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Bio 132 Exam 3 Objectives

Bio 132 Exam 3 Objectives - 12.9 Compare prokaryotic and...

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12.9 Compare prokaryotic and eukaryotic mRNAs, and explain the functional significance of their structural differences. Bacterial mRNA is translated as it is transcribed from DNA. In eukaryotes, chromosomes are confined to the nucleus, and protein synthesis occurs in the cytosol. In eukaryotes, the original transcript, known as pre-mRNA, is modified in several ways while it is still in the nucleus: Post-Transcription Modification prepare mature mRNA for transport and translation Eukaryotic genes and their mRNA molecules are more complex than those of bacteria. After transcription, a 5’ cap (a modified guanosine triphosphate) is added to the 5’ end of a eukaryotic mRNA molecule. Many also have a poly-A tail of adenine- containing nucleotides added to the 3’ end. These modifications seem to protect eukaryotic mRNA molecules from degradation, giving them a longer life span that bacterial mRNA. Stabilizes Eukaryotic genes have interrupted coding sequences . In many eukayoritc genes the coding regions, called Exons , are interrupted by noncoding regions called Introns . Both introns and exons are transcribed, but the introns are later removed from the original transcript, or pre-mRNA , and the exons are spliced together to produce a continuous protein-coding sequence. 12.6 Identify the features of tRNA that are important in decoding genetic information and converting it into “protein language.” Structural differences between a polynucleotide chain and a polypeptide chain prohibit amino acids from directly interacting with an mRNA to make a protein. The gap between mRNAs and protein are the tRNA molecules. Transfer RNAs are the decoding molecules in the translation process. Each tRNA molecule is specific for only one amino acid. Amino acids are covalently bound to tRNA by aminoacyl-tRNA synthetase enzymes. The aminoacyl-tRNA binds to the mRNA coding sequence to align the amino acids to form the polypeptide chain. tRNA properties : One part of the molecule contains an anticodon , which is complementary to a codon of mRNA. Attached to one end of the tRNA molecule is the amino acid specified by the complementary mRNA codon. Has an attachment site for amino acids. It is recognized by ribosomes. 12.7 Explain how the ribosomes function in protein synthesis. Ribosomes bring together all the mechanical machinery necessary for translation. They couple the tRNAs to their proper codons on the mRNA, catalyze the formation of peptide bonds between amino acids, and translocate the mRNA so the next codon can be read. Each ribosome is made of large and a small subunit; each subunit contains ribosomal RNA ( rRNA ) and many proteins. The structure of the ribosome has four binding sites, one for mRNA and three for tRNAs.
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E-site : (exit) where tRNAs that have delivered ther amino acids to the growing polypeptide chain exit the ribosome.
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