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RNA: Structure and Function

RNA: Structure and Function. Biology Vick. What is RNA?. R ibo n ucleic A cid It carries out the instructions encoded in DNA Remember DNA=blueprints for life… but “someone” has to be able to read those blueprints and get that info outside of the nucleus

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RNA: Structure and Function

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  1. RNA: Structure and Function Biology Vick

  2. What is RNA? • Ribonucleic Acid • It carries out the instructions encoded in DNA • Remember DNA=blueprints for life… but “someone” has to be able to read those blueprints and get that info outside of the nucleus • DNA in its “pure form” cannot leave the nucleus…

  3. RNA Structure • Made of nucleotides that have 3 components (very similar to DNA): • Sugar (ribose) • Phosphate group (phosphate + oxygen) • Nitrogen base (A, U, C, G)

  4. Differences from DNA: • Sugar is ribose • Single stranded • Contains uracil instead of thymine as one of the nitrogen bases

  5. 3 Types of RNA:mRNA • Messenger RNA (mRNA) • Carry copies of instructions from DNA for the purpose of assembling proteins • Remember where proteins are assembled in the cell?

  6. rRNA • Ribosomal RNA (rRNA) • a molecular component of a ribosome, the cell's essential protein factory. • Strictly speaking, ribosomal RNA (rRNA) does not make proteins. It makes polypeptides (assemblies of amino acids) that go to make up proteins.

  7. Ribosome Review: • Ribosomes are ancient molecular machines that are responsible for production of protein in all living cells. • They are large macromolecular complexes composed of RNA (2/3) and protein (1/3). • Ribosomes read the nucleotide sequence of a messenger RNA (mRNA) into a protein sequence, using the genetic code. (What are the building blocks of proteins?) • They use transfer RNAs (tRNAs) to mediate this process of translation from the nucleotide language of RNA and DNA into the amino acid language of proteins.

  8. Ribosome Structure • EF-G is an elongation factor found in the ribosome

  9. tRNA • Transfer RNA (tRNA) • carries amino acids to the ribosomes • enables the ribosomes to put this amino acid on the protein that is being synthesized as an elongating chain of amino acid residues, using the information on the mRNA to "know" which amino acid should be put on next. • For each kind of amino acid, there is a specific tRNA that will recognize the amino acid and transport it to the protein that is being synthesized and tag it on to the protein once the information on the mRNA calls for it.

  10. Steps of Protein Synthesis • 1st Step • Transcription • DNA is transcribed to produce a molecule of mRNA • 2nd Step • Translation • tRNA is translated into amino acids or proteins mRNA DNA transcription Protein translation

  11. Transcription • RNA Polymerase is used in the process of transcription • DNA section with desired gene is unzipped • A complementary mRNA strand is made • DNA is rezipped and mRNA moves into the cytoplasm

  12. Transcription to Translation • Vocabulary • Codon – 3 letter sequence or “word” on mRNA • Anti-codon – three bases on tRNA that are complimentary to the mRNA codon • Codons specify a single amino acid that is to be added to the protein • Ex: UCGCACGGU=UCG-CAC-GGU • Specific codons: • AUG is the start codon • Starts protein synthesis • Stop codons • 3 of them • Stop protein synthesis • Do not code for any amino acid

  13. Start Codons • These are used, along with certain other initiation factors to start translation/protein synthesis • The most common start codon is AUG which is read as methionine or, in bacteria, as formylmethionine. • Alternative start codons (depending on the organism), include "GUG" or "UUG", which normally code for valine or leucine, respectively. However, when used as a start codon, these alternative start codons are translated as methionine or formylmethionine. • What do those names mean and where do they come from?

  14. codons are deciphered in a decoder chart to determine the correct amino acids needed in protein synthesis

  15. Stop Codons: • 3 codons are needed to stop the process of translation: • UAG is amber • UGA is opal (sometimes also called umber) • and UAA is ochre • ("Amber" was named by discoverers Richard Epstein and Charles Steinberg after their friend Harris Bernstein, whose last name means "amber" in German.) • (The other two stop codons were named "ochre" and "opal" in order to keep the "color names" theme.) • What are their amino acid names? • STOP • (Remember we already stated they do not code for any amino acids?)

  16. Review: • mRNA • Messenger RNA, a copy of DNA blueprint of the gene to be expressed. (Information) • tRNA • Aminoacyl transfer RNA, also called anticodon or adaptor molecule.  One or more tRNAs for each amino acid. (Supply) • Ribosome • A very large complex of several rRNAs (ribosomal RNA) and many protein molecules. Total molecular weight over 2 million dalton. (Factory) • Protein • Polypeptide chain with sequence dictated by the mRNA sequence.  Also called the gene (Product)

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