Presentation on theme: "Expressing Genetic Information- a.k.a. Protein Synthesis"— Presentation transcript:
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 protein3 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 nucleus3. 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 SynthesisDNA makes RNARNA codes for proteinsProteins carry out ALL of the cell’s important functions and activities
4 Recall: There are Two Types of Nucleic Acids DNA – Deoxyribonucleic AcidRNA – Ribonucleic AcidSimilarities:Nucleic acidsStore genetic materialMade up of strands of nitrogen basesFollow some type of Base Pairing Rules
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 processedContain codons (3-base sequence)Precursor mRNA – exists in nucleusMature 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 floatingOr 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) chainContains 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 proteinsSince 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 Translationanimation
12 Part 1: TranscriptionThe 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 moleculeA poly-A tail is added to the end of the mRNAThe molecule is spliced. Introns are removed (non-coding nucleotides) and exons remain.
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 tRNAInitiation: 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 acidsThe tRNA in the P site detaches and leaves its amino acid behindThe 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 The mRNA strand would be: AUG UUU CAU UGA If a segment of DNA is:TAC AAA GTA ACTThe mRNA strand would be:AUG UUU CAU UGAThis would code for the following amino acids:Met Phe His Stop
19 Types of MutationsPoint 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