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.