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Masaryk University

Biochemistry II

Exam Question$

Rebanil Ahmed & Khuram Ahmed

Typcs of membranę receptors

1.    lon channel receptors mediated by neurotransmitters in synapses - quick responses.

2.    G-protein linkod receptors - "G" because they bind GDP and GTP

- result in specific ligand binging in:

Stimulate/inhibit phospholipase C Stimulate/inhibit phosphodiesterase Stimulate/inhibit phosphodiesterase

3.    Receptors with enzyme activity - granylate cyclase

4.    Receptors activating non-receptor tyrosine kinase activity

G-proteins (response in a few minutes)

•    GTP/GDP binding proteins

•    Freely membranę bound (can move along the inner surface)

•    Participate in various types of second messenger production - Ali have a similar structure and mechanism of activation

•    Heterotrimers consist of subunits A, B, and Y

G-protein linked receptors

Ali have some common structural features:

1)    extracellular parts are slightly glycosylated, have accessory binding sites for agonist

2)    membranę parts: 7 a helical segments span the membranę, connected by intra and extracellular hydrophilic loops

3)    intracellular parts, which have the bingind site for a specific G-protein type G protein aętjygtjon

•    Resting State = a-unit has GDP attached

•    Hormone binds to extracellular part, makes a complex with the receptor, and GDP is phosphorylated to GTP

•    The a-GTP interacts with the effector enzyme - activate/inactivated enzyme which causes an inerease or decrease in secondary messenger signal

EXAMPLE: receptors with adenylate cyclase system

membranę bound receptor that catalyses ATP > cAMP + PPi

cAMP is a secondary messenger

Gs-protein stimulates adenylate cyclase, so the cAMP inereases cAMP activates PKA, which is used in phosphorylation reactions Gi-protein inhibits AC - opposite effect

•    Gq-protein stimulates phospolipase C

•    Gt-protein stimulates cGMP phosphodiesterase

IMasma membranę phosphatith linositols and the phosphoinositide lasiade, the role in signal transduction.

Inositol sources: exogenous (plant food) and endogenous (Glucose-6-phosphate)

General Medicine

4th semester

2009