The Beginning of mRNA Is Not Translated
Interestingly, not all regions of an mRNA molecule correspond to particular amino acids. In particular, there is an area near the 5' end of the molecule that is known as the untranslated region (UTR) or leader sequence. This portion of mRNA is located between the first nucleotide that is transcribed and the start codon (AUG) of the coding region, and it does not affect the sequence of amino acids in a protein (Figure 3).
So, what is the purpose of the UTR? It turns out that the leader sequence is important because it contains a ribosome-binding site. In bacteria, this site is known as the Shine-Dalgarno box (AGGAGG), after scientists John Shine and Lynn Dalgarno, who first characterized it. A similar site in vertebrates was characterized by Marilyn Kozak and is thus known as the Kozak box. In bacterial mRNA, the 5' UTR is normally short; in human mRNA, the median length of the 5' UTR is about 170 nucleotides. If the leader is long, it may contain regulatory sequences, including binding sites for proteins, that can affect the stability of the mRNA or the efficiency of its translation.
Bedrock striations. Striations are marks or lines in the bedrock caused through glacial movement
Answer:
Scientific theories can never be proven true beyond all doubt; they can only be supported by a wide body of evidence. Only one of the statements that follow uses the term theory in its correct, scientific sense.
Explanation:
Diffusion is a spontaneous process in which molecules move with their concentration gradient. For example, if you place food coloring in water, the food coloring will slowly diffuse through the water until the entire solution has been balanced.
Osmosis is specifically the movement of <em>water</em> through a semipermeable membrane - meaning a membrane that can let some substances in but keep others out - and, similar to diffusion, it moves with its concentration gradient. For example, if you place a glucose solution sealed in plastic in water, water will move into the plastic to even out the concentration of glucose in the entire solution because glucose is too large to diffuse freely.
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