BIOSCI 0815 1st Edition Lecture 8Outline of Last Lecture II. DNA Replication Continueda. Origin of ReplicationIII. Steps of DNA Replicationa. Creating a Primerb. Polymerasei. Leading and Lagging strandc. LigaseOutline of Current Lecture I. The Cell CycleII. Surface AreaIII. Phaseso G1o So G2o MIV. New CellsV. CheckpointsCurrent Lecture- The Cell Cycleo Why do cells divide?o Reasons: These 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.o Reproduction: maintaining a species for generations, need to pass information to next generationo Repair: Cells help close up a wound after injury. Skin cells have to heal. o Growth Multicellular organisms (one cell gives rise to many). - Surface Area:o Grow to a certain size and then divide because there are limits to cell size:o Surface area to volume ratio. Substances have to be able to pass through cell membranes (fuel, oxygen, hormones, water).  Have a limit of how much they can pass inside the membrane to service the cell. o The plasma membrane is what covers the cell. This has a certain surface area. It has to service a particular volume (interior area of the cell). As the cell increases, the volume increases faster. 149 surface area. 1827 Volume. o Surface area: volume ratio. o This is why cells have to divide so that the surface area can still continue to service the volume inside. o When you divide, the surface are to volume ratio is restored. - Cell division as part of cell’s life:o Only small part of cell’s existence. - Cell Cycle:o Four Phases (G1,S, G2, M) (G1, S, G2 are combined into interphase)o G1: Pre Synthesis Gap (stands for gap 1). This is prior to synthesis. Cell grows and metabolic activity occurs. Phase when the cell does its life’s work. Liver Cellmetabolizing, Skin cells protecting other inner tissues. Makes components for DNA. Primase… o S: Synthesis. Replication of DNA. Proteins: Helicase, DNA polymerase, primase, SSB, Ligase, etc. Parental strands. Parental DNA separates. New Nucleotides join to make 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 gamete cells: egg and sperm).  Homologous chromosomes: contain information for trait but not same variant. - Ex: both parents contribute information about eye color. These areAlleles for traits. May be the same or may be different One N from mother 1N from father. These are called Haploid. This results in 2N (diploid) Offspring needs to be diploid. Each of the chromosomes from the mother and the father must make a copy of themselves. This occurs during the S Phase. This results in 4N (tetraploid). When the cell is reproduced, one copy gets passed on. o G2: Post Synthesis. Growth and replication preparation. Still have 4N. Haven’t separated them yet.  Get ready for Mitosis. Making Structures (fibers) to separate the chromosomes. Also checking to make sure the DNA is correct.  Makes organelles to divide among two cells. o M (Mitosis) Mitosis is where we are dividing the chromosomes. Phases during which chromosomes condense, line up in paired chromatids, separate into offspring cell. Phase Names:- Protophaseo Pairs of centrioles move apart. Nuclear envelope begins to break. - Metaphaseo Chromosomes line up across the middle (M = middle). Fibers from centrioles attach to one end of sister chromatids. These are called spindles. Other fibers overlap one another- Anaphaseo Fibers are microtubules of two kinds (tubes of protein) Kinetochore (attached to middle of chromosomes and separate chromatids. 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.- Telophaseo Cytoplasmic division occurs. 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: divides up cytoplasm and separates organelles.  Terminology- DNA is packaged in eukaryotes, and has hundreds of thousands of geneso Gene a discrete unit of hereditary…- 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. - Centrioles:o 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.o Duplicate themselves in mitosis. Move to one end of cell orthe other. 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. - New Cellso Solve the problem of maintaining cell size. o Represent faithful reproduction of parent organism. o Precise replication of DNA, and equal distribution of DNA.o Wants to produce 2 identical daughter cells.o Some diseases mess up this 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.- Three checkpoints:o G1, S. 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. o G2/M 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. o Spindle Checkpoint: All chromosomes have to be attached to a spindle and be ready for anaphase. o Sometimes things are found that are wrong (DNA, cell is too