UNIT 3 - D 2.1 - Cell And Nuclear Division Flashcards
Why do cells make copies of themselves?
To maintain the population of a single-celled organism and to keep a multicellular organism growing and repairing itself
What is cell division?
The process of producing two cells from one cell
What is the role of cell division?
To make sure genetic information is passed on to the next generation of cells, along with copies of all the organelles necessary to make the cell function.
What is the parent/mother cell?
The cell that produces a copy
What are daughter cells?
The 2 new cells that are generated from parent cells
How do prokaryotic cells divide?
By binary fission.
What is the process of binary fission?
The DNA’s copied, the 2 daughter chromosomes become attached to different regions on the plasma membrane and the cell divides into 2 genetically identical daughter cells.
How are daughter cells produced for organisms that have multiple chromosomes?
Using mitosis.
What does meiosis involve with egg and sperm cells?
2 divisions that produce 4 daughter cells.
What is cytokinesis?
The process of the cell splitting in 2 after reaching a certain size.
What happens during cytokinesis in animal cells?
The plasma membrane pinches inwards to form cleavage furrows.
What is a cleavage furrow?
A groove along the cell membrane
What do plants form instead of cleavage furrows during cytokinesis?
A cell plate
Why do plants form a cell plate during cytokinesis?
Because of their rigid cell wall
How are cell plates formed?
They are built up by vesicles that collect midway between the 2 poles of the cell and lay down cell membrane and cell wall cells, which then expand outwards towards the sides of the cell from a central region.
What do both types of cytokinesis result in?
2 separate daughter cells that have genetically identical nuclei.
In most instances of cell division, how do the 2 daughter cells compare to one another?
They are identical.
What is oogenesis?
The production of eggs.
What does oogenesis produce?
4 haploid cells.
What do 3 of the 4 haploid cells produced from oogenesis end up doing?
Donating their cytoplasm and organelles to the fourth cell and are not used as eggs.
Why are three of the four haploid cells produced from oogenesis not used as eggs?
Because they are too small to produce a viable zygote
What is oogenesis an example of
Unequal cytokinesis
What does unequal cytokinesis for egg cells provide the zygote with?
The resources it needs to survive until it is implanted in the wall of the uterus.
What kind of cells may cytokinesis also be unequal in?
Yeast cells
How do yeast cells divide?
A process called budding.
What does budding involve?
Generating a small cell from the parent cell
What happens when a daughter yeast cell becomes big enough to survive on its own?
Cytokinesis closes the cell membranes, and each cell is an independent organism.
What does mitosis result in?
2 daughter cells with identical nuclei.
What does it mean to be a anucleate?
To not have the instructions for carrying out its functions or how to divide
What does the process of mitosis make sure of?
That a full copy of the nucleus is made before cytokinesis.
What does the process of having a full copy of the nucleus allow the daughter cells to have
The same number of chromosomes as the parent cell and the same genome
How much genetic information do gamete daughter cells have?
Half the genetic information of the parent
How do organisms receive a total of 46 chromosomes?
They received 23 from their mother and 23 from their father.
Why do chromosomes come in pairs?
Because one of each pair is from each parent.
What does meiosis ensure?
That egg and sperm cells get only half the genetic information
What does meiosis result in?
4 daughter cells that each have a nucleus containing half the parents cells DNA
How does meiosis help generate the genetic variety we observe in offspring?
Each of the 4 daughter cells receives a different combination of genetic information, chromosomes are in random combinations
What is DNA replication?
The process of making a complete copy of the cell’s DNA
What phase of the cell’s life does DNA replication occur?
The S phase or synthesis phase
How is replicated DNA arranged in a chromosome?
as 2 sister chromatids
Where are 2 sister chromatids attached?
At the centromere
What does DNA look like in most of the cell’s life?
Spread out in long unwound chains.
Why is condensation of the DNA necessary before replication.
So that no DNA is misplaced and to prevent the strands from tangling up and braking
What does the process of DNA condensation involve?
The DNA being wrapped around histones.
How are compact pairs of chromatids formed?
The histones help organize the DNA which is coiled, and then supercoiled so that the coils are stacked on top of each other.
When is DNA referred to as chromatin?
When DNA is associated with histone proteins
What ensures that different DNA molecules can be transported in one package rather than being spread out all throughout the nucleus?
The chromosome’s condensed structure after supercoiling is complete.
What does the centrosome organelle do?
Makes the microtubule spindle fibers that are needed to guide the chromosomes to the right place before the cell divides.
Why do microtubules have a directionality?
Because one end has a negative charge and the other has a positive charge.
What do motor proteins do?
Push or pull objects around a cell
How do motor proteins push or pull objects around a cell?
They use the microtubules as tracks, or they can attach to 2 microtubules and get one to slide past the other.
What do motor proteins use to produce a conformational change that moves the microtubules?
ATP
What is a confirmational change?
A change in shape
What are the 3 types of microtubules?
Astral microtubules, kinetochore microtubules and overlap microtubules
What do astral microtubules do?
Reach out from the centrosome.
What do the kinetochore microtubules do?
They attach to the centromere of the chromosome where the 2 sister chromatids are attached.
What do overlap microtubules do instead of attaching to the chromosomes?
They pass beside them.
Where are motor proteins sandwiched in between?
Between the overlap microtubules
How are overlap microtubules pushed in opposite directions?
The motor proteins in between them walk along them in such a way that this happens.
When do motor proteins between the overlapping microtubules become active?
When the cell is ready to separate its chromosomes
What does the action of 2 microtubules sliding past each other do?
It pushes the 2 Poles of the centrosome away from each other.
What happens due to the fact that the 2 sister chromatids are attached to the poles via opposite facing microtubules?
They are pulled away from each other.
Why are each sister chromatid, transported to 1/2 of the cell?
So that when the cell splits in 2, each newly formed cell has a copy of each chromosome.
What happens to the microtubules after the chromatids have been separated?
They are dismantled, and the pieces of track are recycled.
What phase is the cell in when it is not going through cell division?
Interphase
What is the cell doing during interphase?
It is performing its function in the organism and growing and preparing to divide
What are the 4 phases of mitosis?
Prophase, metaphase, anaphase, telophase
What is involved in prophase of mitosis?
- The chromatin fibers become more tightly coiled to form chromosomes
- The nuclear membrane disintegrates and nucleoli disappear.
- A mitotic spindle forms as the centrosome builds new microtubules that will be used to pull the chromosomes into position
- The kinetochores attach to the spindle
- The centrosomes moved towards the opposite poles of the cell as a result of lengthening microtubules
What is the kinetochores?
A region in the centromere of each chromosome.
What is involved in metaphase of mitosis?
- The chromosomes move to the middle or equator of the cell, which is called the metaphase plate.
- The centromere of the chromosome align on the plate.
- The chromosomes move as a result of the action of the spindle, which is made of microtubules.
- The centrosomes are at opposite poles.
When does anaphase start?
When the 2 sister chromatids of each chromosome move apart
What is involved in anaphase of mitosis?
- The chromatids, now each a chromosome, move towards the opposite poles of the cell
- They move as a result of motor proteins pushing microtubules in opposite directions.
- Because the centromeres are attached to the microtubules, they move towards the poles first.
- At the end of this phase, each pole of the cell has a complete identical set of chromosomes.
What is involved in telophase of mitosis?
- A set of chromosomes is located at each pole
- A nuclear membrane begins to reform around each set of chromosomes
- The chromosomes start to elongate
- Nucleoli reappear
- The spindle apparatus disappears
- The cell is elongated and ready for cytokinesis.
How do humans and other animals avoid the problem of accumulating too many chromosomes?
They produce egg cells and sperm cells in such a way that the number of chromosomes in their nuclei is halved
What kind of division is meiosis?
Reduction division
What kind of nuclei does mitosis produce?
Diploid
What kind of nuclei does meiosis produce?
Haploid
How are chromosomes arranged in diploid nuclei versus haploid nuclei?
Diploid has 46 chromosomes organized into 23 pairs. Haploid has 23 chromosomes, each representing half of one pair.
Where does meiosis produce sperm and eggs respectively?
In the human testes and ovaries
What happens to the number of chromosomes during the first round of segregation/meiosis I?
They are halved
What is involved in prophase I of meiosis?
- Chromosomes becoming visible.
- Homologous chromosomes are attracted to each other and paired up
- Crossing over occurs
- Spindle fibres form from microtubules.
How do chromosomes become visible during prophase I?
The DNA is arranged around histone proteins and becomes more compact.
What are homologous chromosomes?
Pairs of the same chromosome, one pair originally coming from the individual’s father and the other from the mother
What do homologous chromosomes carry?
The same genes in the same order but the type of gene (the alleles) may be different
What is a bivalent?
Homologous chromosomes paired up
What is involved in the crossing over process of prophase I in meiosis?
Parts of the homologous pairs can be swapped between chromosomes
What does swapping parts of the homologous pairs between chromosomes allow?
The mixing of alleles
What is involved in metaphase I of meiosis?
- The homologous chromosomes line up across the cell’s metaphase plate.
- The nuclear membrane disintegrates
Why are either of the chromosomes from each pair equally likely to end up at either pole in metaphase I of meiosis?
Because they are randomly oriented
What is involved in anaphase I of meiosis?
Spindle fibers attached to the chromosomes and pull them to the opposite poles of the cell.
What is involved in telophase I of meiosis?
- The spindles and spindle fibers disintegrate
- The chromosomes uncoil and new nuclear membranes form
What happens at the end of meiosis I?
Cytokinesis: cell splits into 2 separate cells
Why is no S phase necessary after meiosis I?
Because each chromatid still has its sister chromatid attached to it.
What happens during the second round of segregation/meiosis II?
The sister chromatids are separated.
What is involved in prophase II of meiosis?
- The DNA condenses into visible chromosomes again
- New meiotic spindle fibers are produced.
What is involved in metaphase II in meiosis?
- Nuclear membranes disintegrate
- Individual chromosomes line up along the metaphase plate of each cell in no special order.
- Spindle fibers from opposite poles attached to each of the sister chromatids at the centromeres
What is involved in anaphase II in meiosis?
- The centromeres of each chromosome split, releasing each sister chromatid as an individual chromosome.
- The spindle fibers pull individual chromosomes to opposite ends of the cell.
- As a result of random orientation, the chromosomes can be pulled towards either of the newly forming daughter cells.
What is involved in telophase II of meiosis?
- In animal cells, cell membranes pinch off in the middle and in plant cells, new cell plates form to make the cell membranes and cell walls of the 4 new cells.
- The chromosomes unwind their strands of DNA.
- Nuclear envelopes form around each of the 4 new nuclei, then cytokinesis can take place.
What is down syndrome caused by?
An extra copy of chromosome 21, child has 47 chromosomes instead of 46
What does the extra chromosome arise from in down syndrome?
A phenomenon called non-disjunction
When does non-disjunction occur for someone with down syndrome?
When the 21st pair of homologous chromosomes fails to separate during anaphase I
What is one of the characteristics that distinguishes meiosis from mitosis?
In meiosis, during prophase I, there is an exchange of genetic material between non sister chromatids in a process called crossing over
What is the process of crossing over in meiosis?
Sections of 2 homologous, but non-sister chromatids, break at the same point, twist around each other, and then each connects to the other’s initial position.
What does crossing over allow?
DNA from the maternal chromosomes to mix with DNA from the paternal chromosomes.
What are the recombinant chromatids that end up in the sperm or egg cells a mix of thanks to crossing over?
The parent cells’ original chromatids
How does mixing parent cells’ chromatids through crossing over help offspring?
It helps increase variety among offspring from the same parents and so increases the chances of survival of at least some offspring if one combination of alleles proves to be more favorable for survival than others.
What are the main adaptations through meiosis that increase variety in offspring?
Crossing over and random orientation.
What is the result of random orientation?
A male will only very rarely produce 2 sperm cells that are identical, and a female is highly unlikely to produce 2 eggs with identical chromosomes in her lifetime.
Why is saying that the chances of a woman to produce the same egg twice is 1 in 2^23 still oversimplified?
Because it does not take into consideration the additional variety from crossing over and it only considers one gamete, even though 2 are needed to produce offspring.
What is mitosis necessary for?
Growth of organisms, development of embryos, tissue repair and asexual reproduction.
What are meristems?
Areas of special tissue found in plant cells
What are maristematic cells?
Undifferentiated cells that can divide rapidly, allowing growth in plants
What are the 2 major types of maristemic tissue?
Apical and lateral
Where does apical meristemic tissue occur?
In root tips, and at the tips of branches
What does apical tissue enable?
A plant to lengthen
Where does lateral marestmatic tissue occur?
In stem tissue.
What does lateral meristematic tissue allow for in plants?
The stems to grow in width
Where does mitosis have to take place in order for growth to be possible for plants?
In meristematic tissue
What is the zone of cell division?
The area where new undifferentiated cells are formed in plants
When do cells start to differentiate from the embryo stage?
After embryonic stem cells go through mitosis to ensure that full copies of the cell’s genome gets passed on to the new cells.
What are the 2 major parts of the cell cycle?
Interphase and the mitotic/meiotic phase
When is the cell metabolically active and both DNA and proteins are being made?
During interphase
What are the 3 smaller phases of interphase?
G1, S and G2
What goes on during the G1 phase of interphase?
The cell grows: at the beginning of the G1 phase, the cell is the smallest it will ever be, and as it grows, it accumulates materials such as proteins and nucleotides.
What goes on during the S/synthesis phase?
Replication of DNA
When does the G2 phase of interphase start?
After the chromosomes have been replicated in the synthesis phase.
What goes on during the G2 phase of interphase?
The cell grows and makes preparations for mitosis.
What preparations are being done during the G2 phase of interphase?
Organelles such as the mitochondria and chloroplasts can increase in number, DNA begins to condense from chromatin to chromosomes and microtubules begin to form
What are cyclines?
A group of proteins that control the cell’s progression through the cell cycle.
What do cyclins bind to?
Cyclin-dependent protein kinases (CDKs)
What do cyclins bind to?
Cyclin-dependent protein kinases (CDKs)
What do cyclins do to enable CDKs to act as enzymes?
They phosphorylate them
What is phosphorylation?
When a phosphate group is attached to a molecule and is a common way to activate an enzyme
What do the activated enzymes (CDKs) make the cell do?
Move from the G1 phase to the S phase and from the G2 phase to the M phase
What are the points where the cyclin activated CDKs function called?
Checkpoints in the cell cycle
What do some cells do during the G1 phase of interphase?
Pause and enter a separate phase called the G0 phase
What does a cell not do in the G0 phase?
Grow
Which cells sometimes never progress beyond the G0 phase?
Nerve cells and muscle cells
When would checkpoints not be reached during the cell cycle?
If a cyclin concentration is low, there aren’t enough bindings to CDKs
What can the cell do when the cyclin concentration reaches a certain threshold?
Move on to the next phase
What does the G1 cyclin tell the cell to do?
To grow and get ready to replicate the DNA (the S phase)
When is the G1 cyclin introduced?
During the first growth phase
What does the mitotic cyclin tell the cell to do?
Start making the microtubules that will form the spindle fibers for mitosis.
What are cancer cells?
Cells that undergo extremely rapid and uncontrolled reproduction with very little or improper differentiation.
What is the result of the uncontrolled reproduction of cancer cells?
A mass of cells (tumour) with no useful function to the organism.
What are oncogenes?
Sections of genes that can mutate, or can be expressed at abnormally high levels.
What do oncogenes contribute to?
A normal cell becoming a cancer cell
What may oncogenes cause a cell to do?
Divide more frequently than they should.
What is a proto-oncogene?
A gene that can turn into an oncogene
What is apoptosis?
The pre-programmed death in cells’ DNA so that when they no longer function, they can be broken down and their materials recycled in the organism.
How do oncogenes make it so that cells keep dividing using mitosis instead of dying and being broken down?
They can modify apoptosis
Why might oncogenes start to change or mutate?
Because they are triggered by an outside agent called a mutagen.
What are tumor suppressor genes (TSGs)?
Specialize genes in healthy cells, which code for proteins that can regulate the cell cycle.
What are examples of roles of TSGs?
Controlling cell growth to ensure cells do not grow too quickly or that apoptosis takes place when necessary and repairing DNA that could lead to uncontrolled cell growth.
Why might the cell cycle be disrupted, cells grow unregulated, apoptosis does not take place and then a tumor can form?
If TSGs are damaged or undergo mutations
What is another way a TSG can be made less effective?
By silencing them
How may TSGs be silenced?
Cells can add chemical tags in the form of methyl groups to the genetic material that can silence them.
What is a primary tumor?
A tumor that occurs at the original site of a cancer
What is a secondary tumor?
A metastasis, a cancerous tumor that has spread from the original location to another part of the organism.
What is an example of a metastasis?
A brain tumor that is composed of breast cancer cells
When is a tumor said to be benign?
If the cells are forming a mass but are not spreading to the rest of the body.
When is a tumor said to be malignant?
If the cells rupture the organ they are in and start to spread to the rest of the body.
What are oncologists?
Doctors who specialize in cancer prevention and treatment
What is trisomy 21
down syndrome
Why is down syndrome also called trisomy 21?
because its when there are three copies of chromosome 21
What is the formula for the mitotic index?
of cells undergoing mitosis/total # of cells
