Answer:
"As a molecule moves through the plasma membrane it passes through <em>a hydrophilic layer of phospholipid heads then a hydrophobic layer of phospholipid tails and then another hydrophilic layer of phospholipid heads".</em>
Explanation:
Biological membranes are formed by two lipidic layers, proteins, and glucans.
Lipids characterize for being amphipathic molecules, which means that they have both a hydrophilic portion and a hydrophobic portion at the same time. These molecules have a lipidic head that corresponds to a negatively charged phosphate group, which is the polar and hydrophilic portion. They also have two lipidic tails that correspond to the hydrocarbon chains -the apolar and hydrophobic portion- of the fatty acids that esterify glycerol.
Membrane lipids are arranged with their hydrophilic polar heads facing the exterior and the interior of the cells, while their hydrophobic tails are against each other, constituting the internal part of the membrane.
Through this lipidic bilayer, some molecules can move from one side of the cell to the other, which happens because of concentration differences. When this occurs, molecules must pass through the hydrophilic layer of phospholipid heads then through the hydrophobic layer of phospholipid tails and then again through another hydrophilic layer of phospholipid heads.
The cell wall gives cells shape, enables plant growth, prevents bursting from water pressure, keeps out water and pathogens, stores carbohydrates and sends signals to cells. The flexible cell wall surrounds plant cell membranes.
Plant cell walls perform many functions. Their main task is to support proper plant growth. This is accomplished by the cell wall creating a skeleton-like frame that enables plants to grow vertically and develop a rigid stem. Cell walls vary considerably in thickness and organization, which accounts for the wide range of plant shapes and sizes on the planet. They consist of two layers ‰ÛÓ a primary cell wall, which supports the cell as it matures, and a rigid secondary cell wall that appears after the primary wall stops growing. The primary cell wall is thinner and more flexible than the secondary wall. Internally, the primary and secondary walls have a similar physical composition. Over the course of a plant's life, they perform complementary functions to keep the plant healthy and vibrant.
When a hairpin loop forms in the nascent mRNA: The hairpin will destabilize the interaction and possibly lead to transcriptional termination.
Transcription in prokaryotes like E. coli is terminated either by a rho-dependent process or a rho-independent process. Intrinsic termination is controlled by the specific sequences of RNA .
When the termination process starts, the transcribed mRNA forms a stable secondary structural hairpin loop, also known as a stem-loop. Several uracil nucleotides follow this RNA hairpin. The uracil and adenine connections are exceedingly weak. NusA, a protein attached to RNA polymerase, attaches to the stem-loop structure so firmly that it momentarily stalls the polymerase.
The polymerase is pausing at the same time that the poly-uracil sequence is being transcribed. The RNA-DNA duplex can unwind and separate from the RNA polymerase because the weak adenine-uracil interactions reduce the energy of destabilization for the RNA-DNA duplex. Overall, transcription is terminated by the modified RNA structure.
Learn more about RNA polymerase here :
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Answer:
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