Movement across Membranes Flashcards
Movement of small, non-polar substances:
Diffuse through phospholipid bilayer
{{Exception: water (polar) but so abundant that it diffuses in}}
Movement of large substances across membrane:
Using transport / carrier proteins Endocytosis/ pinocytosis/ phagocytosis Protein pump (not channel proteins)
Movement of polar substances across membrane:
Through pore/ channel proteins
Using transport/ carrier proteins
Active transport/ use of ATP
Diffusion:
Concentration gradient Diffusion distance (inverse square law): epithelial cells Diffusion area: villi/ microvilli Pores in cell membrane Size/ nature of diffusing molecule
Facilitated diffusion:
Channel proteins
Channel proteins: water filled so allow polar ions
Channel open/ close to signals like change in voltage or binding of another molecule
Facillitated diffusion:
carrier proteins
Carrier proteins bind molecules to them n then change shape as a result of binding in such a way that molecules are released inside membrane
Does facilitated diffusion require energy?
No. It’s passive in all cases and material is moves down conc gradient.
Active transport:
Energy required to move against conc gradient (ATP)
Carrier protein spanning membrane
Molecules bind to carrier protein causing it to change shape - active configuration
(ATP attaches to protein membrane inside cell)
‘Active’ configuration no longer bonds to molecules so molecules released inside
ATP -> ADP + P
Release of molecules: protein reverts to binding configuration to take up more molecules from outside
Diffusion:
Concentration gradient Diffusion distance (inverse square law): epithelial cells Diffusion area: villi/ microvilli Pores in cell membrane Size/ nature of diffusing molecule
Facilitated diffusion:
Channel proteins
Channel proteins: water filled so allow polar ions
Channel open/ close to signals like change in voltage or binding of another molecule
Facillitated diffusion:
carrier proteins
Carrier proteins bind molecules to them n then change shape as a result of binding in such a way that molecules are released inside membrane
Does facilitated diffusion require energy?
No. It’s passive in all cases and material is moves down conc gradient.
Active transport:
Energy required to move against conc gradient (ATP)
Carrier protein spanning membrane
Molecules bind to carrier protein causing it to change shape - active configuration
(ATP attaches to protein membrane inside cell)
‘Active’ configuration no longer bonds to molecules so molecules released inside
ATP -> ADP + P
Release of molecules: protein reverts to binding configuration to take up more molecules from outside
Components of a cell surface membrane. (3mks)
phospholipids; proteins [extrinsic/ intrinsic/ pore]; glycoproteins; cholesterol; glycolipids;
Explain what is meant by the term active transport. [june11 2bi]
(movement of substances) against/ up, concentration gradient or from low to high concentration; using, ATP/ (metabolic) energy; using a, transport/ carrier, protein;
State two examples of active transport in cells. Name the substance that is transported and the cell involved: [june11 2bii]
1) (mineral) ions/ salts/ named e.g, (into) root hair (cell); [e.g. nitrates, phosphates, calcium ions, magnesium ions etc.]
2) hydrogen ions (out of) companion cells; [ref to loading of sucrose into, phloem cell/ companion cell; ref to uptake of glucose by cells lining, (small) intestine/ nephron/ PCT]
3) (mineral) ions/ salts/ named e.g, (across) endodermis;
sucrose out of sieve tube at sink;
[substance// cell// direction;
Na+/ K+// neurone// K+ in Na+ out;
Na+/ K+ // named cell/ Ion pump to drive cotransport;
K+// guard cell (to open stomata)// in;
Na+// cell of loop of Henle// out;
Ca2+// muscle cell// into sarcoplasmic reticulum;
Ca2+// presynaptic knob// out;
H+// in cell, respiring (aerobically)/ photosynthesising//
for chemiosmosis;
named ion(s)// cells lining DCT// in/ out;
Mechanism of release of enzymes into the gut: [june11 2c]
bulk transport
Mechanism of a plant cell taking up water: [june11 2c]
osmosis
Mechanism of calcium ions entering a nerve cell down a concentration gradient: [june11 2c]
facilitated diffusion
Mechanism of oxygen entering a red blood cell: [june11 2c]
diffusion
Function of a cholesterol: [june09 2ai]
stabilise the membrane OR maintain/ affect / control,
fluidity OR reduces permeability to, polar / charged,
particles [reduces / affects, lateral movement of
phospholipids ]
Function of a (glyco)protein: [june09 2ai]
allow communication across membrane OR allow, polar/ charged, particles to pass through membrane [cell recognition / receptor site / cell signalling
/ cell attachment ]
Function of a phospholipid (bilayer): [june09 2ai]
to act as a barrier (to, polar/ charged, particles)/ select what enters or leaves cell [acts as) selectively permeable or partially permeable membrane; [allows small/ fat soluble molecules to pass through]
Explain what is meant by the term cell signalling. [june09 2bi]
communication between cells;
cell, recognition / identification;
cells work together / coordination between action of different cells;
to trigger, response / reaction ( inside the cell);
[e.g. action of hormone / cytokines ]
