Biomembrane April 2014(2)

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BIOMEMBRANE

Rondang R. Soegianto

2014

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MEMBRANE STRUCTURE

- Bilayer

- Fluid

- Asymmetric

- Dynamic

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Peck Ritter P353 Fig 9.22

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Peck Ritter P354 Fig 9.23

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COMPOSITION

- Lipid Phospholipid Sphingolipid Cholesterol

- Protein Extrinsic (Cytoskeleton) Intrinsic (Transmembrane)

- Carbohydrate Oligosaccharide (Sialic acid)

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Harper’s P469 Fig 43-2

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FUNCTION OF COMPONENTS

Phospholipid- Interaction with membrane protein- Effect on protein conformation- Effect on membrane integrity

Sphingolipid- Myelin sheath in nerves

Cholesterol- Contributes to membrane strength- Prevents sticking together of phsphlpd tails - Controls diffusion of water into cells

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Protein

Intrinsic: - Transport - Enzymes - Receptors

Extrinsic: Cytoskeleton

Protein Membrane density Membrane identity

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Carbohydrate

Located on outer surface

Glycoproteins involved in- Cell-cell interaction- Immune system to distinguish self and non-self cells- Blood group substances (individually different but can be matched)

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TRANSPORT

Simple Diffusion- Small molecules: CO2, O2, H2O, Urea Move from high to low concentration

- Facilitated Diffusion by carrier system Transport along concentration gradient Example: Glucose transporter (Glut)

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- Active Transport Involves carrier protein (Transporter) Requires chemical energy (ATP) Moves particles against conc. gradient Ex.: Na+, K+- ATPase, Ca2+-ATPase Proton pump

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Nature of Transport Process

Uniport: Ca-pump

Cotransport Symport: Glucose absorption from intestinal mucosa needs Na+ Antiport: Na-pump, ATP-ADP translocase Anion exchanger (Band 3 in ery- . throcytes)

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Transport of Macromolecules

Endocytosis Receptor-mediated endocytosis Glut 4 carries glucose into muscle and adipose tissue after insulin binding to its receptor

Exocytosis Ex.: In nerve synapse. Vesicles containing neurotransmitter fuse with membranes and secrete vesicle content into synaptic gap.

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CELL COMMUNICATION

Cells communicate physically thru junctions.

Tight junction: Intestinal mucosa

Gap junctions: Cooperation of neighboring cells

Desmosomes: Spot desmosome Belt desmosome

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Harper’s P479 Fig 43-12

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Harper’s P480 Fig 43-13

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Harper’s P482 Fig 43-16

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Harper’s P485 Fig 43-19

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Peck Ritter P368 Fig 9.34