 trillion meters of DNA per human body.

What are origins of replication?

The sites where DNA synthesis begins, not easily observed by microscopy.

What happens to DNA in preparation for cell division?

DNA is replicated and chromosomes condense.

What is the centromere?

The narrow 'waist' of the duplicated chromosome where the two sister chromatids are most closely attached.

What is chromosome segregation?

The equal distribution of chromosomes into each of two daughter nuclei during cell division.

What separates sister chromatids during mitosis?

The enzyme separase hydrolyzes cohesin at the onset of anaphase, allowing chromatids to separate.

What are haploid cells?

Cells that contain one copy of each type of chromosome, such as gametes (sperm and egg).

What are polyploid cells?

Cells that have three, four, or more complete sets of chromosomes.

What is the diploid chromosome number in humans?

2n=46, meaning humans have 46 chromosomes in somatic cells.

What is the role of mitosis?

To divide replicated DNA equally and precisely, generating daughter cells that are exact genetic copies of the parent cell.

What is meiosis?

A process of sexual reproduction that produces daughter nuclei with half the number of chromosomes (haploid) of the parental nucleus.

What does the cell cycle represent?

The life story of a cell, including stages from one division to the next.

What are the two major phases of the cell cycle?

Interphase (period between cell divisions) and M phase (mitotic phase).

What occurs during interphase?

The cell grows, develops, synthesizes DNA, RNA, and proteins, and prepares for cell division.

What are checkpoints in the cell cycle?

Regulatory points that allow or prohibit the cell's division based on the condition of cellular components.

What is the function of cohesins?

To hold sister chromatids together until they are separated during mitosis.

What is the significance of mitotic cytoskeleton?

It separates replicated DNA molecules precisely into daughter cells.

What are homologous chromosomes?

The two chromosomes of each pair in a diploid cell, one from the mother and one from the father.

What is the difference between mitosis and meiosis?

Mitosis produces identical daughter cells, while meiosis produces genetically diverse haploid cells.

What is the role of DNA synthesis in the cell cycle?

To replicate each DNA in a chromosome into two copies with almost perfect fidelity.

What happens to chromosomes during mitosis?

Chromosomes are divided and distributed by mitotic cell division.

What is the function of the master program of molecular checks and balances?

To ensure the accurate replication and distribution of DNA during cell division.

What is the main purpose of the cell cycle?

To pass genetic instructions for all characteristics from parent to daughter cells.

What phase begins the interphase of the cell cycle?

G1 Phase (Gap 1)

What occurs during the G1 phase of the cell cycle?

The cell grows, synthesizes mRNA and proteins necessary for cell division.

How long does a typical dividing mammalian cell spend in G1?

About 10 hours.

What regulates the G1 phase of the cell cycle?

Growth factors and checkpoints, including the restriction point or START.

What is the G1/S checkpoint?

A critical point that holds the cell in G1 until all enzymes for DNA replication are present.

What happens after the G1/S checkpoint is passed?

The cell is committed to divide.

What is the defining feature of the restriction point in G1?

Activation of G1/S- and S-phase cyclin-CDK complexes.

What is the G0 phase in the cell cycle?

A nondividing phase where cells maintain a constant size and can remain indefinitely.

What prompts cells to enter the G0 phase?

Unfavorable conditions, such as nutrient scarcity, or to maintain a specialized state.