Biology 1202B Lecture Notes - Lecture 3: Transmembrane Protein, Membrane Transport Protein, Integral Membrane Protein
23 Jan 2017
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January 16, 2017
Biology Lecture 3 Notes
Transport and Signalling Part 2
Exocytosis
• Sometimes molecules are too big to move through a transmembrane protein
• Membrane bound vesicle contains molecules to be removed/secreted from a cell
o Vesicle fuses with plasma membrane at release
Endocytosis
• Reverse of exocytosis
o Plasma membrane infolds creating a vesicle
• Cells brings in macromolecules too large for transmembrane import
• Pinocytosis—vacuole created around extracellular fluid
o Non-specific, constant, cell drinking
• Receptor mediated endocytosis
• Transmembrane proteins recognize target molecule
o Binding leads to pocket formation, vesicle formation, highly specific, acquire bulk
quantities of a specific molecule
Membranes and cell signalling
• One of the characteristics of life is the ability to respond to changes in the environment
o At the cellular level this means perceiving and reacting to a signal
▪ Directly from the environment in single celled organisms
▪ From the environment or from other cells in multi-cellular organisms
Signal to response
• Receptor specific for signal molecule
o Extracellular signal—intracellular response
• Transduction may have any number of steps and mechanisms
• Response is activation or generation of a product
Surface receptors
• Transmembrane (integral) proteins
• Extracellular signal binding domain
o Highly specific for a particular molecule
o Binding causes conformational change in protein
▪ Transmission of signal through plasma membrane
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Document Summary
Transport and signalling part 2: sometimes molecules are too big to move through a transmembrane protein, membrane bound vesicle contains molecules to be removed/secreted from a cell, vesicle fuses with plasma membrane at release. Signal to response: receptor specific for signal molecule, extracellular signal intracellular response, transduction may have any number of steps and mechanisms, response is activation or generation of a product. Surface receptors: transmembrane (integral) proteins, extracellular signal binding domain, highly specific for a particular molecule, binding causes conformational change in protein, transmission of signal through plasma membrane. Initiates first steps in signal cascade: triggers cellular response. Amplification of signal transduction: once active, proteins which carry out reactions in the pathway can activate hundreds of downstream targets, more steps in a pathway means more potential for signal amplification. Cftr- normal: cystic fibrosis transmembrane conductance regulator, uses atp as energy source to actively transport cl- across the membrane, mutations to cftr gene causes altered cftr protein.
