BIOSC 0815 1st EditionExam # 2 Study Guide Lectures: 8 – 12Lecture 8Why do cells divide?They need to maintain a species for generations, and pass information to next generation. Cells help close up a wound after injury. Cells are also needed for growth into multicellular organisms.Cells need to divide after they grow to a certain size. They then divide because there are limits to cell size of surface area to volume ratio. Substances have to be able to pass through cell membranes (fuel, oxygen, hormones, water). There is a limit of how much they can pass inside the membrane to service the cell. When the cells divide divide, the surface are to volume ratio is restored. What is the cell cycle?There are four phases in the cell cycle. These phases are G1,S, G2, M (G1, S, G2 are combined into interphase). The G1 stage is the Pre Synthesis Gap (stands for gap 1). This is prior to synthesis. In this phase the cell grows and metabolic activity occurs. It is the phase when the cell does its life’s work. Makes components for DNA and primase… The S stage stands for Synthesis. This is the stage when Replication of DNA occurs. Proteins that are used in this stage include Helicase, DNA polymerase, primase, SSB, Ligase, etc. The parental strands of DNA separate and new nucleotides join to make the offspring DNA. In humans most cells are Diploid (2N) meaning that they have DNA from their biological father and their biological mother. Together that’s 46 chromosomes. These are in your somatic cells (not gametecells: egg and sperm). Homologous chromosomes contain information for a trait but are not the same variant. For example both parents contribute information about eye color. These are Alleles for traits. The resulting offspring’s eye color may be the same or may be different. They get 1N from the mother 1N from the father. These are Haploid cells. When they combine, they result in 2N (diploid) cells. The offspring needs to be diploid. Each of the chromosomes from the mother andThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.the father must make a copy of themselves. This occurs during the S Phase. When the cell is reproduced, one copy gets passed on. The G2 phase occurs Post Synthesis. This is when growth and replication preparation occur. The cell gets ready for Mitosis. Structures (fibers) are made to separate the chromosomes. There arechecks in this phase to make sure the DNA is correct. Makes organelles to divide among two cells. Mitosis is where we are dividing the chromosomes. This is the phase during which chromosomes condense, are line up in paired chromatids, and separate into offspring cells.The phases in mitosis are protophase, metaphase, anaphase and telophase. In protophase pairs of centrioles move apart. The nuclear envelope begins to break. In metaphase, the chromosomes line up across the middle (think: M = middle). Fibers from centrioles attach to one end of sister chromatids. These are called spindles. Other fibers overlap one another. In anaphase, polar ends are created and the kinetochore (which is attached to middle of the chromosomes) pulls the chromatids apart. The polar ends push against one another to create poles of the cell. (To remember the purpose of this phase, think of anarchy, analyse: means taking apart). Sister chromatids move apart and when they are separate they are referred to as chromosomes again. In telophase, cytoplasmic division occurs. The cell is squeezed in the middle. Actin pinches the cell in half. Remember By: If pitt panthers make a touchdown, celebrate. Interphase, protophase, metaphase, Anaphase, telophase, cytokinesis. Cytokinesis is the final step which divides up the cytoplasm and separates organelles. Chromatin is what the DNA is called before condensing into chromatid and it looks wispy and disorganized. Once the DNA has gone through replication, the duplicated and attached chromosomes are called sister chromatids. If they are not duplicates, they are called non sister chromatids. What are Centrioles?Centrioles are small structures that appear to send out fibers (called spindles) across the cell. Some attach to chromosomes for separation, they rest at right angles to one another. They duplicate themselves in mitosis. Move to one end of cell or the other (the poles). This separation occurs in the cytoplasm. How do homologous microtubules separate?Motor proteins on the chromosomes move towards the centrioles. Imagine pac man eating the spindle towards the centrioles and the length of the centrioles decreases as the chromosomes get closer to the centrioles. What are DNA checkpoints during division?Checkpoints are critical control points in the cell cycle. This is where cells may stop before proceeding to next phase of their life. It is an opportunity to ensure that the necessary processes have been accomplished. There are three main checkpoints. The first is in the G1, S phases. The cell is at the point ready to replicate DNA and that it has enough nutrients and growth factors. Outside factors can make things go wrong such as exposure to toxic chemicals. Before division, the cell has to be a certain size and have a sufficient number of nutrients. The second is in the G2/M phase. In this phase the cell is getting ready to divide because DNA replication is complete. It has to check that all proteins are ready for cell division, and that all DNA was correctly paired and replicated. The lastcheckpoint is the Spindle Checkpoint. All chromosomes have to be attached to a spindle and be ready for anaphase. Sometimes things are found that are wrong (DNA, cell is too small, not enough nutrients, spindle is faulty, attachment of DNA to spindle is not right). If this happens, the cell activates repair mechanisms to correct the problems. If it cannot be repaired it performs apoptosis whichmeans “self destruct.” A program of cell responses takes over and destroys the cell. The cell is now apoptotic and is broken down. Lecture 9What are the steps of Development of a gametic cell?The steps are fertilization, Cleavage, gastrulation, and organogenesis. In cleavage the cytoplasm is repackaged, and the cell divides rapidly. In Gastrulation the cells reorient and move around to produce the body plan, variations of cells develop. - Cleavage:o After the egg and sperm have combined and mitosis is initiated, there is a series of rapid cell