Expressing Genetic Information- a.k.a. Protein Synthesis

1. Expressing Genetic Information- a.k.a. Protein Synthesis

2. Gene- a series of nucleotides found on a strand of DNA that codes for a particular protein • Protein Synthesis- when the info stored on a gene is “read” and then used to make a protein • 3 Parts to Protein Synthesis: • 1. Transcription- creating RNA from DNA (occurs in the nucleus) • 2. Processing- When RNA is trimmed of its non-protein-coding nucleotides, made small enough that it can exit the nucleus • 3. Translation- The RNA assembles a specific sequence of amino acids to make the desired protein (occurs on the ribosome)

3. The Big Picture!! • There are 3 macromolecules involved in Protein Synthesis • DNA makes RNA • RNA codes for proteins • Proteins carry out ALL of the cell’s important functions and activities

4. Recall: There are Two Types of Nucleic Acids • DNA –Deoxyribonucleic Acid • RNA – Ribonucleic Acid • Similarities: • Nucleic acids • Store genetic material • Made up of strands of nitrogen bases • Follow some type of Base Pairing Rules

5. Differences Between RNA/DNA • DNA: • Double-stranded • Cytosine-Guanine • Adenine- Thymine • 5-carbon sugar = deoxyribose • Never leaves Nucleus • RNA: • Single-Stranded • Cytosine –Guanine • Adenine- Uracil • 5-carbon sugar = ribose • Can leave nucleus

6. RNA types • Three major types: (to be discussed further) • Messenger (mRNA) • Ribosomal (rRNA) • Transfer (tRNA)

7. mRNA • Temporary copy of a gene that encodes for a protein; • Provides the pattern that determines the order and types of amino acids making that protein. • Very unstable, cell WILL try to break it down unless it is processed • Contain codons (3-base sequence) • Precursor mRNA – exists in nucleus • Mature mRNA – genes to be copied by ribosome (has been processed) exists in cytoplasm

8. rRNA • Makes up 80% of RNA in cells • Used to make portions of ribosomes in cells in combination with proteins. • Can be free floating • Or attached to Endoplasmic reticulum (RER)

9. tRNA • Free floating in cell • Enzyme attaches ONE tRNA to ONE amino acid(charged tRNA) • tRNA ‘carries’ the amino acid to ribosome to add to the growing polypeptide (protein) chain • Contains an anti-codon sequence (3-bases as bottom of tRNA), which is complementary to each codon

10. The Genetic Code- •  The nucleotides serve as the four “letters” of the DNA “alphabet” (A,C,G, & T) • 3 nucleotides make a Codon (ex. AAG) • Codons code for an Amino Acid (AAG codes for lysine) • Amino Acids are the building blocks for proteins • Since there are 4 nucleotides, when three are grouped together, there are 64 possible triplet combinations (43 = 64) • However, there are only 20 amino acids so some amino acids have more than one codon (ex. GGA, GGC, and GGG all code for glycine)

11. Summary: DNA = permanent copy (like your hard drive) RNA = Temporary copy (similar to floppy copy) Leads up to two of the most important processes: Transcription and Translation animation

12. Part 1: Transcription The building of mRNA, tRNA, and rRNA (takes place in the NUCLEUS) STEPS: • Initiation: RNA polymerase binds to the gene’s promoter on the template strand of DNA(a specific sequence of the DNA that acts as a “start signal” for transcription) • RNA polymerase unwinds and separates the two strands of the DNA. • Elongation: RNA polymerase adds and then links complementary RNA nucleotides as it “reads” the gene”. • Termination: A “stop” signal on the DNA tells the RNA polymerase to detach from the DNA and release the RNA molecule. • Tutorial/Quiz

13. Part 2: RNA Processing • Before leaving the nucleus…….. • A cap (methyl-guanine or mG) is added by enzymes to the starting end of the mRNA molecule • A poly-A tail is added to the end of the mRNA • The molecule is spliced. Introns are removed (non-coding nucleotides) and exons remain.

14. RNA Processing Animation

15. Part 3: Translation Tutorial The assembly of a protein (occurs on the ribosome in the cytoplasm) mRNA leaves the nucleus through the nuclear pore and forms a functional ribosome with two ribosomal subunits, and a tRNA Initiation: The mRNA “start” codon AUG is oriented in a region of the ribosome called the P site where the tRNA molecule carrying methionine can bind to the start codon.

16. Translation- cont. (another animation) • 3. The codon in the area of the ribosome called the A site is ready to receive the next tRNA. • Elongation: Both the A site and the P site are holding tRNA molecules- each carrying a specific amino acid. A peptide bond forms between the adjacent amino acids • The tRNA in the P site detaches and leaves its amino acid behind • The tRNA in the A site moves to the P site. The tRNA carrying the amino acid specified by the codon in the A site arrives. • Termination: Steps 4-6 are repeated until a stop codon is reached.

17. Translation animation One more Translation animation

18. If a segment of DNA is: TAC AAA GTA ACT The mRNA strand would be: AUG UUU CAU UGA This would code for the following amino acids: Met Phe His Stop

19. Types of Mutations • Point Mutation- a change of one or just a few nucleotides in a gene. 3 Main Types of Point Mutations: • Substitution- • one nucleotide is replaced by another. • Insertion – • an extra nucleotide is added. • Deletion- • a nucleotide is omitted.

20. Mutations can be “Silent” • When a substitution mutation in a base pair does not result in a change in the sequence of amino acids in a protein

21. Mutations can be “Neutral” A change in a base pair results in an amino acid change, but the new amino acid has the same chemical properties as the old amino acid. (ie hydrophobic to hydrophobic; acidic to acidic)

22. Mutations can be “Missense” a mutation results a change in an amino acid where the new amino acids has a different property than the old amino acid. The protein with the new primary structure may have reduced or no activity.

23. Mutations can be “Nonsense” A mutation results in a new “stop” translation condon formed before the naturally occurring one. Translation is stopped prematurely and a shortened protein is made.

24. Mutations can result in “Frameshifts” A deletion or insertion of one base results in a change in the translational reading frame