THE BIG IDEA Transcription From DNA to RNA
THE BIG IDEA!!!!!!!
Transcription From DNA to RNA
What is RNA? • Ribonucleic acid (RNA)
Structure of RNA • • 1 strand Phosphate group 5 carbon Sugar (ribose) Nitrogen base
What are the bases? • • Adenine (A) Guanine (G) Cytosine (C) Uracil (U)
Which are purines? • Adenine and Guanine – 2 rings
Which are pyrimidines • Cytosine and Uracil – 1 ring
Which bases pair? • A, U • G, C • When transcribing RNA, U replaces T
Step one • RNA polymerase binds at a promoter – A region of DNA that says start
Step 2 • RNA polymerase unwinds the DNA – Exposes the nucleotides
Step 3 • RNA polymerase adds complimentary RNA nucleotides
When is transcription finished? • RNA polymerase reaches the stop signal and detaches from the DNA • RNA is released • DNA double helix Reforms Watch
Does RNA polymerase transcribe all of the DNA? • NO • Uses one part of one strand of DNA (the gene)
Does all the DNA transcribed code for proteins? • NO! • Introns – Long segments of “junk” DNA that have no coding info.
What DNA does code for proteins? • Exons – DNA that codes for proteins
When are the Introns removed? • Before the m. RNA leaves the nucleus • An enzyme cuts out the introns & puts exons together
ACTIVITY • Materials: masking tape, pens or pencils (two colors), metric ruler, scissors • Procedure • Place a 15 -20 cm piece of masking tape on your desk. This represents a gene • Use two colors to write appropriately joined • One color represents introns, one exons • Space the letters so they take up the entire piece of tape • Lift the tape • Working from left to right cut apart the groups of letters in the same color • Stick the pieces to a piece of paper as you cut them making two strips according to color. Join the pieces in their original order. • 1. Label the strand that is the intron and label the strand that is the exon. • 2. Predict what might happen to a protein if an intron were not removed. • Turn into the box.
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