Ch 5 – Protein Synthesis

1. Ch 5 – Protein Synthesis

2. Differences between DNA & RNA • Contains the sugar deoxyribose • Contains thymine • Is in the shape of a double helix • There is only 1 type of DNA • DNA can’t leave the nucleus • DNA is much longer • Only organic molecule that can replicate itself • Contains the sugar ribose • Contains uracil instead of thymine • Is a single strand • There are 3 types of RNA (m-RNA, r-RNA, t-RNA) • RNA leaves the nucleus • RNA is shorter • Needs a DNA template to be made DNA RNA

4. 3 types of RNA (ribonucleic acid) • m-RNA – messenger RNA – forms by transcription and copies the “message” of the DNA to take out to the ribosomes to instruct the formation of specific proteins • t-RNA – transfer RNA – responsible for transfering specific amino acids to the ribosome as an amino acid chain is assembled into a protein • r-RNA – Ribosomal RNA – a structural component of a ribosome- along with proteins it forms the ribosomes

6. Protein Synthesis at a glance This is what we did in the DNA lab!

7. The Central Dogma of Molecular Genetics

8. The Delivery Route • Messenger RNA (mRNA) is the blueprint for construction of a protein. • Ribosomal RNA (rRNA) is the construction site where the protein is made. • Transfer RNA (tRNA) is the truck delivering the proper amino acid to the site at the right time. tRNA

9. One Gene- One Enzyme Theory How Protein Synthesis came to be recognized as the Central Dogma of Molecular Genetics

10. Garrod’s Hypothesis • Archibald Garrod – (early 20th century) – studied the disease alkaptonuria and hypothesized that a defective enzyme caused an “inborn error of metabolism” along a reaction pathway - see pg. 234

11. One Gene- One Enzyme Hypothesis • Alkaptonuria – Black urine disease • Ear wax will turn red or black when exposed to air • Sweat is brown in color • Caused by a defective enzyme so the amino acid tyrosine doesn’t degrade properly and a toxic byproduct called homogentisic acid builds up

12. The sclera (whites) of the eyes become pigmented.

13. If there is an accumulation of Substance B then enzyme 2 must be defective.

14. Beadle and Tatum • 33 years later, they worked with bread mold Neurospora crassa & exposed spores to x-rays to create mutant strains. Through their experiments they concluded: a gene acts by directing the production of only one enzyme - called the one gene-one enzyme hypothesis.

15. Vernon Ingram • by using Beadle and Tatum’s work, he showed that sickle cell anemia results from alteration of a single gene . Many hereditary diseases have been traced to this type of alteration in just one gene.

17. Starting Protein Synthesis • DNA controls all the cell activities – largely by controlling the production of thousands of proteins – many of which are specific to each cell. • Protein synthesis begins when the DNA “unzips” – nucleotides of mRNA (messenger RNA) find their complementary base and join into a chain. A pairs with U and G pairs with C

18. TRANSCRIPTION • Once the chain is fused, the mRNA moves away from the parent DNA strand which then rejoins. • This completes the process of transcription (the message of the DNA has been TRANSCRIBED into the mRNA. • The mRNA now leaves the nucleus and goes out to a ribosome.

19. The Language of Genetics • Nucleotides are arranged in a linear sequence, some are several thousands long. • A single base does not contain a code. • Westandonguardforthee

20. Reading the DNA code • Rather three bases or TRIPLETS carry the code. Like a book that contains only three nucleotides (triplets). • From the 4 bases (A, U, C, G) there are 64 possibilities for triplet formation. • These three letter codes determine the exact order in which amino acids will be arranged in a specific protein molecule. Books containing Triplets!

21. UNZIPPING DNA • RNA polymerase (an enzyme) opens the part of the DNA to be transcribed. • Only one strand of DNA (called the template strand) is transcribed. • RNA nucleotides are available in the region of the chromatin and are linked together similar to the DNA process.

23. Codons • After RNA is transcribed it detaches itself and may be stored for a short time in the nucleolus or move immediately through the nuclear pores into the cytoplasm. • The RNA has the code for specific amino acids. • This type of RNA is called mRNA. • Like DNA there are 64 combinations of codons in mRNA.

25. Translation • mRNA acts as the template for the assembly of amino acids and the production of protein molecules. • Ribosomes help read(translate) the mRNA to. determine which amino acids are selected.

26. Amino Acid trains • Throughout the cytoplasm we find amino acids. • The sequence which they join together during synthesis is determined by the mRNA codons. • The amino acids are picked up and brought to the template using tRNA.

27. Anticodon • The tRNA carries the amino acids to the mRNA using coding that is the exact opposite of the code found on the mRNA known as an anticodon. • The anticodon tells the specific amino acid to come to the mRNA. • After the tRNA delivers the amino acid it moves to the cytoplasm.

31. Upon completion of the chain, the protein is released and passes into the cytoplasm where it is used.

32. Protein Synthesis Summary