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Transcription. The Central Dogma of Molecular Biology: DNA------>RNA------>Protein. The central dogma concerns the flow of biological information:

thaddeus-lowery
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  2. The Central Dogma of Molecular Biology:DNA------>RNA------>Protein • The central dogma concerns the flow of biological information: • DNA is a self-replicating molecule containing genetic information that can be transcribed into an RNA message that can be translated into a polypeptide (protein).

  3. DNA • The DNA molecule is a double helix of two long chains of nucleotide molecules. • During DNA replication DNA is duplicated, producing two double helices. • Imbedded in these long strands of DNA are genes that control the production of proteins to the cell.

  4. Transcription • The first step in decoding these genetic messages is to copy part of the genetic sequence from DNA into RNA, or ribonucleic acid. This is called Transcription • These RNA molecules then carry out the process of making proteins.

  5. Structure of RNA • RNA, like DNA, consists of a long chain of nucleotides. • The structure of RNA and DNA nucleotides are very similar.

  6. Structure of RNA • There are three distinct differences; • The sugar in RNA is ribose (two hydroxyl groups) • RNA is generally single stranded • RNA contains the nitrogenous base Uracil in place of Thymine • RNA is like a copy of a master blue print (DNA) that is used to create the building blocks of the cell.

  7. Types of RNA: • RNA molecules have many functions, but most RNA is used in the process of protein synthesis. • The assembly of amino acids into proteins is controlled by RNA.

  8. Types of RNA • The three major types of RNA are: • Messenger RNA (mRNA) • Ribosomal RNA (rRNA) • Transfer RNA (tRNA)

  9. Messenger RNA (mRNA) • Most genes contain instructions for assembling amino acids into proteins. • The RNA molecules that carry copies of these instructions are known as messenger RNA (mRNA) because they serve as the messenger from DNA to the rest of the cell.

  10. Ribosomal RNA (rRNA) • Proteins are assembled on ribosomes. • Ribosomes are made of proteins as well as a form of RNA known as Ribosomal RNA (rRNA).

  11. Transfer RNA (tRNA) • During the construction of proteins, a third type of RNA molecule transfers each amino acid to the ribosomes as it is specified by coded messages in the mRNA. • These RNA molecules are known as Transfer RNA (tRNA).

  12. Transcription • RNA molecules are produced by copying (transcribing) part of the nucleotide sequence of DNA into complimentary sequence of RNA. This is called TRANSCRIPTION.

  13. Transcription • Transcription requires an enzyme known as RNA polymerase that is similar to DNA polymerase. • During transcription, RNA polymerase binds to DNA and separates the DNA strands. • RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA.

  14. Transcription • How does RNA polymerase know where to start and stop? • RNA polymerase will only bind to DNA in an area called the promoter region, which have specific base sequences. • There are also non-coding regions of DNA called termination sequences which tell RNA polymerase to stop transcribing.

  15. RNA Editing • RNA requires editing, just like most of your papers. • Large pieces of RNA are sometimes cut and trimmed before they can go into action (only in eukaryotes).

  16. RNA Editing • The pieces removed are called introns (intervening sequences) and are cut out why the RNA is still inside the nucleus. • The remaining portions, called exons, or expressed sequences, are spliced back together to form the final mRNA.

  17. RNA Editing • Why do cells spend valuable energy to make long strands of RNA just to cut them up and splice them back together? • This is done so RNA can be cut and spliced in different ways so a single gene can be used to produce many different RNA strands.

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