Essay on Bio 141

Submitted By tamichan
Words: 443
Pages: 2

February 19th, 2013 1. Tonicity a. Hypertonic, isotonic, hypotonic: “tonic” refers to the solutes * Usually refers to a solution relative to a cell * i.e. a hypertonic solution has more solutes than a cell

b. Concentration gradient can affect cell survival
Ex. Saline – salty used when dehydration in replace for H20 * Too much salt shriveled * Too little concentration -> burst

(Blood cell example)

2. Transport across membranes a. Passive transport involves solute movement with the concentration gradient b. Do not require energy because molecules are going with gradient * i.e. from high to low concentration * molecules not always allowed across membranes

3. Facilitated Diffusion a. Facilitated diffusion: molecules allowed to cross the membrane via specific proteins * Proteins specific to one or a few similar molecules b. Carrier proteins must change the shape to allow diffusion c. Gated channel open in response to stimulus * Stimulus is ligand, which are chemical signals that binds to carrier protein to open up

4. Diffusion across membranes a. Aquaporins – water mores that allows water to diffuse across membrane * Found in mammal kidneys and plant root cells, both important for H2O absorption

5. Active Transport a. Requires energy (Adenosine Triphosphate, ATP) to move molecules against concentration gradient * This is often known as “pump” instead of “channel” b. Bulk Transport involves moving large volumes into or out of the cell, via membrane-bound vesicles * Endocytosis – into the cell * Exocytosis – out of the cell

c. Membrane receptors can mediate endocytosis * Mediate – cause to happen, “making things happen”

6. Membrane signaling a. Cells interact with their environments at the membrane b. Signaling molecules can generate specific and complex responses c. Signal transduction pathway * Begins when a signal molecule contacts a receptor * Ends with a cellular response * Pathway consists of