MCAT Biochemistry
RNA, or ribonucleic acid, is a molecule that plays a role in the synthesis of proteins by following the central dogma of biology, which involves converting DNA to RNA to protein. There are numerous types of RNA, including messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), each having distinct functions in protein synthesis. During transcription, RNA is synthesized in the nucleus, following the 5'-3' direction with complementary bases to the DNA template strand. The nucleolus, a sub-organelle of the nucleus, is the specialized location for rRNA transcription and ribosome assembly.
mRNA acts as a template for protein synthesis, while tRNA brings amino acids to ribosomes for protein synthesis. rRNA composes the majority of ribosomes, facilitating the attachment of amino acids by converting the energy from engaging tRNA and creating peptide bonds between amino acids. Additionally, there are 64 different possible codons, with each codon representing three RNA nucleotides. However, there are only 20 common amino acids, so more than one codon can code for the same amino acid during translation, referred to as the degenerate characteristic of the genetic code.
Lesson Outline
<ul> <li>Central dogma: converting DNA to RNA to protein</li> <li>Types of RNA <ul> <li>messenger RNA (mRNA)</li> <li>transfer RNA (tRNA)</li> <li>ribosomal RNA (rRNA)</li> </ul> </li> <li>RNAs synthesized in nucleolus <ul> <li>5-3 direction</li> <li>Complementary bases to DNA template strand</li> <li>Thymine replaced with uracil</li> </ul> </li> <li>mRNA <ul> <li>Template to engineer proteins</li> <li>Occurs in cytoplasm</li> <li>Monocistronic (eukaryotes) and polycistronic (prokaryotes)</li> </ul> </li> <li>tRNA <ul> <li>Translates mRNA nucleotides into protein amino acids</li> <li>Requires aminoacyl-tRNA synthetase and ATP energy to attach amino acid</li> </ul> </li> <li>rRNA <ul> <li>Forms ribosomes</li> <li>Catalyzes peptide bonds between amino acids</li> </ul> </li> <li>Codons <ul> <li>Three nucleotides per codon with 64 possible combinations</li> <li>Degenerate code: more than one codon can code the same amino acid</li> </ul> </li> <li>Wobble position <ul> <li>Flexible 3rd position in a codon</li> <li>May not change resulting amino acid if a base changes</li> </ul> </li> <li>AUG start codon <ul> <li>Always results in methionine</li> <li>Can be used after the start of peptide chain</li> </ul> </li> <li>Three stop codons: UGA, UAA, UAG <ul> <li>None of these codons add amino acids</li> <li>Translating ribosome falls off</li> </ul> </li> </ul>
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FAQs
Messenger RNA (mRNA) serves as a template for protein synthesis by carrying genetic information from DNA in the nucleus to the ribosomes in the cytoplasm. Transfer RNA (tRNA) plays a crucial role in translation by carrying amino acids to the ribosome and recognizing the appropriate codons on mRNA. Ribosomal RNA (rRNA) is a structural and catalytic component of ribosomes, facilitating the formation of peptide bonds between amino acids during protein synthesis.
RNA nucleotides are the building blocks of RNA molecules. Each RNA nucleotide consists of a ribose sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), cytosine (C), guanine (G), or uracil (U). The sequence of RNA nucleotides determines the RNA's structure and function, as specific sequences can form various types of RNA, such as mRNA, tRNA, or rRNA, and play crucial roles in the processes of transcription and translation.
The genetic code consists of codons, which are groups of three nucleotides that correspond to specific amino acids. The start codon (AUG) signals the beginning of translation, defining the reading frame and coding for the amino acid methionine. Stop codons (UAA, UAG, or UGA) signal the end of translation and do not code for any amino acids, marking the termination of protein synthesis when they are encountered by the translational machinery.
The genetic code is degenerate, meaning that multiple codons can code for the same amino acid. This degeneracy arises from variation in the third nucleotide position of a codon, also known as the wobble position. Wobble positions often allow for different nucleotides to pair with the anticodon of the tRNA without affecting the encoded amino acid. This degeneracy provides a level of redundancy in the genetic code, reducing the potential impact of mutations on protein function.
Transcription and translation are two sequential processes in the central dogma of molecular biology. Transcription refers to the synthesis of RNA from a DNA template, wherein RNA polymerase reads the DNA sequence and produces a complementary RNA molecule, such as mRNA. Translation occurs in the cytoplasm, where ribosomes, composed of rRNA and protein components, read the mRNA sequence and decode it into a corresponding amino acid sequence, forming a peptide bond and eventually a functional protein.
