Protein Synthesis

1. Protein Synthesis • Humans share most of the same protein families with worms, flies, and plants • Hair grows by forming new cells at the base of the root. As they move upward through the skin they are cut off from their nutrient supply and start to form a hard protein called keratin in a process called keratinization. As this occurs, the hair cells die. The dead cells and keratin form the shaft of the hair. • Fingernails grow about three or four times as quickly as toenails • Each hair grows about 1/4 inch/month and grows for up to 6 years. • The most expressive muscles are the facial muscles. We need 17 muscles to smile and 43 muscles to frown. • The most numerous are the skeletal muscles. When we walk for instance, we use 200 muscles.

2. Unit E Protein Synthesis It is expected that students will… • Demonstrate knowledge of the basic steps of protein synthesis, identifying the roles of DNA, mRNA, and ribosomes in the processes of transcription and translation. (p. 481-486)  • Determine the sequence of amino acids coded for by a specific DNA sequence, given a table of mRNA codons. (p. 481)  • Give examples of two environmental mutagens that can cause mutations in humans. (p. 490) • Use examples to explain how mutations in DNA affect protein synthesis and may lead to genetic disorders (p. 490)

3. VOCABULARY _____ Adenine _____ Anti-codons _____ Central Dogma _____ Code _____ Codon _____ Complementary Base _____ Cytosine _____ Elongation _____ Endoplasmic reticulum _____ Exocytosis _____ Gene _____ Gene mutation _____ Genetic code _____ Golgi body/Apparatus _____ Guanine _____ Helicase _____ Histones _____ Hydrolytic enzymes _____ Initiation _____ Initiation codon _____ Messenger RNA (mRNA) _____ Mutagen _____ Mutation _____ Peptide bonds _____ Peptidyl Transferase _____ Point mutation _____ Polypeptide _____ Polysome _____ Protein _____ Protein synthesis _____ Ribosomes _____ RNA Polymerase _____ Template _____ Terminator codon _____ Thymine _____ Transcription _____ Transfer RNA (tRNA) _____ Translation _____ Triplets _____ Uracil _____ Vesicle

5. Actin & Myosin: muscle proteins Keratin: nails, hair, horns, feathers Collagen: bones, teeth, cartilage, tendon, ligament, blood vessels, skin matrix Proteins Have 2 Main Functions • Structural: proteins help make up all structures in living things

6. Enzymes: lower the energy of activation to digest our food and to assist in cellular metabolism. Hemoglobin 2. Functional:other proteins help us to keep our bodies functioning properly and to digest our food.

7. Protein structure is determined by the genetic code in your DNA. The section of DNA that codes for one protein is called a gene A gene is a section of DNA that determines the 10sequence of amino acids in a protein. Therefore, the gene determines the shape and therefore, thefunction of the protein it codes for.

8. Central Dogma of Biology one gene one type of protein one function in the cell

9. (rRNA)

10. How Does Protein Synthesis Work? If the process of protein synthesis were a play, these would be the roles of all of the people involved The director who has the master plan DNA (genes) mRNA, tRNA, rRNA Three assistant directors The cast Amino acids The stage Ribosome Enzymes The stage crew

11. mRNA A T C G DNA The instructions from a gene are copied from DNA to messenger RNA (mRNA) in the nucleus Then, the mRNA moves through the nuclear pores and into the cytoplasm where the proteins are made. Act One: Transcription(Trans = across, cription = to write) The coded message of a gene on DNA has specific instructions on how to make each particular protein that our bodies need U A G C

12. The process of making mRNA is called TRANSCRIPTION

13. Watch the General Process Step 1: Helicase unwinds the DNA (starting at the promoter). Step 2: Complementary RNA base pairs attach to form the mRNA strand Step 3: RNA polymerase forms the RNA sugar-phosphate backbone and checks for mistakes Step 4: The RNA detaches & leaves the nucleus, & the DNA winds back up

15. Take a closer look(how the RNA strand forms)

16. Act Two: Translation ·The mRNA code is made up of groups of three nucleotide bases known as codons. Each codon codes for a specific amino acid. Eg. AGC = Serine (see text fig. 25.7, p.481) Eg. UGC = Cysteine AUG? CAU? CUU? AAA? UGA? GGC?

17. Why a Triplet Code? It takes 3 nucleotides on the mRNA to code for 1 a.a. Why? We must code for 20 different amino acids and there are only 4 letters (nucleotides) in the alphabet. With a single nucleotide, there are only 4 possible codes (41). For two nucleotides, there are only 16 possible codes (42). However, for three nucleotides there are 64 possible codes (43), and that is enough to code for the 20 amino acids.

18. mRNA codon chart (see text fig. 25.7, p.481)

19. Translation • The written code (codons) on mRNA is ‘translated’ into a specific amino acid sequence by ribosomes in the cytoplasm. • This is carried out with the help of relatively small transfer RNA (tRNA) molecules.

20. The tRNA also has a special sequence of 3 nucleotide bases known as an anticodon. There is at least one type of tRNA for each of the 20 amino acids. A tRNA molecule is a small piece of RNA that has a specific amino acid attached to it.

21. As the correct amino acids are brought to the ribosome by the tRNAs, they are joined together via dehydration synthesis to form the protein that the original DNA coded for.

22. Please note that there is more than one codon for each amino acid: mRNA codons: U C U G C C tRNA anti-codons: C G G A G A SERINE ALANINE Why do you think that is?

23. The Steps of Translation: 1. The mRNA molecule moves through a pore in the nuclear envelope and in to the cytoplasm. It joins with a ribosome and is translated one amino acid at a time. 2. ‘INITIATION’: the first codon on any mRNA molecule is called the ‘INITIATOR’. This codon is always AUG, which codes for the amino acid methionine. This is a message to START translation.  

24. ‘ELONGATION’: the ribosome’s job is to position the tRNA molecule onto the matching mRNA molecule. This makes it possible for a peptide bond to be formed between the amino acids attached to the tRNA molecules. These amino acids chains make up the protein. The enzyme that catalyzes this reaction is called PEPTIDYL TRANSFERASE.

25. The 1st tRNA leaves, the ribosome moves over one codon, and another tRNA brings the next amino acid. Another peptide bond is formed, and the process continues for the length of the mRNA strand.

26. 4. TERMINATION: The last codon on any mRNA molecule is called the ‘TERMINATOR’ codon, which is a message to STOP translation. This codon will be either UAA, UAG, or UGA. None of these have a matching tRNA anticodon, so when no more tRNA’s attach, the ribosome, protein, and mRNA detach from each other.

27. What does translation look like?

28. anticodon CRACKING THE GENETIC CODE * Master Strand of DNA DNA STRAND (one gene) A T G / T G C / G G C / G C T / T G A T A C / A C G / C C G / C G A / A C T codons mRNA STRAND A U G / U G C / G G C / G C U / U G A tRNA STRAND U A C / A C G / C C G / C G A / A C U

29. o o o o 1 2 3 4 AMINO ACID SEQUENCE Methionine---Cysteine---Glycine---Alanine---Stop

30. LET’S REVIEW… • PROTEIN SYNTHESIS ANIMATION • http://www.pbs.org/wgbh/aso/tryit/dna/# http://www.wisc-online.com/objects/index_tj.asp?objID=AP1302

32. A BAD NIGHT AT THE THEATRE Question: What if something goes wrong during translation? Answer: MUTATION • A change in the nucleotide sequence of DNA • When the bases (‘letters’) change, the wrong amino acids are used to make the protein. • The protein will NOT be able to do its job.

33. There are 2 types of MUTATION: • Chromosomal mutations: a mutation of all or part of a chromosome. • This usually involves MANY GENES, and therefore, MANY PROTEINS. • Example: Down’s syndrome. • Gene mutations: a mutation that occurs within a gene at some point along a chromosome. This mutation is only a change of 1 or a few ‘letters’ (nitrogenous bases). • It usually only affects ONE GENE, and therefore, ONE PROTEIN. • Example: Sickle cell anemia.