ch 3 and 4 memb and transport Flashcards
cell membrane structure
- trilaminar app
-7 nm width
the dark layers are phospholipids heads and light are fatty acids tail
fluid mosaic (2 marks)
‘Fluid’ refers to the movement of phospholipids while ‘mosaic’ (constant motion) refers to the scattered proteins (and glycoproteins) in the phospholipid bilayer
effect of tail length on membrane fluidity
longer the tail, the less fluid the membrane
Effect of fatty acid composition on membrane fluidity
the more unsaturated they are, the more fluid the membrane. This is as unsaturated fatty acid tails are bent and fit together more loosely
Cholesterol
- Regulates the fluidity of membrane
- At low temperatures, cholesterol increases the fluidity of the membrane preventing it from being too rigid, this is because it prevents close packing of phospholipid tails
- At high temperatures, cholesterol decreases the fluidity of membrane and stabilises the cell
found in animal imp as leakage of ions will slow down nerve impulses
glycolipids and glycoproteins
carbohydrate chains projecting out of lipids+proteins-
- Stabilises the membrane structure by forming hydrogen bonds with water molecules surrounding the cell
- Glycocalyx - sugary cell coating formed by carbohydrate chains
- Act as receptor molecules: (Signalling receptors - recognise messenger molecules like hormones and neurotransmitters; Endocytosis - bind to molecule to be engulfed by membrane)
- Act as cell markers/antigens allowing cell-cell recognition
channel proteins
- do not require energy
- transport substances through membrane passively, along their concentration gradient
- used for both active transport and facilitated diffusion
cell signaling cascade
- signal arrives at protein receptor in cell membrane
- the receptor’s shape is complementary to the ligand
- the signal brings about a change in the receptor’s shape
- changing the shape of the receptor allows it to interact with the next component of the pathway so the message gets transmitted
- binding triggers/stimulates reactions within the cell
- cell signalling results in a response which may be intracellular or extracellular
carrier proteins
- require energy
- go against the concentration gradient
- take substances from outside and pumps it inside or vice versa
- used for active transport
diffusion
Net movement of non polar molecules or ions from a region of higher concentration to a region of lower concentration down a gradient, as the result of the random movement of particles
facilitated diffusion
- Diffusion of a substance (polar mol) through transport proteins in a cell surface membrane
- The proteins provide hydrophilic areas that allow the molecules or ions to pass through the membrane which can fit and bind to it so they change shape this process require no extra energy from resp
Osmosis
Net movement of water molecules from a region of higher water potential to a region of lower water molecules (dipolar) potential through a partially permeable membrane as a result of their random motion (most by aquaporins because it has hydrophilic lining)
The membrane surrounding the vacuole, called the tonoplast, has a fluid mosaic structure. Describe the structure of this membrane. 4M
1) phospholipid bilayer
2) phospholipids have hydrophilic heads and hydrophobic tails
3) labile nature of bilayer structure is due to phospholipids moving within their monolayer
4) protein molecules, interspersed / scattered / not a complete layer
5) many different protein molecules present
6) idea of most proteins moving / not in fixed position
uniport
pump ones kind of ions into or out cell
Endocytosis
Bulk movement of liquids (pinocytosis) or solids (phagocytosis) into a cell by the infolding of the cell membrane to form vesicles containing the substance
Exocytosis
Bulk movement of liquids or solids out of a cell by the fusion of vesicles containing the substance with the cell surface membrane guided by cytoskeleton using atp
phospholipid molecules
phospholipid molecules have hydrophilic heads which face water and hydrogen bond and hydrophobic tails which repel water.by this the phospholipid molecules arrange themselves tail to tail to form a phospholipid bilayer with hydrophobic core
why cells need cholesterol
1) for membrane stability
2) regulating fluidity of membrane
3) production of steroid hormones
carbohydrates
attached to protein molecule in the cell surface membrane forming glycoproteins,& to lipids forming glycolipids. they point outwards. glycoproteins & glycolipids are also known as glycocalyx
Aquaporin
to increase permeability of membrane to water for more abs of water
protein function
act as enzyme
anchors the cytoskeleton
cotransport
pumps one kind in and another kind out at the same time
pumps two diff mol across memb at same time
what increases fluidity of the cell membrane?
-shorter the length of the fatty acid tails the more fluidity
-the Prescence of many unsaturated fatty acid the more fluidity
-the more cholesterol the more fluidity
there are 4 ways through which charged practicles can move
-simple diffusion and osmosis
-active transport
-facilitated diffusion
-cytosis
explain how CO2 be excreted from the body
CO2 diffuses through phospholipid bilayer of endothelial cell membrane of capillaries and alveolar epithelial cell memb down conc gradient
carbohydrates
attached to protein mol in the cell surface membrane forming glycoprotein and lipids forming glycolipids, they point outwards, glycoproteins and glycolipids are also known as glycocalyx
active transport
movement of polar mol through specific protein transporters “carriers” with complementary vinding site, fit and bind to them changing it shape “conformational change” to pass across the phospholipid bilayer against concentration gradient using ATP
explain what disrupts the permeability cell membrane
alcohol: dissolves the hydrophobic core of the phospholipid bilayer
temp: it increases the KE of phospholipids molecules increasing the fluidity and breaks down the hydrogen and ionic bonds on the protein mol held in the cell surface membrane changing it shape and specificity
acids: changing the PH breaks down the ionic bonds of protein molecules held in the membrane changing it3D shape and specificity
reducing agents: break down the disulfide bonds of protein molecule
explain why glucose cant pass through phoph bilayer
large in size
glucose is polar and water soluble and cant pass through hydrophobic core
protein structure
-intrinsic (span whole protein)
-extrinsic (partial)
-peripheral
role of cell surface membrane
act as barrier between cytoplasm and ext env
cell to cell adhesion
cell recognition
flexibility of the cell
anchors to cytoskeleton
has specific receptors for hormones
sites for enzyme to catalyze rxns
formation of hydrogen bonds with water mol for stability of the memb
