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USMLE

New FA Biochem 2

QuestionAnswer
What is on the 5' end of a nucleotide Triphosphate
What is on the 3' end of a nucleotide Hydroxyl group
True/False: DNA is synthesized 5' to 3' True
True/False: DNA is synthesized 3' to 5' False
True/False: RNA is synthesized 5' to 3' True
True/False: RNA is synthesized 3' to 5' False
True/False: Protein synthesis proceeds 5' to 3' True
True/False: Protein synthesis proceeds 3' to 5' False
Types of RNA and their important qualities ”Massive, Rampant, Tiny” mRNA is the largest type rRNA is the most abundant type tRNA is the smallest type
What does eukaryotic RNA polymerase I make? rRNA
What does eukaryotic RNA polymerase II make? mRNA
What does eukaryotic RNA polymerase III make? tRNA
Which RNA polymerase makes rRNA? eukaryotic RNA polymerase I and prokaryotic RNA polymerase
Which RNA polymerase makes mRNA? eukaryotic RNA polymerase II and prokaryotic RNA polymerase
Which RNA polymerase makes tRNA? eukaryotic RNA polymerase III and prokaryotic RNA polymerase
True/False: RNA polymerase proofreads. False
True/False: RNA polymerase does not proofread. True
Special points about RNA polymerase II 1. Opens DNA at promoter site 2. Inhibited by alpha-amanitin
What does alpha-amanitin do? Inhibits RNA polymerase II leading to hepatic necrosis
mRNA initiation codons 1. AUG (inAUGurates protein synthesis) 2. GUG (rarely)
What does the mRNA initiation codon code for? Methionine in eukaryotes. formyl-methionine in prokaryotes.
mRNA stop codons 1. UGA (U Go Away) 2. UAA (U Are Away) 3. UAG (U Are Gone)
Define promoter of gene expression. Site where RNA polymerase and multiple other transcription factors bind to DNA upstream from gene locus
What characterizes a promoter of gene expression? AT-rich upstream sequence with TATA and CAAT boxes
What is the result of promoter mutation? Dramatic decrease in amount of gene transcribed
Define enhancer of gene expression. Stretch of DNA that alters gene expression by binding transcription factors. May be located close to, far from, or even within the gene whose expression it regulates.
Define operator of gene expression Site where repressors bind
What is alternative splicing? Rearrangement of exons to make unique proteins
What is the sequence of mRNA splicing? 1. Primary transcript combines with snRNP ("snerp") to form spliceosome 2. Lariat-shaped intermediate is generated 3. Lariat is released to remove intron precisely and join two exons
Where and when does eukaryotic RNA processing happen? In the nucleus after transcription
What is the initial RNA transcript called? heterogeneous nuclear RNA (hnRNA)
What are the steps in processing hnRNA to make mRNA? (Note: This is more than splicing.) 1. Capping on 5' end with 7-methyl-G 2. Polyadenylation on 3' end (approximately 200 As) 3. Splicing out of introns
How many nucleotides does tRNA contain? 75 to 90 nucleotides
What sequence does every tRNA share at the 3' end? CCA along with a high percentage of chemically modified bases
Amino acid binding to tRNA: Where (on the tRNA) and how? Where: 3' end How: Covalently
What is the enzyme involved in processing tRNA Aminoacyl tRNA synthetase (uses 1 ATP)
Aminoacyl tRNA synthetase: Mechanism 1. Scrutinizes amino acid before it binds to tRNA 2. Binds AMP-amino group to 3' end of tRNA 3. Scrutinizes amino acid again. If incorrect, bond is hydrolyzed.
What is wrong with a mischarged tRNA Reads the regular bond but inserts wrong amino acid.
Which position on the codon is the wobble position? 3rd position
Created by: Asclepius