Module 5 Cell Cycle & Division

What does cell division produce?

New daughter cells from a parent cell.

What are the 3 main purposes of cell division?

Reproduction, growth/development, and tissue renewal/repair.

What does cell division do during reproduction?

Makes new organisms and increases the population.

How does cell division help growth and development?

Allows development from a zygote or, in plants, from cuttings.

How does cell division help tissue renewal and repair?

Replaces cells lost from normal wear, injury, or accidents.

What is a chromosome?

A threadlike structure carrying genetic information in the form of genes.

What is a plasmid?

A small DNA loop in prokaryotes that can replicate independently.

Are plasmids essential for prokaryotic growth?

No.

What is a nucleosome?

The structural unit of a eukaryotic chromosome made of DNA and histone proteins.

How do prokaryotes divide?

Binary fission.

What do eukaryotic cells follow when dividing?

The cell cycle.

What is the cell cycle?

Events after DNA replication that lead to production of 2 daughter cells.

Are daughter cells usually identical?

Yes, except meiosis produces unique gamete cells.

What types of cells mostly divide?

Undifferentiated cells, such as stem cells.

What is cell differentiation?

A less specialized cell becomes a more specialized cell.

What is an example of a differentiated cell that can still divide?

Skin cells.

What are the 2 major parts of the cell cycle?

Interphase and the mitotic (M) phase.

What happens during interphase?

Cell growth and chromosome copying in preparation for cell division.

What are the 3 stages of interphase?

G1, S, and G2.

What happens during G1?

Cell growth and duplication of non-DNA cell contents.

What happens during S phase?

Chromosome duplication.

What happens during G2?

Cell growth plus duplication repairs and checks.

What is G0?

Cell-cycle arrest or rest.

Which phase uses a lot of energy?

S phase.

What are homologous chromosomes?

Matched pairs of chromosomes.

What are chromatids?

Replicated chromosomes.

What is a centromere?

Connection point between sister chromatids where microtubules attach during mitosis.

What happens during the mitotic (M) phase?

Mitosis separates copied chromosomes and cytokinesis physically divides the cell.

What does mitosis produce?

Daughter cells that are clones of the parent cell.

How many daughter cells does mitosis produce?

Two daughter cells.

What size are daughter cells immediately after mitosis?

About half the size of the parent cell.

What happens to daughter cells before dividing again?

They grow to the size of the original cell.

Technically, what does mitosis divide?

The nucleus.

What does cytokinesis divide?

The cytoplasm.

What two processes are part of cell division?

Mitosis and cytokinesis.

When does mitosis begin?

After DNA replication.

What is the most important step in cellular duplication?

DNA replication.

What is DNA like during interphase?

Replicated, loosely coiled, with no visible chromosomes.

What happens to the nuclear envelope during mitosis?

It degrades.

What happens during early prophase?

The nuclear envelope disintegrates, chromosomes coil, and centrioles move to the poles.

What happens to chromosomes during prophase?

They coil and become visible under a light microscope.

Where do replicated centrioles move during prophase?

To opposite poles.

What are astral rays?

Structures that extend from centrioles.

What are spindle fibers?

Fibers that interconnect centriole pairs.

What is each copy of a replicated chromosome called?

A chromatid.

Where are sister chromatids connected?

At the centromere.

What is the kinetochore?

A raised region at the centromere that attaches to spindle fibers.

What happens during metaphase?

Chromosomes align at the metaphase plate.

What happens to the centromere during anaphase?

It splits.

What happens to chromatids during anaphase?

They separate and move toward opposite sides.

What structure moves chromatids during anaphase?

The spindle apparatus.

What happens during telophase?

Nuclear membranes reform, nuclei enlarge, and chromosomes uncoil into chromatin.

What happens to the cytoplasm during telophase?

It constricts along the metaphase plate, forming a cleavage furrow.

What is a cleavage furrow?

A constriction that forms as the cytoplasm divides.

What happens during cytokinesis?

The cytoplasm physically divides.

What marks the end of cell division?

Completion of cytokinesis.

What happens to chromosomes during early mitosis?

They condense, arrange, and attach to mitotic spindles.

What happens to chromosomes during late mitosis?

They separate and decondense.

What happens to mitotic spindles during late mitosis?

They break down.

What structures define dividing cells?

Cleavage furrows and cell plates.

What is meiosis?

A unique kind of sexual cell reproduction.

Does meiosis occur in both males and females?

Yes.

What happens to chromosome number during meiosis?

It is cut in half from 2n to n.

Why does meiosis cut the chromosome number in half?

So offspring do not have the wrong number of chromosomes.

How does meiosis affect genetic diversity?

It produces daughter cells genetically different from the original cell.

What are 2 sources of genetic variability during meiosis?

Random alignment of homologous pairs and crossing over.

What is crossing over?

Exchange of DNA between nonsister chromatids.

What are nonsister chromatids?

Chromatids of different chromosomes within a homologous pair.

What does crossing over produce?

Recombinant chromatids.

What is another term for genetic crossover?

Recombination.

What is the effect of crossing over?

Increased genetic variability.

What does diploid mean?

A cell has two sets of chromosomes, symbolized as 2n.

Where do the 2 chromosome sets in a diploid cell come from?

One set from each parent.

What is the human diploid chromosome number?

46.

How many homologous chromosome pairs are in a human diploid cell?

23 pairs.

What does haploid mean?

A cell has one set of chromosomes, symbolized as n.

What is the haploid chromosome number?

The number of chromosomes in a gamete.

What is the human haploid chromosome number?

23.

How many members of each homologous pair does a gamete contain?

One member, either maternal or paternal.

What happens when sperm and egg fuse?

They form a diploid, 2n, zygote.

What does meiosis make?

Gametes or spores.

How many nuclear divisions occur during meiosis?

Two: meiosis I and meiosis II.

How many times does DNA replication occur during meiosis?

Once.

How many daughter cells does meiosis produce?

Four haploid daughter cells.

What are the 4 stages of each meiotic nuclear division?

Prophase, metaphase, anaphase, and telophase.

When are chromosomes replicated before meiosis?

During interphase before meiosis I.

What happens during meiosis I?

Crossing over occurs and homologous chromosome pairs separate.

What separates during meiosis I?

Homologous chromosome pairs.

How does chromosome number change during meiosis I?

It decreases from 2n to n.

What is meiosis I called?

Reduction division.

What happens during meiosis II?

Sister chromatids separate.

What separates during meiosis II?

Sister chromatids.

What is meiosis II called?

Equational division.

What does each daughter cell receive during meiosis II?

An equal share of chromosomes.

What is the key difference between meiosis I and meiosis II?

Meiosis I separates homologous pairs; meiosis II separates sister chromatids.

What is the final result of meiosis?

Four haploid daughter cells.

What is Down syndrome also called?

Trisomy 21.

What is Trisomy 21?

A genetic condition in which a person has an extra copy of chromosome 21.

What usually causes Trisomy 21 according to the slides?

Nondisjunction during meiosis.

What is nondisjunction?

Chromatids failing to separate correctly during meiosis.