Chapter 3 Cells Introduction Cells are the smallest living unit in our body that varies in shape & size Differences in cell shape makes different functions possible! Cells have 3 main parts: 1. Plasma membrane 2. Cytoplasm 3. Nucleus Plasma Membrane Function -Regulates movement of substances in & out of cell = selectively permeable -Participates in signal transduction -Helps cells adhere to other cells -Is adapted to increase surface area -seals tiny breaks or cell dies 3 - 5 Plasma Membrane Structure -Double layer that is soluble and allows lipids (steroids, hormones) to pass thru! -Embedded cholesterol (fat) molecules strengthen membrane and make it less permeable to water-soluble substances Cytoplasm Contains: - Cytosol a clear liquid - Cytoskeleton for support 3. Nucleus Has a double layered membrane containing large pores that allow substances to pass thru a. Nucleolus is composed of RNA and protein; site of ribosome production; and directs activities of cell b. Chromatin consists of loosely coiled fibers of protein & DNA Super Eve Mitochondrial DNA Each human has mutations that have replaced or added gene sequences Mitogenomes are passed from mother to offspring, with very few exceptions Cell Membrane Movement 1-Passive Mechanisms: Diffusion -Movement of molecules from area of greater to lesser concentration (like diffusion from alveoli in lungs into capillaries) Cell Membrane Movement 2-Facilitated Diffusion - Membrane proteins actively move molecules through -insulin promotes glucose diffusion in this way -Water moves from area of greater concentration (less pressure) to area of lower concentration (greater pressure) Cell Membrane Movement 3- Osmosis FYI: Preserving Fruits & Meats Dehydration of fruit & salt-curing of meat A solution with: -Same osmotic pressure as body fluids is isotonic -Higher osmotic pressure than body fluids is hypertonic = cell shrinks -Lower osmotic pressure is hypotonic = cell expands Plasma used by hospitals to store RBCs is isotonic to prevent RBC from either bursting or desiccating Filtration Due to osmotic pressure, molecules are forced through membranes by filtration -Blood pressure is a type of osmotic pressure FYI: Dialysis Dialyzing membrane allows water, salts and other wastes in blood to pass into tank of distilled water RBC are too large to enter and return to patient's body Cell Membrane Movement Active Mechanisms 4-Active Transport Uses energy to move molecules from areas of low to high concentration through carrier molecules 40% of our energy fuels this process! Actively Transported Particles: -sugars -amino acids -sodium -potassium -calcium -hydrogen ions -nutrient molecules Series of changes a cell undergoes from time it is formed until it reproduces and dies. Cell Cycle Interphase- is a period of cell growth and new molecules are synthesized S phase- DNA of cell is replicated to prepare for cell division G 1 & G 2 phases- cell grows and other structures are duplicated Cell Cycle Phases Cell cycle is very regulated & most cells dont divide continually, they have a maximum # of times they can divide because of built-in clocks (telomeres) on tips of chromosomes When Dolly, a cloned sheep, died at the premature age of 6, scientists discovered unusually short telomeres in her cells Dolly Cells develop into different types of cells with specialized functions via cell differentiation; shows genetic control of nucleus as some genes are turned on while others are turned off Cell Division Problems Progenitor cells are daughter stem cells that give rise to cells that become tissues and organs These are activated when tissues are injured to rebuild damage The End of Males? Mouse made without sperm National Geographic April 21, Kaguya, a fatherless mouse -She was only one to survive to adulthood out of 450 embryos created, of which 371 were implanted -10 were born alive -Scientists who created her say it would be "completely unethical" to try to create a human this way Cell Death Apoptosis refers to a cells death; like peeling sunburnt skin