Chapter 2.1 Flashcards
What does it mean to be diploid?
Diploid cells contain two copies of each of their chromosomes.
What does it mean to be haploid?
Haploid cells only have one of each chromosome.
What are the four stages of the cell cycle?
G1 (G0), S, G2, and M
What is interphase
Interphase is just a way of referring to the non-reproductive stages of the cycle, i.e. G1, S, G2
What is happening during G1?
In G1, the cell increases its size, synthesizes proteins, and creates new organelles. This is to prepare the cell for division.
What is happening in G0?
In G0 the cell is just living its life and serving its function. At this point the cell is not doing anything to prepare for division.
What is the restriction point?
The restriction point is the quality control checkpoint between G1 and S. If the cell passes the restriction point inspection, it will commit to replicating.
If the cell does not pass the restriction point inspection, it will go into G0 or spend some more time in G1 and try to pass the restriction point again.
Where are the three quality control checkpoints in the cell cycle and for what are they checking?
- G1 to S, is the cell ready to synthesize new DNA and does the DNA need to be repaired before synthesis? (Restriction Point) (p53 plays big role)
- G2 to M, was the DNA replicated correctly and is the cell ready to divide? (p53 also plays a role)
- Metaphase to Anaphase, have all the chromosomes been attached to the spindle?
What is happening in the S stage?
In the S stage, the DNA is replicated, resulting in identical sister chromatids.
Describe Eukaryotic Chromosomes
Eukaryotic Chromosomes are large pieces of DNA that are formed from the wrapping of DNA around histones and the packing of those histones into a linear structure.
What are chromatids?
Chromatid is the name for either individual copy of a duplicated chromosome. Note, just because a chromosome has been duplicated into two sister chromatids does not mean you have two chromosomes. The sister chromatid pair only counts as one chromosome.
What is a centromere?
The centromere is the part of the chromosome where two sister chromatids connect.
Does ploidy increase in the S stage?
No. DNA replication causes each chromosome to double in size, but even though there are now two sister chromatids, there is still only one chromosome.
What happens in G2?
In G2 the cell grows more and synthesizes more proteins to further prepare for Mitosis.
What is happening in the M phase?
In the M phase, the cell undergoes all stages of Mitosis and Cytokinesis, resulting in two new cells.
If DNA is found to be too damaged to move past the G1/S restriction point, what happens?
The cell cycle will be stopped by a protein known as p53 and an attempt will be made to repair the DNA so it can pass the restriction point.
What is a transcription factor?
A transcription factor is a molecule that promotes or inhibits the transcription for certain genes.
What molecules are responsible for the timing of the cell cycle?
Cyclins and Cyclin Dependent Kinases
How do cyclins control the timing of the cell cycle?
- Various cyclins rise and fall in concentration at various stages of the cell cycle.
- As these concentrations rise and fall, certain Cyclin Dependent Kinases (CDKs) are activated and deactivated.
- Active CDK’s activate transcription factors that activate genes that let the cell move on to the next stage of the cell cycle.
What medical condition can arise when the cell cycle becomes disrupted and damaged cells are allowed to reproduce?
Cancer
What is the spread of cancer cells through the blood and lymphatic vessels referred to as?
Metastasis
What is Mitosis?
Mitosis is the process by which two identical daughter cells are created from a single cell.
What are the four stages of Mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
What 5 important things happen in Prophase?
- Chromatin condenses into chromosomes.
- The centrioles migrate to opposite sides of the cell.
- Then the centrioles start to form spindle fibers.
- The spindle fibers extend throughout the cell, most going towards the middle.
- The nucleus dissolves and kinetochores appear at the centromere
What are spindle fibers?
Spindle fibers are the names of the long microtubules that centrioles use to exert their effects during mitosis.
What is an aster?
Aster refers to the microtubules that radiate outward from the centrioles during mitosis and anchor the centrioles to the opposite sides of the cell membrane. Asters are so named because they radiate outwards in all directions, and make the centrioles look like stars.
What is a kinetochore?
Kinetochores are protein structures located at the centromere that serve as attachment points for specific fibers of the spindle apparatus.
What important thing happens in Metaphase?
The spindles push and pull the chromosomes to the metaphase plate, which is an imaginary line that runs down the center of the cell.
What important thing happens in Anaphase?
In anaphase, the chromosomes are reeled in by the centrioles and pulled to opposite sides of the cell.
What happens in Telophase?
Telophase is essentially the reverse of prophase. A nuclei reforms around each of the copies of genetic information. The chromosomes uncoil back into chromatin. The spindle dissappears and the centrioles return to their normal location.
What is chromatin?
Chromatin is the term for unwound DNA in the nucleus.
Mitosis occurs in _____ cells
somatic
Meiosis occurs in ______ cells
gameocyte
Mitosis results in what kind of cells?
Two identical daughter cells
Meiosis results in what kind of cells?
Up to 4 different daughter cells
What is reductional division?
When the result of a division is the reduction of the ploidy number
What is equational division?
Equational division is when division results in the separation of sister chromatids, and therefore it does not change the ploidy number of the daughter cells.
How many chromosomes is the human genome composed of?
23 homologous pairs. (46 chromosomes)
What are the main differences between Prophase 1 of Meiosis and Prophase of Mitosis?
Prophase 1 of Meiosis is bascially the same as Prophase 1 of Mitosis. The only difference is that, in Prophase 1 of Meiosis, homolgous chromosomes undergo synapsis to form tetrads. These homologus chromosomes then undergo crossing over with one another.
What is synapsis?
Synapsis is when homologous chromosomes come together to form a tetrad. This occurs in Prophase 1 of Meiosis.
What is a tetrad?
Tetrad is the name for the synaptic pair of homologus chromosomes that is formed in Prophase I. The tetrad is so named because, although there are only 2 chromosomes, both chromosomes have been duplicated in the previous S stage, and so there are 4 total chromatids.
What is the chiasma?
The chiasma is the point at which homologous chromosomes overlap one another. It is at this point that genetic info will break off and cross over from one chromosome to another.
What is crossing over?
Crossing over is the process by which homologous chromosomes in tetrads exchange chunks of DNA with one another, thereby increasing the genetic diversity of the daughter cells.
Why can’t crossing over happen between sister chromatids?
The cell has ways of making sure that homologous chromosomes and not sister chromatids cross over, but think about it. A sister chromatid is identical to its sister, so even if sister chromatids could trade DNA, it wouldn’t make a difference since all the DNA is identical.
