click below
click below
Normal Size Small Size show me how
USMLE
New FA Biochem 2
Question | Answer |
---|---|
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 |