Organelles Flashcards
Why eukaryotic cells need organelles (2)
Membrane-dependent functions, specialization
Development of organelles
Invagination of cell membrane - explains double nuclear membrane
Areas of cell that are “topographically” equivalent to outside
Nuclear envelope, Golgi, ER
Biggest organelles by volume
Mitochondrion, Golgi, ER (NOT nucleus!)
Size of mitochondria
0.5-1 micron
Cells with high mitochondria content
High energy needs - muscle, nerve, sperm
Where are mitochondria found in cell?
Migrate along microtubules to highest energy need (ie base of cilia)
Endocytosis model of mitochondria
Was separate organism - two membrane are organism and plasma
Structure of mitochondria
Double membrane with christae on inner membrane, lumens in intermembrane space
Mitochondrial ATP production
Pyruvate, fatty acids enter citric acid cycle -> NADH -> electron transport chain pumps H+ into intermembrane space -> ATP synthase driven by gradient
Electron transport chain
Small steps in energy so cell is able to harness, passed to three different complexes
ATP synthase
Lollipop structure, drives oxidative phosphorylation by electro and chemical H+ gradient
Thermogenin
In mitochondria of brown fat, produces heat (no ATP) from electrochemical gradient of inner membrane
Adaptations of mitochondria
Number in cell, density of christae, location in cell
Mitochondrial replication
Fission, also reversible through fusion
Mitochondrial DNA
Replicated before fission, few genes (35?), high mutations/diversity, complement of DNA is inherited from mother
Characteristics of mitochondrial disease
Due to mutations in DNA, maternal inheritence, affects high energy cells (muscle, nerves), often progressive and hard to recognize, can have varying presentation dt different DNA complements or different distribution, example MERRF
Ribosome function
RNA catalyzes peptide bonds, specific binding of tRNAs into three binding sites (A->P->E), reads RNA 5-3, makes peptide N-C
Ribosome synthesis
RNA in nucleolus, proteins imported into nucleus, subunits exported and float free in cytoplasm until bind onto rough ER or polyribosome
“Polyribosome”
Multiple ribosomes bound to single mRNA, often appear as spirals in cytoplasm
Membrane-bound ribosome mechanism
Begin translation, signal recognition protein recognizes signal sequence and directs to ER
Prokaryotic vs eukaryotic ribosomes
Prokaryotic are smaller 3 RNA, 55 proteins, 50S and 30 S subunits vs 4 RNA, 82 proteins, 60S and 40S
Differences are exploited by many antibiotics
Post-translation protein folding
Aided by chaperones, destroyed by proteasome if misfolded
Proteasome
Free in nucleus, destroys misfolded, injured or foreign proteins labeled with ubiquitin
Proteasome function
Four heptameric rings, active site buried inside hollow core, cap recognizes ubiquitin and uses ATP to thread protein into core
Proteasome vs protease
Protease is a specific enzyme that cleaves a protein once
Proteasome much larger organelle, destroys anything ubiquinated, has processivity (cleaves multiple places)
Functions of smooth ER
Lipid synthesis (phospholipids, cholesterol, steroid hormones), drug detox (cytochrome p450), sequestration of Ca++ (“sarcoplasmic reticulum”)
Transport of lipids to membrane
Lateral diffusion through ER, vesicles or transport protein
Cells with high rough ER content
High protein secretion - antibodies, hormones, pancreas, active growth site
Structure of Golgi
Cis face near rough ER, vesicles transport proteins to medial then trans face, each compartment has specific enzymes and functions
Transport through Golgi network
Coat proteins (COP) - COP II moves vesicle “forward” to trans face, COP I moves retrograde towards cis
Golgi enzymes
Add oligosaccharides, disulfide bonds, mannose 6 P, glycosylation, sialic acid on oligosaccarides, sulate to tyrosines
Pathways from Golgi
Lysosome (if mannose 6 phosphate labelled), secretion, regulated secretory vesicle
Lysosome development
Enzymes labelled with mannose 6 phosphate, forms primary lysosome, fuses with endosome or phagosome to become secondary lysosome, can become residual body if indigestible wastes
Lysosomal storage diseases
Missing enzyme, non-metabolized products build up in cell
Ex Tay-Sachs (hexosaminidase -> glycolipids in neurons)
Hurler (GAGs in brain, heart, etc)
Glycogen storage
Development of secretory vesicles
Labelled by clathrin, bud off from trans golgi, excess membrane returns to Golgi to concentrate secretions
Peroxisome functions
Metabolism through oxidation - long fatty acids, EtOH, meds - oxidases create H2O2, catalases process into H20 and O2
Locations of peroxisomes
In every cell, abundant in kidney and liver, often near mitochondria
Peroxisomal diseases
Zellweger syndrome - absence of enzymes, fatal
Adrenoleukodystrophy - fatty acids can’t enter peroxisome, accumulate in nerves and adrenal glands
Approx amount of total membrane in organelles
Mitochondria 40%
ER 50%
Plasma membrane only 2%