Chapter 10 Cell Growth and Division 1/28

10.1 Cell Growth (continued) Limits to Cell Size – Why divide? – The larger the cell gets, the more 1. demands are placed on its DNA 2. trouble the cell has moving nutrients in and waste out across its membrane – As a cell grows, the relationship between the cell’s surface area and the volume changes. – This makes transport difficult 3/28 Click here for Mr Anderson why cells are small (bark demo)

10.1 Cell Growth (continued) Limits to Cell Growth – Why divide? (continued) – You MUST understand the relationship between cell volume and surface area! The cell membrane doesn‘t grow as fast as the volume Ratio of surface area to volume to decrease (page 238) 4/28

10.1 Cell Growth Living things grow by making MORE cells Adult cells are no larger than child cells. There are just more of them. adult cheek cells child cheek cells 5/28

10.1 Cell Growth (continued) Before a cell gets too big – The cell divides forming 2 daughter cells But before cell division occurs DNA is copied so each daughter cell can get a copy – Cell division keeps surface area : volume ratio appropriate 6/28

10.1 Cell Growth (continued) Asexual Reproduction – If an organism is 1 cell (unicellular) then cell division is also reproduction (asexual) Sexual Reproduction – Results from the joining of two cells from different parents 7/28

10.1 Cell Growth (continued) Asexual Advantages – Quick – Genetically identical offspring Sexual Advantages – Slower – Genetically DIFFERENT offspring 8/28

10.2 Cell Division Chromosomes – DNA is folded very carefully inside cells The folding makes a chromosome (c’some) – Carry genetic info – C’somes make it possible to separate DNA easily during cell division 9/28

10.2 Cell Division (continued) Prokaryotes: DNA is in the cytoplasm as one c’some Eukaroytes: DNA is in the nucleus as many c’somes – DNA plus protein = chromatin – When a cell gets ready to divide, the chromatin condenses and individual c’somes become visible. 10/28

10.2 Cell Division (continued) Prokaryotic Cell Cycle (fig p 240) – A cell grows, DNA replicates, cell divides Cell divides by binary fission – Pinching across its center – Divides the cytoplasm – Makes two cells – Is considered asexual reproduction 11/28

10.2 Cell Division (continued) Eukaryotic Cell Cycle (fig p 241) – Cell cycle has 4 phases G 1 - Cell grows S - DNA replicates G 2 - Prepares to divide M - Cell division 12/28 Click here for Mr Anderson Cell Division stop at 7:40

10.2 Cell Division (continued) G 1 – Growth & activity S – DNA replication G 2 – Growth & activity (get ready for mitosis) M – 2 parts Mitosis – division of nucleus Cytokinesis – division of cytoplasm 13/28 INTERPHASE CELL DIVISION

10.2 Cell Division (continued) Mitosis – Division of the nucleus also has 4 phases P-MAT – Prophase » C’somes condense – called sister chromatids » Sister chromatids -held together by a centromere – Metaphase » C’somes line up at the center of the cell » Spindle fibers connect to centromere – Anaphase » Sister chromatids separate – Telophase » C’somes spread out & become chromatin again » Nuclear envelope reforms 14/28

10.2 Cell Division (continued) Cytokinesis (page 243) – Result of mitosis is 2 nuclei in 1 cell – To finish the M phase, cytokinesis (division of cytoplasm), must occur Animal cells, the cell pinches into equal parts Plant cells, a cell plate forms midway between the divided nuclei 15/28

10.3 Regulating the Cell Cycle Cells go through cell cycle at different rates – Most muscle & nerve cells don’t divide after they’re developed – Skin, digestive tract, and bone marrow grow & divide rapidly throughout life 16/28

10.3 Regulating the Cell Cycle (continued) How do cells know when to divide? – Outside signals Petri dish, nutrient broth, sheet of cells grows Remove center, grow until they touch – So… cell growth/division controls can be turned on & off!!! Similar results are noted in the body – Cut your skin, cells at edge of injury are stimulated to divide rapidly 17/28

10.3 Regulating the Cell Cycle (continued) Regulatory Proteins – External Regulators Respond to events outside the cell Cause cell cycle to speed up or slow down – Example: growth factors » Help with healing & embryonic development – Internal Regulators Respond to events inside the cell Control stages of the cell cycle – Make sure that c’somes are doubled before mitosis begins – Example: cyclins 18/28

10.3 Regulating the Cell Cycle (continued) Apoptosis – Process a cell goes through to end the cell cycle (lead to cell’s death) – Programmed/planned death Ex: skin between a mouse toes before birth 18/28

10.3 Regulating the Cell Cycle (continued) Cancer: Uncontrolled Growth! – Cancer cells do not ‘listen’ to regulatory signals Internal & external regulators do not ‘work’ – Divide uncontrollably, form masses = tumors Tumors can damage nearby tissues – Cancer cells can break loose/ spread – Cancer cells can take nutrients away from healthy cells 20/28

10.3 Regulating the Cell Cycle (continued) What causes cancer? – Cell’s DNA is damaged It is supposed to regulate cell growth/division Damage caused by smoking, radiation exposure, viral infections Cancer Treatment – Remove surgically – Radiation – Chemotherapy 21/28

10.4 Cell Differentiation Differentiation – When cells become specialized/different Our body has >200 different kinds of cells yet we all started as a single cell (made by an egg being fertilized by a sperm!) A specialized cell performs a very specific job – Stomach cells excrete digestive enzymes – RBCs carry oxygen 22/28

10.4 Cell Differentiation (continued) Totipotent cells – Cells produced by the first few divisions – Can differentiate into any type of cell In humans, a fertilized egg forms a blastocyst – Hollow ball of cells (totipotent) w/a group of cells inside called the inner cell mass The inner cell mass becomes the embryo The outer layer attaches the baby to the mom 23/28

10.4 Cell Differentiation (continued) Pluripotent cells – Can develop into all cell types in the body – The cells of the inner mass are pluripotent – Are not totipotent though Stem Cells – Develop into differentiated, specialized cells – Stem cells are unspecialized 24/28

10.4 Cell Differentiation (continued) Embryonic Stem Cells – Will produce all the cells of the body – Scientists research them in hopes of helping cure diseases 25/28 Embryonic stem cell in needle’s opening

10.4 Cell Differentiation (continued) Adult Stem Cells – We have stem cells They make skin and blood (need to be replaced all the time) – Are called multipotent Can produce many, but NOT all, types of differentiated cells 26/28

10.4 Cell Differentiation (continued) Frontiers in Stem Cell Research – Scientists want to learn how stem cells keep the ability to differentiate into so many different types of cells – May be able to improve human health Fix damaged cells – maybe one of these days – Think superman! 27/28

10.4 Cell Differentiation (continued) Ethical Issues – To get embryonic stem cells we must kill the embryo! – Scientists are trying to change that 28/28

Click here for Crash Course Biology Mitosis Click here for video on cell division stop at 4:26