How Does a Dna Molecule Code for a Protein – Describe the Process Completely
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How does a DNA molecule code for a protein. Describe the process completely.
The process of creating a protein from the information given from DNA consists of two parts: transcription and translation.
The first process transcription is copying the information from DNA to mRNA. The process starts when DNA double helix opens and in one strand a RNA polymerase attaches and starts to bind free nucleotides to DNA, so G bonds with C and A with U (because RNA does not have T). When this RNA polymerase reaches a part of DNA called the terminator, the transcription process stops and mRNA leaves the nucleus. A sequence of three bases code for one aminoacid. In mRNA this is called a codon.
The second process translation does the “translation” from the language of bases to the language of aminoacids which make up proteins. After mRNA leaves the nucleus it travels to ribosomes, a cell part where proteins are made. In ribosomes, another type of RNA, the tRNA is used as a “translator” between mRNA and aminoacid. In one end of tRNA there is a “anticodon” which is complementary to the codon of mRNA. (example if the codon in mRNA says AGG, the anticodon of tRNA will be UCC). This was the tRNA knows in which specific mRNA to attach to. In the other end of tRNA there is a site where the specific aminoacid is attached. Ribosomes have several sites. The P site holds the growing polypeptide chain, the A site holds the next aminoacid that comes, and the E site is the exit site where the polypeptide chain detaches. A particular tRNA called initiator tRNA comes in and bonds with the mRNA on the P site. This tRNA always carries a particular amino acid – always methionine (MET) which is the “Start” aminoacid. A new tRNA with its amino acid comes in to the ribosome and bonds to the A site. The first tRNA on the P site leave, and the new tRNA with the two amino acids now moves to the P site. This process continues until the whole polypeptide is made. The process stops where mRNA codes for a tRNA that never carries an amino acid. This is called a stop codon. This way the process stops and the newly made polypeptide chain leaves the ribosome.
2.Describe the process of DNA replication
During DNA replication, the DNA makes copies of itself. This happens during the S phase of cell cycle. The replication starts in specific parts of DNA called “origins of replication.” DNA helicase- is an enzyme that opens or unzips the double helix so there are two strands ready to be replicated. SSBP are proteins that keep the strands apart from each other, and DNA topoisomerase deals with the twisting problem. the replication starts when an RNA primer attaches to the origins (because free nucleotides can not attach unless there is something to hold to). Then DNA polymerase starts attaching nucleotides to the strands so A pairs with T and G with C. it is important to mention that the replication only occurs in 5 to 3 direction. As we know the DNA strands are twisted in opposite direction (on in 5 to 3 and the other in 3 to 5 direction). So in one strand, DNA polymerase continuously adds nucleotides to make the new DNA. This process is fast and this is called the leading strand. But on the strand the DNA polymerase has to work kind of backwards because it has to go on the other direction in order to replicate from 5 to 3 direction. This is a discontinoual process and this is the lagging strand. The DNA that is made is fragmented in so called “okazaki fragments.” When the process is stoped, DNA ligase links these fragments and the DNA is replicated in two identical copies.
3. If a DNA molecule has the message: I will insert a DNA sequence here , what would be the amino acids in the protein? What would happen if the DNA message changed to I
will insert a different sequence with a base change? Be specific in your answer.
4. How does DNA replication ensure accuracy.
When DNA is replicated, you wind up with