biological membranes Flashcards
what are the roles of membranes at the surface of cells
plasma membranes are partially permeable, substances can move across the plasma membrane by diffusion or osmosis or active transport. plasma membranes also allow recognition by other cells and cell communication (sometimes called signalling)
what are the roles of membranes within cells
membranes around organelles act as a barrier between the organelles and the cytoplasm, this makes difference functions more efficient.
membranes can form vesicles to transport substances around the cell
membranes within cells are partially permeable so they can control which substances enter and leave the organelle
describe phospholipids in the fluid mosaic model
-hydrophilic head which attracts water, they face outwards
-hydrophobic tails which repels water
-center of phospholipids is hydrophobic so it doesn’t allow water soluble substances to pass through
-fat soluble substances dissolve in the bilayer and pass through the membrane
describe the role of cholesterol in the fluid mosaic model
-gives the membrane stability
-fit between phospholipids
-at high temps they bind to the tails causing them to pack more closely together which makes the membranes less fluid and more rigid
-at low temps, cholesterol prevents phospholipids from packing too close together, this increases membrane fluidity
-has hydrophobic regions, is able to create a further barrier to polar substances moving through the membrane
role of proteins in fluid mosaic model
-controls what enters and leaves the cell
-some form channels in membranes, these allow small charged particles through
-others form carrier proteins which transport larger molecules and charged particles across the membrane by active transport and facilitated diffusion.
-act as receptors for molecules in cell signalling, when a molecule binds to the protein, a chemical reaction is triggered inside the cell.
role of glycolipids and glycoproteins
-stabilise the membrane by forming hydrogen bonds with surrounding water molecules
-act as receptors for messenger molecules in cell signalling and are sites where drugs, hormones and antibodies bind.
-antigens, immune response
How do solvents affect membrane permeability?
Solvents like ethanol dissolve the lipids in the cell membrane, causing it to lose structure and increase permeability. Higher solvent concentrations lead to higher permeability. For example, ethanol increases permeability more than methanol.
What happens to membrane permeability at temperatures below 0°C?
Phospholipids have low energy and can’t move much, making the membrane rigid. Proteins in the membrane denature, increasing permeability. Ice crystals may form, piercing the membrane and causing high permeability when it thaws
How does temperature between 0°C and 45°C affect membrane permeability?
Phospholipids can move around, making the membrane partially permeable. As temperature increases, phospholipids gain more energy, increasing membrane permeability.
What happens to membrane permeability at temperatures above 45°C?
The phospholipid bilayer melts, and the membrane becomes more permeable. Proteins denature, and water enters the cell, increasing permeability further.
What role do membranes play in cell communication (cell signalling)?
Membranes are essential in cell communication by acting as platforms for cell signalling. Receptors embedded in the membrane detect specific signalling molecules, such as hormones or neurotransmitters. These receptors transmit the signal into the cell, triggering a specific response, such as activating enzymes or altering gene expression. This process ensures coordination between cells and tissues in a multicellular organism.
What is the role of membrane-bound receptors in cell communication?
Membrane-bound receptors are proteins on the cell surface that bind to signalling molecules like hormones, neurotransmitters, or drugs. When a ligand (e.g., a hormone or drug) binds to the receptor, it causes a conformational change, activating a signal transduction pathway inside the cell. This allows the cell to respond appropriately, such as by triggering metabolic changes, opening ion channels, or starting gene expression. Examples include insulin binding to its receptor to regulate blood glucose levels.
How do molecules move across membranes by diffusion?
Diffusion is a passive process where molecules move from an area of high concentration to an area of low concentration, down their concentration gradient. It does not require energy and occurs through the phospholipid bilayer for small, non-polar molecules like oxygen and carbon dioxide, or via channel and carrier proteins for facilitated diffusion of polar or charged molecules.
What is osmosis, and how does it work?
Osmosis is the movement of water molecules across a partially permeable membrane from a region of higher water potential to a region of lower water potential. It is a passive process that helps maintain water balance in cells
What effects do solutions of different water potential have on plant and animal cells?
Animal Cells: In hypotonic solutions (higher water potential outside), water enters the cell, causing it to swell and possibly burst (lysis). In hypertonic solutions (lower water potential outside), water leaves the cell, causing it to shrink (crenation).
Plant Cells: In hypotonic solutions, water enters, causing the cell to become turgid due to pressure against the cell wall. In hypertonic solutions, water leaves, and the cell becomes plasmolyzed, as the membrane pulls away from the wall.
what is facilitated diffusion, is it an active or passive process
movement of molecules across membranes through transport proteins. it is a passive process that doesn’t require energy
what processes require ATP for the movement of molecules across membranes, and how do they work?
active transport, endocytosis and exocytosis
active transport moves molecules against their conc gradient
endocytosis involves engulfing of substances into the cell
exocytosis involves the expulsion of substances from the cell
