bio 3.1

Prokaryotic v. Eukaryotic mRNA

Prokaryotic mRNA contains multiple coding sequences (due to operons) [adjacent structural genes transcribed as a unit into a single mRNA molecule] Eukaryotic mRNA contains a single coding sequence

13.5. Describe the critical features of the genetic code.

Each amino acid is specified by a 3 nucleotide sequence: the codon Each Condon specifies a particular AA (4) AUG specifies AA methionine is the "start codon" because it is the first codon in almost all prokaryotic and eukaryotic proteins. 64 posible codons (4^3) but these code for only 20 different meaning more than one codon can specify a given AA's => genetic codes redundant of the 64 only 61 specify an amino acid; three represent "stop" codons which are important for terminating TRANSLATION Genetic code is universal showing ancestry

13.4. Compare eukaryotic transcription to prokaryotic transcription.

Eukaryotic Transcription: Occurs in nucleus because this is where DNA is located Three different RNA polymerases (opposed to 1) RNA polymerase II transcribes mRNA and best understood out of all three transcribing Promoter position and sequence differs with the promoter being just upstream and specific nucleotide sequence are different. Also way RNA polymerase binds to the promoter is more complicated Series of transcription factors recruit and activate RNA Pol II Termination sites are not well defined Primary transcripts are processed to produce mature mRNA

13.3. Summarize the initiation, elongation, and termination phases of prokaryotic transcription.

Initiation: Promoters accurate initiation of transcription requires two sites: promoter site (forms a recognition and binding site for the RNA polymerase) and the actual start site. Polymerase also needs a terminator to end transcription. starts by sigma subunit recognizes promoter and positions RNA polymerase just upstream of the start site. Next, DNA is unwound ahead of the start site. The helix is opened at -10 region, and transcription begins at the start site. forming RNA molecule is antiparallel to the template strand. At this point transcription bubble formed and we transition to elongation. Elongation: adds successive nucleotides. The region containing the RNA polymerase, the DNA template, and the growing RNA transcript is called the transcription bubble because it contains a locally unwound "bubble" of DNA. Bubble is moving left to right. RNA polymerase unwinds DNA ahead of the bubble and rewinds DNA behind the bubble. Termination: end of of a bacterial transcription unit is marked by terminator sequences that "stop" to the polymerase. reaching these sequences causes the the formation of phosphodiester bonds to stop. The terminator sequence is when the RNA base pairs with itself to create a "hairpin" and the hairpin structure disrupts DNA/RNA/RNA pol interaction.

13.6. Summarize the initiation, elongation, and termination phases of translation.

Initiation: Recognition of Translation Start Site PROKARYOTES 1. Small subunits binds Ribosome Binding Sequences (RBS) on mRNA to determine translation start site RBS places AA at or about the start site 2. Initiator tRNA-N-formylMethinonine binds to P site of small subunit. (has the chemically modified methionine as first initiator.) 3. Large subunit binds and complex contains the start codon 4. A Site opens to receive second tRNA-AA => shift to Elongation. *once the complex of mRNA, initiator tRNA, and small ribosomal subunit is formed, the large subunit is added, and translation can begin. Initiator tRNA is bound to the P site w/ A site empty.* EUKARYOTES basics the same except initiator tRNA-Met and bringing in NORMAL methionine Small subunit binds 5' cap to determine translation start site. Alines start at the P site of the ribosome. ELONGATION: adds successive AA's 1. Matching tRNA anticodon w/ mRNA codon incoming tRNA-AA arrives at A site 2. Peptide Bond formation catalyzed by rRNA of large subunit at the same time P site AA released from its tRNA 3. Translocation of the ribosome. Ribosome moves 1 codon in 3' direction E site tRNA released, a site open to accept next tRNA-AA TERMINATION: requires accessory factors 1.continues until stop codon (UAA, UAG, UGA) is translocated into A site) 2. do not bind to tRNA Release factor recognizes stop codon => triggers release of polypeptide from P site tRNA 3. Ribosome moves 1 "codon" & machine disassembles

13.2. List the functions of the different types of RNA.

Messenger RNA (mRNA) "Messenger Hypothesis" codes for protein during translation; intermediate in the flow of information DNA transported out of eukaryotic nucleus to cytoplasms for processing. Ribosomal RNA (rRNA) ribosome components, catalyze peptide bonds during translation. multiple forms and is critical to the function of the ribosome. Transfer RNA (tRNA) Intermediary between mRNA and amino acids covalently attached to codon at the other. Act to interpret information in mRNA and help position the amino acids on the ribosome. Adaptors between mRNA and deliver correct amino acids from synthesis. Small nuclear RNA (snRNA) pre-mRNA splicing (non coding sequences removed from RNA); part of the machinery that is involved in nuclear processing of eukaryotic "pre-mRNA" Micro-RNA (miRNA) regulates gene expression.

13.7. List the different types of DNA mutations and predict the effects of each.

Point Mutations alters a single base 1. Base substitution Silent Mutation: AA unchanged Missense Mutation: Changes AA Nonsense mutation: changes to stop codon (premature termination) 2. Frameshift mutation: addition or deletion of base Alters downstream reading frame often with major consequences Some mutations create extensive changes in chromosome structure. Deletion: part of chromosome is lost Duplication: part of chromosome is copied Inversion: part of chromosome in reverse order Translocation: part of chromosomes is moved to new location EFFECTS *alter gene and Protein sequence and are the starting point for evolution*

13.1. Distinguish between transcription and translation.

Transcription: DNA-to-RNA because it produces an exact copy of the DNA. Messenger RNA serves as an intermediate in the production of protein molecules. Translation: RNA-to-protein step because it requires translating from the nuclei acid to the protein "languages."