1.2 Carbohydrates Flashcards
What are monosaccharides? Give three common examples.
- Monomers from which larger carbohydrates are made
- glucose, fructose, galactose
Describe the structure of alpha glucose
- one oxygen, 5 carbon
- left = H on top, HO on bottom
- right = H on top, OH on bottom
- C6 = CH2OH on top, H on bottom
- C3 = OH on top, H on bottom
- C2 = H on top, OH on bottom
Describe the difference between the structure of alpha glucose and beta glucose
- Isomers - same molecular formula but differently arranged atoms
- OH group is below carbon 1 in alpha glucose but above carbon 1 in beta glucose
What are disaccharides and how are they formed?
- two monosaccharides joined together with a glycosidic bond
- Formed by condensation reaction, releasing a water molecule
List three common disaccharides & monosaccharides from which they’re made
- maltose = glucose + glucose
- sucrose = glucose + fructose
- 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
Describe the basic function and structure of starch
- function = energy store in plant cells
- structure:
- polysaccharide of alpha glucose
- some had 1,4 glycosidic bonds so is unbranched (amylose)
- some had 1,4 and 1,6 glycosidic bonds so is branched (amylopectin)
Describe the basic function and structure of glycogen
- function: energy store in animal cells
- structure:
- polysaccharide of alpha glucose
- 1,4 and 1,6 glycosidic bonds so is branched
Explain how the structures of starch (only amylose) relate to its functions
- helical - compact for storage in cell
- large, insoluble polysaccharide molecule - cant leave cell / cross cell membrane
- insoluble in water - water potential do cell not affected (no osmotic effect)
Explain how the structure of glycogen relates to its functions (and amylopectin)
- 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 - cant leave cell / cross cell membrane
- insoluble in water - water potential of cell not affected (no osmotic effect)
Describe the basic function and structure of cellulose
- function - provides strength and structural support to plant / algal cell walls
- structure :
- polysaccharide of beta glucose
- 1,4 glycosidic bonds so forms straight, unbranched chains
- chains linked in parallel by hydrogen bonds, forming microfibrils
Explain how the structure of cellulose relates to its function
- every other beta 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
Describe the test for reducing sugars
Reducing sugars = monosaccharides, maltose, lactose
1. Add Benedict’s solution (blue) to sample
2. Heat in a boiling water bath
3. Positive result = green / yellow/ orange/ red precipitate
Describe the test for non-reducing sugars
Non-reducing sugars = sucrose
1. Do Benedict’s test and stays blue / negative
2. Heat in a boiling water bath with acid (to hydrolyse into reducing sugars)
3. Neutralise with alkali (e.g. sodium bicarbonate)
4. Heat in a boiling water bath with Benedict’s solution
5. Positive result = green / yellow / orange / red precipitate
Suggest a method to measure the quantity of sugar in a solution
- Carry out Benedict’s test, then filter and dry precipitate
- Find mass/weight
Suggest another method to measure the quantity of sugar in a solution
- Make sugar solutions of known concentrations e.g. Dilution series.
- Heat set volume of each sample with a set volume of Benedict solution for the same time.
- Use colour colorimeter to measure absorbance of a light of each known concentration.
- Plot calibration curve - concentration on X axis, absorbance on Y axis and draw line of best fit
- Repeat Benedict‘s test with unknown sample and measure absorbance
- Rate of calibration curve to find concentration associated with unknown sample’s absorbance.
Describe the biochemical test for starch
- Add iodine dissolved in potassium iodide (orange / brown) and shake / stir
- Positive result = blue-black
