Protein Synthesis : DNA Transcription into mRNA and mRNA Translation into Protein

1. Protein Synthesis:DNA Transcription into mRNA andmRNA Translation into Protein

2. You understand that a gene is a segment of DNA that codes for a certain characteristic or trait. Ex) Blue eyes, Black hair, Dark skin, etc. A more complete understanding of what are gene is requires you to recall a bit of biochemistry. How do you get from a sequence of DNA to having black hair? To have black hair, your body must produce vast amounts of the dark pigment melanin. How do you make melanin? Your cells must have a lot of the right basic materials to build melanin and the enzymes needed to help carry out the synthesis of melanin. Similarly, most jobs the cell needs to carry out require the use of enzymes or other PROTEINS. So, to get from a gene to a specific trait requires the action of specific proteins. Proteins are a major workhorses of the cell, carrying out all sorts of specialized functions. The way genes work is every gene codes for the creation of a different protein, each with its own function! Gene X --> Protein X --> Trait X How does DNA work?What is a gene?

3. Where is the DNA in a eukaryotic cell? Where are proteins made? Problem: DNA is in the _____________ while proteins are made in the ________________ (at structures called ______________). In addition, DNA is too large to fit through the nuclear pores…frustrating! How do we get the information in our DNA (our genes) out to the cytoplasm so we can make proteins? Solution: Use a messenger! In the cell, that messenger is RNA (mRNA). nucleus From Gene to Protein cytoplasm ribosomes

4. Gene to Protein in Two Steps Step 1: Transcription(in nucleus) Make an copy of a segment of DNA (a gene) in the form of mRNA. Step 2: Translation (at ribosome) Translate the sequence of nucleotides in mRNA into a sequence of amino acids (a protein!). transcription translation

5. DNA  mRNA  Protein

6. Transcription: Copying DNA into RNA Steps of transcription: • Initiation: RNA polymerase binds to the promoter sequence at the start of a gene. • Elongation: RNA polymerase moves along the template strand, adding the RNA nucleotide with the correct complementary base. • Note that RNA is synthesized from its 5’ to its 3’ end. • Termination: RNA polymerase lets go of the DNA and releases the mRNA when it gets to the terminator sequence at the end of the gene. Promoter sequence Terminator sequence 5’

7. RNA polymerase uses complementary base-pairing to build RNA during transcription. (just like DNA polymerase does during DNA replication) 5’ 3’ RNA Template DNA

8. Let’s review transcription… • http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html# (Click on Protein Synthesis Link) • http://www.stolaf.edu/people/giannini/biological%20anamations.html • http://www.biostudio.com/d_%20Transcription.htm • http://www.dnalc.org/resources/3d/12-transcription-basic.html • http://www.johnkyrk.com/index.htm • http://207.207.4.198/pub/flash/26/26.html

9. Fromnucleic acidtoprotein:Translation

10. TRANSLATION: From nucleic acid to protein 20 • How is the information for making a protein encoded? • There are ___ different amino acids used to build proteins. But, there are only ___ RNA nucleotides! • If we read the RNA one base at a time, that would mean we could only code for ___ amino acids! For example: BaseAmino Acid • Adenine --> glycine • Cytosine --> tryptophan • Guanine --> alanine • Uracil --> phenylalanine Then we would have run out of bases to code for amino acids! 4 4

11. The Genetic Code • What if we “read” the RNA two bases at a time? How many unique two-letter code words could we make using four bases? AG GG CG UG AC GC CC UC AU GU CU UU AA GA CA UA • This give us 42 = ___ unique code words….Is this enough to code for all 20 amino acids? _____ • So what about three-letter code words? That should give us 43= ___ unique code words… Enough? 16 No! 64 Yes, more than enough…

12. The Genetic Code, Revealed: A set of three nucleotides in an RNA sequence, called a codon, codes for the addition of an amino acid in a polypeptide. GUG = _____ ACU = ________ UUA = ________ AUG = ________ UAA,UGA,UAG = __________ valine threonine leucine Methionine or START codon STOP codons

13. The Genetic Code(how to translate the 64 mRNA codons) The 3 letter Amino Acid abbreviations Phe = Phenylalanine Leu = Leucine Ile = Isoleucine Met = Methionine Val = Valine Ser = Serine Pro = Proline Thr = Threonine Ala = Alanine Tyr = Tyrosine His = Histadine Gln = Glutamine Asn = Asparagine Lys = Lysine Asp = Aspartic Acid Glu = Glutamic Acid Cys = Cysteine Trp = Tryptophan Arg = Arginine Gly = Glycine

14. The mechanics of translation: In the cytoplasm, three players come together… • The mRNA molecule which carries the information in its codons. • Another type of RNA molecule, transfer RNA (tRNA), matches up the right amino acid with the right mRNA codon. • The ribosome – composed of two subunits – is the structure which helps the mRNA and tRNA match up properly. It also catalyzes the synthesis of the new peptide (covalent) bonds between the amino acids. The ribosome is made of proteins and rRNA.

15. TRANSLATION

16. How tRNA anti-codons match up with mRNA codons

17. Protein translation in words • An mRNA molecule carries the information for building a protein (a sequence of amino acids) in the form of a sequence of nucleotides (codons). • Another type of RNA molecule, a tRNA molecule, has two important parts – an anticodon and a site where a corresponding amino acid is attached. • The tRNA anticodon base pairs with the corresponding mRNA codon, and then attaches its amino acid to the growing peptide chain. • The ribosome slides along the mRNA and the protein is assembled, one codon for one amino acid at a time…

18. Let’s look at the genetic code again… What tells translation to start and stop?

19. Let’s review translation… • http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html# (Click on Protein Synthesis Link) • http://www.stolaf.edu/people/giannini/biological%20anamations.html • http://www.biostudio.com/d_%20Transcription.htm • http://www.dnalc.org/resources/3d/15-translation-basic.html (realistic animation, real-time) • http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html • http://www.biostudio.com/demo_freeman_protein_synthesis.htm

20. DNA Mutations Biology

21. What if we mess up one of the nucleotides and change one of the codons? We get a mutation! • Mutations in DNA sequence: • Point mutations • Frame-shift mutations • Insertions • Deletions • These are mutations that cannot be seen in a karyotype

22. Point Mutation • A point mutation is a simple substitution in one base of the gene sequence. • This is equivalent to changing one letter in a sentence, such as this example, where we change the 'c' in cat to an 'h': Original The fat cat ate the wee rat. Point Mutation The fat hat ate the wee rat.

23. Point Mutations may or may not cause problems… • A point mutation can result in the wrong amino acid being incorporated into a protein (this could be disastrous for protein structure or not, depending on the amino acid substitution…Why?)

24. Silent point mutations don’t change the protein that is coded for by a gene • A point mutation could also result in a SILENT mutation, one that does not alter the amino acid that is incorporated, due to the redundancy of the genetic code. Example: The mutation that changes AUU to AUC still codes for the same amino acid, isoleucine. Thus, the polypeptide created would be identical to that made by the un-mutated form of the gene.

25. Frame-shift mutation • In a frame shift mutation, one or more bases are inserted or deleted, resulting in a change in the reading frame for the rest of the sequence • Because our cells read DNA in three letter "words", adding or removing one letter changes each subsequent word. This type of mutation can make the DNA meaningless and often results in a shortened protein. Original The fat cat ate the wee rat. Frame Shift (deleted the ‘t’ in ‘cat’) The fat caatet hew eer at.

26. What are some genetic disorders caused by DNA mutations?

27. Breast Cancer • Is the second major cause of cancer death in American women. • In 1994, two breast cancer susceptibility genes were identified: BRCA1 on chromosome 17 and BRCA2 on chromosome 13. • When an individual carries a mutation in either BRCA1 or BRCA2, they are at an increased risk of being diagnosed with breast or ovarian cancer at some point in their lives. • These genes participate in repairing radiation-induced breaks in double-stranded DNA. It is thought that mutations in BRCA1 or BRCA2 might disable this mechanism, leading to more errors in DNA replication and ultimately to cancerous growth.

28. Colon cancer • Colon cancer is one of the most common inherited cancers. • Among the genes found to be involved in colorectal cancer are: MSH2, MSH6 both on chromosome 2 and MLH1, on chromosome 3. • Normally, the protein products of these genes help to repair mistakes made in DNA replication. If the MSH2, MSH6 and MLH1 proteins are mutated and therefore don't work properly, the replication mistakes are not repaired, leading to damaged DNA and, in this case, colon cancer.

29. PHENYLKETONURIA (PKU) • An inherited error of metabolism caused by a deficiency in the enzyme phenylalanine hydroxylase (PAH). • Loss of this enzyme results in mental retardation, organ damage, and unusual posture. • Is caused by mutations in both copies of the gene for phenylalanine hydroxylase (PAH), found on chromosome 12.

30. Other Genetic Disorders: • Severe combined immunodeficiency syndrome (SCID) – “The boy in the bubble” • Duchenne muscular dystrophy • Marfan syndrome • Alzheimer disease (early onset) • Epilepsy • Parkinson’s disease (inherited form) • Hemophilia • Sickle-cell anemia