1. BUT MOM... I don’t want to be a protein! Too bad.

2. Once upon a time... In 1902... Archibald Garrod, a UK physician, noticed certain illnesses recurring in families He came up with a hypothesis – Enzymes are under the control of THE hereditary molecule – A defective enzyme causes an “inborn error of metabolism”

3. Once upon a time... In 1902... He analyzed blood/urine samples of patients with alkaptonuria – A condition that turns urine black due to the presence of alkapton He proposed that individuals with alkaptonuria had a defective enzyme – A alkapton-metabolizing enzyme!

4. 33 years later... George Beadle and Edward Tatum confirmed Garrold’s hypothesis studying red bread mold – Neurospora Crassa (N. Crassa) Hoped to discover a relationship between genes and enzymes Used multiple strains of N. Crassa and grew them on different media

5. 33 years later... Procedure: Grew one strain of N. Crassa on a nutrient medium with simple inorganic salts, sugars, and vitamins – Result: N. Crassa was able to synthesize all complex AAs Mutant strains were produced via x-rays – Result: Descendents could NOT grow on medium they could no longer produce all essential compounds to sustain life

6. 33 years later... To find out which AA they could not produce – They placed mutant strains in vial that had basic nutrients plus ONE EXTRA AA The only growth occurred with ARGININE – Thus, 1+ enzymes in the arginine pathway were defective Conclusion: a lack of a specific enzyme corresponded to a mutation in specific gene

7. Final piece of the puzzle... In 1956, Vernon Ingram confirmed all previous experiments using sickle cell anemia – Condition where red blood cells are deformed He studied the AA sequence of hemoglobin for individuals that had sickle cell anemia He found a single AA mutation that completely altered the shape of the red blood cell

8. Final piece of the puzzle... Ingram found that valine replaces glutamic acid in individuals with sickle cell anemia Conclusion: genes specify the type and location of each amino acid in polypeptide chain Other examples of simple AA mutations: hemophilia and cystic fibrosis

9. What’s the deal with proteins? Are the REAL building blocks of life. Technically… they shouldn’t exist at all. – There may be as many as a million types of proteins & each one is a miracle! You need to assemble AA in a particular order – Similar to assembling letters to spell a word – Except… Words using the AA alphabet are INCREDIBLY LONG

10. Try this out… Collagen needs 1,055 AA in its sequence – Get this! You don’t make it, it creates itself… AUTOMATICALLY Picture a slot machine… *That has 1,055 wheels (not 3) *that’s 90ft long! *20 symbols on each wheel What are the odds of getting all AAs in order?

11. Try this out… Most proteins have 200 AA – The odds of creating that is 1 in 10 260 That’s A LOT of zeros Hemoglobin has 146 AAs – Max Perutz took 23 years to unravel the sequence “Assembling a protein is like a whirlwind spinning through a junkyard… … and leaving behind a fully assembled jumbo jet” - Fred Hoyle

12. So how are proteins made? There is a problem: DNA makes proteins, but… – DNA can’t leave the nucleus or it will be destroyed – Proteins are constructed outside the nucleus mRNA acts as the middle man – It can take the DNA message out of the nucleus to synthesis polypeptides

13. RNA – RiboNucleic Acid The world’s greatest translator Different from DNA in 3 ways 1.DNA has deoxyribose sugar RNA has ribose sugar (-OH on 2’ carbon) 2.DNA contains Thymine (A  T) RNA contains Uracil (A  U) 3.DNA is double stranded RNA is single stranded

14. RNA – RiboNucleic Acid 3 types of RNA 1.mRNA – messenger RNA *synthesizes proteins using DNA’s info 2.tRNA – transfer RNA *transfer appropriate AAs to build proteins 3.rRNA – ribosomal RNA *structural component of ribosome that is used to build proteins

15. TRANSCRIPTION The process of converting DNA’s genetic information into a more usable form (mRNA) There are 4 phases in transcription 1. Initiation 2. Elongation 3. Termination 4. Post-transcriptional Modifications **VERY SPECIFIC ENZYMES ARE USED**

16. PHASE 1: INITIATION A promoter is used to signal where RNA polymerase should bind to DNA strand – A promoter is a segment of DNA that is usually high in A & T They only have 2 H-bonds and will break open easily If RNA polymerase were to bind randomly, – correct genes & proteins wouldn’t be produced RNA polymerase will unwind DNA and begin to synthesize the complementary RNA strand

17. PHASE 2: ELONGATION RNA polymerase starts to build mRNA in the 5’  3’ direction – Starts as soon as RNA polymerase hits promoter **The promoter DOES NOT get transcribed** RNA polymerase uses one strand as a template is the TEMPLATE STRAND The strand not used for transcription is called the CODING STRAND

18. PHASE 3: TERMINATION mRNA will continue elongation until RNA polymerase hits the terminator sequence – Causes dissociation of RNA from DNA RNA polymerase is then free to bind to another promoter region

19. PHASE 4: Post-transcription mod’s mRNA can’t leave nucleus immediately after transcription ◦ Primary transcript The following 3 steps must first occur: 1.5’ cap of GTP is added to start of mRNA *this protects mRNA from enzyme attack which is inevitable in the cytoplasm

20. PHASE 4: Post-transcription mod’s mRNA can’t leave nucleus immediately after transcription ◦ Primary transcript 2. 3’ end obtains a poly-A tail (string of 200 As)

21. Introns vs. Exons The very interesting part of DNA is that 97% of it does nothing – Only 3% of our DNA code for genes that make proteins INTRONS = non-coding DNA EXONS = coding DNA

22. Introns vs. Exons If introns are not removed, proper protein folding will not occur – Leads to decreased function or death of proteins Introns are removed by spliceosomes Once removed, introns remain in nucleus – Broken down by enzymes to recycle parts

23. Errors with Transcription DNA replication used DNA polymerase I & III to act as proof readers to fix mistakes – Chances of mistakes are less likely Transcription has no quality control mechanism – Errors are more likely However, errors aren’t as detrimental because a gene is transcribed hundreds of times – If one copy of the gene has an error, it won’t have a huge effect Errors are a bigger problem in replication – error will be passed onto every cell