Biochem Chap 2 Flashcards
What are the 5 primary proteins of the cytoskeleton and ECM?
Actin, tubulin, collagen, elastin and keratin. Actin and tubulin primarily found in cytoskeleton and collagen, elastin and keratin make up ECM.
Describe actin and treadmilling
Actin - most abundant protein in eukaryotic cells - assembles into long polymers- microfilaments - have polarity between both ends - positive and negative end - barbed and pointed ends. The + end is where new actin monomers attack and minus where monomers dissociate. This association and dissociation is regulated by ATP. When ATP is bound, the actin monomer attaches, when hydrolyzed, it detaches. This cycle is treadmilling - causes apparent motion of actin strands across cytoplasm
What does actin play role in? What does it associate with?
Actin plays role in muscle movement along with motor protein myosin - creates movement. The myosin heads interact with actin filaments to pull actin close and shorten sarcomere - causing muscle contraction.
Describe the crossbridge cycle.
The first step of crossbridge cycle involves ATP binding to myosin, myosin relaxes grip to actin and dissociates from microfilament. Myosin then hydrolyzes ATP causing myosin head to swing back and bind to microfilament. Once myosin releases Pi it starts its power stroke - re-cocking of head while attached. Once finished, ADP is released and cycle restarts.
How does tubulin form microtubules?
Inside cell, alpha and beta forms of tubulin monomers assemble into long polymers called microtubules
Describe a microtubule
inside is hollow. Tubulin monomers associate into heterodimers of alpha and beta tubulin. They have a polar structure with positive and negative ends. Alpha is exposed at negative and tends to be located at centrosome of cell. Beta at positive - edges of cell.
Describe collagen structure and purpose
Collagen is helical fiber made of 3 interwoven strands and composes a large portion of ECM in connective tissue. Provides structure to tissues, bones, ligaments and tendons.
Describe elastin purpose
structure to body, long and coiled, when stretched become more linear while preserving cross-linked structure of ECM. Allows tissues to stretch and snap back without damage.
Describe keratin purpose
not directly in ECM but concentrated in epithelial cells - provides cells structure and stability to protect and provide hard barrier - largely found in hair and fingernails.
What are kinesins and dyneins?
Kinesins and dyneins use polarity to walk along microtubules. They are motor proteins - move by hydrolyzing ATP - move in stepwise manner. Kinesins travel toward positive end - periphery of cell and dyneins toward the negative - nucleus. Vesicles and organelles attach to their heads. Responsible for bulk of active molecular transport within cells.
Describe a GPCR
G-protein coupled receptor is transmembrane receptor that changes conformation when ligand binds - activates nearby G-protein on inside of cell (active when bound to GTP and inactive when GTP is hydrolyzed). The G-protein is trimeric - alpha beta and gamma subunits. Alpha hydrolyzes GTP and beta and gamma have other functions. When GTP binds, the 3 subunits dissociated to execute their functions. Also called 7-transmembrane receptors as they span membrane with 7 diff hydrophobic regions.
What is a hormone?
slow-acting chemical messenger that travels through blood. Two types: steroid and peptide
What is a peptide hormone?
hormones that are peptides ie. oxytocin, insulin, FSH. They bind to receptors on cells and cause conformational changes to receptor. Steroid hormones directly pass through membrane
Describe the HPG axis
Peptide hormones are important in HPG axis (hypothalamic-pituitary-gonadal axis). Hypothalamus produces gonadotropin-releasing hormone (GnRH) - acts on anterior pituitary gland - releasing LH and FSH - in males this stimulates testosterone synthesis and spermatogenesis. In females they stimulate estrogen and progesterone production to promote ovulation and menstrual cycle.
What is the strength of the peptide hormone signal related to?
Strength of peptide hormone signal is directly related to its ability to bind to its receptor: R+H ↔ RH Where R is receptor, H is peptide hormone and RH is bound system.
