Week 1 Flashcards
What happens to the Lac Operon when you have high glucose levels?
When glucose is high, cAMP is low so cAMP can no longer bind CAP. CAP = gene activator protein. Thus, the gene is operon is turned off.
Explain what happens to the Lac Operon when Lactose levels are high.
When lactose levels are high, allolactose levels are high. Allolactose binds to the repressor protein and removes it from the DNA.
What two things need to happen for the Lac Operon to be turned on?
Glucose level must be low (high cAMP and high CAP so activator CAP is bound to DNA)
Lactose level must be high (high allolactose which binds to the Lac repressor protein and frees it from the DNA, allowing the DNA to be transcribed)
What happens if you have high glucose and high lactose with a bacterial cell that has the Lac Operon?
First the bacteria will use the glucose and then it will use the lactose. First the glucose will prevent the production of cAMP and CAP and prevent the activator from binding to the DNA. Then when glucose is no longer present, the activator will bind and (allolactose from lactose removes the repressor) and then the DNA will be transcribed. The first gene, Lac Z, will produce a produce that splits lactose into glucose and galactose
What molecule exhibits positive cooperativity?
Oxygen binding to hemoglobin. This is when an oxygen molecule binds to a single heme (at this pt. hemoglobin has relatively low affinity for oxygen) and then makes the oxygen affinity increase, allowing the second molecule to bind more easily and the third and fourth even more easily. This behavior makes the affinity curve for hemoglobin more sigmoidal, rather than hyperbolic - like myoglobin’s.
What are the shapes of hemoglobin and myoglobin’s affinity curves?
Hemoglobin - sigmoidal
Myoglobin - hyperbolic
Eukaryotic Translation: eEF-1
One of the factors that carries out elongation. It has an alpha and beta-gamma subunit. It mediates the entry/binding of the aminoacyl tRNA to the binding site [Like EF-Tu]
Eurkaryotic Translation Factor: eEF-2
Catalyzes the translocation of the tRNA and mRNA down the ribosome at the end of each round of polypeptide elongation [EF-G]
Xeroderma Pigmentosum
- Genetically heterogeneous, autosomal recessive disease of defective DNA repair. Causes extra sensitivity to UV radiation.
- Patients have shortened life span (less than 30 yrs) and are more susceptible to skin cancers along with brain, lung and GI cancers
- Most XP mutation are found in the genes that code for NER (nucleotide excision repair) like exonucleases
- Associated with families that inbreed - India caste system
NER (nucleotide excision repair) [DNA repair mech./mutation associated with Xeroderma Pigmentosa]
- Usually mutations cause by dimers (pyrimidine or thiamine)
1. After mutation is detected, then excision nuclease cuts out a chunk of DNA strand and DNA helicase helps unwind things
2. Then DNA polymerase reads the correct base and adds the correct pair along with DNA ligase
Base Excision Repair
Cuts out single base and puts in correct one
- Deaminated C is detected
- Uracil is removed by Uracil DNA glycosylase
- AP Endonuclease and phosphodiesterase remove the sugar phosphate (backbone)
- DNA polymerase adds new nucleotides, DNA ligase seals the nick
[Strand-directed] Mismatch Repair
- Happens after DNA synthesis mechanisms are all done
1. There is an error in the strand that is detected and bound by mismatch proofreading proteins (MutS)
2. Mut L is bound to MutS and works by scanning the DNA nearby for a nick.
3. When the nick is found, MutL triggers the degradation of the nicked strand all of the way back through the mismatch.
What is the order of events in RNA polymerase mediated transcription in bacteria?
- Sigma factor binds to the polymerase complex
- The complex binds to the promoter
- DNA is unwound and transcription begins
What is the rho factor?
rho is a termination factor that binds late in the transcription process
Wobble Base Pairing
Allows some mismatches at the third position of the codon. tRNAs do not require accurate base-pairing at all three positions of the mRNA codon.
