Answer:
<em> e) Ala</em>
Explanation:
Alpha helix is a secondary structure of proteins, it is made of 3.6 aminoacids residues per turn, this structure is possible thanks to local hydrogen bonding between C=O and N-h groups. The result is a cylindrical structure with a hydrogen-bonded backbone and the outside studded with side chains.
Glycin has an -H in its side chain, this makes it a too flexible molecule, therefore it's unusual to find them in alpha-helical structures because their presence could cause the helix to deform. Large R-groups can also affect this stability, phenylalanine has a bulky aromatic side group, this discards it as a stabilizer. Serine has a hydrogen bond donor or acceptor as a side chain, due to the proximity to the main chain it competes with the main chain to form NH and CO bonds. Alanine is the most common amino acid in alpha-helix structures because it has a short and no charged R group (unlike arginine that even when it's short it has a charged R-group), this makes it flexible enough to keep the structure stabilized.
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8. (F) Facilitated diffusion: For water to travel across the cell membrane at a substantial rate, the water molecules travel through protein channels known as aquaporins.
9. (S) Simple diffusion: While water molecules are polar, they are also very small. One fact not mentioned in the video is that some water molecules are able to squeeze directly through the phospholipid bilayer due to their small size.
10. (S) Simple diffusion: Charged ions are traveling through a cell membrane with the concentration gradient.
11. (A) Active transport: Cells lining the gut need to take in glucose, but at a certain time, the concentration of extracellular glucose is lower than the concentration already stored in the cells.
12.(F) Facilitated diffusion: At a certain time, glucose is in a high concentration outside of a cell and needs to travel through the membrane into the cell.
The above choices are made based on the basic definitions of active transport, facilitated diffusion and simple diffusion.
Active transport: The movement of the ions or molecules to a region having higher concentration across the membrane requiring the help of energy or enzymes is active transport.
Facilitated diffusion: This type of transport involves passive movement of the molecules or is a type of passive transport where the movement of the molecules takes place from higher to lower concentration region occurs with the aid of a carrier molecule such as a transport or carrier protein.
Simple diffusion: This process involves movement of ions or molecules from high concentration region to low concentration region through a semipermeable membrane.
Water quality can be processed in many different ways
The oceans on earth act as carbon sinks
the combustion of fossil fuels
atmospheric carbon dioxide is continuosly exchanged
vegetation and soil take in more co2 than they release
