Chapter 12: Cellular Division Flashcards
What type of chromosomes are in eukaryotes?
Linear chromosomes. Cells often contain 2 copies of each chromosome (homologous chromosomes)
What are the 6 stages of the eukaryotic cell cycle?
G0, G1, S, G2, Mitosis, and Cytokinesis
What are chromosomes?
Long strands of DNA wrapped around proteins called histones
What are external factors that impact cell division?
Growth factors, density dependent inhibition, and anchorage dependence
What is the spindle apparatus (MTOC) made of?
Microtubules and other proteins
What does interphase consist of?
Gap 1 (G1), Synthesis (S), and Gap 2 (G2)
What does cytokinesis indicate?
Division of organelles and cytoplasm
What is securin?
A protein that secures separase
What phases of the eukaryotic cell cycle is the cell dividing in?
Mitosis and cytokinesis
What are homologous chromosomes? Where do they come from?
Two copies of each chromosome. One from mom and one from dad
What is separase?
An enzyme that cuts the sister chromatids apart to be pulled to opposite poles
What is anchorage dependence?
Normal cells need to be anchored to the extracellular matrix and each other
What type of chromosomes are in prokaryotes?
Single circular chromosome
What are condensins?
Targets of G2 checkpoint (MPF) that help DNA pack together in prophase
How much DNA is in the human body?
2 x 10^13 (67 trips to the sun and back)
What does fission indicate?
There is no nucleus
What do microtubules that aren’t attached to chromosomes do in anaphase?
They push against each other to move the cell apart
What is the G2 checkpoint?
M phase-promotion factor (MPF). Allows G2 to continue to mitosis. Last check before mitosis
What two signals can a cell receive at the G1 checkpoint?
A green light to continue to s phase or a red light to exit the cell cycle and enter G0
What phase are chromosomes easiest to see under a microscope?
Metaphase
What forms in prophase?
Spindle apparatus (MTOC - microtubule organizing center)
What are the three parts of chromosome structure?
Centromere, telomere, and kinetochore
What happens with density dependent inhibition in cancer cells?
It doesn’t do anything. Cancer cells don’t stop dividing
What targets of the G2 checkpoint (MPF) are needed for mitosis to proceed?
All of them
What is a telomere?
Chromosome structure that is the region of repetitive DNA sequences at the end of chromosomes
What happens in prometaphase?
The nuclear envelope disassembles (DNA no longer protected) and spindle fibers attach to kinetochores
What does condensing before division do for cells?
Makes it easier for the cell to split the chromosomes evenly between the two cells
Example of a growth factor
Platelet-derived growth factor (PDGF). When you cut your leg, it triggers cells to divide to heal the wound
How does cytokinesis occur in animals?
Cleavage furrow pinches off separated nuclei
How much DNA is in a single cell?
2 meters
When can chromosomes be seen?
When cells are getting ready for division only, but they are always there
What happens when a microtubule doesn’t attach?
The cell doesn’t pass the M phase checkpoint (APC - metaphase to anaphase)
What are the two things that can happen in asexual cellular division?
Mitosis and binary fission (bacteria)
What is the metaphase plate?
The location where chromosomes align in metaphase. It is not an actual physical structure
Example of a growth factor
Rb attached to E2F (transcription factor) preventing it from transcribing DNA. Growth factor added to Ras pathway to cdk-cyclin complex which phosphorylates the Rb protein with ATP to allow E2F to transcribe
How is cell cycle regulation controlled?
A system of signaling molecules which trigger and coordinate the events of the cell cycle
How are sister chromosomes pulled to opposite poles of the cell in anaphase?
Microtubules shorten due to being disassembled which causes the sister chromosomes to be pulled to opposite poles
What can happen in G0?
Some cells, like liver cells, can be called back into division
What factors can cause a cell to enter G0 from the G1 checkpoint?
Is the cell big enough, are conditions favorable, any DNA damage, etc.
What type of animal is the G1 checkpoint most important in?
Mammals
What are the targets of the G2 checkpoint (MPF)?
Condensins (help DNA pack together in prophase), proteins involved in mitotic spindle formation, lamins (proteins involved in nuclear envelope assembly/breakdown), and also shutting itself down and allowing the cell to continue to mitosis
What are the two types of cellular division?
Asexual and sexual
What do the tails of histones do?
They are important in gene expression. Can block genes or turn them on
What happens in G1 of interphase?
Growth, protein synthesis, and organelle synthesis. The cellular contents (excluding chromosomes) are duplicated
How many genes are in the human body? What percentage of DNA is this? What is the other percent?
20,000-25,000 genes that are 2% of DNA. Other 98% are critical non-coding regions
What is the end product of mitosis?
2 identical daughter cells
What happens when cytokinesis doesn’t follow mitosis? Is this possible?
A cell with multiple nuclei will be the end product. It is possible, however, rare
What happens in metaphase and why does it occur?
Chromosomes align along the metaphase plate and it occurs because of tug of war between the two poles
What is interphase?
When the cell is getting ready for division
What is a kinetochore?
Chromosome structure that is a disc shaped protein that spindle fibers attach to. It attaches to the centromere
What happens in G2 of interphase?
Growth, synthesis of microtubules, cell cycle checkpoints (the cell double checks the duplicated chromosomes for error, making any needed repairs)
How do cyclin dependent kinases work?
They are present at constant concentrations but usually are inactive. They are activated by attaching to cyclins and their activity matches cyclins when they attach to them
How many phases is mitosis divided into? What are they? Why is this sort of hazy?
5 phases. Prophase, prometaphase, metaphase, anaphase, and telophase. It is hazy because mitosis is a continuous process and there are no starting or stopping points.
What happens in anaphase?
Sister chromatids are cut apart and pulled to opposite poles of the cell
What does mitosis indicate?
Nuclear division
What is the M phase checkpoint (anaphase promoting complex - APC)
A complex of 11-13 proteins that marks cell cycle proteins for degradation. Metaphase to anaphase checkpoint
How does cytokinesis occur in plants?
A new cell wall is formed between two cells. Golgi-derived vesicles bring materials to the middle that fuse to form cell plate which becomes a cell wall between the two cells
What is a genome?
The DNA of a cell. It is the same in all cells in a person but varies per person
What happens in cytokinesis?
The cytoplasm divides
What is a centromere?
Chromosome structure that is the condensed region of the chromosome that stays condensed. The kinetochore connects here
How do cyclins work?
Levels fluctuate cyclically. They go up and down at certain points of interphase
What happens to chromosomes in prophase?
They begin to condense and can be seen under a microscope
What is bacterial binary fission and what does it produce?
A form of asexual reproduction carried out by bacteria that produces no genetic diversity but is very fast
What happens in S of interphase?
DNA is duplicated (each of the 46 chromosomes duplicated)
What usually follows mitosis?
Cytokinesis
How does the cell ensure it is ready to proceed to the next step?
Multiple checkpoints
How does the cell plate form in plant cell cytokinesis?
Golgi-derived vesicles bring materials to the middle to create it
Where does the kinetochore connect?
Centromere
What two main regulatory molecules are involved in cell cycle clocks?
Cyclins and cyclin-dependent kinases (cdks)
How are sister chromatids cut apart in anaphase?
Cohesion that holds them together is cleaved by enzymes
What percentage of time do cells spend in interphase?
90%
How do cyclin dependent kinases get activated?
They attach to cyclins
What is the G1 checkpoint?
The restriction point that comes before DNA replication
What happens in telophase?
Nuclear envelopes reform around DNA (2 nuclei) and chromosomes unfold back into chromatin (reversal of prophase)
Why is tight cell cycle regulation important?
It ensures normal growth and development
What stage are most cells in the human body at?
G0
What do telomeres do?
They are the ends of chromosomes that don’t code for anything. Division causes the ends to not be replicated so telomeres act as a buffer to ensure all the DNA gets replicated. They tell the cell to stop dividing when they are gone. They cause the cell to have a limited number of divisions
What happens in sexual cellular division?
Meiosis
What does the protein dimer consist of in the G2 checkpoint?
A cyclin and a cdk
What happens when chromosomes are duplicated?
It creates sister chromatids (two arms that are identical copies making up a chromosome)
When are chromosomes duplicated?
Before cell division
What is density dependent inhibition?
Cells grow and divide until they touch their neighbors, then they stop
What happens at the G1 checkpoint?
The cell has to commit to dividing or not
What are the four reasons why cells divide?
Reproduction, growth and development, tissue renewal, and maintain a favorable surface area to volume ratio
What are lamins?
Targets of G2 checkpoint (MPF) that are proteins involved in nuclear envelope assembly/breakdown
How are sister chromatids held together?
At the centromere
What are growth factors and what do they do?
Signals from other cells (social cues) that multicellular organisms rely on
What is the spindle apparatus (MTOC) and when does it form?
It is the machine responsible for pulling apart the chromatids. It is formed during prophase
What is chromatin?
DNA and protein (histone) complex
How many base pairs of DNA are in the human body?
3 billion
What are cyclins and cyclin dependent kinases?
Proteins that are the 2 main regulatory molecules
When phase does cytokinesis occur in? Alongside of?
It occurs in its own phase. It usually occurs along with mitosis beginning in telophase
When are sister chromatids pulled apart?
Mitosis
What happens in G0?
It is the quiescent or resting state. Cells are not preparing to divide but are metabolically active
What phase does cytokinesis begin in?
Telophase
What does the cell start to do in telophase?
Divide
