Explain how RNA differs from DNA. Describe the structure and functions of mRNA, tRNA, and rRNA.?
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DNA contains all the genetic coding that the body needs to create more cells, where as RNA only contains half of the genetic coding needed to replicate.
mRNA is made by copying the gene from the DNA. It's kind of a long strand. It goes out of the nucleus to the ribosome where it gets read, 3 bases at a time, codon by codon.
tRNA is in the cytoplasm. One part of the tRNA has a sequence of three bases that makes up the anticodon. The anticodon has to match the mRNA's codon to tell it that it's the next tRNA in line. Another part of the tRNA molecule picks up an amino acid to bring to the ribosome to be added on to the growing protein.
rRNA is part of the structure of a ribosome.
Here's a whole explanation of the protein synthesis process. Students always find this hard to understand, but just look at it a piece at a time.
Protein synthesis is the process of building proteins.
1. Transcription: The DNA unwinds and "unzips" in the area of the gene. Enzymes match RNA nucleotides to the unzipped nitrogen bases of the gene, forming a single strand of mRNA.
2. The strand of mRNA detaches from the gene and goes out of the nucleus through one of the pores in the nuclear envelope. The DNA zips back together and winds back up.
3. The mRNA finds a ribosome where protein synthesis will happen.
4. Each set of 3 bases on the mRNA is called a codon. Each codon calls for a specific amino acid to be brought to the building site. The first codon is always AUG, so it is called the start codon.
5. In the cytoplasm are molecules of tRNA. On one end of a tRNA molecule is the anticodon: a set of three bases that will match a certain codon. The other end of the tRNA can pick up and hold a certain amino acid. Each tRNA can only hold one kind of amino acid.
6. A tRNA with an anticodon that matches whichever codon is in place on the ribosome (think of that codon as being "at bat") clicks into place. The codon and anticodon fit together like two pieces of a jigsaw puzzle. Since the first codon is AUG, the first anticodon must have the matching bases UAC. (Memory trick: AU match like in AUstralia; CG match and they both are round letters.)
7. The process moves along to the next codon, or the next "batter". Lets say that the next codon is UCC. Then a tRNA with the anticodon AGG will fit.
8. The amino acid brought by the first tRNA bonds to the amino acid brought by the second tRNA. The first tRNA is free to go, and the second tRNA stays in place for now.
9. Steps 7 and 8 repeat until finally they come to an mRNA codon that is the STOP codon. At this point the amino acid chain breaks off, folds up, and the protein is ready to use.