2.1 - Mitosis and Cell Cycle Flashcards
What is typically the goal of cell division?
The goal of cell division typically is to equally partition two more-or-less identical copies of genetic material between two daughter cells
Who has an easier time with cell division: Eukaryotes or Prokaryotes?
Prokaryotes are comparatively simple, with only one chromosome, so have a relatively easy time sorting daughter chromosomes to daughter cells
Eukaryotes, with their longer DNA and multiple chromosomes, don’t have it nearly so easy
What are chromosomes?
- Chromosomes are tightly packaged DNA
- They are found only during cell division
- DNA is not being used for macromolecule synthesis (creation of polymers)
What is chromatin?
- Chromatin is unwound DNA
- It is found throughout interphase
- DNA is being used for macromolecule synthesis (creation of polymers)
How is DNA organized?
DNA is organized in chromosomes
- Double helix DNA molecule wrapped around histone proteins like thread on spools
- DNA-protein complex = chromatin organized into long thin fiber condensed further during mitosis
Chromatin = long strand of spaghetti (gets squished even smaller during mitosis)
What is a chromatid?
Each of the two threadlike strands into which a chromosome divides during cell division. Each contains a double helix of DNA.
Chromosome contains two sister chromatids (lines) that look like this: II
The two sister chromatids are held together by a centromere, making the chromosome look like an X
What is a telomere?
A telomere is a compound structure at the end of a chromosome (the tip)
What is a centromere?
Centromeres are small round segment that holds two chromatids together.
It is also the region of a chromosome to which the microtubules of the spindle attach, via the kinetochore, during cell division.
What is a centrosome?
The centrosome is the centre of the microtubule production in a cell. It consists of 2 centrioles.
What is a centriole?
A centriole consists of microtubules, and a pair of centrioles makes up a centrosome.
What is a kinetochore?
A kinetochore is a protein structure in eukaryotes which assembles on the centromere and links the chromosome to microtubule polymers from the mitotic spindle during mitosis and meiosis.
- Protein structure near centromere/middle of chromosome where microtubules attach
What is a nucleus?
- Control center of the cell
- Holds the cell’s genetic material (DNA)
- Regulates cell activities
What are nucleoli?
- Found inside the nucleus
- Involved in making components for protein production (ribosomes)
- Not a separate membrane-bound structure
What are the 4 phases of the cell cycle (in mitosis)?
G1, S, G2, mitosis
- Note: G1, S, and G2 are grouped together as ‘interphase’
What occurs during interphase (general description)?
During G1, S, and G2 cell grows and continues to make proteins and organelles
Only replicates DNA during S phase
What are the 2 different kinds of cell life cycle?
- Cell grows/matures to divide again
- Cell grows/mature to never divide again
What kinds of cells divide multiple times?
- Epithelial cells
- Blood cells
- Stem cells
What kinds of cells divide only once?
- Brain/nerve cells
- Muscle cells
What occurs during G1 phase?
Beginning of a cell’s life:
- Follows Cytokinesis
- Cell begins growing to full size
- Transcription and Translation occur
- DNA only in single strands now
What occurs during S phase?
DNA replicates itself (makes 2 double stranded DNA molecules):
- No more RNA will be made BUT leftover RNA (translation) can still be used for repairs etc.
- Centrosomes replicate
- Cells which do not go through this phase – can’t divide. (Eg. brain cells, some nervous tissue)*
- Research with this might help cancer
What occurs during G2 phase?
Nucleus is well defined and still has the membrane
- Centrosomes present
- Chromosomes (DNA) has duplicated but is still a mess of strands
- New RNA transcribed to make proteins necessary for division – spindle fibers
- Leftover RNA (S phase) is used now for repairs
Cells are ready for mitosis
By the end of G2 phase, what qualities does the cell have?
- Nucleus is defined
- Nucleoli are present
- Replicated Centrosomes
- DNA is duplicated
- DNA is still chromatin
Define mitosis
Mitosis is unicellular reproduction (making 2 cells out of 1)
What is mitosis used for?
- Used for repair, growth, and development from a fertilized egg
- Used to produce somatic cells (not sexual cells - gametes)
What is the end result of mitosis?
Mitosis yields 2 identical daughter cells (produced asexually)
How is mitosis affected by genetic variation?
Genetic variation is comparatively slow in mitosis (MUCH greater in meiosis)
What are the 4 stages of mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
What occurs during prophase (mitosis)?
- Chromatin fibers condense, becoming more coiled
- Chromosomes are seen as two identical sister chromatids
- Nucleoli vanish, and the nuclear membrane starts breaking down
- A mitotic spindle forms from centrioles
- Centrosomes move apart to poles
- No more RNA is transcribed
- The nucleus is still visible, and chromosomes are condensing, becoming thicker and visible
By the end of prophase, what has occured?
- Chromosomes condense
- Nucleoli vanish
- Mitotic spindle forms
- Centrosomes move apart
What occurs during prometaphase?
In the transition from prophase to metaphase:
- Nuclear envelope breaks apart
- Microtubules enter the nucleus and engage with chromosomes
- Kinetochores (handles for mitotic spindle) form at centromeres
What occurs during metaphase?
- Spindle fibers connect with chromosomes
- Centrioles are now on opposite sides
- Fibers grab onto kinetochore
- Chromosomes form a line in the middle of the cell (called metaphase plate)
- The nucleus breaks down, and chromosomes line up in the middle
By the end of metaphase, what has occured?
- Centrosomes are at opposite poles
- Metaphase plate is formed
- Chromosomes line up on the plate
- Mitotic spindle is in action
- Brief, static phase
What occurs during anaphase?
- Sister chromatids split, moving to opposite poles of cell
- By the end, each pole has a complete set of chromosomes.
- Spindle fibers move chromosomes apart (chromosomes split and go to opposite sides).
By the end of anaphase, what has occured?
- Starts with “sister” separation
- Chromatids become chromosomes
- “Sisters” go to opposite ends
- All movement led by centromeres
- Poles separate even more
What occurs during telophase?
- Unconnected microtubules move even farther
- New nuclei start to form
- Protective membrane around nuclei begins to reappear
- Chromatin is now less tightly wound
By the end of telophase, what has occured?
- “Sisters” are at opposite ends
- Protective layer around nuclei is reforming
- Chromosomes are relaxing
- Cytokinesis (cell division) is already happening
What is cytokinesis?
Cell division ends with cytokinesis in telophase. This is when the cell actually splits into two identical daughter cells.
How is cytokinesis different in animals and plants?
- Animals have a tightening middle part (cleavage furrow) like squeezing a water balloon
- Plants use a cell plate (a line forms within the cell wall) to divide the cell
What is the role of microtubules in mitosis?
Microtubules create spindle fibers that pull and arrange chromosomes, ensuring they separate correctly and go to the right places in daughter cells.
