Proteins which make up much of the body and regulate

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proteins, which make up much of the body and regulate most of the chemical reactions in it - and DNA, which carries the directions for creating the proteins - In order to grow and function, organisms have to make proteins, in a process that involves these two players - DNA physically controls the production of proteins in a complex process that we will cover only very superficially here - Protein synthesis : the process in which DNA guides the creation of proteins that make up and operate cells and the body as a whole - the process of protein synthesis, in turn, has two major stages: - 1. Transcription : in which the code in the DNA is copied, or “transcribed” to a molecule of messenger RNA (mRNA) - 2. Translation : in which the mRNA actually produces the protein - More detail on the first stage, transciption, - in which the code in a segment of DNA is copied to a new strand of messenger RNA - DNA normally is inside the cell nucleus , a specialized sack of material inside the cell - inside the nucleus, part of the DNA unzips into two strands, each with an exposed sequence of bases - only one strand is active - individual nucleotides are floating around inside the nucleus - bases that are complementary to the ones exposed on the active strand stick onto the exposed bases - the new nucleotides bond to each other, then peel off as a one-stranded inverse copy of the exposed portion of the DNA - this single-strand copy is messenger RNA , or mRNA - the mRNA is then “edited” - segments called introns are clipped out, and the remaining pieces ( exons ) are spliced back together
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Intro to Biological Anthro F 2011 / Owen: Molecular genetics p. 4 - in many cases, a single stretch of DNA may produce multiple mRNA sequences, depending on which exons are spliced back together, and in what order - this seems unnecessarily complicated, but that is how it works - and I have left out quite a few details already… - this process of producing mRNA from DNA is called transcription - the exposed portion of DNA typically makes many mRNA molecules that carry its information - the more mRNA that is made, the more of the protein will ultimately be made - More detail on the second stage, translation - in which the protein is actually made from the code of the mRNA - the mRNA moves out of the nucleus into the cytoplasm , - the main mass of the cell, where most of the functions of the cell are carried out - in the cytoplasm, the mRNA encounters a structure called a ribosome - where the ribosome is in contact with the mRNA, a particular reaction occurs - small molecules called transfer RNA ( tRNA ) can attach to the mRNA with the help of the ribosome - these molecules have three bases exposed on one part - and another part that can bond to one specific amino acid - there is one type of tRNA for each possible codon - and each type of tRNA can carry only one of the 20 amino acids - so the various types of tRNA define the translation of codons into specific amino acids - in this way, only the tRNA with the right three complementary bases can bond to the mRNA at a given point -
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