Post on 14-May-2015
Fig. 1.11
Nucleus: structure and function
Nucleolus Nucleoplasm
nuclear envelope
Heterochromatin = too compacted,
transcriptionally inactive
Euchromatin = can be transcriptionally active
Nuclear envelope and lamina
Nuclearpore
N. lamina
cytoplasm
heterochromatin
Nuclear laminaNuclear lamina
Lamins are filamentous proteins in the intermediate filament family
Lamin phosphorylation in prophase disassembles the nuclear lamina & allows for nuc. envel. breakdown
Laminins are extracellular proteins, unrelated
Nuclear pore
• nuclear localization signals (nuclear import signals)
• nuclear export signals
• highly regulated
Mitochondria(on)
outermembrane
innermembrane
DNAmatrix
cristaeribosomes ATP synthase
Inner Membrane and matrix
electrontransportsystem
ADP3-
ATP4-
pyruvate
Krebscycle
NADH
ATPsynthaseFADH2
hi [H+]
Antiporter
P04-2 H+
symporter
Endosymbiotic theory: Mitochondria are similar to prokaryotes
• Own circular, naked DNA
• Own ribosomes - similar to prokaryotic– e.g. sensitive to same inhibitors
• Divide by fission
• Double membrane suggests endocytosis
Lysosomes: membranous organelles filled with digestive enzymes
• Breakdown endocytosed materials– Thru’ phagocytosis or
receptor mediated endocytosis
• Breakdown old organelles (residual body)
• Acidic pH
Phagocytosis vs. Autophagy
Phagocytosis
Autophagy
lysosomes
Membrane trafficking
•RER to cis Golgi
•Modified in Golgi (glycosylation, phosphorylation)
•Sorted at trans Golgi network into
•Lysosomal
•Regulated
•constitutive
Synthesis of secreted and membrane proteins
Ribosomes
Rough endoplasmic reticulum
Rough Endoplasmic reticulum
Signal hypothesis: signal peptide, SRP, SRP-receptor, translocon
SRP = signal recognition particle
Smooth ER, lipid synthesis, detox, Ca2+ sequestration
Golgi
Transport thru’ Golgi cisternae is vectorial
Cis Medial Trans
mannose removalN-acetylglucosamine addition MEDIAL
RER retrieval, PO4 on mannose,mannose removal
CIS &CGN
fucose and glucose addition TRANS
sialic acid addition, sorting TGN
Protein modifications occur in steps in the Golgi. The extent of changes varies.
Glycosylation
Karp, Fig. 8.20
trans Golgi network
regulatedsecretion
lysosomalpathway
constitutivesecretion
Sorting at the TGN
Receptor Mediated endocytosis
Plasma membrane & Fluid mosaic model
Phospholipids are most common in membranes
PolarHead
Fattyacidtails
phospholipids, glycolipids, and cholesterol
Thermodynamics drives membranes to form sealed compartments
H2O
Cut open liposome
Fluidity means that lipids (& proteins) can “float” in the membrane via
diffusion
Time
Three classes of membrane proteins: Transmembrane proteins (a type of IMP)
OUT
IN
Extracellulardomain (ECD)
Intracellulardomain (ICD)
Transmembranedomain
Oligosaccharides - always face out
Three classes of membrane proteins: Lipid-anchored membrane proteins (IMPs)
OUT
IN
Covalently linked to a glycophospholipid.
E.G.: Normal cellular scrapie protein & alkaline phosphatase
Covalently linked to fatty acid
E.G.: ras
Three classes of membrane proteins: Peripheral membrane proteins (PMPs)
OUT
INOr, PMPs could bind to specific lipid heads.
Specific interaction between IMP & PMP
IMPs as -helix or -barrel
Selective permeability
Osmosis causing cell lysis.
Four mechanisms by which solute molecules move ACROSS membranes
Simple diffusionacross bilayer
Simple diffusionthru channel
FacilitatedDiffusion
thru’ passive transporters
Activetransport
Membrane Potential Affects Molecular Movement
A. neutral
No effect on inward transport No effect on outward transport
B. cation
Favors inward transport Opposes outward transport
C. anion
Opposes inward transport Favors outward transport
Passive transport by channel proteins: don’t bind solute & can
be ligand-, voltage-, or stress-gated
Passive Transport by Facilitated diffusion
•Solute binds transporter protein
•So, transport is saturable
Kinetics of carrier-mediated transport
Active transport by the Na/K pump or ATPase