cell bio exam 3

ECM

consists of secreted proteins and polysaccharides

basal lamina

thin sheetlike layer around cells

collagen

most abundant protein in ecm

elastin

forms elastic fibers on a cross linked network, can stretch and relax under tension, found in stretchy structures

hyaluronic acid

polysaccharide called glycosaminoglycan (GAG)

adhesion proteins

connect matrix proteins together or to cells

collagen structure

triple helix of protein chains, repeats of G-X-Y, commonly G-P-hydroxyproline, lack of proline modification causes scurvy, assembled in ER

collagen fibrils

staggered array of collagen triple helicesco

collagen fibers

aggregation of collagen fibrils assembled in ECM

mutations in collagen

weakens bone, sequence mutations are dominant and folding mutations are recessive

type IV collagen

cross-linking collagen, G-X-Y repeats interrupted by non-helical sections for flexibility

glycosaminoglycans (GAGs)

repeating units of disaccharides, one sugar is N-acteyl-(gluco/galacto)samine and other is acidic, some modified by sulfate groups, all but hyaluronic acid are linked to proteins

proteoglycan

core protein modified by up to 100 GAGs other than hyaluronic acid, GAG chains can be 100 sugars long, negatively charged from sulfate groups, can interact with + ions and water

GAG and PG function

strong neg charge pulls water into ECM, important for cartilage structure and function and joint lubrication. also sponges for growth factors

fibronectin

enormous long dimeric glycoprotein which links components of ECM to each other and cell, has binding sites for collagen, proteoglycans, and integrins

laminins

T-shaped heterotrimers that self assemble into mesh-like networks, bind proteins and proteoglycans at cell surface

integrins

transmembrane proteins with alpha and beta subunits which connect ECM and cytoskeleton to cell membrane

selectins

adhesion proteins which recognize carbohydrates in leukocytes, endothelial cells, and platelets with transient binding, first step to allow leukocytes to enter tissue

cadherin

adhesion proteins which recognize other cadherins, link epithelial cells to one another as adherens junctions, link actin to extracellular space, loss of function is step in metastasis

desmosomal cadherins (desmoglein and desmocollin)

adhesion proteins which link intermediate filaments to extracellular space, form desmosomes

tight junctions

prevent passage of molecules between cells of epithelial sheets, separates apical and basolateral domains

gap junction

permits small molecule exchange between cells

electrical synapses

coordinate neural activity and heart muscle signaling with gap junctions

loss of Cx32 function

causes CMT disease where loss of Cx32 gap junctions causes demyelination and loss of muscle stimulation

tunneling nanotubes

long and thin protrusions which seem to allow sharing of molecules and vesicles between cells

glucocorticoids

steroid hormones which cross plasma membrane, activate receptor, and activate genes regulating immune system

thyroid hormone

transcriptional complex will already be bound to DNA target, activated upon binding of hormone

peptide hormones

do not cross membrane, include neuropeptides and growth hormones

G-protein coupled receptors (GPCRs)

more than 1000 in human genome, 7 membrane spanning domains and Guanine Exchange Factor (GEF) intracellularly which interacts with heterotrimeric G protein

G protein activation

inactive a,b,y subunits bound to GDP, when hormone activates receptor the GEF domain phosporylates to GTP and G protein releases, a subunit dissociates from b/y

GPCR pathway

after dissociation of G protein, a subunit activates adenylyl cyclase which synthesizes cAMP from ATPG

GPCRs and glycogen

cAMP binds to protein kinase A (PKA), PKA activates phosphorylase kinase, which breaks down glycogen

GPCRs and gene transcription

cAMP activates PKA, catalytic subunit of PKA enters nucleus and phosphorylase transcription factor (TF) CREB, CREB binds to something else to activate target gene transcription

PKA activity reversal

PKA activates by phosphorylation, phosphatases can remove phosphate to inactivate

GPCRs and smell

odorant receptors are GPCRs, cAMP directly opens ligand-gated sodium channels, no PKA

receptor tyrosine kinases

dimerize when activated by ligand, activates internal kinase domains which cross-phosphorylate on tyrosines, phosphorylation allows additional binding of SH2 domain proteins

SH2 domain proteins

can bind to phosphorylated tyrosines, may be enzymes or serve as scaffolds for other proteins

non-receptor tyrosine kinases

associate with cytosolic domains of receptor proteins with membrane domains, mediate phosphorylation, activated by ligand binding to receptor

JAK/STAT pathway

JAK is non-RTK activated by cytokine binding, JAK self-phosphorylation allows TF STAT to bind, STAT is phosphorylated and activated

FAK (focal adhesion kinase)

non-RTK activated by integrin binding to ECM, recruits other proteins for cell migration/proliferation/survival

GAPs/GEFs

Ras-GDP activated to Ras-GTP by GEF, inactivated by GAP

MAP kinase pathway

ligand activates RTK, Ras-GEF recruited to phosporylated RTK, Ras activated to GTP, Ras activates a chain of phosphorylation until ERK, a kinase which activates a TF

KSR

organized Raf, MEK, and ERK to happen sequentially

Ras as an oncogene

Ras mutated in 20% of cancers, reduces rate of GTP hydrolysis, Ras active longer, more cell proliferation

PI-3 kinase/Akt pathway

PI-3 kinase recruited to RTK, activated, phosphorylates PIP2 to PIP3, PIP3 binds mTORC2, PDK1, and Akt, first two activate Akt

Akt function

when Akt is on, FOXO is off, cell death. also inhibits mTORC1 by inhibiting TSC, which down regulated protein synthesis and autophagy

TGFb receptor family

Type I and II receptors dimerize from ser/thr residue phosphorylation, activated TF Smad

NF-kB pathway

ligand activates TNF, activated IkB kinase, phosphorylates and degrades IkB, NLS of NF-kB is exposed so it enters nucleus to activate transcription

Wnt pathway

Wnt proteins are ligands which bind to cell surface receptors, in absence TF B-catenin is degraded

Notch signaling

Notch and Delta are cell surface receptors in adjacent cell, binding causes Notch conformational change that cleaves cytoplasmic domain, becomes TF

NF-kB regulation

negative feedback loop, one of target genes is IkB which will eventually block NF-kB from entering cell again

signaling pathway crosstalk

crosstalk between PI-3 and MAP kinase pathways, each can activate or inhibit the other

yeast mitosis regulation

must overcome START point, after that they are committed to S phase

cell cycle control in animal cells

once restriction point is passed, committed to DNA replication. without growth factors, cell cycle will arrest, called G0, or senescence

fission yeast cell cycle control

controlled at G2 to M transition

cell cycle regulation by proteins

regulated by activation of kinases and degradation from ubiquitin tagging by APC

maturation promoting factor (MPF)

discovered in frog oocytes by injecting cytoplasm and inducing M, made of cyclin-dependent kinase 1 (Cdk1) and cyclinB

discovery of Cdk1 purpose

when cdc28 mutated, at nonpermissive temperature cell cycle arrests in G1, cdc28 encodes for Cdk1

protein synthesis required for cell cycle

in sea urchin embryos, inhibiting protein synthesis caused cell cycle blockage because cyclins could not reconstruct

interactions of cyclinB and Cdk1

CyclinB is regulatory subunit for Cdk1, cyclical expression of cyclinB ensures Cdk1 is most active at G2-M transition, both proteins are required

MPF phosphorylation regulation

CyclinB binding to Cdk1 causes 3 phosphorylations, dephosphorylations of 2 sites allows activation at the end of G2

cyclinD

induced by MAPK growth factors, promotes G1, continual stimulation of expression is needed because it is rapidly degraded by APC, targets Rb

Rb gene

tumor supressor gene, loss is associated with retinoblastoma and other cancers, when phosphorylates it dissociates from TF E2F and allows cell cycle

Cdk2/cyclinE

promotes S phase, inhibited by p27, cyclinE expression from E2F degrades p27

regulation of DNA replication

loading of origin replication complexes (ORCs) and helicases during G1, Cdk2/cyclinE activates helices and ORC removes, cannot be added again until next G1

kinase DNA damage response

Chk1 and 2 are activated in response to damage, inhibiting cdc25, inhibiting cyclins

p53 DNA damage response

when damage, Chk2 phosphorylates p53 and it is not degraded, promotes txn of p21, a cdk inhibitor, Cdk2/CyclinE is inhibited to cycle arrests in G1

mitotic protein kinases

positive feedback loop, help activate each other to do early mitosis stuff