1. RNA
February 3rd/4th, 2009

2. Warm Up and H.W. Reflection
List one difference between DNA and RNA.
RNA is made of up ribose sugar; DNA is made up of deoxyribose sugar.
RNA is single-stranded; DNA is double stranded.
RNA has the base Uracil; DNA has the base Thymine.
Give the three types of RNA and what the lower case letter before each stands for.
mRNA (messenger RNA).
rRNA (ribosomal RNA).
tRNA (transfer RNA).
What do ALL the types of RNA have in common?
They are all single-stranded.
They are all made up of ribose sugar, a phosphate group, and a nitrogenous base.

3. RNA vs. DNA RNA Ribose sugar Single-stranded Base Uracil DNA
Deoxyribose sugar
Double-stranded
Base Thymine
You can compare the roles played by RNA and DNA to the two types of plans used by builders. In construction, a master plan has all the information needed to construct a building. But builders never bring the valuable master plan to the building site, where is might be damaged or lost. Instead, they make inexpensive, disposable copies of the master play called blueprints. The master plan is safely stored in and office and the blueprints are taken to the job site. Similarly, the cell uses the vital DNA master plan to prepare RNA blueprints. The DNA remains safely stored in the nucleus and the RNA goes out to the ribosomes.

5. Transcription
Transcription is the process by which part of the nucleotide sequence of DNA is copied into a complimentary strand of mRNA

6. During transcription,
RNA polymerase (similar to DNA polymerase) binds to DNA and separates the DNA strands.
RNA polymerase then binds to promoter regions in the DNA which tell it where to start making the RNA.
Finally, it uses one strand of DNA as a template to construct a complimentary strand of RNA.

8. RNA Editing
Remember that DNA has the ability to turn some genes on, and others off, meaning that not all of the DNA is used every time we need to make a protein.
Introns are sequences of DNA that are not involved in protein synthesis. They are “turned off”.
Exons are sequences of DNA that are involved in protein synthesis. They are “turned on”.
Depending on which protein you are trying to build, introns can become exons, and exons can become introns.

9. When transcribing DNA, RNA makes a complete copy of the DNA sequence
When transcribing DNA, RNA makes a complete copy of the DNA sequence. It then cuts out the introns and then splices (or connects) the exons together.

10. The Genetic Code The “language” of mRNA is called the genetic code.
The genetic code is read three letters at a time, so that each “word” of the coded message is three base pairs long.
Each three-letter “word” in mRNA is known as a codon.

11. Serine-Histidine-Glycine
In addition, each three letter “word” – or codon – means something in this genetic language.
Each codon codes for a single amino acid, that will eventually combine with other amino acids to make the finished protein. This process is called translation.
Consider the following RNA sequence:
UCGCACGGU
This sequence would be read three bases at a time as:
UCG-CAC-GGU
The codons are then translated into three different amino acids:
Serine-Histidine-Glycine

12. Come on down! You’re the next contestant on “The Wheel of Amino Acids”!!

13. Reflection What are introns and exons?
Introns are DNA sequences that are not used in protein synthesis and exons are DNA sequences that are used in protein synthesis.
What do you think would happen if the introns were not cut out of the pre-mRNA?
RNA would not code for the correct protein during translation.
What is the name of the three-letter “words” that make up the language of genetic code?
Codon.
Given the following sequence of DNA, transcribe an mRNA strand: GACAAGTCCACAATC
CUG-UUC-AGG-UGU-UAG
Given the following RNA sequence, translate the correct amino acid sequence: AUG-CAU-GCC-UAG
Methionine-Histidine-Alanine-Stop