Chapter 12 - The Cell Cycle & its Regulation Flashcards
Some eukaryotes have cell division that is intermediate between binary fission and mitosis such as what? (Give the two main examples)
- Dinoflagellates ~2000-4000 species
Single celled organisms with two flagella
2.Diatoms and yeast ~ 100,000 species
Extremely important phytoplankton
What happens to dinoflagellates during mitosis?
Nuclear envelope remains intact during mitosis and the chromosomes attach to it
Microtubules pass through the nucleus dividing it, similar to binary fission.
What happens to diatoms & yeast during mitosis?
Nuclear envelope remains intact
And, microtubule spindle forms inside the nucleus
Within the nucleus, ANDA separates similar to how it would in eukaryotes.
What is a genome?
A genome is an organism’s
Complete set of DNA
including all of its genes. Each genome contains all of the information needed to build and maintain that organism. In humans, a copy of the entire genome—more than 3 billion DNA base pairs—is contained in all cells that have a nucleus.
Prokaryotic cells have a single DNA molecule.
Eukaryotic cells have a # of DNA molecules.
What’s the difference between a somatic cell and a gamete cell?
Somatic cell
(non reproductive cells) have two sets of chromosomes. Human somatic cells = 23 pairs of chromosomes.
Gamete cell
(reproductive cells: sperm and eggs) have one set of chromosomes. Human gametes = 23 chromosomes
Briefly describe the process of gene replication
(see picture)
In the cell cycle, what are the 2 main phases, along with the respective subphases?
Also provide a brief description of each
1. Interphase - 90% of cell cycle
Cell growth and copying of chromosomes in preperation for cell division. Grows during all three processes.
A) G1 phase
B) S phase
C) G2 phase
2. Mitotic phase
The actual process of division of one nucleus into genetically identical nuclei.
A) Mitosis
I) Prophase
II) Prometaphase
III) Metaphase
IV) Anaphase
V) Telophase
B) Cytokinesis
Describe the process of each subphase during Interphase
1. G1 phase (“first gap”)
The “restriction point” – point of no return in cell cycle
Up until this point (found in G1) all cellular growth has been regulated by growth factors.
After this point, the cell cycle will continue to the next checkpoint at the end of G2.
2. S phase (“synthesis”)
DNA in the nucleus is replicated
Centrosomes are duplicated
Just after mitosis (M-phase) they move to opposite sides of cell.
3. G2 phase (“second gap”)(see picture)
All of machinery needed for mitosis is replicated
The cell continues to grow until it is twice the original size
After this checkpoint, mitosis occurs.
End of phase (going into mitotic phase):
* Nuclear envelope still intact
* Nucleus still intact
* Two centrosomes formed
DNA and chromatin have not yet condensed into chromosomes
Describe the process of each subphase (5) during the Mitotic (M) phase (cell division)
1. Prophase
Nuclear envelope still intact
Nucleolus disappears
DNA and chromatin condenses into chromosomes
Mitotic spindle forms (centrosome and microtubules)
Centrosomes push apart (pushed by extending microtubules)
2. Prometaphase
Nuclear membrane fragments
Microtubules from spindles connect to chromosomes
Microtubules connected to kinetochores on chromatids are called kinetochore microtubules
Other microtubules interact with microtubules from opposite side of cell
3. Metaphase
Longest stage in mitosis
Centrosomes are on opposite sides of cell
Mitosis does not proceed until chromosomes have all lined up on the metaphase plate
4. Anaphase
Shortest stage of mitosis
Stage begins when sister chromatids part
The chromosomes begin moving towards each centrosome
Cell elongates as the non-kinetochore microtubules lengthen
5. Telophase
Two daughter nuclei begin to form
Chromosomes become less dense
Daughter cell nuclear envelopes arise from the fragments of the parental cell’s nuclear envelope.
Describe the process of prophase (First phase in mitotic phase)
1. Prophase
Nuclear envelope still intact
Nucleolus disappears
DNA and chromatin condenses into chromosomes
Mitotic spindle forms (centrosome and microtubules)
Centrosomes push apart (pushed by extending microtubules)
Describe the process of prometaphase (second phase in mitotic phase)
2. Prometaphase
Nuclear membrane fragments
Microtubules from spindles connect to chromosomes
Microtubules connected to kinetochores on chromatids are called kinetochore microtubules
Other microtubules interact with microtubules from opposite side of cell
Describe the process of metaphase (third phase in mitotic phase)
Metaphase
Longest stage in mitosis
Centrosomes are on opposite sides of cell
Mitosis does not proceed until chromosomes have all lined up on the metaphase plate
Describe the process of Anaphase (fourth phase in mitotic phase)
4. Anaphase
Shortest stage of mitosis
Stage begins when sister chromatids part
The chromosomes begin moving towards each centrosome
Cell elongates as the non-kinetochore microtubules lengthen
Describe the process of Telophase (fourth phase in mitotic phase)
5. Telophase
Two daughter nuclei begin to form
Chromosomes become less dense
Daughter cell nuclear envelopes arise from the fragments of the parental cell’s nuclear envelope.
Humans have how many chromosomes?
23
Somatic Cells (non reproductive) - 23 pairs of chromosomes
Gametes (reproductive) - 23 chromosomes
Describe the process of cytokinesis (after telophase)
1 cell becomes 2
In animal cells, cytokinesis occurs by a process known as cleavage, forming cleavage furrow.
In plant cells, a cell plate forms during cytokinesis
Before mitosis can begin, the cell must go through interphase for cell preperation. But, there are several “stop and go checkpoints” that must be passed first. What are these checkpoints? (four of them)
G1 Checkpoint
Called the “restriction point” , Often viewed as the most important checkpoint
If cell passes through G1 checkpoint, then the cell with proceed through the G1, S and G2 phases of the cycle.
If the cell does not pass through this checkpoint, it can go into G0.
G0 Checkpoint
Most cells do not need to actively grow in size and divide and are in a quiescent (“quiet”) state.
Cells such as bone marrow, skin and lining of the guy do not go into G0 as they need to continually divide and grow.
Some cells can be in the G0 for a long time, such as nerve cells which stay like that for over 20 years.
Most cells in your body are G0.
G2 Checkpoint
Makes sure the cell is big enough and the environment is favourable. Also checks for damaged DNA.
Two types of regulatory proteins are involved in cell cycle control at the G2 checkpoint:
Cyclin – named for cyclically changing concentration in the cell
Cyclin-dependent kinases (Cdks) - present in cell at relatively constant concentration, but not activated until connected to cyclin.
When cyclin and Cdk bind together, they are called MPF (maturation-promoting factor)
MPF triggers a cell’s passage past the G2 checkpoint into the M phase.
Metaphase (M) Checkpoint
Makes sure the chromosomes are aligned on the metaphase plate.
at the G2 checkpoint, there are two types of regulatory proteins involved in the cell cycle control. What are they? and when bound together, what is this called?
G2 Checkpoint
Makes sure the cell is big enough and the environment is favourable. Also checks for damaged DNA.
Two types of regulatory proteins are involved in cell cycle control at the G2 checkpoint:
Cyclin
named for cyclically changing concentration in the cell
Cyclin-dependent kinases (Cdks)
present in cell at relatively constant concentration, but not activated until connected to cyclin.
MPF (maturation-promoting factor)
When cyclin and Cdk bind together, this is called the MPF.
MPF triggers a cell’s passage past the G2 checkpoint into the M phase.
What are the two signals that stop the cell cycle?
Density-dependent inhibition
crowded cells stop dividing.
Anchorage dependence
cells must be attached to a surface in order to divide.
Some external signals are growth factors to the sell, what is an example of an external signal?
Plate-derived growth factor (PDGF)
stimulates the division of human fibroblast cells in culture.
Fibroblasts are loose cells in connective tissue that make up part of the Extra-cellular Matrix (ECM)
In terms of cancer terminology, what does transformation mean for the cell? How does this happen?
Transformation
A normal cell converted to a cancerous cell.
How?
Cancer cells may not need growth factors to grow and divide:
* They may make their own growth factor
* They may convey a growth factor
* They may have an abnormal cell cycle control system
Occasionally non-cancerous cells with lose control of the cell cycle.
Normally these cells will undergo apoptosis, also known as “programmed cell death”.
If the cells do not undergo apoptosis then they will continue to grow and can eventually become cancerous
What is a benign tumor and a maligant tumor?
Benign tumor
abnormal cells remain at the original site
Malignant tumor
abnormal cells can metastasize (invade surrounding tissues) where they may form secondary tumors
What is metastasis?
Metastasis
Cancerous cells can detach from surrounding cells in the tissue/organ and the travel through the blood or lymph vessels and begin to grow elsewhere in the body. If this occurs, the cancerous cells have become “metastasized” making the tumours very difficult to treat.
Drugs like Paclitaxel and toxol have been used to treat certain forms of cancer. How does it do this ?
Paclitaxel has been shown to act as a mitotic inhibitor.
How? Microtubules are stabilized
- Prevents the depolymerisation of the microtubules attached to kinetochores.
- Thus, the mitotic spindle is frozen
- Actively dividing cells then cannot proceed beyond Metaphase.
