2.5 biological membranes Flashcards
Why is the fluid mosiac model called ‘fluid’?
- phospholipids and proteins can move by diffusion
- phospholipids move side to side
Why is the fluid mosiac model called ‘mosiac’?
- scattered pattern produced by proteins within the phospholipid bilayer
Structure of a phospholipid
- hydrophillic head
- hydrophobic fatty acid tail (non-polar)
- fatty acid tails face inwards creating a barrier against water soluable substances (polar substances)
Role of cholesterol in the fluid mosiac model
regulate fluidity and stability of the membrane
* stops it being too rigid at low temperatures and too fluid at high temperatures
* stops phospholipids packing too close together
Role of glycoproteins and glyolipids in the fluid mosiac model
- forms hydrogen bonds with water to stabilise membrane
- cell adhesion in tissue formation
- receptors for cell signaling
- antigens for cell recognition
Role of extrinsic proteins in the fluid mosiac model
partly embedded in the bi-layer
contain mainly hydrophillic R-groups
What are the key internal membrane functions
- isolation
- comparmentalisation
- control what enters and leaves the cell
- site of chemical reactions
Definition of bulk transport
a form of active transport that requires ATP but doen’t require a concentration gradient
Definition of endocytosis
bulk transport into cells
2 types: phagocytosis (solid) and pinocytosis (liquid)
Function of the phospholipids in the bi-layer
to create a partially permeable membrane
Defintion for exocytosis
bulk transport out of the cell
Process of exocytosis
- transport out of the vesicles from the golgi appartus
- move towards and fuse with the cell surface membrane
- the contents are released outside of the cells
Process of endocytosis
- cell membrane invaginates (bend inwards) when in contact with the substance to be transported
- membrane enfolds until the membrane fuses to make a vesicle
- this pinches off and moves to the cytoplasm for further transfer ( moved by cytoskeleton )
Role of the cytoskeleton
- changes cell shape to engulf materials
- movement of secertory vesicles
- fusion with the cell membrane
Definition of cell signaling
communication between cells to trigger a reaction within the target cell
How do glycoproteins act as a receptor
specific shape which is complementary to the shape of the signalling molecule
Definition of diffusion
net movement of a substance from a region of high concentration to a region of low concentration
- caused by natural kinetic energy
What can pass through the PL bi-layer
- oxygen/carbon dioxide (small)
- lipid soluable molecules (alcohol, steriod hormones)
- water
What cannot pass through the PL bi-layer
- ions (charged - so they are repelled against non-polar fatty acid tails)
- polar/ large molecules (too large)
Definition of faciliated diffusion
net movement of molecules from an area of high concentration to an area of low concentration across a partially permeable membrane via protein channels
Functions of a channel protein
transport charged substances (ions)
acts as gates so part of the inside surface of the membrane can moves to close or open the pores
Function of carrier proteins
can change between two shapes
creates a binding site to be open
the direction of movement depends of the concentrations
Factors affecting diffusion
- concentration gradient
- temperature
- surface area
- distance
- membrane
- size of diffusing molecule
How does the concentration gradient affect diffusion
the steeper the concentration gradient the faster the rate of diffusion
