Lecture 15 - Lecture 15 Proteins and their synthesis The...

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Lecture 15 Proteins and their synthesis
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Translation, the synthesis of polypeptides from amino acids based on mRNA nucleotide sequence constitutes a conversion of the information from one language to another : nucleotide sequence to amino acid sequence. The synthesis of RNA from DNA is described by the term transcription; the ‘language’ of DNA and RNA is nucleotides…
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Protein synthesis proceeds through the action of functional RNAs and is supported by interacting proteins. Transfer RNA (tRNA): the adapters that ‘translate’ the three nucleotide codon in the mRNA into the corresponding amino acid. The amino acid is brought to the ribosome by the tRNA. Ribosomal RNA (rRNA): the major component of the ribosome that catalyzes the synthesis of polypeptides from amino acids according to the mRNA sequence. Ribosomes: composed of 65% rRNA and 35% ribosomal proteins. . Their active sites are made of RNA, so ribosomes are now classified as "ribozymes”.
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Although most genes encode mRNA functional RNAs make up the largest fraction of cellular RNA, up to 95%. Lower panel is stained for total RNA in extract; 28S and 18S rRNA are clearly represented. mRNA species cannot be detected in this manner – low abundance.
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Labeled functional RNAs Using isotopic labeling all transcription products are labeled… …rRNA and tRNA is directly visualized, mRNA not detected.
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Amino acids are covalently linked through peptide bonds to yield polypeptides. N-terminal C-terminal The R (reactive) group confers unique properties to otherwise identical monomeric units.
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Levels of protein structure Hydrogen bonds are non-covalent interactions, influenced by the local environment. Other non-covalent forces may influence: electrostatic interactions and van der Waals forces.
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Figure 9-3b Secondary structure Protein monomers may have domains with helical α structure, pleated sheet structure or both.
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Figure 9-3c Tertiary structure in proteins Interactions between R- groups of amino acids with each other or with the local environment drives establishment of tertiary structure.
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Figure 9-3d Quaternary structure Many functional proteins are composed of two or more folded polypeptides. These subunits may be identical or different Quaternary structure relies on proper folding of individual subunits.
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Levels of protein structure Many proteins, including enzymes, assume compact structures and are referred to as globular proteins Proteins with linear shape are called fibrous proteins . Fibrous proteins usually have no biological activity, are more often they are important structural components of skin, hair and tendons (keratins, collagens, elastins. ..). Shape or conformation of a protein is of the utmost importance as it enables the protein to do its job in the cell. For example the active site of an enzyme is defined by the
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This note was uploaded on 11/11/2009 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.

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Lecture 15 - Lecture 15 Proteins and their synthesis The...

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