Membranes and Membrane Proteins Flashcards
What are the general functions of the Plasma Membrane?
- Highly selective permeability layer
- Control on an enclosed chemical environment
- Recognising Signalling molecules
What is the composition of a Lipid Bilayer?
In reference to Protein, Carbs, Water, Fat
- 20% of total weight is water
Of dry weight:
40% Lipid
60% Protein
1-10% Carbs
What are the 4 methods of Phospholipid movement?
- Lateral Diffusion
- Rotation
- Flip Flop
- Flexion
Compare Cerebrosides and Ganglioside Glycolipids
Cerebro: Sugar monomer on head group
Ganglio: Sugar multimer on head group
Describe the structure of Cholesterol
- Polar head group
- Rigid planar steroid ring structure
- Non polar hydro carbon tail
Explain how Cholesterol has paradoxical effects on fluidity?
- Reduced phospholipid chain motion, REDUCED fluidity
- Reduced phospholipid packing, INCREASED fluidity
Outline the Functional and Biochemical evidence of Membrane Proteins?
Funcional :
- Facilitated Diffusion
- Specific Cell responses
- Ion gradients
Biochemical:
- Freeze Fracture
- Gel Electrophoresis of Proteins
What are the 3 ways protein move?
- Lateral Diffusion
- Rotation
- Conformational change
What are 3 restrictions on Protein mobility?
- Association of Membrane proteins
- Association of extra membranous proteins
- Proteins tend towards fluid phase/ low cholesterol regions
Compare the 2 different membrane protein types?
Integral:
- Span entire Membrane
- Act as channels
- Hydrophobic interactions
Peripheral:
- On surface
- Structural strength
- Hydrophilic interactions
Describe the RBC skeleton composition
Identify the Adapter and Integral proteins
Spectrin and Actin are held in place by Band 4.1 and Ankyrin (Adapter proteins), binded to Glycophorin A and Band 3 (Integral proteins)
Compare the 2 types of Haemolytic Anaemias
- Cellular basis
- Physiological Result
Which abnormal cell is removed by which organ?
Hereditary Spherocytosis:
- Spectrin deleted by 40%-50%
- RBCs round up, less resistant to lysis
- Cleared by spleen
Hereditary Elliptocytosis:
- Defect In Spectrin
- Elliptical RBCs
Describe the biosynthesis of Secreted proteins in 5 steps
- Two ribosome subunits come together to read mRNA, make a Signal Sequence
- Signal Sequence is recognised and binded to by a Signal Receptor Particle (SRP), which prevents further peptide Synthesis
- SRP binds to a Docking Protein bringing the ribosome complex to the ER membrane.
- Signal Sequence is released and picked up by a Signal Sequence Receptor, and moved through a Protein Translator Complex
- Signal peptidase cleaves the Signal Sequence, as it is no longer needed to move Protein towards ER
Describe Membrane Protein Biosynthesis after the Signal Sequence is picked up by Signal Sequence Receptor
- Protein is fed through the ER membrane until a hydrophobic Stop-Transfer is reached. Ribosome is pushed away
- Ribosome makes rest of protein in cytoplasm
How is the Orientation of a secretory protein controlled?
- N terminal goes through ER membrane towards lumen
- (+)ve charges on N terminal stick to Signal Sequence Receptor, forming a loop of protein
- Signal Peptidase cleaves N terminal, so that it can continue growing into lumen
How is the orientation of a Membrane Protein controlled?
- While passing through membrane, Hydrophobic Stop-Transfer sequence holds N terminal in membrane
- Signal peptidase cleaves N terminal
- Peptide growth continues with C terminal being inside cytoplasm
