<span><span>anonymous </span> 3 years ago</span>Proteins are involved in almost all of the cell's functions. They can act as:
Transportation: they can transport hydrophobic molecules in blood for example
Regulation: protein hormones and enzymes
Receptor: can act as receptors on cell surface and in the subsequent signal transduction (G-protein for instance)
It is true that all proteins are made up of up to 20 amino acids, but there are several reasons for their diverse actions:
-One reason is the possible sequence and number of amino acids: Met-Ser-His is different from Met-His-Ser for example. Besides, you have different chain length, for a protein is made up of long chain of polypeptide (longer than 50-70 amino acids) and can have any of the 20 amino acids with repetition, so using simple probability, this can provide up to practically unlimited combination with proteins that have chains of thousands of amino acids.
-Another very crucial reason for the diversity of protein action is the conformation. A protein passes by at least 3 conformational stages before becoming mature. The straight amino acid chain is the primary structure of the protein that can never be active. Spatial modification of this primary structure results in a secondary structure, Helix or Beta-pleated sheets (or other coiling structure), that is also inactive. Further coiling and bending of the secondary structure produce a 3-dimentional conformation that is the active form of the protein. Moreover, many proteins can undergo further conformational rearrangement and combination with other protein sub-units producing a quaternary structure.
Answer:
b. di uses across a synaptic cleft from a neuron to a muscle cell.
Explanation:
A neurotransmitter is di uses across a synaptic cleft from a neuron to a muscle cell. Neurotransmitters are chemicals which enable neurotransmission. In reaction to an impulse a motor neuron axon secretes a neurotransmitter and causes the muscle fiber to contract. It is a chemical messenger which passes on the signals across the chemical synapse.
Natural regeneration of forests and woodlands is the process by which new trees grow from seeds that have fallen and germinate where they have fallen. The biggest problem with natural regeneration is that is unpredictable. As a result, it cannot be used for commercial farming. For most of the last two or three hundred years, forests and woodlands have restocked by using transplants grown in nurseries. The young trees are planted in equidistant rows. This allows each tree the best possible change of optimal growth.
Greater portions of the beach begin to appear during ebbing tides, until the maximum amount of beach is visible at low tide. They usually happens twice in a day. Beaches results from wave action by which waves or currents move sand or other loose sediments of which the beach is made as these particles are held in suspension.
