Cellular Flashcards
CDKs
Regulation of cell cycle
Constitutive and inactive
Cyclin-CDK complexes
Phosphor late other proteins to coordinate cell cycle progression
Must be activated and inactivated at appropriate times for cell cycle to progress
Cyclin
Regulatory proteins that control cell cycle events
Phase specific
Activated CDKs
Tumor suppressors
p53 induces p21 which inhibits CDKs - hypo phosphorylation (activation) of Rb
Hypophosphorylated Rb binds to and inactivates transcription factor E2F - inhibition of G1-S progression
Mutations in these genes result in unrestrained cell division (e.g. Li-Fraumeni syndrome)
Cell types: permanent
Remain in G0
Regenerate from stem cells
Neurons, skeletal and cardiac muscle, RBCs
Cell types: Stable (quiescent)
Enter G1 from G0 when stimulated
Hepatocytes, lymphocytes
Cell types: Labile
Never go to G0, divide rapidly with a short G1
Most affected by chemotherapy
Bone marrow, gut epithelium, skin, hair follicles, germ cells
Rough Endoplasmic Reticulum (RER)
Site of synthesis of secretory (exported) proteins and of N-linked oligosaccharide addition to many provinces
Free ribosomes: unattached to any membrane site of synthesis of cytosolic and organellar proteins
Mucus-secreting goblet cells of the SI and Ab secreting plasma cells are rich in RER
Nissl Bodies
RER in neurons
Synthesize peptide neurotransmitters for secretion
Smooth Endoplasmic Reticulum (SER)
Site of steroid synthesis and detoxification of drugs and poisons
Lacks surface ribosomes
Liver hepatocytes and steroid hormone producing cells of the adrenal cortex and gonads are rich in RER
Cell cycle phases
Checkpoints regulated by cyclin-dependent kinases (CDKs) and tumor suppressors M phase (shortest phase) includes mitosis (prophase, prometaphase, metaphase, anaphase and telophase) and cytokinesis (cytoplasm splits in two) G1 and G0 are variable duration
Cell trafficking: Golgi
Golgi is the distribution center for proteins and lipids from the ER to the vesicles and plasma membrane
Modifies N-oligosaccharides on asparagine
Adds O-oligosaccharides on serine and threonine
Adds mannose-6-phosphate to proteins for trafficking to lysosomes
Cell trafficking: endosomes
Sorting centers for material from outside the cell or from the Golgi, sending it to lysosomes for destruction or back to the membrane/Golgi for further use
I-cell disease
Inclusion cell disease/mucolipidosis type II
Inherited lysosomal storage disorder with a defect in N-acetylglucosaminyl-1-phosphotransferase and failure of the Golgi to phosphorylate mannose residues on glycoproteins
Thus proteins are secreted extracellularly rather than delivered to lysosomes
results in coarse facial features, clouded corneas, restricted joint movement and high plasma levels of lysosomal enzymes
Often fatal in childhood
Signal Recognition Particle (SRP)
Abundant cytosolic ribonucleoproteins that traffics proteins from the ribosome to the RER
Absent or dysfunctional SRP - proteins accumulate in the cytosolic
Vesicular Trafficking Proteins
COP I: Golgi to Golgi (retrograde); cis-Golgi to ER
COP II: ER to cis-Golgi (anterograde)
Clathrin: trans-Golgi to lysosomes; plasma membrane to endosomes (receptor mediated endocytosis - LDL receptor activity)
Peroxisome
Membrane enclosed organelle involved in catabolism of very long chain fatty acids (beta oxidation), branched chain FAs, AAs and EtOH
Proteasome
Barrel-shaped protein complex that degrades damaged or ubiquitin-tagged proteins.
Defects in ubiquitin-protea some system have been implicated in some cases of Parkinson disease
Microfilaments
Function: muscle contraction; cytokinesis
Examples: actin, microvilli
Intermediate filaments
Function: maintain cell structure
Examples: vimentin, desmin, cytokeratin, lamins, glial fibrillary acid proteins, neurofilaments
Microtubules
Function: Movement, cell division
Examples: cilia, flagella, mitotic spindle, atonal trafficking, centrioles
Vimentin Stain
Cell type: mesenchymal tissue (fibroblasts, endothelial cells, MPs)
Identifies: mesenchymal tumors (sarcoma) but also other tumors (endometrial carcinoma, renal cell carcinoma, meningiomas)
Desmin Stain
Cell type: muscle
Identifies: muscle tumors (rhabdomyosarcoma)
Cytokeratin Stain
Cell type: epithelial cells
Identifies: epithelial tumors (squamous cell carcinoma)
GFAP stain
Cell type: neuroglia (e.g. Astrocytes, Schwann cells, oligodendroglia)
Identifies: astrocytoma, glioblastoma
Neurofilament Stain
Cell type: neurons
Identifies: neuronal tumors (e.g. Neuroblastoma)
Microfilament structure
Cylindrical outer structure composed of a helical array of polymerized heterodimers of alpha and beta Tubulidentata
Each dimer has 2 GTP bound
Incorporated into flagella, cilia, mitotic spindles (grows slowly and collapses quickly), also involved in slow axoplasmic transport in neurons
Molecular motor proteins
Transport cellular cargo toward opposite ends of Microtubule tracks
Dynein- retrograde to microtubule (+ - -)
Kinesin - anterograde to microtubule (- - +)
Drugs that act on Microtubules
Microtubules Get Constructed Very Poorly Mebendazole (anti-helminthic) Griseofulvin (antifungal) Colchicine (anti-gout) Vincristine/Vinblastine (chemotherapy) Paclitaxel (chemotherapy)
Cilia structure
9+2 arrangement of microtubule doublets
The base of a cilium below the cell membrane, called the basal body, consists of 9 microtubule triplets with no central Microtubules
Axonemal dynein
ATPase that links peripheral 9 doublets and causes blinding of cilium by differential sliding of doublets
Kartagener Syndrome
Primary ciliary dyskinesia
Immotile cilia due to a dynein arm defect
Results in male and female infertility due to immotile sperm and dysfunctional Fallopian tube cilia
Increased risk of ectopic pregnancy
Can cause bronchiectasis, recurrent sinusitis, and situs in versus (e.d. Dextrocardia on CXR)
Plasma membrane composition
Asymmetric lipid bilayer
Contains cholesterol, phospholipids, sphingolipids, glycolipids, and proteins
Fungal membranes contain ergosterol
Na+/K+ pump
Na-K ATPase is located in the plasma membrane with ATP site on cytosolic side
For each ATP consumed - 3Na+ go out of the cell and 2K+ enter the cell
Ouabain inhibits by binding to K+ site
Cardiac glycosides (digoxin) directly inhibit Na/K ATPase which lead to indirect inhibition of Na/Ca exchange increasing intracellular Ca and increasing cardiac contractility
Collagen
Most abundant protein in the human body
Extensively modified by post-translational modification
Organizes and strengthens extracellularly matrix
Type I collagen
Most common
Bone (made by osteoblasts), skin, tendon, dentin, fascia, cornea, late wound repair
Type I: Bone (decreased production in osteogenesis I perfecta type I)
Type II Collagen
Cartilage (including hyaline), vitreous body, nucleus pulposus
Type II: CarTWOlage
Type III Collagen
Reticulin - skin, blood vessels, uterus, fetal tissue, granulation tissue
Type III: deficient in the uncommon, vascular type of Ehlers-Danlos syndrome
Type IV Collagen
Basement membrane, basal lamins, lens
Type IV: under the floor (BM)
Defective in Alport syndrome; targeted by some autoAb in goodpasture syndrome
Collagen Synthesis (1)
Translation of collagen alpha chains (preprocollagen)
Usually Gly-X-Y (proline-lysine)
Glycine content best reflects collagen synthesis
Collagen Hydroxylation (2)
Hydroxylation of specific proline and lysine residues
Requires VitC
Deficiency = scurvy
Collagen Glycosylation (3)
Glycosylation of pro-alpha-chain hydroxylysine residues and formation of procollagen via hydrogen and DS bonds (triple helix of 3 collagen alpha chains)
Problems forming triple helix - osteogenesis imperfect a
Collagen exocytosis (4)
Exocytosis of procollagen into extracellular space
Collagen Proteolytic processing (5)
Cleavage of disulfide rich terminal regions of procollagen –> insoluble tropocollagen
Collagen Cross Linking (6)
Reinforcement of many staggered tropocollagen molecules by covalent lysine-hydroxylysine cross linkage (by copper containing lysyl oxidase) to make collagen fibrils
Problems with cross linking - Ehlers-Danlos syndrome, Menkes disease
Osteogenesis Imperfecta
Genetic bone disorder (brittle bone disease) caused by a variety of gene defects (most commonly COL1A1 and COL1A2)
Most common form is the AD with decreased production of otherwise normal type I collagen
Manifestations: multiple fractures with minimal trauma (may occur during birthing process), blue sclerae due to the translucent CT over choroid all veins, hearing loss (abnormal ossicles)
Some forms have tooth abnormalities (opalescent teeth that wear easily due to lack of dentin)
Ehlers-Danlos Syndrome
Faulty collagen synthesis causing hyperextensible skin, tendency to bleed (easy bruising) and hypermobile joints
Multiple types: inheritance and severity vary, can be AR or AD
-Hypermobility type: joint instability, most common type
-Classical type: joint and skin symptoms, caused by a mutation in type IV collagen
-Vascular type: vascular and organ rupture, deficient type III collagen
May be associated with joint dislocation, berry and aortic aneurysms, organ ruptures
Menkes Disease
X-linked recessive CT disease caused by impaired copper absorption and transport due to defective Menkes protein (ATP7A)
Leads to decreased activity of lysyl oxidase (copper is a cofactor) resulting in brittle, kinky hair, growth retardation and hypotonia
Elastin
Stretchy protein within skin, lungs, large arteries, elastic ligaments, vocal cords, ligaments flava (connect vertebrae - relaxed and stretched conformations)
Rich in no hydroxylases proline, glycine and lysine residues
Tropoelastin with fibrillin scaffolding
Cross-linking takes place extracellularly and gives elastin its elastic properties
Broken down by elastase, which is normally inhibited by alpha-1 antitrypsin
Wrinkles of aging are due to decreased collagen and elastin production
Marfan Syndrome
Caused by a defect in fibrillin (a glycoprotein) that forms a sheath around elastin
Emphysema
Can be caused by an alpha-1 antitrypsin deficiency resulting in excess elastase activity
Regulation by fructose-2,6-bisphosphate
FBPase-2 and PFK-2 are the same bifunctional enzyme whose function is reversed by phosphorylation by PKA
Fasting state: increased glucagon - increased cAMP - increased PKA - increased FBPase-2, decreased PFK-2, less glycolysis and more gluconeogenesis
Fed state: increased insulin - decreased cAMP - decreased PKA - decreased FBPase-2, increased PKA, more glycolysis and less gluconeogenesis
Pyruvate Dehydrogenase Complex
Mitochondrial enzyme complex linking glycolysis and TCA cycle. Differentially regulated in fed/fasted states (active in fed)
Reaction: pyruvate + NAD+ + CoA – acetyl-CoA + CO2 + NADH
Complex (TLC For Nancy)
Thiamine pyrophosphate (B1)
Lipoic Acid
CoA (B5, pantothenic acid)
FAD (B2, riboflavin)
NAD (B3, niacin)
Activated by: increased NAD+/NADH ratio, ADP, Ca2+
Pyruvate dehydrogenase complex deficiency: findings
Causes a buildup of pyruvate that gets shunted to lactate (via LDH) and alanine (via ALT) - X-linked
Neurologic defects, lactic acidosis, increased serum alanine starting in infancy
Pyruvate dehydrogenase complex deficiency: treatment
Increased intake of ketogenic nutrients (high fat content or increase lysine and leucine
Lysine and Leucine - the onLy pureLy ketogenic amino acids
Pyruvate metabolism
Functions of different pyruvate metabolic pathways (and their associated co-factors)
- Alanine aminotransferase (B6): alanine carries amino groups to the liver from muscle
- Pyruvate carboxylase (biotin): oxaloacetate can replenish TCA cycle or be used in gluconeogenesis
- Pyruvate dehydrogenase (B1, B2, B3, B5, lipoic acid): transition from glycolysis to the TCA cycle
- Lactic acid dehydrogenase (B3): end of anaerobic glycolysis (major pathway in RBCs, WBCs, kidney medulla, lens, testes, and cornea)
TCA cycle (Krebs cycle)
The TCA cycle (in mitochondria) produces 3NADH, 1FADH2, 2CO2, 1GTP per acetyl-CoA = 10 ATP/acetyl-CoA (2x everything per glucose)
Alpha-ketoglutarate dehydrogenase complex requires same cofactors as the pyruvate dehydrogenase complex (B1,B2,B3,B5, lipoic acid)
Substrates in TCA cycle
Citrate Is Krebs’ Starting Substrate For Making Oxaloacetate
(Acetyl-CoA + Oxaloacetate) – citrate – Isocitrate – alpha-KG – Succinyl-CoA – Succinate – Fumarate – Malate – Oxaloacetate
Electron Transport Chain and oxidative phosphorylation
NADH electrons from glycolysis enter mitochondria via the malate-aspartate or glycerol-3-phosphate shuttle
FADH2 electrons are transferred to complex II (at lower energy level than NADH)
The passage of electrons results in the formation of a proton gradient that, coupled to oxidative phosphorylation, drive the production of ATP
ATP produced by ATP synthase
1 NADH = 2.5 ATP
1 FADH = 1.5 ATP
Electron Transport inhibitors
Directly inhibit ETC, causing a decrease in proton gradient and block of ATP synthesis
- rotenONE: complex ONE inhibitor*
- An-3-mycin (antimycin) A: complex 3 inhibitor*
- CO/CN: complex 4 inhibitor (four letters)*
ATP synthase inhibitor
Directly inhibit mitochondrial ATP synthase, causing and increase in proton gradient. But not ATP is produced because ETC has stopped
Oligomycin
Uncoupling Agents
Increased permeability of membrane, causing a decreased proton gradient and increased O2 consumption. ATP synthesis stops but ETC continues –> produces heat
2,4 Dinitrophenol (used illicitly for weight loss), aspirin (fever often occur after aspirin overdose), thermogenenin in brown fat
Gluconeogenesis: Pyruvate carboxylase
In mitochondria
Pyruvate to Oxaloacetate
Requires biotin, ATP, activated by acetyl-CoA
Gluconeogenesis: Phophoenolpyruvate carboxykinase
In cytosol
Oxaloacetate to phosphoenolpyruvate
Requires GTP
Gluconeogenesis: Fructose-1,6-bisphosphate
In ER
Glucose-6-phosphate to fructose-6-phosphate
Citrate (+), fructose 2,6 bisphosphate (-)
Gluconeogenesis: Glucose-6-phosphatase
In ER
Glucose-6-phosphate to glucose
Gluconeogenesis: facts
Occurs primarily in the liver serving to maintain euglycemia during fasting (also found in kidney, and intestinal epithelium)
Deficiency in key gluconeogenic enzymes cause hypoglycemia (muscle cannot participate because it lacks glucose-6-phosphatase)
Odd-Chain FAs & TCA
Odd-chain FAs yield 1 propionyl-CoA during metabolism, which can enter the TCA cycle (succinyl-CoA), undergo gluconeogenesis, and serve as a glucose source
Even chain FAs cannot produce a new glucose
HMP Shunt (pentode phosphate pathway)
Provides source of NADPH from abundantly available G6P
-NADPH is required for reductive reactions, eg glutathione reduction inside RBCs, FA and cholesterol biosynthesis)
Also provides ribose for nucleotide synthesis and glycolytic intermediates
2 distinct phases (oxidative & nonoxidative), both of which occur in the cytoplasm
No ATP is used or produced
HMP shunt: Sites
(Sites of FA or steroid synthesis) Lactating mammary glands Liver Adrenal cortex RBCs
HMP: oxidative phase
Irreversible
G6P to CO2, 2 NADPH, Ribulose-5-phosphate via glucose-6-phosphate dehydrogenase
HMP: nonoxidative phase
Reversible
Ribulose-5-phosphate to Ribose-5-P, Glyceraldehyde-3-phosphate and fructose-6-phosphate via phosphopentose isomerase, transketolases (requires B1)
Glucose-6-phosphate dehydrogenase deficiency
NADPH is necessary to keep glutathione reduced, which in turn detoxifies free radicals and peroxides
Decreased NADPH in RBCs leads to hemolytic anemia due to poor RBC defense against oxidizing agents (eg fava beans, sulfonamides, primaquine, antituberculosis drugs)
Infection (most common cause) can also precipitate hemolysis; inflammatory response produces free radicals that diffuse into RBCs causing oxidative damage
Glucose-6-phosphate dehydrogenase deficiency: Genetics
X-linked recessive disorder (most common human enzyme deficiency)
More prevalent among African Americans
Increased malarial resistance
Findings: Heinz bodies - denatured Hemoglobin precipitates within RBCs due to oxidative stress, Bite cells - result from the phagocytic removal of Heinz bodies by splenic MPs
Essential fructosuria
Involves a defect in fructokinase (AR)
Benign, asymptomatic condition since fructose is not trapped in the cell
Symptoms: fructose appears in blood and urine
Fructose intolerance
Hereditary deficiency of aldolase B (AR)
Fructose-1-phosphate accumulates causing a decrease in available phosphate which results in inhibition of glycogenolysis and gluconeogenesis
Symptoms after consumption of fruit, juice or honey: hypoglycemia, jaundice, cirrhosis, vomiting
Urine dipstick will be negative, reducing sugar can be detected in urine
Tx: decrease intake of both fructose and sucrose (glucose+fructose)
Galactokinase deficiency
Hereditary deficiency of galactokinase (AR). Galactitol accumulates if galactose is present in diet
Symptoms develop when infant begins to feed (lactose present in breast milk and routine formula): galactose in blood and urine, infantile cataracts
May present as failure to track objects or to develop a social smile
Classic galactosemia
Absence of galactose-1-phosphate uridyltransferase (AR)
Damage is caused by accumulation of toxic substances (including galactitol - esp in lens of eye)
Symptoms: FTT, jaundice, hepatomegaly, infantile cataracts, intellectual disability, can lead to E. Coli sepsis in neonates
Tx: exclude galactose and lactose (galactose+glucose) from diet
Fructose is to Aldolase B as Galactose is to UridylTransferase (FAB GUT)
