Lecture 13 Membrane Structure Flashcards
What are the essential functions of biological membranes? (4) RCCS
Regulate the import/export of molecules.
Compartmentalize processes to increase efficiency.
Facilitate cell-cell recognition through glycoproteins and glycolipids.
Mediate signalling across the membrane using proteins and lipids.
what are cell membranes composed of?
lipid bilayers
what type of molecule characteristic makes the cell membrane and what interactions does it need to do this?
Formed by amphipathic molecules via non-covalent interactions.
what are cell membranes impermeable to?
polar or charged molecules.
what is membrane fluidity maintained by?
lipids and cholesterol
Why is membrane fluidity important? (2)
Enables movement of molecules and signals across the membrane.
Allows proteins to change conformation for function.
What do the terms “fluid” and “mosaic” mean in the Fluid Mosaic Model?
Describes membranes as fluid because components move within the membrane and mosaic referring to the mixture of lipids, proteins, and carbohydrates
who created the fluid mosaic model and when?
Proposed by Singer and Nicolson in the 1970s.
what does FRAP stand for?
Fluorescence Recovery After Photobleaching
what does FRAP measure?
measures molecule movement
describe the process of FRAP
A fluorophore is bleached with a laser, and the movement of unbleached molecules into the area is tracked
What does FRAP demonstrate about lipids and proteins?
Lipids and proteins move from side to side within the membrane.
What does FRAP demonstrate about lipid rafts?
Lipid rafts can restrict molecule movement.
What does FRAP demonstrate about protein diffusion?
depends on interactions with other proteins or the cytoskeleton.
What enzymes maintain membrane asymmetry?
Flippases, floppies, Scramblases
what is the job of Flippases and what does it use to do this?
Move lipids within the membrane using ATP.
Why are biological membranes asymmetric?
Each leaflet of the membrane has different lipid and protein compositions.
Sugars are added to lipids and proteins in different ways as post-translational modifications.
what is the job of floppies and what does it need in order to do this?
Move lipids to the outter part of the membrane using ATP.
what is the job of Scramblases?
Move lipids down their gradient to create symmetry.
What are the three main types of lipids?
storage, structural and signalling
what is an example of a storage lipid and what does it store?
Triacylglycerides store energy.
what are examples of structural lipids and what are their jobs?
Phospholipids and sphingolipids form membranes.
how do Saturated lipids affect membrane fluidity?
reduce fluidity
what are examples of signalling lipids and what are their jobs?
Sterols and eicosanoids participate in signalling pathways.
how do unsaturated lipids affect membrane fluidity?
increase fluidity
How do harsher detergents help purify membrane proteins?
Detergents form micelles around hydrophobic regions to solubilize proteins.
how does cholesterol affect membrane fluidity?
modulates fluidity by preventing extremes, like the membrane becoming too rigid or too fluid
What is a key characteristic of how milder detergents help purify membrane proteins compared to harsher ones?
Milder detergents preserve protein structure; harsher ones denature proteins.
How can the topology of a membrane protein be predicted?
DNA sequencing and protein prediction algorithms identify hydrophobic regions.
how many hydrophobic amino acids are needed to span the membrane in an alpha helix?
About 20
