movement of substances Flashcards
The membrane of cells is made almost entirely of ___ and ___, together with a small amount of ____.
The lipid of membranes is ____ and ____.
The membrane of cells is made almost entirely of protein and lipid, together with a small amount of carbohydrate.
The lipid of membranes is phospholipids and cholesterol.
What makes up a phospholipid molecule?
A glycerol-phosphate hydrophilic “head”, and a hydrophobic tail made out of 2 hydrocarbon chains
When mixed with water, phospholipid molecules arrange themselves into a _____ in the ___ ____ _____, in which the hydrophobic tails are _____ to each other.
When mixed with water, phospholipid molecules arrange themselves into a bilayer in the cell surface membrane, in which the hydrophobic tails are attracted to each other.
What are the two types of proteins in the phospholipid bilayer?
Integral proteins: partially/fully buried in the phospholipid bilayer
Peripheral proteins: superficially attached on either surface of the phospholipid bilayer
What are the roles of membrane proteins in the phospholipid bilayer?
Channel proteins (for passage through the membrane): each channel allows one specific substance to pass Pump proteins: for active transport across the membrane, energy from ATP is used selectively to move one or two specific substances across
Why is it called the fluid mosaic model?
The membrane is described as fluid because the components (lipids and proteins) move around within their layers
The word “mosaic” describes the scattered pattern of the proteins
Why is the membrane so fluid?
Phospholipids of the membrane are a mixture of saturated and unsaturated fatty acid tails. An excess of unsaturated fatty acid tails makes the membrane more fluid.
- Because the kinks in the tails prevent close-packing of the lipids
(presence of cholesterol reduces fluidity by preventing/reducing movements of lipid molecules)
Diffusion is…
Diffusion is the net movement of molecules from a region of higher concentration to a region a lower concentration, down a concentration gradient, using kinetic energy from the continuous random movement of molecules.
What kind of molecules diffuse through simple diffusion?
- Small, non polar molecules (e.g. oxygen/carbon dioxide)
- Fat-soluble molecules (e.g. vitamin A)
- Membrane is fully permeable
Facilitated diffusion is…
Facilitated diffusion is the diffusion of ions and polar molecules through cell surface membranes using specific protein channels or carriers, down a concentration gradient, from a region of high concentration to a region of low concentration.
What are channel and carrier proteins?
- Carrier proteins are protein-lined pores that are large enough for a molecule to pass through
- Channel proteins are globular proteins that can form pores large enough for diffusion. Pores close up when molecules are no longer present
What is active transport?
Active transport involves the movement of molecules from a region of lower concentration to a region of higher concentration, AGAINST a concentration gradient, using metabolic energy in the form of adenosine triphosphate (ATP) produced by the cell.
What are the key/defining features of active transport?
- It occurs against a concentration gradient
- for useful molecules and ions - It is a highly selective process
- only molecules that are very needed will be more likely to be taken in - It involves special molecules of the membrane called “pumps”
- globular proteins that transverse the lipid bilayer, require ATP, specific to particular molecules (selective), either uni/bidirectional
What is bulk transport?
Bulk transport occurs by the movement of vesicles of matter (solids/liquids) across the cell surface membrane. This requires ATP
- Exocytosis (exit) and endocytosis (enter)
- Phagocytosis (solids) and pinocytosis (fluids)
Osmosis is…
Osmosis the net movement of water molecules from a region where water is at a higher water potential through a partially/selectively permeable membrane to a region with a lower water potential
