Molecular Review (White) Flashcards
endocrine signaling
- long distance signaling
- long lasting, freely diffusible signals
- moves through bloodstream
paracrine signaling
- acts locally
- short lived, affects nearby cells
synaptic signaling
- acts locally
- short lived, NEUROTRANSMITTERS
autocrine signaling
- cells respond to signals that they themselves release or release to cells of the same type
- growth factors –> cells grow, divide, mature
direct cell signaling
- immune cells
- Ag presentation to T cells
G protein coupled receptors
- extracellular domain: binds ligand
- transmembrane domain: anchors receptor
- cytoplasmic domain: associated with G protein
associates with heterotrimeric G proteins –> alpha subunit regulate target enzymes (activated G protein)
- alpha subunit binds GTP –> activates adenylyl cyclase
- alpha subunit binds GDP –> binds to beta subunit (inactive)
Cholera and G protein
- cholera toxin keeps G-alpha in GTP active form indefinitely
- pump Cl/water out of cells in intestine and causes severe diarrhea
cAMP
- generated by adenylyl cyclase –> interacts with target protein to cause biological response
- activates PKA (2 cAMP molecules bind to regulatory subunits of PKA which releases 2 catalytic subunits)
Receptor Tyrosine Kinases (RTKs)
- enzyme-linked receptors (enzymatic domain in cytoplasm) –> transmit signal through tyrosine kinase domain
- used for response to growth factors
- adds phosphate to tyrosine on proteins
Receptor Tyrosine Kinase activation
- ligand binding causes dimerization (autophosphorylation occurs)
- acts as scaffold to recruit other proteins to plasma membrane (Grb2 –> SH2 binds)
- SH3 domain of Grb2 binds SOS, which binds Ras (SOS is GEF that adds GTP to Ras)
- Ras binds Raf –> activates MAP kinase pathway (phosphorylates and makes changes in protein activity and gene expression)
What was the first discovered human oncogene?
Ras
- plays crucial role in cell division and a frequent mutation in cancer
JAK-STAT receptors
- ligand binds to receptors (dimerization) then bind JAK
- JAK phosphorylates each other and the receptor
- STATS bind and are phosphorylated by JAK
- STATS dimerize and enter nucleus –> bind DNA and cause transcription of target genes
Serine-threonine receptor and Smad
- ligand binds type II receptor, which phosphorylates second receptor (type I)
- Type I phosphorylates R-Smad, which associates with Co-Smad
- moves into nucleus to impact transcription of target genes
helix-turn-helix
- simplest DNA-binding motif
- 2 alpha helices connected by short chain of AAs
- longer helix portion = recognition module (DNA binding module)
- bind DNA as dimers
zinc finger domain
- DNA binding motif with Zn atom
- binds to major groove of DNA
Leucine zipper motif
- two alpha helical DNA binding domain
- dimerization through leucine zipper region
- grabs DNA like clothespin
- hydrophobic AA side chain interactions at every 7 AA down one side of alpha helix
helix-loop-helix
- short alpha chain connected by loop to second longer alpha chain
- can occur as hetero or homodimer
RNA stability regulation
- remove 5’ cap –> mRNA degraded from 5’ end
2. mRNA degraded from 3’ end through poly-A tail
Checkpoints of the Cell Cycle (3)
Checkpoint 1: Start –> cell commits to cell cycle entry and chromosome duplication
Checkpoint 2: G2/M –> move into chromosome alignment on spindle in metaphase
Checkpoint 3: metaphase-to-anaphase transition - trigger sister chromatid separation and cytokinesis
Cdks
- heart of cell cycle control system
- dependent on cyclins (must be bound to cyclin to have protein kinase activity)
- activities rise and fall during cell cycle
CAK
- causes phosphorylation at T-loop of Cdk (normally blocks active site) –> fully activates enzyme
- cyclin binding causes T-loop to move out of active site
condensins
- help reorganize sister chromatids to be pulled apart during anaphase with NO breakage
- chromosomes condensation and resolution
M-Cdk
- activates APC/C to complete mitosis
- ubiquitinates and causes degradation securin and allows separase to activate
- separase cleaves cohesins, causing metaphase to enter anaphase (pull apart sister chromatids)
Two major classes of caspaces
- synthesized as inactive precursor (procaspases)
- initiator caspases and executioner caspases
- executioner destroys actual targets (apoptosis)
Intrinsic Apoptosis
cytochrome c released from mitochondria binds to Apaf1 –> assembles into apoptosome and recruits caspase-9
caspase-9 cleaves and activates executioner procaspases (APOPTOSIS)
BH123
form aggregation in mitochondrial outer membrane, releasing cytochrome C
Bcl2
prevents aggregation of BH123 (inhibits apoptosis)
BH3
apoptotic stimulus that inactivates Bcl2 proteins
- allows BH123 to assemble
IAPs
bind to caspases and prevent their activity
anti-IAPs
- released from mitochondria and bind to IAPs
- prevent IAP association with caspases, allowing for normal executioner caspase activity
Overactivity vs Underactivity mutations
Overactivity - GAIN OF FUNCTION (oncogenes) –> single mutation event, activation of gene causing proliferation (dominant)
Underactivity - LOSS OF FUNCTION (tumor suppressor genes) –> one mutation, no effect; two mutations, cause problem (recessive): involve genes that inhibit growth
Hereditary Retinoblastoma
- loss of function/deletion of one copy of Rb in every cell (defect inherited)
- somatic event occurs that eliminates the good copy = tumor formation (loss of heterozygosity)
Sporadic Retinoblastoma
- non-hereditary
- first Rb gene obtains mutation, increasing the likelihood that second gene mutates
Polyp
- precursor of colorectal cancer
- slow progression (10 years)
- cut off polyp = CURE
Colorectal Cancer mutations (3)
> 80% –> loss of Apc (tumor suppressor gene)
40% –> point mutation in K-Ras
60% –> loss of p53
Actin Filaments
- determine shape of cell’s surface and are necessary for whole-cell locomotion, secretion, endocytosis
Microtubules
- forms tube-like structure
- determine the positions of membrane-enclosed organelles
- direct intracellular transport
Intermediate Filaments
- provides mechanical strength, strong filament
- resists mechanical stress, allow formation of hair/fingernails
Actin filament assembly
- monomer contains ATP/ADP binding
- two protofilaments that twist around each other (right handed helix)
- held together by lateral contacts (arranged head-to-tail
- flexible, easily bent
Tubulin assembly
- formation of microtubules
- end-to-end and side-to-side protein contacts
- heterodimer of a/B tubulins (binding sites for GTP)
(+) end –> fast growing/shrinking end
(-) end –> slow growing/shrinking end
Hereditary Spherocytosis
- RBCs spherical, not bi-concave (get shape from cytoskeleton, defective SPECTRIN –> durability/stability)
- fragile RBCs burst = hemolytic anemia
Listeria
- pathogenic bacteria that invade intestinal cells
- causes food poisoning especially if immunologically deficient or immunocompromised
- smashes through organelles (leaves actin track aka ‘comet trails’)
Listeria and ARP (Arp 2/3)
- Arp complex is responsible for generating the actin trails that Listeria uses to move
- actin branch filaments pushes the bacteria
Duchenne Muscular Dystrophy
- most common fatal neuromuscular disorder in boys
- severe, progressive muscle degeneration
- patients in wheelchairs by 12 years of age
- no medical treatment, just maintain patients general health and improve quality of life
Duchenne Muscular Dystrophy genetics
- X linked recessive
- caused by dystrophin gene mutations; present at birth but does NOT show symptoms until about 3 years of age
What is the main function of the dystrophin protein?
to provide structural stability to the muscle cell membrane during contraction and relaxation
- 4 functional domains
4 functions domains of dystrophin
- N-terminus (actin binding domain)
- Long spectrin-like repeat domain
- Cysteine rich domain
- C-terminus domain
Dystrophic myopathy
progressive muscle degeneration w/loss of functional muscle tissue over time with resulting weakness
DMD Clinical Presentation
necrosis of muscle fibers occurs with replacement of fat or connective tissue
- leads to pseudohypertrophy: replacement of muscle w/adipose tissue and fibrous CT (enlarged calves)
Lordosis vs Kyphosis
Lordosis: excessive inward curvature
Kyphosis: upward back curvature outward
Gower Maneuver
- boys with DMD rising from floor
- first get on hands and knees, then elevate posterior, then ‘walk’ their hands up the legs to raise upper body
Becker Muscular Dystrophy
- milder than Duchenne (similar symptoms but milder)
- increased workload on left ventricle = left ventricular enlargement (severity results in heart failure and death)
- some dystrophin protein of abnormal quantity and size (Duchenne = NO dystrophin)
Mitochondrial Myopathies w/Ragged Red Fibers
- degeneration of muscle fibers caused by accumulation of abnormal mitochondria
- abnormal mitochondrial aggregates for red sarcolemmal blotches (Ragged Red Fibers)
heteroplasmy
mixture of normal and mutant mitochondria in one cell
- threshold effect of mutant mitochondria are required for disease manifestation
MERRF
- myoclonus epilepsy
- INVOLUNTARY JERKING
- ataxia, myclonic epilepsy, ragged red fibers
- 90% caused by 2 mutations of tRNA(Lys)
MERFF Mutations (2)
85% –> due to A to G mutation
5% –> due to G to C mutation
MELAS
- Mitochondrial Encephalopathy, Lactic Acidosis with Stroke-like episodes
- onset = 2-10 years
- BLINDNESS, Ragged Red Fibers, vomiting, anorexia, headaches, seizures
- mutation in tRNA(Leu) –> A3243G
Kearns-Sayre Syndrome
- retinosis pigmentosa (degenerative eye disease leading to blindness
- onset before age 20
- at least one: cardiac conduction abnormality, cerebellar ataxia, cerebral spinal protein level above 100 mg/dL
- 85% of KSS due to mtDNA rearrangements
Chronic Progressive External Ophthalmoplegia (CPEO)
- mild to moderate mitochondrial myopathy (ragged red fibers observed in skeletal muscle) –> mtDNA rearrangements
- PTOSIS (drooping of eyelid)
Leber Hereditary Optic Neuropathy (LHON)
- mitochondrial mutation ONLY affects optic nerve
- acute or subacute, bilateral, central vision loss
- degeneration of retinal ganglion cell layer and optic nerve
- initially affects one eye but eventually both eyes affected at the same time (Maternal inheritance)
Hemoglobin Structure
- multi-subunit protein (tetramer) –> 2 alpha/beta chains
- heme: one per subunit, has iron atom
4 types of hemoglobin chains
alpha, beta, delta, gamma
Hemoglobin forms
HbA –> 2 alpha and 2 beta chains (adult form)
HbA2 –> 2 alpha and 2 delta (3%)
HbF –> 2 alpha and 2 gamma (fetal form) (0.5%)
Sickle Cell Anemia and HbF
- sickle shaped RBCs that impede circulation = hemolytic anemia
- HbS–> substitution of valine for glutamic acid at AA #6
- use hydroxyurea to induce HbF
Modular HbF
- fetus needs Hb that has higher affinity for oxygen than mother’s Hb
- HbF does not bind well to 2,3-BPG = has a HIGHER affinity for oxygen
