- 1 Nucleus
- 2 electron Microscopy
- 3 Cell exocytosis
- 4 cellular energy production
- 5 Cell adhesion
- 6 Lecture 10 Homework
- 7 Methods of Confocal Microscopy
- 8 S Phase in cell division
- 9 Separase
- I found the membrane of the nucleus to be interesting. I always thought the nucleus membrane was impermeable, so finding out there were pores was interesting.
- The mRNA doesn't leave the nucleus until it has matured, and that it is extremely unstable, and as a result is one of the main reasons for There being a cell nucleus in eukaryotes.
- Link to home page of the confocal microscope (UNSW) 
- Link to the home page of the Electron microscope unit (UNSW) 
- Proteins are made in the lumen and are only allowed into the cytoplasm with a membrane. I'm not sure what the proper reason for this is, Is it to protect the protein, or to prevent the poteins from makig chages to the cytoplasm.
- I found the golgi apparatus pretty interesting. I did not know that each of the compartments were different sizes and that they do not touch.
cellular energy production
- There are 3 main types of energy production in a cell.
- Phosphocreatine - resynthesizes and resupplies callular ATP
- Aerobic metabolism - requires oxygen to drive the chemical reactions
- Glycolosis - this is an anaerobic system that uses glucose and glycogen
- Mitochondria and energy production are found in the area of the cell where the most energy is required
- Cell Adhesion Molecule (CAM)
- L-CAM is a liver cell adhesion molecule
- NG-CAM is a Neuron-Glia cell adhesion molecule
- I-CAM is an Intercellular cell adhesion molecule
Lecture 10 Homework
- strata spinosum
Methods of Confocal Microscopy
- the two methods used in confocal microscopy are Spinning and Laser
S Phase in cell division
- S Phase stands for Synthesis Phase
Separase is a protein that is a cornerstone of cell division. Serperase is also known as Separin or Esp1. It allows for replicated chromosomes to be separated from their sister chromatids and pulled to opposite poles of the cell by the mitotic spindle, allowing for microfilaments to dissect the cell in half causing two genetically identical daughter cells from the single mother cell in mitosis or some haploid cells in Meiosis. The sister chromatids are held together by a protein called Cohesin, Separase catalyses and breaksdown cohesin allowing the sister chromatids to break apart, which in turn allows the mitotic spindle to draw the chromatids to either sides of the cell. Separase is crucial to the cell division process, not only does it physically separate the sister chromatids, it triggers the start of the anaphase period of cell division. Separase causes the cell to replicate accurately and on some occasions cause some problems if the protein is present or absent in excess quanitities. Separase is a large part of the cell cycle as its initiation begins the anaphase cycle of the M phase in the cell cycle.
Role of Separase in cell division
Seperase has an extremely important role in cell division, it allows the chromatids to be pulled to opposite sides of the cell by the Mitotic spindle. Cohesin holds the chromatids together to allow them to replicate, seperase catalyses the cohesin holding the chromatids together allowing for separation. It has been found DNA does not stimulate but mediates cohesion breakdown via allowing seperase to interact with Cohesin. (Sun, Kucej, Fan, Yu, Sun, Zou. 2009) There are 2 main roles seperase undertake in their use, the first is to ‘separate sister-chromatid attachments, and the second is the dissociation of cohesin from the chromasomes’ (Uhlmann, Lottspeich, Nasmyth, 1999). Seperase is the marker for the end of the G2 phase and the initiation of the M phase. Separase must be inhibited before the cell cylce reaches the anaphase, separase initiates the anaphase but it must be inhibited before anaphase begins (Huang et.al, 2009). Huang also state there are 'two inhibitory mechanisms exist in vertebrates that that block the protease activity. One mechanism is through binding and inhibition by securin, and another is phosphorylation on Ser1126 in humans' (2009).
driving factors of Separase
Sun et.al. have hypothesised that separase is not stimulated by DNA but is mediated by DNA (2009). Separase also requires other proteins have catalysed other proteins. ‘The dissolution of sister-chromatid cohesion is catalysed by separase, after the destruction of securing by the anaphase-promoting complex/cylosome’ (Yuan, Li, Huo, Yan, Yang, Ward, Jin, Yao, 2009). In order for Separase to have the desired affect, it must work in order and conjunction with other proteins. Aurora B is the regulator of Separase, which forces the separase protein to be accumulated during the M phase and then degraded at the end of telophase (Yuan et.al. 2009). Yuan et.al. has also discovered the Aurora B kinase helps the coordinate the association of separase with the chromosome to begin degradation of cohesion (2009).
Possible complications caused by Seperase
The accuracy of transmission of chromosomes is crucial to prevent complications arising. Complications arise if there is an over abundance of or a lack of a protein, in this case, the seperase protein. One of the major complications of seperase during cell division is aneuploidy. Aneuploidy happens to be a major cause of cancers as chromosomes are not separated equally leading to a malfunction in the cell. Huang et.al have discovered a small amount of overexpression of separase does not cause harm, but too much can have serious complications (2009), Zhang et.al have also researched the area of separase overexpression and have found it ‘induces premature separation of chromatids, lagging chromatids and anaphase bridges’ (2008). An underexpression of separase will not allow the mitotic spindle to pull apart the sister chromatids, which may pull the spindle towards the middle of the cell or the chromatids may not be separated leading to a mutated cell. Huang et.al have also hypothesised the deregulation of separse may cause infertility in humans (2009). It is crucial to have the right amount of separase to catalyse the cohesin, too little or too much will cause complications, which may eventually lead to cancer. A normal amount of separase will lead to proper cell division and function.
- Sun Y, Kucej M, Fan HY, Yu H, Sun QY, Zou H. 2009. Seperase is recruited to mitotic chromosomes to dissolve sister chromatid cohesion in a DNA dependent manner. Cell. 137(1):123-32
- Uhlmann F, Lottspeich F, Nasmyth K. 1999. Sister-chromatid separation at anaphase is promoted by cleavage of the cohesion subunit. Nature. 400:37-42
- Yuan K, Li N, Huo Y, Yan F, Yang Y, Ward T, jin C, Yao X, 2009. Recruitment of separase to mitotic chromosomes is regulated by Aurora B. Cell cycle. 8(9)
- Huang X, Andreu-Vieyra CV, Wang M, Cooney AJ, Matzuk MM, Zhang P. 2009. Preimplantation mouse embryos depend on inhibitory phophorylation of separase to prevent chromosome missegregation. Molecular Cell Biology 29(6):1498-505
- Zhang N, Ge G, Meyer R, Sethi S, Basu D, Pradhan S, Zhao YJ, Li XN, Cai WW, El-Naggar AK, Baladandayuthapani V, Kittrell FS, Rao PH, Medina D, Pati D, 2008. Overexpression of Separase induces aneuploidy and mammary tumorigenesis. Proc Natl Acad Sci USA. 105(35):13033-8