Intro to Transcription Protein Synthesis Intro to Transcription

REVIEW- DNA Structure & Replication A nucleotide does NOT contain: A. a 5-carbon sugar B. an amino acid C. a nitrogen base D. a phosphate group The bonds that hold the two strands of DNA together come from: A. the attraction of phosphate groups for each other B. strong bonds between nitrogenous bases and the sugar-phosphate backbone C. weak hydrogen bonds between nitrogenous bases D. carbon-to-carbon bonds in the sugar portion of the nucleotides In chromosomes, DNA is tightly coiled around proteins called: A. DNA polymerase B. chromatin C. Chromosomes D. Histones

Human DNA Model 8 Phosphates 8 Sugars 2 Adenines 2 Thymines 2 Guanines 2 Cytosines

Transcription Transcription is the synthesis (making of) an RNA molecule from a DNA template. It occurs in three steps: 1. Initiation 2. Elongation 3. Termination

The starting molecule We know that DNA is Double Stranded The bases in the primary strand match up to those in the complimentary strand. Practice: Primary strand: A T C G C T T A G Complimentary:

Transcription- 1st Step: Initiation The enzyme Helicase unzips the two strands of DNA and separates them into two parts. Each strand serves as a new template IMPORTANT! DNA contains: RNA contains: Deoxyribose sugar Ribose sugar Phosphate phosphate 4 nitrogenous bases (A,T,C,G) 4 nitrogenous bases (A,U,C,G)

Transcription- 2nd step: elongation RNA Polymerase forms a strand of mRNA that is complementary to the starting DNA strand.

Transcription- 3rd step: Termination At the end of a gene, RNA polymerase encounters a sequence of DNA called a Termination Signal or Stop codon. There are 3 stop codons in the genetic code UAG, UAA, UGA RNA polymerase detaches from the DNA and translation begins.

Transcription: practice Original Strand of DNA Top Strand (DNA) Bottom Strand (DNA) A T G C A T G C T A C G

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