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Unit 4 Exam

by: TCU2461

Unit 4 Exam BIOL 30603


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These notes include a variety of detailed topics including systems on the cell cycle, mitosis/meiosis, sexual reproduction, and stem cells.
Molecular, Cellular, and Developmental Biology
Dr. Akkaraju, Dr. Misamore, Dr. Chumley, Dr. McGillvray
Study Guide
cellular biology, Cell Cycle, Mitosis, Meiosis, stem cells
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This 10 page Study Guide was uploaded by TCU2461 on Tuesday May 3, 2016. The Study Guide belongs to BIOL 30603 at Texas Christian University taught by Dr. Akkaraju, Dr. Misamore, Dr. Chumley, Dr. McGillvray in Spring 2016. Since its upload, it has received 53 views. For similar materials see Molecular, Cellular, and Developmental Biology in Biology at Texas Christian University.


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Date Created: 05/03/16
Dr. Misamore - Cell Cycle: • Embryonic cells will replicate the quickest. • The cell cycle can be divided into two large groups - M phase - Interphase • The newly divided cell enters G1 phase where the cell grows and becomes metabolically active. It also monitors external environment to know when conditions are right to divide. - Sometimes, the cell will to into G0 phase while in G1 and sort of shut down. They do have the ability to start reproducing again, though. - Terminal differentiation is when cell enters G0 and remains in that state terminally. • The S phase is where the DNA replicates. • After replication the cell enters the G2 phase where it continues to grow and prepare for mitosis. • During development and very quick reproduction, G1 and G2 are often reduced and sometimes completely eliminated. Because of this though, daughter cells are smaller than parent cell. • Check points: - The entry into the S phase checks the external environment. - Once you go into G2, you are checking replicated DNA and make sure it is correct before you enter the M phase. Lastly, there is a checkpoint in the M phase that makes sure all the chromosomes are properly attached to the mitotic spindle. One you pass this checkpoint, then the chromosomes can split. - Check points are also used to regulate the timing of the cell cycle so it is not going all the time (cancer). - Cyclins: • There is a system of enzymes phosphorylating proteins that drive these checkpoints. Kinases get turned on by another kind of protein called a cyclin, making them cyclin dependent kinases (Cdk). There is a constant supply of kinases, it is simply when they get turned on and off that is going to differ. The MCdk activity will spike on entry to the M phase of the cell Dr. Misamore cycle. The activity spike is due to an increase in concentration of the cyclins. • Cyclin/ Cdk discovery: - The eggs in females arrested in development because environmental factors did not allow it to pass a checkpoint. - Cytoplasm from an oocyte was placed in the cytoplasm of another arrested cell, it was noted that arrested egg began to differentiate. This is the Maturation Promoting Factor (MPF). • The cyclin concentration is what allows a checkpoint to be passed. So before the cell enters the S phase, the S cyclin increases its concentration and eventually tapers off. - The increase is an increase in transcription of cyclin while the decrease is destruction by ubiqutination by adding ubiquitin chain which is a target for destruction. - Anaphase Promoting Complex (APC)—This is what ubiquinates the cyclin • Cdk activation/inhibition - Transcription is gradual and cyclin is built up over time and their activity happens more suddenly. One of the ways it gets activated is by inhibitory phosphorylation. The M-Cdk will get phosphorylated by the inhibitory kinase Wee1 and cyclin comes to bind to it but is not active. An activating phosphatase (Cdc25) will come remove the inhibitory phosphate and the M-Cdk complex is activated. It is an abrupt removal of phosphate group. - Another inhibitory protein (p27) will wrap around the cyclin-Cdk complex making it inactive. - Cdk inhibitors block entry to the S phase - Inhibition of of Cdc25 blocks entry to mitosis - Inhibition of APC activation delays exit from mitosis. - G1 • A cell in G1 has different paths to choose. It can remain in G1, or if it stays long enough it can move over to a non- proliferating phase of G0, or it can terminally differentiate, or it can continue on to the rest of the cell cycle. • Environmental signals will tell the cell that conditions are good and continue to the S phase. Mitogens are the extracellular signal; if there are no mitogens, the cell remains in G1. • Mitogen signals allow activation of G1-Cdk and G1/S-Cdk which will phosphorylate the inhibitory Rb protein (which inhibits transcription factors) allowing the cell to continue with the cell cycle. • You do not want to proliferate damaged DNA, p53 becomes active and will bind to DNA and transcribe P21—this is an inhibitory protein which binds the cyclin- Dr. Misamore Cdk complex which pushes the cell from G1 to S. In many cancers, the p53 is often damages as well as allowing the damaged DNA to proliferate. • Most liver cells are in G0 phase since they don’t need to proliferate. Cells that drive over to terminal differentiation include neurons and muscle cells. Intestinal cells are constantly proliferating and replacing themselves. - S Phase: • Preparation for replication happens in G1. • Origin Recognition complex (ORC) sits on top of DNA and will recruit DNA helicase. Cdc6 helps turn on and regulate the complex and dissociates and you now have the pre- RC (prereplicative complex) and are ready for replication. The S-Cdk will come in and phosphorylate pre-RC which activates helicase and promotes assembly of the rest of the complexes needed for DNA replication. - G2 • There is another checkpoint to block entry into mitoses. Cdc25 phosphatase removes phosphate from M-Cdk making it active. As M-Cdk becomes activated, it will also go back and activate more Cdc25 as positive feedback—this gives you A LOT of complexes being active at once. - M Phase • In order to divide two things must happen: - 1.) Chromosomes have to separate (karyokinesis) - 2.) Actual cell must divide (cytokinesis). - M-Cdk drives this process past this checkpoint as it helps prepare DNA that has been duplicated and induce formation of the spindle. • Condensin rings wind up DNA to tightly compact it while cohesin rings keep the sister chromatids together. • Mitotic spindle/Centrosome: - The centrioles replicate prior to the M phase into mitosis, and during M phase migrate to ends of the cell. - Mitosis contains the following steps: • Prophase: - Duplicated chromosomes condense - Mitotic spindle assembles - Centrosomes begin to move • Prometaphase: - Breakdown of nuclear envelope - Chromosomes begin to attach to spindle microtubules via kinetochores • Metaphase: - Chromosomes align along metaphase plate Dr. Misamore • Anaphase: - Sister chromatids are pulled apart towards the spindle poles. Kinetochore microtubules get shorter and the spindle poles move apart, both contributing to chromosome segregation. • Telophase: - Chromosomes arrive at poles and new nuclear envelope beings to form. - Division of cytoplasm begins with assembly of contractile ring. • Cytokinesis: - Contractile ring made of actin and myosin filaments pinch the cell into two daughter cells. - Spindle Formation: • MTOS—Microtubule Organizing Center • Microtubules need an origin point to start building themselves—this is the centrosome. • Microtubules that help the centrosome move are called Astral microtubules. • Interpolar microtubules are also known as non-kinetochore or overlapping microtubules. • In the centromere region of the chromosome is the kinetochore which is where kinetochore microtubules attach. • Karyotypes are made by adding colchicine to a cell during metaphase. Colchicine inhibits tubulin from binding and microtubules fall apart. - Sister chromatids are held together by cohesin rings, but the rings are broken down by separase. However, separase is initially inactive due to the binding of securin. When APC is active, it ubiquinates the securin which activates separase, which allows cohesin rings to be broken down. - Anaphase A: Chromosomes are being pulled apart which is driven by shortening of kinetochore • microtubules. - Anaphase B: • Poles are pushed and pulled apart. • Driven by motor proteins kinesins and dyneins. There is one force due to kinesins that push the interpolar microtubules from each other. The second force is due to dyneins as they anchor to the cortex and pull centrosomes poleward. - There is an anaphase attachment checkpoint that makes sure all the microtubules are connected to kinetochore…if not, the cell won’t divide. • Aneuploidy—having an unusual number of chromosomes - Telophase—nuclear envelope reassembly: Chromosomes have moved and have reformed nuclear envelopes around the • chromosomes. What separated prophase and pro metaphase was the breakdown of the nuclear envelope. This happens through phosphorylation of nuclear pore proteins and lamins. In order to reform the nuclear envelope, you simply dephosphorylate the lamina and nuclear pore proteins. - Cytokinesis: • The cell develops a structure called the contractile ring which forms between two separating cells. Generally, it will happen right in the middle and create two daughter cells of equal size. • When the cleavage furrow forms actin in that region becomes concentrated and more active forming a circular ring around the cell. Myosin II binds the actin filaments together Dr. Misamore pulls them together. Actin filaments are also bound to formin on the cortex which pull the membranes together, ultimately cinching them off. • A big player in forming the contractile ring is the protein RhoA, which gets activated by having GTP bind to it. It then activates formin which helps recruit and amplify the actin filament component of the contractile ring. It also is going to start a cascade system that will lead to activation of myosin II. • The location of the spindle dictates where the furrow will be. - A bead was placed on an egg causing the spindle to be pushed to one side. This caused a furrow to form on one side of the bead. Once the spindles moved again and split, the astral microtubules overlapped causing a furrow to occur. • This proves that just having the spindle was enough to make the cell divide. • It also suggests that kinetochore microtubules are not really involved in cytokinesis. • Models for cleavage furrow location: - Astral stimulation model—the astral microtubules will send signaling molecules to the cortex to become the contractile ring. - Central spindle stimulation model—central area of overlapping microtubules produce some kind of signaling molecule making that region the location of the contractile ring. RhoA protein is associated with this region which is some evidence for this theory. - Astral relaxation model—if you relax the rest of the actin in the cortex but keep the region where contractile ring forms build up actin, this will help create the ring. • Rocking spindle - Spindle will often move within the cytoplasm before it divides. This changes orientation of how that cell is going to divide. • Organelle distribution - PAR2 is a morphogen that tells the cell what it is going to form. It is initially scattered throughout an egg about to divide. During the process of cell division though, the PAR2 gets distributed to only one of the daughter cells so that when the cell divides PAR2 is only found in one cell. This is important because this will determine the fate of the cell because it gets an unequal distribution of morphogen in the cytoplasm. - Cell Death • Necrosis - typically occurs when there is injury to the tissue causing it to break down. The cell membrane will rupture and spill its contents out. The internal enzymes may go and attack other cell for invoke the immune response causing inflammation. Apoptosis • - the cell gets broken down but without inducing an immune response. - During development, the tissue that connects the fingers forming a webbed paddle will undergo apoptosis to form individual fingers. The same goes for the tail in a tadpole as it turns into a frog. - C. elegans is responsible for the discovery of apoptosis since they all have about the same number of cells and develop very systematically. Researchers knew there were 113 specific apoptotic events throughout the lifecycle. - Caspase Cascade: • Procaspase is the inactive form but is eventually cleaved and recombine to form the active caspase molecule. Dr. Misamore • There are two main groups of caspases one of which are initiator caspases which activate executioner caspases. The latter target lamina and other cytosolic proteins. • Activation of caspases can be due to an intrinsic or extrinsic pathway. - Intrinsic: Bcl2 Family—Bax and Bak • This is a group of proteins that help turn on caspase process. Bax and Bak, when activated, allow cytochrome c to be released from the mitochondria and interact with adaptor proteins found in cytoplasm and assemble a wheel-like complex. This complex recruits procaspase molecules ultimately creating an apoptosome which will activate the caspases within the complex and initiate the caspase cascade leading to the destruction of the cell. - Extrinsic: • Fas death receptors located on the surface of the cell are activated by ligands. This allows the Death Inducing Signaling Complex (DISC) to form which will activate the rest of the caspase cascade. - Meiosis • Know the differences between mitosis and meiosis. • Prophase I is where homologous recombination (crossing over) occurs. • Metaphase is when duplicated homologous chromosome pairs line up in meiosis, while in metaphase it is simply the duplicated homologs chromosomes that line up. • Kinetochore of sister chromatids are the location where kinetochore microtubules connect. • Germ cells create the “next generation” while somatic cells create everything else. • Gametogenesis: - The cells that give rise to gametes that come about early on are Primordial Germ Cells (PGCs). - The PGC is uncommitted allowing it to be able to form the male or female gametes. • A somatic cell expressing Sry gene on Y chromosome calls for the PGC to go down the male pathway. If the Sry gene is not expressed, the female pathway is taken instead. - Male: • Testis - Sertoli cells—sperm are embedded in these and sertoli cells take care of sperm as they grow. Also create the Anti-Müllerian hormone which keeps the male from developing female characteristics. - Leydig cells—produce testosterone - Female: • Ovary - Follicle cells—these surround the egg and process hormones, in particular estrogen. Theca cells are the same thing as follicle cells and produce estrogen as well. Dr. Misamore • Spermatogenesis: - Spermatogonium ——> Spermatogonia ——> Primary spermatocytes ——> Secondary spermatocytes ——> Spermatids ——>Differentiating spermatids ——> residual bodies + mature sperm - Spermatogonia are stem cells because it can differentiate into another cell type and it can self-proliferate. - Cytoplasmic bridges • synchronize development so that all sperm develop at same rate. Also, each sperm will have either na X or Y sex chromosome and there are genes essential for development of the sperm on the Y chromosome which would mean that any sperm that gets X chromosome cannot develop—clearly this is not the case. The bridges are used for gene products to be shared between cells. - Spermiogenesis is a special name for the cellular differentiation in sperm. - The spermatogonium begin in the Sertoli cell and develop there until they are mature sperm. • Oogenesis: - Oogonia ——> primary oocyte ——> secondary oocyte ——> mature egg (ovum) - Spermatogenesis begins in puberty for guys. For eggs, the oogonia will start the process in utero, enter into meiosis I then stop at prophase I (diplotene arrest). • The cyclin/Cdk complex (MPF) is phosphorylated and therefore inactive. Cdc25 (the activating phosphatase) is inhibited due to the large amount of cAMP which makes a protein inhibiting the Cdc25. Another protein that breaks down cAMP allows for the activating phosphatase to be active and remove the inhibiting phosphates on the MPF allowing it to be active. - In oogenesis you have an asymmetrical division where at the end of meiosis I, the spindle will get pushed off to the side and divide into one larger daughter cell and one smaller one. The large daughter cell becomes secondary oocyte and the small daughter cell becomes polar body which gets rid of excess DNA. - Each month a handful of follicles (egg plus all its accompanying cells) will start to develop and grow. Only one of them will be ovulated while the others die off. Shortly before ovulation, the egg will release prophase I arrest and continue on with meiosis where it stops again at metaphase II. Fertilization releases it from metaphase II arrest. • The metaphase II arrest is due to the inhibition of APC by CSF complex. The APC usually ubiquinates the cyclin allowing metaphase II to proceed to anaphase II, but the APC is inhibited by the CSF complex. After fertilization, though, Dr. Misamore calcium is released which leads to the CSF complex to be degraded releasing hold on APC. - Reasons for Sexual Reproduction—sources of variability • 1.) Independent assortment of chromosomes. 23 • The number of chromosome combinations is 2 . • 2.) Homologous recombination of chromosomes • 3.) Random fertilization - Mammalian Development • After zygote divides several times, compaction occurs and cells begin to flatten and seal off allowing certain cells to get pushed to the center. The collection of cells that remain on the outside are the trophoblast cells while the ones on the inside are the inner cell mass. The trophoblast gives differentiate and contributes to extraembryonic membranes such as: • - Chorion—interacts with uterine tissue forming the placenta - Yolk sac—source where primordial germ cells come from - Allantois—contribute to formation of umbilical cord - Amnion—the tissue that creates the amnionic cavity where the embryo develops • The inner cell mass forms the embryo - Stem cells • Hallmark feature of stem cells is the fact that they can divide and make more of itself (self-proliferation) and it can divide and differentiate into another cell. • Single-cell asymmetry • Population asymmetry Dr. Misamore • Adult stem cell lineage - Different types of stem cells: • Differ based on potency which is how flexible their ability is to differentiate into different cell types. • Totipotent - Zygote—this is really the only totipotent cell since it can make everything. Specific example is the splitting in the embryo creating twins. • If the cell splits before the ICM has formed, two ICM will form and they will have separate amnion, chorion and placenta. • It is possible for identical twins to share a chorion and placenta but have separate amnions. • If two embryos share an amnion, then you get conjoined twins. • Pluripotent - Pluripotent stem cells can become anything within the embryo which means the source of pluripotent stem cells are found within the inner cell mass. - For example, pluripotent stem cell scan form fat cells, neurons, macrophage, hear muscle cell, glial cells, etc. • Multipotent - These are the primary germ layers which get developed after gastrulation (zygote ——> morula ——> blastula ——> gastrula). - Primary germ layers: • Ectoderm - Epidermis an nervous system • Mesoderm - Bone, cartilage, kidney, gonad, circulatory system, muscles • Endoderm - Digestive system, respiratory system, pancreas, liver - An example of this is the hemopoietic stem cell which can form anything in the blood such as RBC, platelets, neutrophil, lymphocytes, etc. • Unipotent - Skin cells, oogonia, spermatogonia - Stratum basalae are the stem cells at the bottom of the epidermis an can divide and make more of itself and it can differentiate into a keratinocyte. The keratinocyte will build up keratin, nucleus will break down and you achieve a specialized mature cell which is the skin. - Adult stem cells • Multi- or unipotential—their fate is much more limited. - Examples include bone marrow transplant or skin grafts. - Induced pluripotent stem cells • There are certain genes that say it will differentiate to go to the skin, those genes can be shut off and other genes can be activated found in the pluripotent cells to form something else. The advantage of this is the fact that you’re using your own cells and less likely for rejection. Dr. Misamore - Stem cell concerns: • Tissue integration - You must make sure the individual can’t reject the stem cells, and even if they are incorporated it must integrate with the tissues. • Oncogenesis - You want to make sure that when the stem cells are placed that they are regulated properly rather than taking off and potentially causing cancer. • Directed differentiation - IF you want to prepare a nerve cell, is it best to send in an adult nerve cell and at what stage do we put stem cell into tissue?—that’s the question. • Uniformity and consistency - As you repeat this process of stem cell insertion, the other cells should respond the same way each time.


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