SLG 15.1 Transport Across Membrane.pdf - ENERGY IN MATTER...

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ENERGY IN MATTERTRANSPORT ACROSS MEMBRANEAt the end of this module, you should be able to:1.Discuss the structure of the cell membrane.2.Differentiate passive and active transport of materials.3.Define diffusion and osmosis, and explain the effects of hypotonic, hypertonic, andisotonic solutions on a cell.Time Allotted: 1 minActual Time: __________Do you remember the three major parts of a cell? Indeed, regardless if the cell isprokaryotic or eukaryotic, it always has its DNA where genetic material is stored, acytoplasm where metabolic processes essential to survival occur, and a cell membrane thatserves as a protective barrier of the cell from its environment. As a protective barrier, thecell (plasma) membrane acts as a “gatekeeper”, determining which materials can move inandoutofthecell.Howdoesitdothis?Playagame!Clickthelinktounderstand how the cell membrane works.Time Allotted: 5 minActual Time: __________Structure of the cell membraneThe structure of the cell membrane plays a very important role in how it is able to serve asthe “gatekeeper” of the cell. Notice in the diagram above that there are three primarycomponents of the cell membrane – the phospholipid bilayer, proteins and carbohydrates.How do these components help in making the membrane selectively permeable?Figure 1:The cell membrane issemi-permeable due to its hydrophilic headsand hydrophobic tails. The different moleculesfound in the membrane like carbohydrate,proteins and protein channels help in its roleto transport materials.Learning Guide 15.1 |page 1 of 7
The primary structure responsible for thesemi-permeability of the cell membrane isthe phospholipid bilayer. As you see in thediagram on the right, phospholipids havetwo parts - thehydrophilichead and thehydrophobictails. Being “water-loving”, theheadsofthephospholipidlayer alwaysface the watery surroundings (inside andoutside) of the cell. (Recall that blood is90%water.)whereasthetails,being“water-hating”, automatically avoid it.Figure 2:Phospholipids are part water-loving (hydrophilic) and partwater-fearing (hydrophobic) molecules.Source: Wikimedia Commons..svgThe cell membrane also includes a large number of proteins embedded in the phospholipidbilayer.Otherthantransportacrossmembranes,theseproteinsalsohelpincellularcommunication.Finally,noticethecarbohydratesattachedtothemembrane proteins andphospholipid. These carbohydrates help in cell recognition, the ability to distinguish one cell fromanother.Because the cell membrane looks like a mosaic of phospholipids, proteins and carbohydrates,and because the phospholipids and membrane proteins slide freely around the surface of the cell,the cell membrane is described as afluid mosaic. The fluidity of the cell membrane is essential toits ability to control the movement of substances into and out of the cell.

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