Transcription

Central Dogma of Biology Information flows from DNA  RNA  Proteins Think of it as exchanging money in a different country: proteins cannot be built directly from DNA Three main processes involved: – Replication (copies DNA) – Transcription: DNA  RNA – Translation: RNA  Protein

RNA vs. DNA 3 main differences: – Sugar is called ribose (DNA has deoxyribose) – Uracil (U) instead of thymine pairs with adenine (A) – Single-stranded

RNA Molecules 3 major types – Messenger RNA (mRNA): codes for proteins – Ribosomal RNA (rRNA): part of the ribosome – Transfer RNA (tRNA): helps read the mRNA code to build proteins during the process of translation

What is Transcription? Transcription is a process that uses a portion of DNA to make a complementary RNA strand – Similar to replication Just one gene at a time is transcribed, not the whole DNA molecule

Transcription Process 3 basic steps, just as in replication: – Part of DNA double helix unwinds (initiation) – Complementary RNA bases are assembled (elongation) – Completed RNA strand detaches from DNA (termination)

Initiation RNA polymerase finds the beginning of a gene A transcription complex made of RNA polymerase and other enzymes begins to unwind part of the DNA strand

Elongation RNA polymerase uses the DNA strand as a pattern to build a complementary RNA strand – C pairs with G – A pairs with U RNA strand hangs off the DNA strand, and DNA helix zips back together

Termination After the whole gene has been transcribed, the RNA strand detaches completely from the DNA. The transcription complex made of RNA polymerase and other proteins falls apart.

Replication vs. Transcription Where does the process take place? Enzymes involved Step 1Step 2Step 3 Replication Transcription

Replication vs. Transcription Where does the process take place? Enzymes involved Step 1Step 2Step 3 ReplicationNucleus TranscriptionNucleus

Replication vs. Transcription Where does the process take place? Enzymes involved Step 1Step 2Step 3 ReplicationNucleus DNA helicase, DNA polymerase TranscriptionNucleus RNA polymerase

Replication vs. Transcription Where does the process take place? Enzymes involved Step 1Step 2Step 3 ReplicationNucleus DNA helicase, DNA polymerase DNA strand is unzipped TranscriptionNucleus RNA polymerase DNA strand is unzipped (initiation)

Replication vs. Transcription Where does the process take place? Enzymes involved Step 1Step 2Step 3 ReplicationNucleus DNA helicase, DNA polymerase DNA strand is unzipped Complementary bases attached; whole DNA strand TranscriptionNucleus RNA polymerase DNA strand is unzipped (initiation) Complementary RNA bases attached; only one gene (elongation)

Replication vs. Transcription Where does the process take place? Enzymes involved Step 1Step 2Step 3 ReplicationNucleus DNA helicase, DNA polymerase DNA strand is unzipped Complementary bases attached; whole DNA strand Two identical DNA molecules TranscriptionNucleus RNA polymerase DNA strand is unzipped (initiation) Complementary RNA bases attached; only one gene (elongation) mRNA strand floating free from DNA (termination)

Transcription Practice List 3 differences between DNA and RNA. Write the following DNA sequence: GTTCACTAG Write the complementary DNA strand. Circle one DNA strand. Simulate transcription by writing its complementary RNA sequence. Does the RNA strand more closely resemble the DNA strand from which it was transcribed or the complementary strand that wasn’t used? Why? What is the main enzyme involved in transcription? What is its function? List 3 types of RNA and briefly describe each one.