RNA Synthesis

Transcription

Genes in cells are made of DNA, which is a complex molecule. The structure of a DNA molecule contains the information that a cell needs to carry out all of its functions. In a way, DNA is like the cell’s encyclopedia .Suppose that you go to the library to do research for a science project. You find the information you need in an encyclopedia. You go to the desk to sign out the book, but the librarian informs you that this book is for reference only and may not be taken out.

1. Why do you think the library holds some books for reference only?

2. If you can’t borrow a book, how might you take home the information in it?

3. How is this method similar to processes that occur in cells?

1. What does transcription begin with?

•DNA molecule• In prokaryotes, RNA synthesis (transcription) occurs in the ??• In eukaryotes, RNA synthesis (transcription) occurs in the ??

2. First step of transcription…Initiation

• DNA unwinds and unzips• RNA polymerase binds to DNA at promoter sequences, specific codes that signal RNA polymerase • In transcription, segments of DNA

(specific genes to be copied) serve as templates to produce complementary mRNA molecules

3. Second step of transcription…Elongation

•Complementary RNA nucleotides (ribonucleotides) are added according base pairing rules to the DNA template•Only one side of the DNA serves as the template

4. Third step of transcription…Termination

• A “stop” sequence in the DNA gene code (called a terminator) signals RNA polymerase that it has come to the end of the gene that is to be transcribed; that the mRNA molecule is now complete• Newly synthesized mRNA detaches & DNA “rezips”

• http://www.phschool.com/science/biology_place/biocoach/transcription/complete.html

5. What are you “left” with when transcription is complete?

•Original DNA molecule•New mRNA molecule

6. What is the product (what is made) of transcription?

•mRNA• This mRNA is then edited–Introns removed–Exons put back together

RNA Editing

• http://www.youtube.com/watch?v=NJxobgkPEAo

7. How many nucleotides makes up mRNA? List them.

•Adenine•Uracil•Guanine•Cytosine

8. Explain two differences between DNA replication and DNA transcription.

• Products–??

• Purpose–??

• ??

Translation

• http://www.youtube.com/watch?v=D3fOXt4MrOM&feature=related• http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html