Types of RNA and Mechanism of Transcription

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Need help preparing for the Biology section of the MCAT? MedSchoolCoach expert, Ken Tao, will teach everything you need to know about Types of RNA and Mechanism of Transcription. Watch this video to get all the MCAT study tips you need to do well on this section of the exam! • Transcription is the conversion of DNA into RNA. Several types of RNA can be transcribed from DNA, including messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), and catalytic RNA. Messenger RNA is RNA that gets translated into proteins. Transfer RNA are RNA molecules that contain an anticodon sequence that is complementary to codons in the mRNA. They also contain a site where an amino acid can be bound. The role of tRNA, therefore, is to carry amino acids to the ribosome/mRNA complex during translation. Ribosomal RNA is a component of ribosomes, which are made from both RNA and proteins. Finally, catalytic RNA are catalytic agents, also known as ribozymes. Since RNA contains carbon, catalytic RNA are biological enzymes that are involved in several biological reactions in the cell. • Mechanism of Transcription • Transcription involves the enzyme RNA polymerase, which performs all of the functions of transcription. In contrast, DNA replication involves several enzymes. So transcription is, in fact, a much more straightforward process than DNA replication. Transcription begins when RNA polymerase binds to the promoter. The promoter is a specific sequence of DNA that can be thought of as the transcription start site. In order for DNA to be transcribed into RNA, and in order to express a particular gene, RNA polymerase must first bind to the promoter region. • Once RNA polymerase binds to the promoter region on DNA, it will begin to unwind the DNA. This process occurs because RNA polymerase will use DNA as a template to create RNA. So, in addition to having polymerase activity, RNA polymerase has helicase activity as well. The primary function of helicase enzymes is to unpack, or unwind, genetic material. Once DNA is unwound, two separate strands will be formed. One strand of DNA is called the template strand, and the other strand is called the coding strand. • RNA polymerase binds to the template strand, and using it, creates a complementary RNA sequence. The complementary RNA sequence can produce mRNA. In this way, mRNA is complementary to the template strand of DNA, and it has the same sequence as the coding strand. One exception to this rule is that DNA contains the base pair thymine, while RNA contains uracil. • DNA dependent RNA polymerase • Also, it is important to note that RNA polymerase is a DNA dependent RNA polymerase, meaning that it uses DNA as a template to produce RNA. RNA polymerase will continue until it reaches a transcription stop site. At this point, it stops transcribing the DNA. In contrast, DNA replication will not stop until the entire chromosome is replicated. Therefore, in transcription, only a small portion of the chromosome is transcribed. • Proofreading • Lastly, it is essential to note that RNA polymerase, unlike DNA polymerase, does not have proofreading activity. When RNA polymerase adds nucleotides to synthesize RNA molecules, it can make mistakes. In other words, RNA polymerase is error-prone. Furthermore, if RNA polymerase makes mistakes, then the translated protein may not be functional. • The reason RNA polymerase does not have proofreading activity is not fully understood, but one reason may be because RNA is not as stable as DNA. After RNA is made, it can be degraded relatively quickly. However, DNA is meant to stick around for the entire duration of an organism’s lifespan. Since this is the case, DNA must remain error-free. However, if a mistake is made when transcribing RNA, it may not have as severe an effect because of its short lifespan. After it is degraded, a brand-new RNA molecule will be created that is error-free. • MEDSCHOOLCOACH • To watch more MCAT video tutorials like this and have access to study scheduling, progress tracking, flashcard and question bank, download MCAT Prep by MedSchoolCoach • IOS Link: https://play.google.com/store/apps/de... • Apple Link: https://apps.apple.com/us/app/mcat-pr... • #medschoolcoach #MCATprep #MCATstudytools

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