Cells(membrane) Dla Flashcards
What are the3 major classes of lipids?
- phospholipids
- cholesterol
- glycerolipids
What are the types of lipids?
About 50% membrane mass
- amphipathic
- hydrophilic
- water-loving (polar head)
- hydrophobic (water-fearing) nonpolar tail
- hydrophilic
What are the classifications of proteins in the cell membrane ?
About. 50% membrane mass
2 major classes:
- integral membrane
- embedded in or pass through the lipid bilayer
Peripheral membrane
- associate with integral membrane proteins
What are phospholipids?
Most abundant membrane lipid
- phosphatidyl serine
- phosphatidylethanolamine
What is the effect of cholesterol on the membrane?
Intercalates between phospholipids
Affects membrane fluidity in temperature dependent manner
What is the effect of glycolipids in the membrane?
- constitute ~5% of lipid molecules
- Sugar containing lipid molecules
- found exclusively in outer monolayer
What are the types of membrane proteins?
- Integral membrand proteins
Transmembrane
-single and multi passAnchored- alpha helix
- lipid chain
- oligosaccharide linker
- Peripheral membrane proteins
- noncovalent association with integral membrane proteins
What are the 6 general categories of integral membrane proteins?
- Pumps/carriers/ transporters
Transport specific ions across the membrane
-sodium
-potassium
Transport metabolic precursors
- amino acids
- sugars
- Channels
- transport of ions, small molecules and water- passive diffusion
- aqua porins
- water
- gap junctions
- passage of ions, small molecules between adjacent cells
- Receptors
- Linkers
- Enzymes
- Structural proteins
What is a glycocalyx?
Card rich zone on the cell surface
- glycolipids
- glycoproteins
- proteoglycans
What are the functions of the glycocalyx ?
-Helps establish the micro environment at cell surface
- protection
- mechanical storage
- chemical storage
-cell recognition
- cell to cell interaction
- lectins
- carbohydrate binding proteins
- lectins
Describe the lipid bilayer
- hydrophilic head ground face exterior and cytosol
- fatty acid tails create a hydrophobic core
Described the asymmetry of the membrane
- specific phospholipids localize to outer and inner leaflets
- phosphatidylserine localized to the inner leaflet
- eznymatically transferred to the outer leaflet during programmed cell death
- triggers phagocytic removal of dying cells
Summarize the fluid mosaic model
-lipids and proteins have ability to move within the plane of the membrane
Describe the fluidity of the membrane
-membrane lipids and proteins are mobile
- cholesterol serves to stabilize the membrane
- reduce membrane fluidity
Describe the selective permeability of the membrane
Permeable
- hydrophobic, non-polar, uncharged
- oxygen, carbon dioxide
Less permeable
- small, polar, uncharged
- water
Highly impermeable
- charged (ions)
- polar
- charged
Summarize Transmembrane proteins
- channels & transporters
- increase the permeability of the membrane to molecules that cannot cross the lipid bilayer
What is exocytosis?
Substance exits the cell by the fusion of a vesicle with the plasma membrane
What is endocytosis ?
Substance enters the cell by a vesicle formed from the plasma membrane
Contrast the 3 types of endocytosis
- Receptor mediated
- cargo-specific
- Clathrin dependent - Pinocytosis
- non-specific
- clathrin-independent - Phagocytosis
- clathrin-independent
- actin-dependent
Contrast the types of exocytosis
Regulated
- secretory cells
- endocrine
- exocrine
- neurons
- stimulus
- CA2+ influx
- fusion of secretory cvesicles with plasma membrane
Constitutive- substance for export continuously delivered to plasma membrane
Describe the functioning of receptor mediated endocytosis
- selective uptake of large molecules and particles
- clathrin-dependent
- Clathrin costed pits
- Clathrin molecules interact with cargo receptors via Adaptin
- Clathrin forms a basket-like cage
- drives vesicle formation
- Dynamin mediates the vesiclepinching off from the plasma membrane
- GTPase
In receptor mediated endocytosis, in what cases are receptors recyc’ed, with the ligand degraded ?
- low density lipoprotein (LDL) receptor
- insulin-glucose transporter
- other peptide hormone & their receptors
In receptor mediated endocytosis, in what cases are receptor and ligand recycled?
- iron, transferrin& transferrin receptor
- major histocompatibility complex I & II
In receptor mediated endocytosis, in what cases are receptor and ligand degraded?
-epidermal growth factor (EGF) & receptor
In receptor mediated endocytosis, in what cases are receptor & ligand transcytosis?
- secretion of immunoglobin (secretory IgA) into saliva
- secretion of maternal IgG into milk
What is vesicle targeting?
-Rab-GTPase interaction with tethering proteins
- docking complex
- Rab-GTPaseand receptor immobilize the vesicle near target membrane
- Accurate targeting
- vesicle specific membrane protein= v-SNARE
What is an endosome ?
Membrane-enclosed structure associated with endocytosis pathway
Contrast the early and late endosome pathway
Early endosome
- functions to sort and recycle proteins
Late endosome
-receives proteins for degradation
- receives newly synthesized lysosomal enzymes from the Golgi
- matures into a lysosome
Explain the functioning of pinocytosis
- cell drinking
- non-specific ingestion by small vesicles -constitutive
- invagination of plasma membrane
- no receptor proteins
- Clathrin-independent
- vesicle pinches-off
- fusion with lysosome
Explaine the functioning of phagocytosis
Ingestion of large particles
- microorganisms
- apoptotic cells
- non-biological materials
Generally performed by specialized phagocytes
- macrophage
- neutrophil
Particle binds to plasma membrane receptor (e.g. antibodies)
Extension of pseudopods
-dependent on actin microfilament polymerization
Phagosome fuses with lysosome
-digestion
Residual body-indigestible substances
