Topic Cell Membrane Essay - Key Points!

Q) Describe the roles of phospholipids, cholesterol and glycolipids in the cell membrane

Main points
Key idea:	Phospholipids
· Roles : (i) main component of cell membr, (ii) determine permeability of membr toward diff substances · Ref to each mol having 1 polar head, 2 non-polar hydrocarbon tails + its orientation to form bilayer struc · Ref to polar heads of phospholipids pointing towards aq medium while hydrocarbon tails form hydrophobic core · Ions or polar mol unable to diffuse a/x hydrophobic core of bilayer struc via simple diffusion · Ref to special transmembrane proteins (e.g. carriers or channel proteins) embedded w/n membr to regulate transport of these substances a/x membr
Key idea:	Cholesterol
· Roles : (i) Regulate fluidity of membr + ref to changes in fluidity under diff temp · Details : -   when temp increases, cholesterol decreases fluidity by interacting w hydrocarbon chains of phospholipids which are prevented fr moving too far fr each other. -   when temp decreases, cholesterol increases fluidity of membr by disrupting close packing of phospholipids which prevents membr fr solidifying · (ii) Provide mechanical stability to membr, so it does not break easily · (iii) As impt component of myelin sheath + ref to reducing uncontrolled leakage of ions a/x membr of neurones, for efficient nerve transmission t
Key idea:	Glycolipids
· Only on ext surf of cell membr · Roles : (i) cell recognition + adhesion roles ; (ii) stabilizes membr struc due to orientation of carbo chains toward ext aq envt, H bonds form b/w carbo chains + water mol (iii) In some white blood cells, glycolipids may serve to detect pathogens + signal for their destruction
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min)

Topic Membrane Essay - Key Points!

Q) Discuss the functional significance of membranes in photosynthesis and respiration

Main points
Key idea:	Increase surface area for attachment of electron carriers + stalked particles
· Due to infolding of inner mitochondrial membranes (IMM)(to form cristae) + thylakoid membr of chloroplast · Ref to electron transport chain (ETC) · Ref to stalked particles – consist of hydrophilic protein channels embedded in membr + ATP synthase at tip of struc
Key idea:	Flow of energized e throu ETC
· Energized e flow throu ETC + ref to down an energy gradient · Energy released during transfer of e, used to pump H+ (protons) · Ref to fr mitochondrial matrix to intermembrane space · Ref to fr chloroplast stroma to thylakoid space
Key idea:	Establish proton gradient
· Ref to membr being impermeable to H+ · Results: H+ (proton) conc gradient a/x IMM and thylakoid membrane · H+ flow back into matrix or stroma throu stalked particles by facilitated diffusion, where ATP synthase catalyzes phosphorylation of ADP to form ATP
Key idea:	Membranes compartmentalize enzymes
· Enz involved in : i) link rx + Krebs cycle w/n matrix of mito ii) light indep rx (i.e. Calvin cycle) w/n stroma of chloroplast
Key idea:	Membranes facilitate reactions
· Maintain optimal cond for various rx w/n organelles · Membranes - in close proximity to mitochondrial matrix and chloroplast stroma, for oxidative phosphorylation and photophosphorylation, to occur efficiently
Key idea:	Outer and inner mitochondrial membranes create intermembrane space
· Ref to H+ entering intermembrane space fr matrix – required for H+ (proton) conc gradient, then syn of ATP (as described)
Key idea:	Attachment of photosynthetic pigments on thylakoid membrane
· Ref to photosynthetic pigments (e.g. chlorophyll) functionally grouped into  photosystem I or II · Ref to maximizing absorption of light + photoactivation of chlorophyll - excitation, subsequent displacement of energized e fr rx centres of photosystems · Energized e flow throu ETC, leads to syn of ATP (as described)
Key idea:	Permeability of membranes
· Ref to both outer and inner membr of organelles being permeable substrates or products of cellular respiration and photosyn · E.g. O2, CO2, H2O, ADP, inorganic phosphate and ATP · Ref to mitochondrial membr being permeable to pyruvate fr glycolysis + pyruvate = substrate for link rx in matrix of mitochondrion
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) The proton gradient gives rise to the proton motive force which is the source of potential energy for the synthesis of ATP.

Topic Cell Membrane and Transport a/x Membrane - Main Points!

Q) Describe the roles of three components of plasma membrane

Main points
Key idea:	Functions of cholesterol
1) Regulates fluidity of membr · When temp rises, mol decrease fluidity by interacting w hydrocarbon chains of phospholipids, to prevent them fr moving too far fr each other. · When temp decreases, mol increase fluidity by disrupting close packing of phospholipids, to prevent membr fr solidifying 2) Provides mechanical stability to membr so it does not break easily 3) Important component of myelin sheath ·  Reduces uncontrolled leakage of ions a/x membr of neurones, needed for efficient nerve transmission
Key idea:	Functions of glycoproteins and glycolipids
· Both found only on ext surf of cell membr (ref to carbo component, glycocalyx) 1) Cell to cell recognition and adhesion (e.g. aid wbc to detect + destroy pathogens) 2) Some glycoproteins serve as receptors - bind to specific signal mol (e.g. hormone), activate signal transduction pathways, result cellular responses 3) Stabilizes membr struc - orientation of carbo chains toward ext aq environment + ref to H bonds b/w the carbo chains + water mol
Comments: (i) Visualize the answer with the aid of a labelled cross section of the cell membrane (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) Each specific role is worth 1 mark

Topic Cell Membrane and Transport a/x Membrane Essay - Main Points!

Q) Using named examples, describe the functions of proteins in membranes

Main points
Key idea:	Structural function
E.g. Integrin, transmembrane protein · Attach cell to fibres of extracellular matrix - stabilize + maintain shape of cell
Key idea:	Transport of substance a/x membrane
E.g. glucose carriers, ion channels · Regulate transport of large polar sub, ions which cannot cross membr by simple diffusion · Ref: phospholipid bilayer (hydrophobic core) of cell surf membr  E.g. Na+/K+ pump · Active transport of Na+/K+ a/x membr - to maintain resting potential (-70mV) of neurone · Ref: energy from ATP + against conc gradient
Key idea:	Cell communication with external environment
E.g. ion channel-linked receptors at post synaptic membr · Binds to acetylcholine for synaptic transmission · Protein receptors for cell to respond appropriately to extracellular signal mol E.g. Adenylate cyclase, embedded in cell membr · Catalyzes ATP to cAMP · Second messenger, cAMP, activates transduction pathways, for cellular responses to signal mol (e.g. glucagon) bound to cell surface receptors
Key idea:	Cell recognition and adhesion
E.g. Cadherins · Transmembrane proteins for cell adhesion during tissue formation
Key idea:	Energy transducer
E.g. Electron carriers · Arranged in sequential manner, at inner mitoch membr or thylakoid membr (chloroplast) for transfer of electrons throu ETC · Energy released during transfer,use to transport protons into intermembr space or thylakoid thus establish proton gradient a/x membr (i.e. proton motive force) E.g. ATP synthase embedded in membr · Flow of proton down conc gradient for ATP syn (chemiosmosis)
Comments: (i) Visualize the answer with the aid of a labelled cross section of the cell membrane (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) 8 named examples w elaboration provided easily exceed the maximum marks