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Review Questions Transcription 1. Why is transcription necessary? DNA, the recipe for making proteins, never leaves the nucleus (nucleoid region in bacteria). Yet all the protein-making machinery is located out in the cytoplasm. So how does the information get to the cytoplasm? DNA is transcribed into messenger RNA. 2. What is a transcript? A transcript is not a copy of the original but has the same information but stored in a different form. Court reporters make a transcript of courtroom proceedings. They type out what everyone says during a trial. Rather than speech, the information has been transcribed into a written form. Since DNA is locked inside the nucleus, enzymes transcribe the DNA into messenger RNA. Like any good transcript, mRNA has the same recipe as the gene but the information now is in the form of an RNA molecule. Aptly named, mRNA, once formed, moves out of the nucleus and into the cytoplasm where the proteinbuilding molecules are stationed. 3. Explain the process of transcription. Transcription begins with a gene. Rather than transcribing the entire DNA molecule, only one gene at a time is transcribed. RNA polymerase is a group of enzymes that makes the RNA transcript. First off, the RNA polymerase binds to a promoter site on the DNA molecule (the promoter indicates the start of the gene). Next, RNA polymerase unwinds and unzips the length of one gene on the double helix. The RNA polymerase only transcribes one of the DNA strands by using the other strand as a template. The mRNA elongates as complementary bases are added until the RNA polymerase reaches a termination point. The hydrogen bonds are broken separating the newly formed mRNA from the DNA template strand. The mRNA leaves the nucleus through tiny pores in the nuclear envelope and enters the cytoplasm to be translated into a sequence of amino acids. The last act of RNA polymerase is to zip-up and rewind the DNA. Coding Strand Template Strand 5’ A T C G A T C G 3’ 3’ T A G C T A G C 5’ ↓ Coding Strand mRNA Template Strand 5’ A T C G A T C G 3’ 5’ A U C G A U C G 3’ 3’ T A G C T A G C 5’ ↓ Coding Strand Template Strand mRNA 5’ A T C G A T C G 3’ 3’ T A G C T A G C 5’ 5’ A U C G A U C G 3’ → leaves the nucleus 4. List three differences between RNA and DNA. RNA is an abbreviation of ribonucleic acid. Instead of the sugar deoxyribose, like in DNA, the nucleotide of an RNA molecule has ribose. Deoxyribose has one less oxygen atom than ribose. DNA is double-stranded whereas RNA is single-stranded. The complementary bases in DNA are A=T and G=C. In RNA, G=C but A=U. U is uracil and takes the place of thymine.