polysaccharides and glycolipids Flashcards
condensation reaction
● 2 molecules join together
● Forming a chemical bond
● Releasing a water molecule
monosaccharides
Monomers from which larger carbohydrates are made
● Glucose, fructose, galactose
What are disaccharides and how are they formed?
Two monosaccharides joined together with a glycosidic bond
● Formed by a condensation reaction, releasing a water molecule
Maltose
Glucose glucose
Sucrose
Glucose friction
Lactose
Glucose galactose
What are polysaccharides and how are they formed?
● Many monosaccharides joined together with glycosidic bonds
● Formed by many condensation reactions, releasing many water molecules
Starch structure
● Polysaccharide of α-glucose
● Some has 1,4-glycosidic bonds so is unbranched (amylose)
● Some has 1,4- and 1,6-glycosidic bonds so is branched (amylopectin)
Energy store in plant cells
Starch s2f
● Helical → compact for storage in cell
● Large, insoluble polysaccharide molecule → can’t leave cell / cross cell membrane
● Insoluble in water → water potential of cell not affected (no osmotic effect)
Glycogen s2f
● Branched → compact / fit more molecules in small area
● Branched → more ends for faster hydrolysis → release glucose for respiration to
make ATP for energy release
● Large, insoluble polysaccharide molecule → can’t leave cell / cross cell membrane
● Insoluble in water → water potential of cell not affected (no osmotic effect)
Glycogen structure
Energy store in animal cells
● Polysaccharide made of α-glucose
● 1,4- and 1,6-glycosidic bonds → branched
Cellulose
● Provides strength and structural support to plant / algal cell walls
Structure
● Polysaccharide of β-glucose
● 1,4-glycosidic bonds so forms straight, unbranched chains
● Chains linked in parallel by hydrogen bonds, forming microfibrils
Cellulose s2f
● Every other β-glucose molecule is inverted in a long, straight, unbranched chain
● Many hydrogen bonds link parallel strands (crosslinks) to form microfibrils (strong fibres)
● Hydrogen bonds are strong in high numbers
● So provides strength to plant cell walls
Reducing sugar test
Monosaccharides maltose lactose
- Add Benedict’s solution (blue) to sample
- Heat in a boiling water bath
- Positive result = green / yellow / orange / red precipitate
Non reducing
Sucrose
- Do Benedict’s test (as above) and stays blue / negative
- Heat in a boiling water bath with acid (to hydrolyse into reducing sugars)
- Neutralise with alkali (eg. sodium bicarbonate)
- Heat in a boiling water bath with Benedict’s solution
- Positive result = green / yellow / orange / red precipitate
Name two groups of lipids
Triglycerides and phospholipids
How to trigycleride form
● 1 glycerol molecule and 3 fatty acids
● 3 condensation reactions
● Removing 3 water molecules
● Forming 3 ester bond
How does structure of triglyceride relate to function
● High ratio of C-H bonds to carbon atoms in hydrocarbon chain
○ So used in respiration to release more energy than the same mass of carbohydrates
● Hydrophobic / non-polar fatty acids so insoluble in water (clump together as droplets, tails inwards) ○ So no effect on water potential of cell (or can be used for waterproofing)
How do properties of phospholipid relate to s2f
Function: form a bilayer in cell membrane, allowing diffusion of lipid-soluble (non-polar) or very small substances and restricting movement of water-soluble (polar) or larger substances
Lipid test
Add ethanol
Add water
Shale
White cloudy emulsion
Fluid mosaic model
● Molecules free to move laterally in phospholipid bilayer
● Many components - phospholipids, proteins,
glycoproteins and glycolipids
Describe the arrangement of the components of a cell membrane
● Phospholipids form a bilayer - fatty acid tails face inwards, phosphate heads face outwards
● Proteins
○ Intrinsic / integral proteins span bilayer eg. channel and carrier proteins
○ Extrinsic / peripheral proteins on surface of membrane
● Glycolipids (lipids with polysaccharide chains attached) found on exterior surface
● Glycoproteins (proteins with polysaccharide chains attached) found on exterior surface
● Cholesterol (sometimes present) bonds to phospholipid hydrophobic fatty acid tai
Arrangement of phospholipids in cell membrane
● Bilayer, with water present on either side
● Hydrophobic fatty acid tails repelled from water so point away from water / to interior
● Hydrophilic phosphate heads attracted to water so point to water
Explain the role of cholesterol (sometimes present) in cell membranes
● Restricts movement of other molecules making up membrane
● So decreases fluidity (and permeability) / increases rigidity
How is cell membrane adapted to other functions
● Phospholipid bilayer is fluid → membrane can bend for vesicle formation / phagocytosis
● Glycoproteins / glycolipids act as receptors / antigens → involved in cell signalling / recognition
How does movement across cell membrane occur by simple diffusion
● Lipid-soluble (non-polar) or very small substances eg. O2, steroid hormones
● Move from an area of higher concentration to an area of lower conc., down a conc. gradient
● Across phospholipid bilayer
● Passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances)
Explain the limitations imposed by the nature of the phospholipid bilayer
Restricts movement of water soluble (polar) & larger substances eg. Na+ / glucose
● Due to hydrophobic fatty acid tails in interior of bilayer
Describe how movement across membranes occurs by facilitated diffusion
● Water-soluble / polar / charged (or slightly larger) substances eg. glucose, amino acids
● Move down a concentration gradient
● Through specific channel / carrier proteins
● Passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances)
Carrier and channel protein role in FD
● Shape / charge of protein determines which substances move
● Channel proteins facilitate diffusion of water-soluble substances
○ Hydrophilic pore filled with water
○ May be gated - can open / close
● Carrier proteins facilitate diffusion of (slightly larger) substances
○ Complementary substance attaches to binding site
○ Protein changes shape to transport substance
Movement across cell membrane osmosis
● Water diffuses / moves
● From an area of high to low water potential (ψ) / down a water potential gradient
● Through a partially permeable membrane
● Passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances
Movement across cell membrane by active transport
● Substances move from area of lower to higher concentration / against a concentration gradient
● Requiring hydrolysis of ATP and specific carrier proteins
Describe the role of carrier proteins and the importance of the hydrolysis of ATP in active transport
- Complementary substance binds to specific carrier protein
- ATP binds, hydrolysed into ADP + Pi, releasing energy
- Carrier protein changes shape, releasing substance on side
of higher concentration - Pi released → protein returns to original shape
Describe how movement across mem
Describe how movement across membranes occurs by co-transport
● Two different substances bind to and move simultaneously via a co-transporter protein (type of carrier protein)
● Movement of one substance against its concentration gradient is often coupled with the movement of another down its concentration gradient
Explain the adaptations of some specialised cells in relation to the rate of transport across their internal and external membranes
Cell membrane folded eg. microvilli in ileum → increase in surface area
● More protein channels / carriers → for facilitated diffusion (or active transport - carrier proteins only)
● Large number of mitochondria → make more ATP by aerobic respiration for active transport
