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USMLE

New FA Biochem 1

QuestionAnswer
What does it mean for genetic code to be commaless? Read from a fixed starting point as a continuous sequence of bases
What does it mean for genetic code to be non-overlapping? Read from a fixed starting point
What does it mean for genetic code to be universal? Genetic code is conserved throughout evolution
What are the properties of the genetic code? 1. Unambiguous. 2. Degenerate/redundant. 3. Commaless/nonoverlapping 4. Universal
When is genetic code not commaless/nonoverlapping? In some viruses
What are exceptions to universality of genetic code? 1. Mitochondria 2. Archaebacteria 3. Mycoplasma 4. Some yeasts
Name that mutation: Same amino acid, often with a base change in 3rd position of codon Silent mutation
What kind of mutation is called: silent Same amino acid, often with a base change in 3rd position of codon
What mutation is masked by tRNA wobble? Silent mutations
Name that mutation: Changed amino acid whose structure is dissimilar to proper amino acid Missense mutation (not conservative)
Name that mutation: Changed amino acid whose structure is similar to proper amino acid Conservative missense mutation
What kind of mutation is called: missense Amino acid is changed. If the structure of the new amino acid is similar to the original, it is called conservative.
Name that mutation: Change resulting in early stop codon Nonsense mutation (Mnemonic: Stop the nonsense!)
What kind of mutation is called: nonsense Change resulting in early stop codon (Mnemonic: Stop the nonsense!)
Name that mutation: change resulting in misreading of all nucleotides downstream, usually resulting in a truncated protein Frame shift mutation
What kind of mutation is called: frameshift change resulting in misreading of all nucleotides downstream, usually resulting in a truncated protein
Mutations ordered by decreasing severity of damage 1. Nonsense 2. Missense 3. Silent
Eukaryotic genome: single/multiple origins of replication multiple
Prokaryotic genome: single/multiple origins of replication single
Eukaryotic genome: Trigger for replication Consensus sequence of AT-rich base pairs
Prokaryotic genome: Describe DNA replication Continuous bidirectional DNA synthesis on leading strand and discontinuous (Okazaki fragments) on lagging strand
Enzyme function: DNA topoisomerases Create a nick in the helix to relieve supercoils
DNA Topoisomerase I: Mechanism cuts one strand, passes the other through it then reanneals the cut strand
DNA Topoisomerase II: Mechanism cuts both strands, and passes an unbroken double strand through it then reanneals the cut strand
Enzyme function: Primase Makes an RNA primer on which DNA polymerase III can initiate replication
DNA polymerase III: Mechanism 1. Adds deoxynucleotides to the 3' end until it reaches primer of preceding fragment 2. 3' to 5' exonuclease activity "proofreads" each added nucleotide
DNA polymerase III: Which direction does it read? 3' to 5'
DNA polymerase III: Which direction does it write? 5' to 3'
DNA polymerase III: Which direction does it proofread? 3' to 5'
Enzyme function: DNA polymerase III Elongates the chain
Enzyme function: DNA polymerase I Degrades RNA primer and fills in the gap with DNA
DNA polymerase I: Which direction does it read? 3' to 5'
DNA polymerase I: Which direction does it write? 5' to 3'
DNA polymerase I: Which direction does it proofread? 5' to 3'
Enzyme function: DNA helicase Separates the two strands of DNA into single strands allowing for replication to occur. The position of these separated strands is called the replication fork.
Types of DNA repair - Single stranded: 1. Nucleotide excision repair 2. Base excision repair 3. Mismatch Repair
Types of DNA repair - Double stranded: 1. Nonhomologous end joining
Nucleotide excision repair: Mechanism 1. Specific endonucleases release the oligonucleotide containing damaged bases 2. DNA polymerase and ligase fill and reseal the gap, respectively
In what condition is nucleotide excision repair mutated? Xeroderma pigmentosa (dry skin with melanoma and other cancers)
Base excision repair: Mechanism 1. Specific glycosylases recognize and remove damaged bases 2. AP endonuclease cuts DNA at apyrimidinic site 3. Empty sugar is removed 4. Gap is refilled and resealed
Mismatch repair: Mechanism 1. Unmethylated, newly synthesized string is recognized 2. Mismatched nucleotides are removed 3. Gap is refilled and resealed
In what condition is mismatch excision repair mutated? Hereditary Nonpolyposis Colon Cancer
Nonhomologous end joining: Mechanism Brings together two ends of DNA fragments (no requirement for homology)
Define operator of gene expression Site where repressors bind
Created by: Asclepius
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