Mitosis Flashcards
Why does a prokaryotic cell divide?
It is reproducing, gives rise to a new organism (cell). This is the same for unicellular eukaryotes (like amoeba)
Why does a multicellular eukaryotic cell divide?
It enables each organism to develop from a single cell (fertilized egg) / growth and development; asexual reproduction; tissue renewal
What eukaryotic cells never divide?
Mature nerve and muscle cells
What is the crucial function of most cel divisions (besides meiosis)?
The distribution of identical DNA to 2 daughter cells
What is the genome?
A cell’s DNA/genetic info
What is the prokaryotic genome?
often a single DNA molecule
What is the eukaryotic genome?
multiple DNA molecules because they are packaged into chromosomes
What is chromatin?
the entire complex of DNA and proteins that together build chromosomes
What are somatic cells?
All body cells except reproductive cells
How many chromosomes are in each nuclei of a human somatic cell?
46 chromosomes in 2 sets of 23, 1 set inherited from each parent
What are gametes? How many do humans have?
reproductive cells (egg or sperm); 1 set of 23 chromosomes
what is a sister chromatid?
identical copies of a replicated chromosome, joined at the centromere, that are separated during cell division (mitosis or meiosis) to ensure each new cell receives a complete set of chromosomes
what are some features of sister chromatids?
- each contain an identical DNA molecule
- attached all along lengths by protein complexes called cohesins
- each has a centromere (a region made of repetitive sequences in chromosomal DNA where sister chromatids are most closesly attached)
what happens when sister chromatids separate from each other?
- they move into 2 new, separate nuclei
- after separation they are individual chromosomes
- this step double # of chromosomes during cell division
what is mitosis?
the division of genetic material in the nucleus
what happens after mitosis?
cytokinesis (division of the cytoplasm)
what is meiosis?
a type of cell division which yields daughter cells with only one set of chromosomes, producing gametes (in humans, only occurs in ovaries or testes/gonads for gametes)
how is a chromosome duplicated and distributed during cell division?
1) chromosome is a long, thin chromatin fiber containing one DNA molecule and associated proteins
2) once duplicated, the chromosome consists of 2 sister chromatids connected by sister chromatid cohesion
3) molecular and mechanical processes separate the sister chromatids into 2 chromosomes and distribute them to 2 daughter cells
What does the cell cycle cover?
The life of a cell from when it’s first formed during division of parent cell
-> its own division into 2 daughter cells
What happens in the mitotic phase (M)?
Both mitosis and cytokinesis, the cell physically divides into 2
what is usually the shortest part of the cell cycle?
the mitotic phase (M)
what is alternated with the mitotic phase?
interphase
what is interphase? what stages does it include?
~90% of the cell cycle, a growth period where a cell grows by producing proteins and cytoplasmic organelles (like mitochondria and endoplasmic reticulum)
1) G1 phase (first gap)
2) S phase (synthesis)
3) G2 phase (second gap)
what happens during G1 phase (first gap)?
cell grows by producing proteins and organells
what happens during S phase (synthesis)?
DNA synthesis/replication. Each chromosome now consists of 2 sister chromatids
what happens during G2 phase (second gap)?
cell grows more, completing preparation for cell division (mitosis)
what is the effect of S phase on chromosome structure?
Before S phase → Chromosomes are single-stranded (one chromatid).
After S phase → Each chromosome consists of two identical sister chromatids, still loosely packed in the nucleus.
What happens during mitosis?
the distribution of chromosomes into 2 daughter nuclei
what happens during cytokinesis?
division of the cytoplasm, producing two daughter cells. each daughter cell can start a new cell cycle. (cytokinesis begins before mitosis ends)
what are the stages of mitosis?
prophase, prometaphase, metaphase, anaphase, telophase
what happens during prophase?
1) Chromosome Condensation – Chromatin coils into visible duplicated chromosomes, each with two sister chromatids joined at a centromere.
2) Spindle Fiber Formation – The mitotic spindle (made of microtubules) begins to form from the centrosomes.
3) Nucleoli disappear
4) Centrosome Migration – Centrosomes move to opposite poles of the cell, organizing the spindle apparatus.
what happens during prometaphase?
1) Nuclear Envelope Disintegrates – Fully breaks down, allowing spindle fibers to interact with chromosomes.
2) Kinetochore Formation – Proteins form at the centromeres of chromosomes, serving as attachment points for spindle fibers.
3) Spindle Fiber Attachment – Microtubules from opposite poles attach to kinetochores, starting to move chromosomes.
4) Chromosome Movement – Chromosomes begin aligning toward the center (metaphase plate) but are not fully positioned yet.
what happens during metaphase?
1) Chromosome Alignment – Sister chromatids line up single-file along the metaphase plate.
2) Spindle Checkpoint – The cell ensures all kinetochores are correctly attached to spindle fibers from both poles.
3) Spindle Tension – Microtubules pull chromosomes slightly to test proper attachment.
4) Metaphase ensures equal chromosome separation before moving into anaphase.
what happens during anaphase?
Begins when the cohesins holding together sister chromatids are cleaved by separase (an enzyme)
1) Chromatid Separation – The centromeres split, and spindle fibers pull sister chromatids apart.
2) Chromosome Movement – Separated chromatids (now individual chromosomes) move to opposite sides of the cell.
3) Spindle Fiber Shortening – Microtubules contract, pulling chromosomes closer to the centrosomes.
what happens during telophase?
1) Chromosomes Decondense – They loosen back into chromatin for gene expression.
2) Nuclear Envelopes Re-form – Two new nuclei develop around the chromosome sets.
3) Spindle Fibers Disassemble – Microtubules break down as division completes.
what happens during cytokinesis?
1) Cleavage Furrow (Animal Cells) – The cell membrane pinches in due to actin filaments, splitting the cytoplasm.
2) Cell Plate Formation (Plant Cells) – A cell plate forms in the middle, eventually becoming the new cell wall.
3) Organelle Distribution – Organelles are divided between the two cells.
appearance of a cleavage furrow -> actin microfilaments interact with myosin molecules causing ring to contract -> cleavage furrow deepens until parent cell pinched in two
what is the mitotic spindle?
- mitosis events rely on it
- made of microtubules and associated proteins
- begins to form in cytoplasm during prophase
what is a kinetochore?
a structure made of proteins that assemble on specific sections of DNA at each centromere, each sister chromatid has one
what’s the difference between haploid and diploid chromosomes?
Haploid (n): Contains one set of chromosomes. Found in gametes (sperm and egg cells).
Example: Humans have 23 chromosomes in gametes.
Diploid (2n): Contains two sets of chromosomes (one from each parent). Found in somatic (body) cells.
Example: Humans have 46 chromosomes (23 pairs) in body cells.
describe the structure of a eukaryotic chromosome
1) DNA Double Helix – Long, linear DNA molecule containing genes.
2) Histone Proteins – DNA wraps around histones, forming nucleosomes (bead-like units).
3) Chromatin – Loosely packed DNA-protein complex, existing as euchromatin (active) or heterochromatin (inactive).
4) Chromatid(s) – Before replication, a chromosome has one chromatid; after replication, it has two sister chromatids.
5) Centromere – The central region where sister chromatids attach and where spindle fibers bind during division.
6) Telomeres – Protective ends that prevent DNA damage and degradation
Know which level of DNA packaging a chromosome is in before mitosis and after mitosis starts
Before Mitosis (Interphase - G1, S, G2): DNA is in a loosely packed chromatin state.
This allows for gene expression and DNA replication (S phase).
Chromosomes are not visible under a microscope.
After Mitosis Starts (Prophase-Onward): Chromatin condenses into distinct chromosomes.
Each chromosome has two sister chromatids joined at the centromere.
This tight packaging ensures accurate chromosome segregation during mitosis.
why do microtubules grow and shrink during cell division?
During cell division, microtubules grow and shrink to ensure accurate chromosome separation. Here’s why:
Spindle Formation – Microtubules form the mitotic spindle, which is crucial for moving chromosomes. They grow from the centrosomes to attach to chromosomes at the kinetochores.
Chromosome Alignment and Movement – As microtubules shrink and grow, they help align chromosomes at the metaphase plate and pull sister chromatids apart during anaphase.
Dynamic Instability – Microtubules rapidly grow and shrink (a process known as dynamic instability) to search for and bind to kinetochores. Once attached, they stabilize to facilitate chromosome movement.
how do prokaryote cells divide?
binary fission
what happens during binary fission / asexual reproduction of single-celled eukaryotes?
1) chromosome replication begins at the origin of replication. 1 copy of the origin moves rapidly toward the other end of the cell
2) replication continues. one copy of the origin is now at each end of the cell. meanwhile, the cell elongates by actin-like proteins
3) replication finishes. plasma membrane is pinched in 2 by tubulin-like protein, new cell wall is deposited
4) 2 daughter cells result
what might mitosis have evolved from?
prokaryotic cell reproduction
what are the functions of mitosis?
1) growth (zygote -> embryo ->…)
2) repair/replacement (dividing bone marrow cells -> red blood cells)
3) asexual reproduction (budding yeast)
what happens to the endomembrane system after cell division?
fragments into vesicle structures, reforms in daughter cells
what happens to mitochondria at the end of cell division?
split between 2 daughter cells, divide by binary fission to reproduce in new cell
