L1 Flashcards
Hierarchical organisation of the human body
Atoms and molecules < Macromolecules and organelles < Cells < Tissues < Organs < Organ systems
What’s cytology?
Branch of science studying cells which differ in size/shape/function etc. but are the structural and functional units of all living organisms
Main features of eukaryotic cells
- nucleus with genetic information
- membrane-bound organelles
- cytoplasmic matrix
- cell membrane
Cell or plasma membrane:
- where?
- why?
Around cells and organelles.
- to maintain structural integrity
- to enable movement and expansion
- to receive and transmit info
- selective barrier
- trafficking of molecules
What are the main components of the cell membrane?
- phospholipids 30-40%
- proteins 40-50%
- cholesterol
- sugars (glycoproteins, glycolipids)
Main features of the plasma membrane
Heterogenous
Dynamic
Asymmetry
Bilayered
Phospholipids
- amphipathic
- phosphoglycerides vs. sphingolipids
- residues
What’s peculiar about phosphatidyl-serine?
Found only on the internal layer.
If on outer layer, signal of apoptosis
What are the 3 functions of cholesterol in the plasma membrane?
- less deformable
- less permeable
- prevents crystallization of FA tails
Thickness of cell membrane
7.5 nm
Glycocalyx : composition and functions
Mucus layer of glycoprotreins and glycolipids, on external layer ONLY!
Selective barrier and molecular filter, may contain enzymes (ie. GI tract).
Also involved in cell-to-cell adhesion and recognition (ie. diapedesis of WBCs)
Structural classification of proteins in the bilayer (2 groups)
Extrinsic vs. Integral
Functional classification of proteins in the bilayer (4 groups)
- Enzymes
- Linkers
- Receptors (ie. EGFR and lipid rafts)
- Transporters
Fluid-mosaic model
Mosaic - because of its heterogenous appearance
Fluid - phospholipids and proteins able to move (mostly laterally, flip-flop movement rare)
Evidence for fluid mosaic model?
Hybrid mouse-human cell - mixed molecules in plasma membrane
Factors affecting fluidity?
Temperature and unsaturated FA chains - direct proportionality
Proteins, cholesterol, longer FA chains - inverse proportionality
3 forms of transport across the membrane (for small-medium molecules only)
- simple diffusion ie. O2, CO2
- facilitated diffusion ie. glucose, aquaporins
- active transport ie. sodium-potassium pump
…how about transport across the plasma membrane of large molecules?
Vesicle-mediated
= endocytosis and exocytosis
Clinical drop. Vincristine and ABC transporter
Chemotherapeutic drug able to enter cancer cells via simple diffusion. However, if ABC transporter present, drug expelled.
What can be done? Inhibit the transporter to reinstate drug sensitivity
Endomembrane system
System of intracellular, membraneous organelles including:
- nucleus
- endoplasmic reticulum
- golgi apparatus
- mitochondria
- lysosomes
General features of endoplasmic reticulum
System of tubules/cisternae of variable shape, extension based on cell needs
rER
Rough - many ribosomes
Continuation of nuclear envelope
Functions include:
- PROTEIN SYNTHESIS
- post-translational modifications (ie. proteolysis, phosphorylation, glycosylation only at asparagine)
- protein steric conformation
- hydroxylation of lysine and proline residues
Import of proteins into rER
Signal hypothesis (SRPR - signal recognition particle receptor)
Soluble vs. membrane proteins
Ribosomes, main features
Molecules of DNA, RNA and proteins
2 subunits, bound only for protein synthesis (60, 40, 80 in eukaryotes, 50, 30, 70 in prokaryotes)
Free (proteins remaining within the cell) vs. rER ribosomes (proteins for cell membrane or to be secreted)
sER
Smooth - no ribosomes
Functions include:
- synthesis of lipids and steroids
- storage of ions
- glucose-6-phophatase in hepatocytes (glycogen catabolism)
- biogenesis of cell membranes (phospholipids and flippases)
- detoxification processes (addition of OH group to facilitate elimination)
