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Imagine you are a glucose molecule. To be of use to the cell
Transcript of Imagine you are a glucose molecule. To be of use to the cell
The cell membrane
The main job of the membrane is to control what enters and exits the cell. For this important reason, every cell, including prokaryotes have a membrane. However, the membrane has other important features. Try to find your way into the cell.
Bi - Layer
This is the main part of the membrane. It is selectively permeable, meaning that not everything can slip through it. As a glucose molecule, you are too big to enter here. It is a bi-layer because it is made of two layers of polar lipid molecules, each with hydrophobic fatty acid tails on the inside facing each other, and hydrophillic phosphate heads on the outside (against the cytoplasm and outside of cell). Since there is intracellular and extracellular fluid, both watery, there has to be 2 sides of hydrophillic heads.
Carbohydrates, or sugars, are found attached to proteins in the membrane, forming the glycocalyx. The glycocalyx both protects the cell by providing cushioning, and is important for cell recognition (like the marker proteins). It is also used to stick cells together, to form tissue.
These are embedded in the membrane. Marker proteins identify the cell as part of the organism, so that white blood cells will not attack it. Receptor proteins identify hormones for cell communication. These are important for maintaining homeostasis in the organism. The third kind is channel proteins. These act as a pathway for larger molecules, like glucose, to enter. This is how you would enter the cell. They are transmembrane proteins, meaning that they extend to both sides of the membrane, inside and outside of the cell.
Cholesterol, which has a bad reputation, is actually vital for our cell membranes. It is in the phospholipid bi-layer to keep some molecules from entering freely, and keeping the tails of the lipids from crystallizing. It only becomes a problem when people eat excessive amounts of cholesterol, so only people with heart problems should eat 'cholesterol - free'.
The Cell Membrane
by Ellis Bronstein
There are three places for proteins in the membrane. Transmembrane proteins cross the membrane, these are difficult to remove from the cell. Peripheral proteins are attached to the outer side of the membrane, and are easily removed without harming the membrane. Lipid - bound proteins are proteins located entirely inside the cell membrane
Exiting through the membrane
Some smaller molecules can diffuse across the membrane if there is a concentration gradient. Molecules to exit the cell in a vesicle formed by the Golgi bodies (different project topic) a.k.a. Golgi apparatus can bind with the membrane because it is made of phospholipids, which would eject the molecule, letting it leave the cell. This movement is called exocytosis, where molecules exit the cell.
There are different sizes of channel proteins, so they only let some sizes of molecules in. Smaller ions can enter most sizes of channel proteins. To avoid letting too many ions in, proteins also weed out ions by charge. A positive channel, with extra protons, will allow only negative ions to enter, positive ones will be repelled. There are also aquaporin channels, which are specifically for water. Channel proteins are responsible for a type of movement is called endocytosis, where molecules enter the cell using the cell's energy.
Sodium and Potassium ions can enter or exit the cell through the membrane against the concentration gradient with the
Sodium Potassium Pump
, located in the plasma membrane. 3 Na+ (sodium ions) leaves the cell through the pump, and 2 K+ (potassium ions) enter. Energy from removing a phosphate (PO4H2) with hydrolysis from a molecule of ATP gives the pump for this exocytosis and endocytocis against the concentration gradient.
Sodium Potassium Pump
Image from education-portal.com/academy/lesson/cell-membrane-functions-role-structure
From Google Images :
Cholesterol in the cell membrane
Image from http://education-portal.com/academy/lesson/cell-membrane-functions-role-structure
Images from http://askabiologist.asu.edu/venom/protein-channels
Image from Google Images: Proteins in cell membrane
Image from Google Images: cellular vesicle
Image from http://hyperphysics.phy-astr.gsu.edu/hbase/biology/nakpump
Image from Google Images: Cell membrane all parts labeled