19. Which statement about epithelium is correct?
1 answer:
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Explanation:
-Q. <em>How do membrane proteins aid in the movement of hydrophilic substances across the membrane?</em>
Transport proteins spanning the plasma membrane facilitate the movement of ions and other complex, polar molecules which are typically prevented from moving across the membrane from the extracellular or intracellular space.
Lipids are composed of fatty acids which form the hydrophobic tail and glycerol which forms the hydrophilic head; glycerol is a 3-Carbon alcohol which is water soluble, while the fatty acid tail is a long chain hydrocarbon (hydrogens attached to a carbon backbone) with up to 36 carbons.
Their polarity or arrangement can give these non-polar macromolecules hydrophilic and hydrophobic properties. Via diffusion, small water molecules can move across the phospholipid bilayer acts as a semi-permeable membrane into the extracellular fluid or the cytoplasm which are both hydrophilic and contain large concentrations of polar water molecules or other water-soluble compounds. The hydrophilic heads of the bilayer are attracted to water while their water-repellent hydrophobic tails face towards each other- allowing molecules of water to diffuse across the membrane along the concentration gradient.
Similarly via osmosis, molecules of water pass through the membrane due to the difference in osmotic pressure on either side of the phospholipid by layer this means that the water moves from regions of high osmotic pressure/concentration to regions of low pressure/ concentration to a steady state.
Transmembrane proteins are embedded within the membrane from the extracellular fluid to the cytoplasm, and are sometimes attached to glycoproteins (proteins attached to carbohydrates) which function as cell surface markers. Transport proteins are transmembrane proteins involed in moving molecules across the membrane.
There are two types:
- Channels or pores are filled with water, enabling charged molecules to diffuse across the membrane, from regions of high concentration to regions of lower concentration down the concentration gradient -this is a passive part of facilitated diffusion. Channels may undergo minor changes to become open or closed whereas pores are always in open states <em>e.g. H2O movement into and out of the cell via aquaporins.</em>
- Carrier proteins bind specifically bind to molecules and move them across or against concentration gradients. Unlike facilitated diffusion, carrier proteins directly or indirectly use energy in the form of ATP and modify solute specific regions, that aid in regulating ion exchange, through the hydrophobic layer of the plasma membrane- this is called <em>active transport.</em> <em>e.g. Na+/K+transported by the enzyme ATPase </em>
<em>Learn more about membrane components at brainly.com/question/1971706</em>
<em>Learn more about plasma membrane transport at brainly.com/question/11410881</em>
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