100 percent bio flashcards

What causes cholera?

The bacterium Vibrio cholerae; symptoms are caused by cholera toxin, an AB5 toxin

How does cholera toxin's B subunit work?

The B subunits bind to the intestinal epithelial cell surface

How does cholera toxin's A subunit work?

The A subunit enters the cell and modifies a G protein (Gsα) via ADP-ribosylation

What does ADP-ribosylation of Gsα cause?

It prevents Gsα from hydrolyzing GTP to GDP, locking it in its active GTP-bound form

What happens after Gsα is locked active?

Adenylyl cyclase stays continuously activated, raising intracellular cAMP abnormally high

How does cAMP lead to diarrhea in cholera?

cAMP activates PKA, which phosphorylates CFTR, causing massive Cl- secretion; Na+ and water follow osmotically, causing watery diarrhea

What is protein phosphorylation?

The reversible addition of a phosphate group to a protein, catalyzed by a protein kinase

Where does the phosphate come from in phosphorylation?

ATP: Protein + ATP -> phosphorylated protein + ADP

Which amino acids are commonly phosphorylated?

Serine, threonine, and tyrosine, because they contain hydroxyl groups that accept the phosphate

What effects can phosphorylation have on a protein?

Shape, electrical charge, activity, binding partners, cellular location, stability, and membrane interaction

Does phosphorylation always activate a protein?

No, it can either activate or inactivate a protein depending on context

What is dephosphorylation?

Removal of a phosphate group by a protein phosphatase, returning the protein toward its original state

Why is phosphorylation useful in signaling?

It is rapid, reversible, acts as an on/off switch, creates binding sites, and allows signal amplification

What is a kinase cascade?

Sequential phosphorylation where one kinase activates another, amplifying and propagating a signal

What is splicing?

The removal of introns from pre-mRNA and joining of exons to form mature mRNA

What is the spliceosome made of?

A large complex of snRNPs (U1, U2, U4, U5, U6), each combining RNA and protein

What are the steps of spliceosome assembly?

U1 binds the 5' splice site, U2 binds the branch point, U4/U6 and U5 join and loop the intron, then U4 leaves to activate the catalytic core

What is the lariat structure in splicing?

A loop formed when the branch point adenosine attacks the 5' splice site, freeing exon 1 and forming a 2'-5' bond

How is mature mRNA formed after splicing?

The freed 5' exon attacks the 3' splice site, releasing the intron lariat and ligating the two exons together

What is the GPCR signaling pathway?

Ligand binds GPCR -> G protein exchanges GDP for GTP -> alpha subunit dissociates -> activates adenylyl cyclase or PLC -> second messengers (cAMP, IP3, DAG, Ca2+) activate PKA or PKC

What is the RTK signaling pathway?

Ligand binds RTK -> receptor dimerizes -> kinase domains autophosphorylate each other on tyrosines -> phosphotyrosines recruit signaling proteins -> activates Ras/MAPK and PI3K/Akt pathways

What is the main structural difference between GPCRs and RTKs?

GPCRs have seven transmembrane domains and use G proteins; RTKs are single-pass proteins with intrinsic kinase activity and no G protein