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Protein Synthesis and DNA Flashcards | Quizlet

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Begins when a strand of DNA unravels.

Protein synthesis begins with the formation of an initiation complex. In , this complex involves the small 30S ribosome, the mRNA template, three initiation factors (IFs; IF-1, IF-2, and IF-3), and a special , called . The initiator tRNA interacts with the AUG (or rarely, GUG), links to a formylated methionine called fMet, and can also bind IF-2. Formylated methionine is inserted by at the beginning of every polypeptide chain synthesized by , but it is usually clipped off after translation is complete. When an in-frame AUG is encountered during translation elongation, a non-formylated methionine is inserted by a regular Met-tRNAMet.

Figure 1 Figure 2 Protein synthesis begins in figure 1 ..

Figure 4-13, Lodish5e: Structure of the 5' methylated cap of eukaryotic mRNA. The 5' end of the primary transcript becomes capped and methylated, probably to protect this RNA from enzymatic degradation. The cap is essentially a nucleotide added in an unusual 5' to 5' linkage. the 5' cap has the following functions: a) protects an mRNA from degradation by a 5' exonuclease, b) assists mRNA movement out of the nucleus and into the cytoplasm and c) binds a protein factor required for initiation of protein synthesis (translation).

DNA Replication & Protein Synthesis Test Flashcards | …

The synthesis of proteins consumes more of a cell’s energy than any other metabolic process. In turn, proteins account for more mass than any other component of living organisms (with the exception of water), and proteins perform virtually every function of a cell. The process of translation, or protein synthesis, involves the decoding of an mRNA message into a polypeptide product. Amino acids are covalently strung together by interlinking peptide bonds in lengths ranging from approximately 50 amino acid residues to more than 1,000. Each individual amino acid has an amino group (NH2) and a carboxyl (COOH) group. Polypeptides are formed when the amino group of one amino acid forms an amide (i.e., peptide) bond with the carboxyl group of another amino acid (). This reaction is catalyzed by ribosomes and generates one water molecule.

A. Initiation. RNA polymerase binds to its promoter sequence, usually the TATA box in double helical, also called duplex, DNA (called the "closed complex" at this stage) and as RNA synthesis begins, a transcription bubble forms, a 'melted DNA duplex' region of about 14 base pairs. This bubble is called the "open complex". The RNA polymerase catalyzes the linkage by phosphodiester bonding of the two initial ribonuleotides. Transcription initiation is complete when this covalent bond forms. As we will discuss later, initiation by RNA polymerase requires several proteins called general transcription factors to both locate the promoters and initiate transcription.

DNA Replication & Protein Synthesis Test

A combination of nucleotide signals identifies the beginning of an mRNA sequence to be translated into its protein product. The nucleotide triple AUG is the start codon that directs the ribosome to begin reading an mRNA and orients the message in the right frame (for example,… CUA GUG CAC C… rather than … C UAG UGC ACC…, which would be a different protein). However, AUG is also the codon for insertion of the amino acid methionine into the body of the polypeptide chain. What distinguishes the start AUG from other identical codons elsewhere in the message? A stretch of 3-10 nucleotides located about 10 nucleotides upstream (in the 5′-direction) from the start codon is called the Shine-Dalgarno sequence, after the researchers who identified it. This sequence is rich in A and G nucleotides, and is partially complementary to a short region of U and C nucleotides near the 3′-end of an RNA molecule embedded within the ribosomal small sub-unit. Such complementarity positions the incoming message properly on the ribosome, so that the start codon is in the ribosomal decoding site for initiation of protein synthesis. Once translation begins, the rest of the codons in the message need to be read, so the base-pairing interaction between mRNA and rRNA at the Shine-Dalgarno sequence must be transient.

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