NCEA EXAM QUESTIONS Flashcards
Protein Synthesis - EXAM QUESTION
Discuss the relationship between DNA, mRNA, and tRNA in protein synthesis.
In your answer include:
* an explanation of the key stages of protein synthesis
* an explanation of why tRNA is shorter than mRNA, when considering their function
* a discussion, with two justified reasons, why DNA is not directly translated into a
polypeptide chain.
DNA is a double stranded molecule containing genetic information in the stages of protein synthesis.
It starts with transcription. DNA must be copied identically so it can leave the nucleus to undergo translation, but it cannot as it is double stranded.
So a single strand (template strand) is used to be copied onto mRNA strand which is only a single strand so it can leave the nucleus. DNA begins transcription by using a promoter region whcih enables RNA polymerase to start transcribing to the template strand onto the mRNA. Once the RNA polymerase enzyme reaches a terminator region it stops transcribing the DNA. The mRNA strand is identical to the coding strand apart from changing the nucleotide base of thymine to uracil. According to base pairing rules, adenine now bonds with hydrogen bonds to uracil and guanine to cytosine. The group of 3 bases are called codons on the mRNA rather than triplets on the DNA strand. The mRNA strand leaves the nucleus through nuclear pores and into the cytoplasm in order to start translation. A ribosome will attach to the mRNA strand and begin translation. tRNA molecules attach to amino acids and join by their corresponding anti-codons to the codon sequence on the mRNA. Building a chain of amino acids as more anticodons and codons are bonded. Amino acids are a monomer. Proteins are a polymer made up of repeating units of amino acids. The amino acids bond by peptide bonds to form a polypeptide chain and therefore a protein. tRNA is shorter than mRNA as mRNA contains al the condons on the strand, whereas the tRNA is only bringing one anti-codon per molecule to bond to the mRNA strand. DNA is not directly translated into a polypeptide chain as it is a double stranded molecule. And double stranded molecules are too big to leave the nucleus which must occur for translation to occur. Therefore, a single strand of mRNA is formed to leave and be translated because the DNA cannot. It can also be directly translated into a polypeptide chain as some proteins are made into molecules. If the DNA is removed from the nucleus, and translated directly into a polypeptide chain it will not be able to create another identical enzyme or or protein as the genetic material has been used. This is why the mRNA strand is used rather than directly translating the DNA into a polypeptide chain.
