1. 2/22/12
Objective: Recognize the central dogma of genetics Describe the process of transcription Describe the structure of messenger RNA
Warm-Up: What does the term “DNA sequence” refer to?

3. Protein Synthesis
Protein synthesis is the complex, multi-step process of using the information encoded in DNA to build protein
The sequence of nucleotides in the DNA determines the amino acid sequence of polypeptides
Recall from 1st quarter that a polypeptide is a string of amino acids bonded together by (covalent) peptide bonds
There are two main parts of protein synthesis: transcription and translation
A gene that is transcribed and translated is said to be expressed

4. Transcription
During transcription, DNA is used as a template for the synthesis of messenger RNA (mRNA)
An enzyme complex called RNA polymerase is responsible for transcription
RNA polymerase “reads” the DNA and builds a single strand of messenger RNA

5. 2/23/12 Objective: Understand reverse transcription and RNA processing
Warm-Up: Contrast DNA and messenger RNA
Homework: Transcription Practice
Due Friday 24 Feb, 10 pts
FYI: Interim grades close Friday (tomorrow)
Please be sure your composition book is in the classroom Friday afternoon so I can update scores

7. Misconception!
“It doesn’t matter which side of the DNA you use to make the messenger RNA because you end up using both”
Not true! It makes a big difference! The two strands of a double helix are complementary, not identical. This means that each strand will yield a different messenger RNA sequence. mRNAs that are different carry completely different messages to the ribosomes in the cytoplasm.

8. RNA Structure It is a nucleic acid Single stranded
Ribose instead of deoxyribose
Uracil instead of thymine
There are several different varieties of RNA; we will cover messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).

10. Retroviruses
Retroviruses are unique because they carry an RNA genome, not a DNA genome
HIV
When the viral RNA genome is introduced into a host cell, the enzyme reverse transcriptase “reads” the viral RNA and synthesizes DNA
The newly synthesized viral DNA is then integrated into the host’s DNA genome
Once there, the viral DNA sequence is expressed along with the host’s own genome

11. messenger RNA Processing
Your DNA has coding regions and non-coding regions
Non-coding regions do not contain sequence that codes for amino acids
Coding regions are exons
Non-coding regions are introns
When messenger RNA is synthesized, it contains both exons and introns
The introns are spliced (cut) out of the mRNA during processing

12. mRNA processing
After splicing, there are two important modifications made to the messenger RNA strand
A specialized nucleotide called GTP is added to the “head” of the mRNA
This is called a GTP cap
A long string of adenines is added to the “tail” of the mRNA
This is called a poly-A tail
Both the GTP cap and the poly-A tail protect the mRNA from being degraded in the cytoplasm