1/5/15 1 Chapter 2: Cells and Cell Processes I. Cells A. Membranes B. Epithelia II. Metabolism III. Enzymes IV. Cell Signaling I. Cells A. Membranes: Control and regulate movement of substances across and between body regions, organs, etc. Chapter 2: Cells and Cell Processes Cell membrane structure 1. Phospolipids 2. Proteins 3. Carbohydrates Phospholipids • Primary component of cell membrane – Made up of lipids (fats) and phosphates – Provides barrier at cell membrane Phospholipids • Bilayer structure is due to polarity and hydrophilic properKes of phospolipid structure Phospholipids • Bilayer chemical composiKon is highly diverse – Affects cell membrane properKes • Membrane fluidity (rigidity) • Saturated tails have NO double bonds • Unsaturated tails have one or more double bonds Double bonds = Fluidity
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Chapter 2: Cells and Cell Processes
I. Cells A. Membranes B. Epithelia
II. Metabolism III. Enzymes IV. Cell Signaling
I. Cells A. Membranes:
Control and regulate movement of substances across and between body regions, organs, etc.
• Most physiological processes will NOT proceed without appropriate enzymes – Cells must
synthesize their own enzymes
Enzymes • Only catalyzes or regulates reacKons with
substances to which it is bonded: enzyme-‐substrate complex
Enzymes as catalysts • CATALYST: Molecule that accelerates a
reacKon, without being altered itself • Note that Enzyme emerges unaltered!
Enzymes as catalysts • ReacKon rate determined by:
1. Amount of enzyme and substrate available
• ReacBon rate/velocity: Amount of substrate converted to product per unit Kme
Enzymes as catalysts • ReacKon rate determined by:
1. Amount of enzyme and substrate available 1. Substrate concentraKon low, relaKve to enzyme
2. As E-‐S complexes form, rate slows • Fewer free
substrate molecules 3. When all enzymes
“used”, reacKon reaches Vmax OR Maximum Velocity
• CatalyBc effecBveness: Extent to which enzyme lowers the acKvaKon energy required for reacKon
Enzymes as catalysts • ReacKon rate determined by:
1. Amount of enzyme and substrate available 2. Enzyme’s catalyKc effecKveness
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• Enzymes and substrates don’t always bond when come into contact
Enzymes as catalysts • ReacKon rate determined by:
1. Amount of enzyme and substrate available 2. Enzyme’s catalyKc effecKveness 3. Enzyme-‐substrate affinity
Enzymes as regulators 1. Speed chemical reacKons 2. Regulate chemical reacBons • Synthesizing specific (new and/or different)
enzymes
Denaturing of enzyme and proteins • Physiological stressors can denature proteins – Can disrupt and/or halt their funcKon – High temperature, low O2, toxic chemical
exposure
• Molecular chaperones correct this damage – Heat-‐shock
proteins in snails and mussels on clear days at low Kdes
Chapter 2: Cells, Enzymes, and Cell Signaling
• Take aVendance!!
Enzymes as regulators 1. Speed chemical reacKons 2. Regulate chemical reacBons • Synthesizing specific (new and/or different)
enzymes • Changing catalyKc properKes of exisKng
enzymes
Enzymes operate at all Kme scales
Mediated by exisKng enzymes Mediated by synthesizing new enzymes Genes coding for specific enzymes adapt
to changing environment
Enzymes synthesized at different Kme intervals during development
CatalyKc acKvity of some enzymes
fluctuate throughout the day
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Chapter 2: Cells, Enzymes, and Cell Signaling
I. Cells A. Membranes B. Epithelia
II. Metabolism III. Enzymes IV. Cell Signaling
Cell signaling
• Coordinate cell funcKons throughout the body • CommunicaKon
between cells necessary for all cellular funcKons
This looks complicated....
Cell signaling • Receptor proteins in cell membrane control transfer of specific molecules
Cell signaling: Receiving signals • Starts when ligand binds with receptor protein – Ligand: any molecule that bonds with a receptor protein
– Receptor site: where that bond occurs • Four types of receptors
1. Ligand-‐gated channels 2. G protein-‐coupled 3. Enzyme/enzyme-‐linked 4. Intracellular
1. Ligand-‐gated channel • Protein is both receptor and channel
Video
1. Ligand-‐gated channel • Protein is both receptor and channel • Channel opens in presence of ligand
Video
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2. G-‐protein coupled receptors 1. Protein receptor ac/vates a G-‐protein aner
binding to ligand (1st messenger) 2. G-‐protein + enzyme (or other membrane
protein) à disKnct signaling compound (2nd messenger)
Molecules DO NOT pass through cell membrane
video
3. Enzyme/enzyme-‐linked receptors • Cell membrane proteins are also enzymes
• Molecules DO NOT pass through cell membrane
• Binding with ligand triggers acKvaKon of catalyKc site – Produces 2nd messenger
4. Intracellular receptor • Receptor proteins inside the cell
• Only small ligands that can diffuse through membrane
• Intracellular process proceeds normally – E-‐S complexes formed