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Cell Specialization Unicellular Organism – consists of only one cell - that one cell carries out all functions required to maintain the life of the organism Multicellular Organism – consists of more than one cell - Cells are specialized to perform certain functions (cell specialization/differentiation) Examples of Cell Specialization 1. Neuron (nerve cell) - sends info from one part of the body to another - very long and thin Examples of Cell Specialization 2. Red Blood Cells - carry oxygen throughout body - flattened disks so that they can easily flow through blood vessels Examples of Cell Specialization 3. Sperm Cell - fertilizes egg - strong tail for quick swimming, distinct head for entering egg cell Cell differentiation is a result of different gene expression. • Most cells in your body have the same DNA • Cells use only the DNA that they need; the rest is inactive • For example, skin cells use the DNA that codes for melanin (a skin pigment that protects from UV light) • Heart cells do not need melanin, so it is “turned off” in heart cells Stem Cell Research • stem cells – cells of humans that can develop into different cell types • 2 kinds: embryonic and adult • some researchers believe that they can be a source of replacement cells to treat disorders (ex. Parkinson’s disease and burn injuries) Embryonic stem cells Adult stem cells Cell Communication - Cells communicate with one another by secreting and receiving chemicals - Chemicals released by one cell can influence the activity of another cell http://learn.genetics.utah.edu/content/begin/cells/cellcom/ Example of Cell Communication - Sensory cells to nerve cells to muscle cells Cell Communication (cont.) Hormone – communication chemicals that travel through the blood (ex. insulin, estrogen) - Secreted by endocrine glands - Acts much slower than nerve impulses but effects last much longer - Only influence the action of target cells that have specific receptors Two Hormone Mechanisms 1. Negative Feedback – the end product stops the production of the hormone Negative Feedback 2. Positive Feedback – the last step triggers more release of the initial hormone or other hormones - triggers a series of events • Cell Growth and Size Limitations – Most cells are 2 – 200 micrometers (largest cell is the ostrich egg – 8 cm) http://www.cellsalive.com/howbig.htm Cells cannot get very big because … 1. Volume increases faster than surface area. - a bigger cell means that you have more nutrient demand with limited surface area for diffusion Cells cannot get very big because … 2. Diffusion is a SLOW process. - Organelles might not get the nutrients they need in time. Cells cannot get very big because … 3. A bigger cell needs more proteins. - DNA is used to make proteins, and cells have a limited amount of DNA. - Therefore, when a cell starts to get too big, it must divide.