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Questions and Answers
What characteristic of cell membranes allows them to regulate the movement of substances?
What characteristic of cell membranes allows them to regulate the movement of substances?
Which part of a phospholipid is hydrophilic?
Which part of a phospholipid is hydrophilic?
What is the primary reason that phospholipid bilayers restrict the passage of water-soluble substances?
What is the primary reason that phospholipid bilayers restrict the passage of water-soluble substances?
What type of interactions help hold the phospholipid bilayer together?
What type of interactions help hold the phospholipid bilayer together?
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What allows for the fluidity and flexibility of the phospholipid bilayer?
What allows for the fluidity and flexibility of the phospholipid bilayer?
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What role do proteins play in the phospholipid bilayer?
What role do proteins play in the phospholipid bilayer?
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What is the arrangement of phospholipids in a membrane when exposed to water?
What is the arrangement of phospholipids in a membrane when exposed to water?
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What is the significance of endocytosis and exocytosis in relation to cell membranes?
What is the significance of endocytosis and exocytosis in relation to cell membranes?
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Study Notes
Cell Membranes
- Membranes enclose the contents of a cell, separating internal components from the external environment.
- This separation allows internal conditions to be regulated.
- Cell membranes have two key properties:
- Semi-permeability: Only certain materials can pass through.
- Selectivity: Membranes control the movement of materials.
- Primarily composed of two biomolecules:
- Phospholipids (non-polar barrier).
- Proteins (selectivity).
Phospholipids
- Structure:
- Polar head (glycerol and phosphate).
- Two non-polar tails (fatty acids).
- The head is hydrophilic (attracted to water).
- The tails are hydrophobic (repelled by water).
- Phospholipids are amphipathic molecules.
- Arrangement in membrane:
- In water, phospholipids form a spontaneous bilayer.
- Tails face inwards, heads face outwards.
Phospholipid Bilayer
- Properties:
- Held together by weak hydrophobic interactions between the fatty acid tails.
- A central hydrophobic layer restricts the passage of most water-soluble substances.
- Individual phospholipids move within the bilayer, contributing to membrane fluidity and flexibility.
- Fluidity allows for spontaneous breaking and reforming of membranes (endocytosis/exocytosis).
Membrane Proteins
- Embedded within the phospholipid bilayer.
- Can be classified as integral or peripheral.
-
Integral Proteins:
- Permanently attached to the phospholipid bilayer.
- Require detergents to remove (transmembrane).
-
Peripheral Proteins:
- Temporarily associated with membrane periphery.
- Can be removed with salts or pH changes.
Protein Functions
- Membrane proteins have a variety of functions:
- Junctions: Connect cells.
- Enzymes: Localize reactions.
- Transport: Facilitated diffusion and active transport.
- Recognition: Function as markers for "self."
- Anchorage: Attachment points for the cytoskeleton and extracellular matrix (ECM).
- Transduction: Function as receptors for peptide hormones.
Glycosylation
- Phospholipids and proteins can have carbohydrate chains attached (glycolipids or glycoproteins).
- The carbohydrate extends from the extracellular side of the membrane.
- Functions in adhesion and recognition.
- Can serve as attachment points (e.g., sperm binding).
- Can act as recognition points (e.g., ABO blood groups).
- Functions in adhesion and recognition.
- Plays a role in anchoring cells to the extracellular matrix (ECM).
Fluid Mosaic Model
- A model describing the structure of cell membranes.
- Phospholipid bilayer with proteins embedded and carbohydrates attached.
- Proteins and phospholipids can move laterally within the membrane.
Topic Connections
- Carbohydrates: Glycoproteins in cell-cell recognition.
- Cell Theory: Freeze-fracturing visualized membrane proteins.
- Cell Respiration: Membrane-bound enzymes in aerobic respiration.
- Cell Signaling: Integral proteins as transmembrane hormone receptors.
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