Cell Cycle & Mitosis PDF

CellCycle & mitosis By Doaa Elsherif Cell Types Two categories: 1. Cell that have membrane-bound organelles – Called Eukaryotic Cells Multicellular organisms such as plant and animal cells. 2. Cells that do not have membranebound organelles – called prokar...

CellCycle & mitosis By Doaa Elsherif Cell Types Two categories: 1. Cell that have membrane-bound organelles – Called Eukaryotic Cells Multicellular organisms such as plant and animal cells. 2. Cells that do not have membranebound organelles – called prokaryotic cells Unicellular organisms such as bacteria are examples of prokaryotes.  How do the differences line up? Prokaryotes Eukaryotes Organelles lack a Organelles covered by a membrane membrane Genetic material floats Membrane covered in the cytoplasm (DNA Genetic material (in and RNA) (in nucleoid) nucleus) Circular DNA Linear DNA  chromosomes in eukaryotes and prokaryotes are different PROKARYOTES EUKARYOTES single chromosome plus plasmids many chromosomes circular chromosome linear chromosomes made of chromatin, a made only of DNA nucleoprotein (DNA coiled around histone proteins) found in cytoplasm found in a nucleus copies chromosomes, then the copies its chromosome and cell grows, then goes through divides mitosis to organise immediately afterwards chromosomes in two equal groups DNA DNA is located in the nucleus and controls all cell activities including cell division Long and thread-like DNA in a non-dividing cell is called chromatin Doubled, coiled, short DNA in a dividing cell is called chromosome Consists of 2 parts: chromatid and centromere o 2 identical “sister” chromatids attached at an area in the middle called a centromere o When cells divide, “sister” chromatids separate and 1 goes to each new cell  Chromatin to chromosomes illustration: DNA double DNA and Chromatin Supercoiled helix histones DNA Why does DNA need to change from chromatin to More efficient division chromosome?  Numbers of chromosomes ❖Constant for all members of a species – Humans have 46 chromosomes – Maize (corn) has 20 ❖Constant throughout the life of an individual (you don’t lose or gain chromosomes) ❖Constant for each cell in the body except sex cells which only have half sets  Every organism has its own specific number of chromosomes Examples: Human = 46 chromosomes or 23 pairs Dog = 78 chromosomes or 39 pairs Goldfish = 94 chromosomes or 47 pairs Lettuce = 18 chromosomes or 9 pairs  Notes Cell Division — process by which a cell divides into 2 new cells Why do cells need to divide? 1.Living things grow by producing more cells, NOT because each cell increases in size 2.Repair of damaged tissue 3.If cell gets too big, it cannot get enough nutrients into the cell and Mitosis – division of the nucleus into 2 nuclei, each with the same number of chromosomes Mitosis occurs in all the somatic (body) cells So each new daughter cell Why does mitosis occur?has nucleus with a complete set of chromosomes  The Cell Cycle and Mitosis Due to the loss and death of cells → must replace them. How many cells in your body? – 50-100 million trillion – Every minute your body produces about 300 million new cells Three stages in the cell cycle: 1. Interphase: cell carries out normal functions. 2. Mitosis (nuclear division): nucleus contents duplicated and divided into two equal parts. 3. Cytokinesis: separation of two nuclei and cell contents into two daughter cells.  Interphase (about 95% of the cell cycle) can be divided into subphases – G1 phase (“first gap”) to prepare for cell division – S phase (“synthesis”) The cell duplicate its DNA – G2 phase (“second gap”) the cell enter the second Gap prior to beginning Mitosis The cell grows during all three phases, but chromosomes are duplicated only during the S phase  Mitosis is the shortest stage of the cell cycle where the nuclear contents divide, and two daughter nuclei are formed. Mitosis is conventionally divided into four phases – Prophase – Metaphase – Anaphase – Telophase Cytokinesis overlaps the latter stages of mitosis  Interphase (Preparatory phase) Growth Stage 1 (G1)  Synthesis Stage (S) Growth Stage 2 (G2)  During G1 (Growth Stage 1): – pre-DNA synthetic phase –Cell increases in size –synthesizes new proteins and organelles  During the S phase (Synthesis Phase): chromosomes are replicated DNA synthesis takes place Once a cell enters the S phase, it usually completes the rest of the cell cycle.  The G2 Phase (Second Growth Phase): Post DNA synthetic phase organelles and molecules required for cell division are produced Once G2 is complete, the cell is ready to start the M phase—Mitosis  Late interphase Chromatin is in its loosely coiled form so that DNA can be copied into RNA for proteins to be made in preparation for cell division. Nucleus is distinct with a nucleolus Nuclear membrane is present At the end of interphase, the cell continues to grow and make proteins in preparation for mitosis and cytokinesis. Reminder, most (~95%) of the time the cell is in interphase (doing its job, growing, surviving, etc.)  Motisis 1. Prophase chromatin condensing nucleus chromosomes nucleolus Three Major Events centrioles 1. chromosomes condense 2. spindle fibers form 1. (spindle fibers are specialized microtubules radiating out from centrioles) 3. chromosomes are captured by spindle From the Virtual Cell Biology Classroom on ScienceProfOnline.com  2. Metaphase Centriole pairs move to opposite ends of the cell Spindle fibers are still attached to the centriole pairs. Chromosomes line up along the midline (equator) of the cell and are attached to the spindle fibers. centrioles chromosomes spindle fibers Images: Metaphase drawing, Henry Gray's Anatomy of the Human Body; Metaphase Onion Cell Drawing & Photo, Source Unknown  3. Anaphase sister chromatids separate -Repulsion force -Attractive force spindle fibers attached to kinetochores shorten and pull chromatids towards the poles. Images: Anaphase drawing, Henry Gray's Anatomy of the Human Body; Anaphase Onion Cell Drawing & Photo, Source Unknown From the Virtual Cell Biology Classroom on ScienceProfOnline.com  4. Telophase Nuclear membranes form around the two new sets of chromosomes. The spindle fiber disappears. Chromosomes start to uncoil (chromatin) and become less visible. Cell starts to make a groove (furrow) in the middle to eventually split into two identical cells. Images: Telophase drawing, Henry Gray's Anatomy of the Human Body; Telophase Onion Cell Drawing & Photo, Source Unknown From the Virtual Cell Biology Classroom on ScienceProfOnline.com  Cytokinesis – Plant vs. Animal Cell The division of material outside of the nucleus. – Occurs after telophase. Divides the organelles and other substances in the cytoplasm into roughly two equal halves. Plant cells form a cell plate # chromosomes in daughter cell = the # chromosomes in parent cell. Daughter cells are genetically identical to parent. Images: Telophase drawing, Henry Gray's Anatomy of the Human Body; Ciliate dividing, TheAlphaWolf; Telophase Onion Cell Photo, Source Unknown From the Virtual Cell Biology Classroom on ScienceProfOnline.com mitosis in root tip Summary: Cell Cycle Interphase Mitosis (PMAT) Cytokinesis When cells become old or damaged, they die and are replaced with new cells  checkpoints in the cell cycle will prevent cell division if: – If the cell is short of nutrients – If the DNA within the nucleus has not been replicated – If the DNA is damaged