Lecture 7: Mitosis Flashcards
What is mitosis? Why is it important?
Mitosis is the process of cell division that results in two identical daughter cell. It is important for growth and development, tissue repair and healing and asexual reproduction in some organisms.
What is the definition of genome?
defined as the “total genetic information that a cell has.”
Explain prokaryotes vs. eukaryotic genome.
Prokaryotes possess a single circular double-stranded DNA molecule, while eukaryotes have at least one or two double-stranded linear DNA molecules.
Explain DNA packing.
Your cells contain about 6 ft of DNA but it all has to fit inside a tiny nucleus—this is where DNA packing comes in.
- A nucleosome is formed when DNA wraps around a group of histone proteins (like thread around a spool).
- Each nucleosome is the basic unit of DNA packaging.
- Under a microscope, this looks like beads on a string.
- Nucleosomes coil together to form chromatin.
- When a cell is about to divide, chromatin coils even more tightly into a chromosome.
What are Homologous chromosomes ?
-Homologous chromosomes: A pair of chromosomes with similar genes.
What are sister chromatids?
Two identical replicas of a single chromosome, joined at the centromere.
What is a spindle?
A network of protein cables (microtubules).
What is kinetochore?
A protein disk where spindle fibers attach to the sister chromatid.
What are centromere and centrosome, and centrioles?
-Centromere: The region joining two sister chromatids via cohesion proteins.
-Centrosome: helps divide the contents of nucleus into 2 made up of 2 centrioles
-Centrioles: made up of microtubules found in the region of centrosome and During cell division, they move to opposite sides of the cell to help form the spindle fibers that guide chromosomes.
What is the cell cycle and its two stages? Explain interphase and M phase.
The eukaryotic cell cycle consist of 2 main phases interphase and M phase.
-Interphase is a period of growth and preparation for division divided into G1, S and G2
-M phase is the mitotic phase it includes mitosis and cytokinesis.
What happens in the G1 phase? how long does it take?
cell growth, stocking up essential materials, increase protein synthesis, new cell organelles and producing macromolecules, cytoplasm volume increases
it takes 9hrs.
What happens in the S phase? How long does it take?
Replication of DNA and duplication of the centrosome.
It takes 10 hrs.
What happens in the G2 phase? How long does it take?
Prepares for cell division, cell continues its growth mitochondria doubles.
It takes 4.5 hrs.
What happens in prophase?
Chromosomes condense “2 sister chromatids”, the nuclear envelope breaks down, separation of centriole poles to opposite poles of the cell, formation of mitotic spindle.
What happens in metaphase?
Chromosomes align at the metaphase plate, with microtubules from opposite spindle poles attached to the kinetochores of sister chromatids.
What happens in Anaphase?
Sister chromatids separate and move toward opposite poles due to the degradation of cohesin proteins and the pulling action of microtubules. The kinetochore fibers shorten, pulling sister chromatids to opposite poles.
What happens during telophase?
-uncoiling of Chromosomes (decondense)
-the nuclear envelope reforms around each set of chromosomes
-formation of cleavage furrow
-the mitotic spindle breaks down.
2 NEW NUCLEI FORM
What happens during cytokinesis?
The division of the cytoplasm, resulting in two genetically identical daughter cells
How do cytokinesis in animal cells differ from in plant cells?
-In animal cells, cytokinesis happens through a process called the cleavage furrow. A ring of actin filaments forms just beneath the cell membrane at the center of the cell. This ring contracts like a drawstring, pinching the cell membrane inward until the cell is split into two.
-In plant cells, cytokinesis is different because plant cells have a rigid cell wall. Instead of a cleavage furrow, plant cells build a new structure called the cell plate in the middle of the cell. Vesicles from the Golgi apparatus carry cell wall materials to the center of the cell, where they fuse to form the cell plate. This plate eventually develops into a new cell wall, dividing the cell in two.
What is the goal of cell cycle checkpoints?
Prevent mutant cells from replicating and causing cancer
-detect DNA damage will be repaired or apoptosis
What are the three checkpoints of the cell cycle? What happens in each checkpoint?
G1 checkpoint – Checks for DNA damage, sufficient resources, and proper growth signals.
G2 checkpoint – Ensures DNA replication is complete and error-free.
M checkpoint – Ensures chromosomes are properly attached to the spindle before division.
What external factors can control the cell cycle?
-Growth-promoting hormones such as human growth hormone which influences cell divison
-cell density since it influxes contact inhibition (cells stop dividing when they come in contact with neighboring cells)
-death of neighboring cells
-anchorage dependence (when a cell needs to be attached to a surface to divide and grow)
How do growth hormones affect cell cycle?
Receive growth-promoting hormones, such as human growth
hormone (HGH or hGH)
* Too much: Gigantism
* Too little: Dwarfism
* Get large: The cell becomes inefficient due to a decreased surface-to-volume
ratio.
* Can’t divide if they get too crowded
What are positive regulators of the cell cycle? How do they contribute to the progression of the cycle?
Proto-oncogenes (cyclins, cyclin-dependent kinases)
* Help the cell progresses through
the cell cycle by ensuring that each phase of the cell cycle starts only when the previous one has been properly completed
-positive regulators help maintain proper timing and order in cell division. Without them, the cycle would stall or become disorganized.
What are negative regulators?
- Tumor suppressor proteins: Stop the cell cycle, they do not allow the cell to divide under unsafe conditions such as when the DNA is damaged or not growth enough
- Examples:
- Retinoblastoma protein (Rb)
- p53-triggers apoptosis when needed
- p21
they halt the cell cycle if conditions are not right.
What is needed for the cell to pass each checkpoint?
For the cell to pass each checkpoint, all the negative regulators
should be off, and all positive regulators should be on.
Explain the role of positive regulators (photo-oncogenes, cyclins, and Cdks) in cell cycle.
Cyclins are proteins that increase and decrease in concentration throughout the cell cycle. They bind to CDKs, activating them. Once activated, CDKs phosphorylate target proteins, which triggers the cell to move into the next phase of the cycle (like from G1 to S or from G2 to M).
What are the concentrations of the cyclin proteins?
The concentrations of cyclin proteins fluctuate throughout the cell cycle, regulating progression through different phases by activating cyclin-dependent kinases (CDKs). Each cyclin type has a distinct pattern of accumulation and degradation:
- Cyclin D: Levels gradually increase in early G₁ and remain relatively stable throughout the cell cycle, helping transition into the S phase.
- Cyclin E: Peaks at the G₁/S transition, promoting DNA replication initiation.
- Cyclin A: Rises during S phase and remains high through G₂, facilitating DNA replication and mitotic entry.
- Cyclin B: Increases in late G₂ and peaks at mitosis, then rapidly degrades to allow cell cycle exit.
Would you like a diagram to visualize these fluctuations?
What is nucleotide excision repair?
It is in the G1 phase and it repairs damage in DNA
What are tumor suppressor genes? What do they do? What happens if they have a mutation?
Rb and p53. They act as breaks and repair DNA mistakes or trigger apoptosis, if they have a malfunction they can no longer stop damage or abnormal cells from dividing.
What are Tumor-suppressor genes?
These genes normally stop cell division. Mutations in tumor-suppressor genes can lead to a loss of control over cell proliferation.
What is apoptosis?
crucial processor eliminating cells with mutations or damage that cannot be repaired
what are telomere?
shortening with each cell division can eventually trigger apoptosis. they are made out of DNA sequence and proteins found at the ends of chromosomes. with each cellular replication the telomere get shorter until they are so short and can’t divide (causes tissues age)
What will happen if your telomere never shorten?
If telomere never shorten, it means that they keep dividing uncontrollably and it overcomes it libations which can lead to cancer tumors.
What enzyme rebuilds telomere?
telomerase is the enzyme used to restore cell division.
What is cancer?
Abnormal growth of cells. Gene disorder often resulting in a tumor
What is metastases?
Metastases refers to the spread of tumor cells to other parts of the body.
What mutations?
DNA damage can lead to mutations that disrupt normal cell cycle control.
What are proto-oncogenes and oncogenes?
-Proto-oncogenes are normal genes that promote cell division. When damaged, they can become oncogenes, -oncogenes which are Cancer-causing genes due to damaged proto-oncogenes.
