Molecular Biology III Flashcards
What is the pathology associated with an adenosine deaminase deficiency?
Excess ATP and dATP imbalances nucleotide pool via feedback inhibition of ribonucleotide reductase. This prevents DNA synthesis and decreases lymphocyte count; autosomal recessive (p.66)
What is the clinical presentation of an adenosine deaminase deficiency?
SCID, an autosomal recessive condition (p.66)
What is the pathology associated with Lesch-Nyhan syndrome?
Defective purine salvage owing to absence of HGPRT which converts hypoxanthine to IMP and Guanine to GMP. This results in excess uric acid production and de novo purine synthesis. X-linked recessive (p.66)
What are some clinical features of Lesch-Nyhan syndrome?
Retardation, self mutiliation, aggression, hyperuricemia, gout, choreoathetosis (p.66)
Which amino acids are only coded for by one codon?
Methionine (AUG), Tryptophan (UGG) (p.66)
What is a nonsense DNA mutation?
Change resulting in an early stop codon (p.67)
Name 3 differences between prokaryotic and eukaryotic DNA replication.
1.) Prokaryotes have a single origin of replication; eukaryotes can have many; 2.) Prokaryotes contain DNA Pol III (which elongates leading strand by adding deoxynucleotides to the 3’ end; 3.) Prokaryotes contain DNA Pol I which degrades RNA primer and replaces it with DNA (p.68)
What is the function of single strand binding proteins?
Prevents strand from reannealing (p.68)
What is the function of DNA topoisomerases?
To create nicks in the DNA helix to relieve supercoils created during replication (p.68)
Which class of drugs inhibit prokaryotic topoisomerase II (or DNA gyrase)?
Fluoroquinolones (p.68)
What is the function of primase?
To make an RNA primer on which DNA polymerase III can initiate replication (p.68)
What is DNA Polymerase III?
Prokaryotic enzyme that elongates the leading strand by adding deoxynucleotides to the 3’ end. It elongates the lagging strand until it reaches the primer of the proceeding fragment. Contains 3’–> 5’ exonuclease activity and proofreads each added nucleotide. Synthesis: 5’ –> 3’; Proofreading: 3’ –> 5’ exonuclease (p.68)
What is DNA Polymerase I?
A prokaryotic enxyme that degrades RNA primer and replaces it with DNA. It has the same functions as DNA Pol III but also excises RNA primer with 5’ –> 3’ exonuclease (p.68)
What is DNA ligase?
Catalyzes the formation of phosphodiesterase bonds within a strand of double stranded DNA; joins Okazaki fragments (p.68)
What is telomerase?
An enzyme that adds DNA to the 3’ end of chromosomes to avoid loss of genetic material with every duplication (p.68)
Describe the process of nucleotide excision repair.
Single stranded DNA repair system where specific endonucleases release oligonucleotide containing damaged bases; DNA polymerase and ligase fill and reseal the gap (p.69)
What types of errors are corrected by nucleotide excision repair (NER)?
Repairs bulky, helix distorting lesions (p.69)
What condition is caused by a mutation in nucleotide excision repair?
Xeroderma Pigmentosum –> prevents repair of pyrimidine dimers due to UV light exposure (p.69)
Describe the process of base excision repair.
Single stranded DNA repair system where specific glycosylases recognize and remove damaged bases and apurinic/apyrimidinic enconucleases cuts DNA at both apurinic and apyramidinic sites, removing the empty sugar and filling/ resealing the gap. This is important in the repair of spontaneous/ toxic deamination (p.69)
Describe the process of mismatch repair.
Single stranded DNA repair system where newly synthesized strand is recognized, mismatched nucleotides are removed, gap is filled and resealed (p.69)
What condition is caused by a mutation in Mismatch Repair?
Hereditary Nonpolyposis Colorectal Cancer (HNPCC) (p.69)
Describe the process of non-homologous end joining.
Double stranded DNA repair system where 2 ends of DNA fragments are brought together to repair double stranded breaks. There is no requirement for homology (p.69)
What condition is caused by a mutation in Nonhomologous end joining?
Ataxia Telangiectasia (p.69)
How is protein synthesis terminated?
Stop codon is recognized by the release factor and the completed protein is released from the ribosome (p.73)
Name two classes of antibiotics that act as protein synthesis inhibitors at the 30s subunit.
1.) Aminoglycosides –> bind 30s and inhibit formation of initiation complex. Cause mRNA misreading; 2.) Tetracyclines –> block aminoacyl tRNA from entering the acceptor site (p.73)
Name two classes of antibiotics that act as protein synthesis inhibitors at the 50s subunit.
- Chloramphenicol –> binds 50S and inhibits peptidyl transferase; 2.) Macrolides –> bind 50S and prevent release of uncharged tRNA after it has donated its amino acid (p.73)
List three possible posttranslational modifications.
1.) Trimming (removal of N or C terminal peptides); 2.) Covalent Alterations (phosphorylation, glycosylation, hydroxylation, methylation, acetylation); 3.) Proteasomal degradation (attachment of ubiquitin to defective proteins to tag them for breakdown) (p.73)
