Unit 6: Cell Cycle Flashcards
Define and describe
Sister chromatids
Identical copies of DNA made by the process of DNA replication
Held together at a centromere
Define and describe
Homologous chromosomes
Chromosomes that have the same genes, but are inherited from different parents and may contain different versions of the genes
Ex: You get a copy of Chromosome 1 from each parent and therefore you have a homologous pair of chromosome 1
n Number
How many different chromosomes an organism or cell contains
In humans, n=23
Dipoid
2n
Having two sets of chromosomes
In many organisms, these are the somatic cells
Haploid
1n
Having one set of chromosomes
In many organisms, these are the gametes (sex cells)
Define / describe
somatic cells
Body cells
Contain two full sets of chromosomes (diploid)
Made via mitosis
Define / describe
gametes
Sex cells (sperm or eggs)
Contain one set of chromosomes (haploid)
Made via meiosis
What are the general steps involved in cell division?
- Replicate DNA
- Separate DNA into distinct “piles” (or nuclei)
- Separate the rest of the cell
Two main parts of the cell cycle
M Phase
Interphase
What happens during interphase?
Cell is not separating into two
Cell is still very active, doing things like maintaining homeostasis, carrying out metabolic reactions, expressing genes, communicating with other cells, etc
Interphase can include G0 or G1, S, and G2
What happens in G1
Cell does most of its growth, roughly doubling in size
May progress to G0 or S
What happens during S phase
DNA replication
What happens during G2
A cell prepares for M phase, checking that all DNA has been properly replicated and that there are adequate organelles
What are the two steps of M phase?
Nuclear division (mitosis or meiosis)
Cytokinesis
List the steps of mitosis
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Define/describe
Centriole / centrosome
Structure that makes the microtubules (spindle fibers)
Define/describe
kinetochore
“kin-EH-tə-core”
Connecting structure between the centromere of a pair of sister chromosomes and the spindle fiber
Outline the defining events of
prophase
- Chromatin condense into chromosomes (sister chromatids)
- Nucleolus no longer present / visible
- Centrioles build spindle fibers and begin pushing apart from each other
Outline the defining events of
prometaphase
- nuclear membrane is fully broken down
- spindle fibers from each centriole connect to sister chromatids at the centromeres and begin pushing them toward the cell’s center
Outline the defining events of
metaphase
- each sister chromatid is lined up onto the cell’s center (metaphase plate)
Outline the defining events of
anaphase
- cohesins (proteins of the centromere) break down, allowing sister chromatids to split into two chromosomes
- spindle fibers shorten, pulling a chromosome from each pair of sister chromatid toward opposite poles of the cell
Outline the defining events of
telophase
- spindle fibers are almost completely broken down
- chromosomes decondense into chromatin
- nuclear envelopes appear around each pile of chromosomes
Compare and contrast cytokinesis in plants and animals
Both: follows nuclear division and results in formation of two identical daughter cells
Plants: Cell plate forms to divide one cell into two; will become a cell wall
Animals: Cleavage furrow forms to pinch one cell into two
What is this showing?
Interphase
* Nucleus / nuclear envelope still visible
* Chromatin still in relaxed form
What is this showing?
Prophase
* Sister chromatids still joined
* Spindle fibers forming and starting to join to sister chromatids at the centromere
* Nuclear envelope mostly broken down
What is this showing?
Metaphase
* Sister chromatids still joined together
* Lined up along cell’s midline (metaphase plate, or equator)
What is this showing?
Anaphase
* Sister chromatids are no longer joined; are now chromosomes
* Spindle fibers are being broken down, although you can’t tell without comparing that to the metaphase images
What is this showing?
Telophase
* Two nuclear envelopes are being formed
* Chromosomes are relaxing into chromatin
Cytokinesis
* Cleavage furrow is pinching the cells in two
What is this showing?
Interphase
* No discernable chromosomes
* Nucleolus (dark spot) visible
What is this showing?
Prophase
* Chromosomes are becoming visible / condensed
This is fairly early, as a nucleolus can still be seen
What is this showing?
Metaphase
* Very clear spindle fibers visible extending to each side of cell
* Sister chromatids lined up along center of cell
What is this showing?
Anaphase
* Sister chromatids have been split (are now chromosomes) to opposite sides of the cell
* Spindle fibers still visible but are not as well-defined as in metaphase
What is this showing?
Anaphase
* Chromosomes are still quite condensed
* Spindle fibers still visible
This is definitely late anaphase, but not quite telophase, yet
What is this showing?
Telophase
* Chromosomes are in distinct regions at opposite ends of cells and are starting to relax
* Spindle fibers no longer visible
Cytokinesis
* Cell plate formed along middle
What is this showing?
Interphase
* This is two daughter cells that have probably recenty completed M phase
* Nucleoli (two nucleolus…s) are visible
* Chromatin is in relaxed state
