Lesson 15 - Structure and function of membranes Flashcards
Compartmentalisation
The formation of separate membrane-bound areas in a cell. It is vital to a cell as metabolism includes many different and often incompatible reactions. Allows for specific conditions, maintains chemical gradients and protects vital cell components
Name of cell-surface membrane
Plasma membrane
Describe phospholipid bilayer:
Phospholipids composed of a phydrophilic phosphate head and hydrophobic fatty acid tails.
Therefore, there is a hydrophobic core of phospholipid tails and the hydrophilic heats interact with water / aqueous solution.
When were cell membranes first seeN/
After the invention of the electron microscope.
- Two black parallel lines.
- Theory = Composed of a lipid bilayer
Who proposed the fluid-mosaic model?
Singer and Nicolson
Fluid-mosaic bilayer:
- Proteins embedded in the bilayer vary in shape, size and position. (particular to each type of cell)
- Phospholipids are free to move within the layer relative to each other. Provides flexibility.
Two types of cell-surface membrane proteins:
- Intrinsic
- Extrinsic
Intrinsic proteins: (Integral proteins)
- Transmembrane proteins that are embedded in both layers of a membrane.
- Have amino acids with hydrophobic R-groups on their external surfaces, which interact with hydrophobic core of the membrane. This keeps them in place.
Types of intrinsic proteins?
- Channel proteins
- Carrier proteins
Channel proteins:
- Hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient through membranes. They are held in position by interactions between hydrophobic core of the membrane and the hydrophobic R-groups on the outside of proetins.
- Passive / diffusion gradient
Carrier proteins:
Important role in both passive and active transport into cells. This often involves the shape of the protein changing.
- Sodium / potassium pump
Glycoproteins?
- Intrinsic proteins.
- Embedded in the cell-surface membrane with attached carbohydrate (sugar) chains of varying lengths and shapes.
- Play a role in cell adhesion and as receptors for chemical signals.
Receptors in chemical signals?
- Receptors for neurotransmitters such as acetylcholine at nerve cell synapses. Binding of neurotransmitters triggers or prevents an impulse in the next neurone.
- Receptors for peptide hormones, including insulin and glucagon, which affect the uptake and storage of glucose by cells.
- Drugs: beta blockers (reduce response of the heart to stress.
Cell adhesion
When cells join together to form tight junctions in certain tissues
Permeability of cell membranes:
- Water can diffuse through lipid bilayer
- Aquaporins (protein channels that allow the passage of water)
- Partially permeable
Glycolipids:
Lipids with carbohydrates chains attached.
- Cell markers / antigens and can be recognised by the cells of the immune system as self or non-self.
Can large, lipid soluble molecules move through cell membranes?
Yes
Extrinsic proteins:
Normally have hydrophilic R-groups on their outer surfaces and interact with the polar heads of the phospholipids or with intrinsic proteins.
- Present in either layer or between.
Cholesterol:
Lipid with a hydrophilic end and a hydrophobic end, like a phospholipid.
- Regulates fluidity of membranes.
ATPase / ATP synthase
Manufactures ATP - embedded in the mitochondrial membrane.
- Membrane bound
Cholesterol in membranes structure:
- Positioned between phospholipids in membrane bilayer
- Hydrophilic end interacting with heads and hydrophobic end interacting with tails. Pulls them together
- Adds stability to membranes (without making too rigid)
- Prevents membranes from becoming too solid by stopping phospholipid molecules from grouping too closely and crystallising.
Enzymes in membranes:
Need to be in particular positions for chemical reactions to take place.
- Eg. ATP synthase and electron carriers within the cristae (inner membrane of mitochondrion) for production of ATP in respiration.
- Enzymes in photosynthesis are found on the membrane stacks within the chloroplasts.
Cytoskeleton:
Acts as an anchor and maintains the integrity of the membrane (prevents falling apart)
