The Cell Cycle Flashcards
In terms of general cell cycle, how are cancer cells different from normal functioning cells?
Cancer cells have a defect that causes these cells to divide continuously rather than to go into its growing phase. Normal cells tend to spend about 90% of their life in the growth phase.
As you’re studying a sample of tissue you obtained from your patient’s liver during a biopsy, you note that these hepatocytes are creating organelles and their nucleus have no visible chromosomes. What state of cell cycle are these cells in? What determines if this cell will move onto its next stage in cell cycle?
These cells are in interphase, specifically the G1 phase where the cells grow in size and transcribe proteins. The cell will move onto S phase if it meets the restriction point requirements - G1-S phase - regulation point before DNA replication
In assessing a biopsied specimen of the spinal cord, you note that this cell is simply sitting there. There is no growth in cell size, but there does seem to be DNA transcription. What portion of the cell cycle must this cell have come from? What portion of the cell cycle is it currently in?
This cell appears to be in a Go phase - this is characterized by no more division. In order for cells to enter this stage, it must have gone through the G1 Phase where it was able to grow and synthesize proteins. Then with some checkpoints, and markers, this cell is directed to the Go phase
A nucleus exits S phase and is ready to enter into G2 phase. What is the ploidy of this nucleus?
The ploidy of this nucleus remains the same after synthesis. Though the amount of DNA in the cell has effectively doubled from 46 chromosomes to 92 chromosomes, the ploidy, or number of sets of chromosomes, of the cell remains at 2n. There are more copies of the same sets of chromosomes, but the number of different sets of chromosomes remain the same.
Define homologous chromosomes. What is the number of homologous chromosomes after DNA synthesis during the cell cycle.
Homologous chromosomes are two pieces of DNA within a diploid organism. These carry the same genes and come from each parental source. After S phase, there are still only 46 chromosomes. These are replicated and thus has a sister chromatid attached to the original homologous chromosome, but this new chromatid DOES NOT change the count of homologous chromosomes. This is essentially referring to the organisms ploidy - Ploidy refers to the number of sets of homologous chromosomes in the genome of a cell or an organism
Microtubules are noted to be produced initially in what stage in the cell cycle? What stage comes after this stage? Where are these MT used in the cell cycle
In the G2 phase - which is another growth stage in which the cell undergoes after DNA replication. However, the difference is that this stage is characterized by preparations for cell division. MT is first made in this phase, and prophase follows when this stage is completed, but MT is not used until the anaphase
Looking at a video you see a keratinocyte has been arrested in its cell cycle. What check point must this cell be at if the cell has sister chromatids? What molecular substance must be present to induce this cell into the next stage?
G2-M phase - regulation before mitosis. In G2 phase - production of cyclin B protein occurs. This Cyclin B binds to CDK 1 to form complex, and this complex activates the cell to to the step: mitosis AKA cell division
True or false, cyclin [ ] remains constant in the cell most times and cdks are the molecules needed to be transcribed in different cell cycles in order to push cell further into cell cycle.
False. all different types of cdk are ALWAYS present in a cell.
In general, Cdk levels remain relatively constant across the cell cycle, but Cdk activity and target proteins change as levels of the various cyclins rise and fall. These cyclins change based on the nucleus’s transcription
On a lab report, you note that there is a strange molecule, CDK, floating in the blood. What is its purpose in the body when it is activated?
Cyclin Dependent Kinases - a kinase is something that adds a Pi on other enzymes or proteins to activate or inactivate them. These cyclin dpd kinases work together with cyclin. In this manner, it regulates cell cycle.
What cdk - cyclin complex encourages DNA replication?
CDK4-cyclin D complex - phosphorylate a protein called RB. This causes RB to be unable to inhibit DNA replication. This means that the PO4 causes the RB protein to be inactive thus encouraging DNA replication
Mnemonic to remember cdk - cyclin in cell cycle phases
DAB 4 -> 2 Remember that cdk-syslin complexes are only in interphase and don’t forget cdk e Cdk D - 4 Cdk E - 2 Cdk A - 2 Cdk B - 1
Often in times of cell cycle regulation, tumor suppressors and the cdks come up in the discussion. How are these generally different, how are they the same?
Both contribute to regulation of the cell cycle.
As a general rule of thumb, Cyclin dependent kinases are when bounded by cyclin induce the cell to continue in its cell cycle. Meanwhile, tumor suppressors hinder the cell and prevent the cell from continuing into cell cycle
Mnemonic: Cdk - C for Continue Cell cycle.
Tumor suppressors are self explanatory
In Grey’s anatomy, Bailey mentions cardiomyopathy (a Dx of the heart muscle that makes it harder for your heart to pump blood to the rest of your body) in a patient is linked to the deficiency of p53. What do you know about p53’s role in cell cycle?
These function in tumor suppressing and are termed the guardians of the genome. In general, p53 has the ability to bind to DNA directly encouraging transcription of proteins that will inhibit the progression of cell cycle.
As you observe a mouse cardiocyte, you note there is a high concentration of p21 is seen in the nucleus. What causes the transcription of this protein? What affect will it have in the cell?
P53 binds to genes, causing p21 to be transcribed and translated. This protein inhibits cdk, causing the hindrance of DNA replication and prevent active mitosis
Contrast RB proteins from p21 proteins
Both are stimulated by the p53 transcription factor.
p21 proteins inhibit cell cycle while RB proteins are tumor suppressors.
