D2.1: Cell and Nuclear Division Flashcards
What is cell division
- one cell into two cells (mitosis and meiosis)
- TERMS: once cell (mother cell) → two cells (daughter cells)
The implications of cell division
- Cells come from Pre-existing cells (Cell Theory)
- Implications: every cell could be traced to the first cells of our being — the zygote (sperm + egg)
- A continuity of life — going back to our origins to the present.
Do all living things reproduce?
They all can reproduce but some might have problems (e.g. infertile humans)
- has the capacity but, depending on the organism themselves, may not have the ability to reproduce
How does bacteria reproduce when they have no nucleus?
- Binary fission
Asexual reproduction
one parent only, genetically identical to the parent (e.g. binary fission)
Some examples of asexual reproduction
- e.g. flatworms can undergo binary fission
- When you cut them, they can produce two offspring
- e.g. hydra
- they use budding, making a mini version, cut off small part → offspring.
- e.g. starfish
- fragmentation, cut off the arm of a starfish, offspring will form from the arm
How do bacteria create genetic variance
bacterias conjugate with each other
Before binary fission
“conjugation” they transfer DNA to each other to create genetic variance, 1 giver and 1 recipient
Sexual reproduction
2 parents -> genetically unique offspring, increases genetic variation within species -> ^ chance of favourable traits for survival
- Meiosis form of cell division, cell divides, → 4 daughter cells.
How do we grow?
By increasing our cells (like lego blocks to build a castle)
Why do we produce more cells? Aren’t we grown?:
- for repair and maintenance — platelets for example
- reproduction
- continuity of life — can trace back to our ancestors
- reproduction
- growth
Cytokinesis definition
the cytoplasm is split into two, for each of the daughter cells
Cytokinesis process
When does it begin?: Telophase —After the chromosomes are pulled away to opposite poles so that it can stay on different cells
What is the Proportion of the Mother Cell split?: GENERALLY, Evenly between the daughter cells — the cytoplasm and its contents
Ask Miss
Cytokinesis in animal cells
Forming the cleavage furrow — The plasma membrane “bends inwards”, like cinching an hourglass corset
- Done by a ring of contractile proteins, Actin and Myosin, that are similar to proteins that contract the muscle
Cytokinesis in plant cells
Cell plate formation — making the cell wall
- prior, doubled the organelles, nucleus, etc. (??)
- golgi apparatus produces the vesicles
- microtubules are built into “a scaffolding [metaphorically] straddling along the equator” which is used to create a layer of vesicles. The layer of vesicles form platelike structures (cell plates). The vesicles fuse, creating two layers of plasma membrane along the equator making new plasma membranes for the two daughter cells (”adjacent to the new dividing walls”)
- Vacuoles make the cell membrane → the microtubules “scaffold”/build the cell wall
- The vesicles bought pasulubong (pectins and other substances, presumably for the cell wall) for the two cells. To divide its contents, exocytosis between the two new membranes (its like a road that leads to two ways). The two daughter cells agrees to give their cellulose to each other. They bring the cellulose to the equator and sent it to the shopee delivery center (ie. the middle lamella)
- Why to the equator first then the middle lamella (is the equator a necessary stop or something along the way to the middle lamella?)
- Then each cell builds its own cell wall across the equator
Which is more common? Equal or unequal cytokinesis?
- Most cases: Mother cell split into “equal halves” of daughter cells.
Cytokinesis in onion root cells
- new cell walls have divided the cytoplasm equally but not all cookies come out perfect—some may be unequal
- (so both equal an unequal cell division could happen)
How can unequal cytokinesis occur
can only occur with at least 1 nucleus and 1 mitochondrion.
- so only the ones “luck enough” to gain the non-formable elements (such as mitochondria) to survive.
In onion root cells, cytokinesis is typically equal due to the symmetrical formation of the cell plate, which ensures that both daughter cells receive similar amounts of cytoplasm and organelles. However, the process is not always simultaneous due to the inherent variability in the timing of cell plate formation and the complex nature of plant cell cytokinesis.
Why is mitochondria a “non-formable element”??
The cell cannot produce the mitochondria. Because in the endosymbiosis, the mitochondria is engulfed by the host cell. It’s is own organism so mitochondria can only be produced from pre-existing mitochondria
Yeast reproduces by budding
- Nucleus mitosis
- The formation of a “small outgrowth of mother cell” called a “bud” (what does that mean? OHH like, see the second step in the illustration, there’s the formation of a mini version of the mommy cell!)
- It gains a small portion of the cytoplasm and inherits one of the daughter nucleus from the nucleus mitosis
- A division between the two cells (mother and daughter) via the formation of plasma membrane
- After the split there would be two scars: Bud scar (Daughter cell), Birth scar (Mother cell)
Oogenesis
- an example of unequal cytokinesis
- egg cell –> mature ovym
- genesis: transformation; oo - like yes mom;
- the production of four offspring: 3 polar bodies and one mature ovum
- the mature ovum is the bigger cell who gains everything. There are three small polar bodies because its required to split to 2 cells in cell division
The small polar bodies also serve purpose: to make the mature ovum a haploid
The production of sperm
- unlike oogenesis, the cytoplasm is divided equally
- undergoes meiosis
- Process: Two stages of division
- The first results: two daughter cells
- The second division: four equally sized small cells
- Final results: the four cells mature into mature sperm cells (why there are so many sperm cells)
- But in creating a new cell in general, there must always be two outputs.
I think it’s equal because the journey of the sperm to the egg cell is tumultuous and, to increase the chances of fertilization, the sperm count must be plenty.
Plus, they aren’t the ones to nurse the child so they dont need too much volume unlike the egg cell
Nuclear division
The splitting of a nucleus to produce two neclei offspring
Anucleate
- an organism or a cell (? wording and knowledge) with no nucleus
Why is it bad to be anucleate?
- Cannot synthesize polypeptides/proteins (which has a lot of essential functions)
- no instruction
- nucleolus (from the nucleus) produces the protein-makes/the ribosomes
- Cannot be able to sustain itself
- small lifespan
- e.g. red blood cells can only live for 120 days :(
diploid (2n)
A cell with two sets of chromosomes.
- 1 n/set of chromosome from father and mother
Difference between mitosis and meiosis
mitosis is for continuity, meiosis is for change
- mitosis: genetically identical, meiosis: genetic variance
What comes before nuclear division?
DNA replication
- - Because if you’re producing more of cell X you need the instructions to make cell X not just its packaging.
- So they need the DNA. Meiosis and Mitosis replicates all of the DNA → the daughter cell can perform any function required.
What are chromatids?
Two condensed strands of DNA from DNA replication
