Carbohydrates & Lipids 1.1-1.3 Flashcards
☆ Oral rehydration solutions (ORS) are used to treat diarrhoeal disease. What does an ORS consist of and
how does it work? (5)
(Contains glucose / starch / carbohydrate / sugar);
1. Candidates may be aware of food based ORS. Accept appropriate carbohydrate sources such as rice/maize flour.
2. Sodium / salt;
3. Co-transport / symport;
4. Sodium and glucose taken up (from lumen);
5. Lowers water potential in cells/ increases water potential gradient;
6. Water taken up by osmosis.
What is a monomer? (1)
- A monomer is a small, repeating unit from which larger molecules (polymers) are formed.
(Monosaccharide sugar units are monomers)
Starch and cellulose molecules have different functions in plant cells. Each molecule is adapted for its function.
Explain one way in which starch molecules are adapted for their function in plant cells (2)
- Insoluble - doesn’t affect water potential;
- Helical/compact
- Large (macro)molecule, cannot leave the cell.
Where is the compound polysaccharide starch found?
(Why?) (1)
Starch is present in the leaves, roots, tubers (storage), fruits, and the embryo of plants (STORAGE compound polymer)
- It is synthesized in the chloroplasts of leaves in sunlight
Compare how starch is digested in animals and humans (2)
Starch (in plants) is readily digested in animals by Cellulolytic enzymes (break down cellulose cell wall)
In humans, it is digested into maltose monosaccharides by amylase enzyme in the oral cavity and small intestine. Maltose is then digested into a-glucose by maltase enzyme in the small intestine (and absorbed).
☆ Describe and explain the structure and function of Starch in plant cells (BLURT)
STARCH:
1. Main storage compound carbohydrate in plants (polysaccharide made up of repeating glucose subunits)
2. In Starch Granuels - made up of repeating glucose subunits Amylose and Amylopectin “wrapped” in semi-crystalline granuels.
3. Amylose consists of unbranched, linear or helical polymeric chains of a-glucose molecules with 1-4 glycosidic bonding, makes up 20/30% of starch, insoluble, helix with intermolecular H-bonds so compact.
4. Amylopectin consists of branched polymeric chains of (MORE) a-glucose in 1-6 glycosidic bonding, makes up 70/80% of starch.
Branched so has many terminal ends for hydrolysis into glucose monosaccharides (for respiration/growth/photosynthesis) glucose molecules are weakly bonded, making it water-soluble.
5. Starch is insoluble - no osmotic effect
6. Large (macro)molecule - does not diffuse out of cells
Name the bonding in starch (1)
a-Glucose 1-4 and 1-6 glycosidic bonds
(In starch granum polysaccharide Amylopectin is branched whereas Amylose is unbranched)
Describe the test for Starch (1)
Iodine test -
Add potassium iodide solution (insoluble in water) to a sample,
Qualitative colour change from orange to Blue/black in positive test
Explain how cellulose molecules are adapted for their function in plant cells (3)
- Long, straight, unbranched chains of B-glucose monomers in 1-4 glycosidic bonding (hydrogen bridges/H bonds from adjacent chain hydroxyl groups of B-glucose)
- Become linked together by many weak hydrogen bonds to form fibrils (lots of polysaccharide microfibrils) for strength.
- Gives cell wall strong turgid structure (high tensile strength of cellulose allows it to be stretched without breaking, keeps the cell’s shape)
☆ Describe and explain the structure of Glycogen (BLURT)
- Main energy storage polysaccharide in animals/fungi (but also found in small granuels in cytoplasm of plant cells)
- 1-4 and 1-6 glycosidic bonds of a-glucose monosaccharides in granuels
- Many short, branched chains, many terminal ends for hydrolysis of glucose
- Few coiled chains, compact
- Insoluble so no osmotic effect.
Name the monosaccharides of which the following disaccharides are composed:
(I) Sucrose
(II) Lactose
(I) a-glucose and fructose
(II) a-glucose and galactose
Name the products of the hydrolysis of sucrose.
Glucose and fructose
The enzyme sucrase catalyses the breakdown of sucrose into monosaccharides. What type of reaction is this breakdown?
Hydrolysis (catabolic exothermic reaction)
☆ Lactulose is a disaccharide formed from one molecule of galactose and one molecule of fructose. Other than both being disaccharides, give one similarity and one difference between the structures of lactulose and lactose.
- Both contain galactose and glycosidic bonding
- Lactulose contains fructose, whereas lactose contains glucose.
Name the monomers from which a maltose molecule is made (1)
a-Glucose and a-Glucose
Name the type of chemical bond that joins two monosaccharides to form a disaccharide (1)
Glycosidic (Between carbon 1-4 of Carboxyl and Hydroxyl group)
Describe the role of enzymes in the digestive system in the complete breakdown of starch.
- Amylase enzyme;
- Hydrolysis of glycosidic bond;
- Starch polysaccharide to maltose disaccharide;
- Maltase enzyme;
- Hydrolysis of maltose to a-glucose monosaccharides
What is the difference between Qualitative and Quantitative?
Qualitative - Observable, e.g colour change
Quantitative - Numerical. e.g data recording
☆ Outline how colorimetry could be used to give qualitative results for the presence of sugars and starch.
- Make standard solutions with known concentrations.
Record absorbance or % transmission values. - Plot calibration curve: absorbance or % transmission (y-axis), concentration (x-axis).
- Record absorbance or % transmission values of unknown samples. Use calibration curve to read off concentration.
What are emulsified droplets of fat (in aqueous solutions) called?
Micelles
Compare and contrast the structure and properties of triglycerides and phospholipids (5)
Compare:
1. Both contain ester bonds
2. Both contain glycerol (C3H8O3)
3. (Hydrophobic) Fatty acids in both may be saturated or unsaturated
4. Both are insoluble in water
5. Both contain Carbon, Hydrogen and Oxygen
Contrast:
1. Phospholipids contain a hydrophilic polar phosphate head (PO43-) whereas triglycerides don’t.
2. Phospholipids only have two fatty acid tails whereas triglycerides have three.
3. Phospholipids form a (double) bilayer in aqueous solution - form the surface cell membrane for eukaryotes.
4. Triglycerides are hydrophobic whereas phospholipids have both hydrophobic and hydrophilic (phosphate) regions.
(Need a mix of both to get 5 marks)
What are emulsified droplets of fat in an aqueous solution called?
Micelles
What is a polymer?
A molecule made from a large number of repeating monomers joined together
A starch molecule has a spiral shape. Explain why this shape is important to its function in cells.
Compact/occupies small space/tightly packed
The structure of cellulose is related to its role in plant cell walls. Explain how.
• Long, straight, unbranched chains of Beta glucose;
• Joined by many WEAK hydrogen bonds;
• Form microfibrils to;
• Provide rigidity/strength/support
Give the features of STARCH that explain how it acts as a storage substance.
• Helical/spiral so compact
/Tightly packed/can fit lots into a cell;
• Insoluble so no osmotic effect
/Does not affect water potential/Doesn’t leave cell
• Large molecule so does not leave cell/contains lots of glucose subunits;
• Branched chains so rapid hydrolysis of glucose for respiration.
Hydrogen bonds are important in cellulose molecules. Explain why (3 points)
• Holds cellulose molecules together to form MICROFIBRILS;
• Provides strength/rigidity to cell wall;
• Weak H bonds provide strength in large numbers.
Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.
• Glucose and galactose;
• Joined by condensation;
• By glycosidic bond;
• Added to polypeptide in GOLGI
Describe what latent heat means
The amount of energy needed for a substance to change state
How is maltose formed?
• a-Glucose and a-Glucose
(disaccharide)
What are the 3 disaccharides that make up carbohydrates & their molecular formula?
• Maltose (glucose + glucose)
• Lactose (galactose + glucose)
• Sucrose (fructose + glucose)
All have the molecular formula of C12H22O12
Describe what heat capacity means.
• The amount of energy needed to raise the temperature of a substance by a specific amount (e.g 3 degrees)
What is a triglyceride?
A type of lipid formed by the condensation of 1 molecule of glycerol and 3 molecules of fatty acid.
Name the 3 hexose monosaccharides & their molecular formula.
• Glucose
• Fructose
• Galactose
All have the formula C6H1206
What type of reactions are hydrolysis (adding H2O) and condensation (losing H2O)?
Hydrolysis -> Catabolic
Condensation -> Anabolic
Describe how a student would show that reducing sugars were present in a solution (3)
- Add Benedict’s reagent;
- Heat to 95 degrees C;
- Brick red precipitate in strong + reaction
OR orange/yellow/green all show reducing sugar
Describe how you would test a sample of food for the presence of starch.
- Add potassium iodide (KI) solution to the food sample;
- Purple sample indicates starch is present.
Describe how you would test a liquid sample for the presence of lipid and how you would recognise a positive result.
• Mix/shake sample with ethanol (2cm^3)
• Then mix sample with water (2cm^3)
• and SHAKE
• Cloudy white emulsion
Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid? (2)
• Contains one or more double bond;
• Between carbon atoms in the hydrocarbon chain.
Describe how an ester bond is formed in a phospholipid molecule.
• Condensation / loss of H2O;
• Between glycerol and fatty acid.
Some seeds contain lipids. Describe how you could use the emulsion test to show that a seed contains lipids.
- CRUSH/GRIND seeds
- add ETHANOL/alcohol to dissolve lipid;
- Add water and shake;
- Forms a cloudy white emulsion.
What are the differences between a triglyceride and a phospholipid?
- Fatty acid removed;
- Replaced with a phosphate PO43- group.
What are the differences between saturated and unsaturated fatty acids?
Saturated:
• More single H bonds
• Straight chain molecules
• Higher melting point, solid at room
• Found in animal fats.
Unsaturated:
• Contain 1 or more double bond (C=C)
• Lower melting points, liquid at room
• Found in plant oils
A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that they could use to measure the quantity of reducing sugar in a solution.
- Filter and dry the precipitate;
- Find mass.
Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample.
Lipid:
1. Add equal parts of ethanol then water and SHAKE;
2. Milky/cloudy white emulsion.
Non-reducing sugar:
1. Benedict’s test with BLUE precipitate i.e sucrose
2. Boil with HydroChloric acid (HCl) then neutralise with sodium hydrogen carbonate (NaHCO3)
3. Heat with benedict’s to 95 degrees, precipitate brick red.
Amylase (enzyme):
1. Add Biuret reagent, becomes purple (enzymes are proteins);
2. Add starch and leave for time, test for normal reducing sugar, if starch is not present then amylase enzyme denatured.
What are the bonds in lipids and the bonds in carbohydrates?
- Ester (3 in triglycerides)
- Glycosidic
Describe the structure and functions of STARCH
Storage polymer of a-glucose in plant cells
- insoluble so no osmotic effect
- large so does not diffuse out of cells
made from amylose:
- 1,4 glycosidic bonds
- helix with intermolecular H bonds so compact
made from amylopectin:
- 1,4 and 1,6 glycosidic bonds
- branched so many terminal ends for rapid glucose hydrolysis
Describe the structure and functions of glycogen
main energy storage polymer (polysaccharide) of a-glucose in animal/fungal cells
• 1,4 & 1,6 glycosidic bonds
• many short branched chains so many terminal ends for rapid glucose hydrolysis
• Few coiled chains so compact
• insoluble so no osmotic effect and does not diffuse out of cells
(also found in small granuels in cytoplasm of plant cells)
Describe the structure and functions of cellulose
main b-Glucose polymer (polysaccharide) found in plant cell walls
• prevents bursting under turgor pressure (holds stem up, prevents swelling)
• 1,4 glycosidic bonds
• straight-chain unbranched molecule
• many weak H bonds between parallel strands so has strength and rigidity
• H bond crosslinks form microfibrils so HIGH TENSILE STRENGTH
• alternate glucose molecules are rotated 180 degrees
Describe the Benedict’s test for NON-reducing sugars
- Carry out Benedict’s test - blue precipitate = negative reaction
- Hydrolyse non-reducing sugar (sucrose) - add 1cm^3 of HCl and heat in waterbath for 5 mins
- Neutralise mixture using sodium hydrogen carbonate solution
- Redo Benedict’s test - brick red precipitate
Describe the test for starch
- Add iodine (KI) solutuion
- Positive result = colour change from orange to blue-black
Outline how colorimetry can be used to give qualitative results for the presence of sugars and starch (4)
- Make standard solutions with known concentrations
- Record % absorbance
- Plot calibration curve with absorbance (y-axis as dependent) and concentration (x-axis as independent)
- Use calibration curve to read off concentration.
Relate the structure of triglycerides to their functions
• High-energy:mass ratio = high calorific value from oxidation (energy storage)
• Insoluble hydrocarbon chain = no osmotic effect & used for waterproofing
• Slow conductor of heat = thermal insulation e.g adipose tissue
• Less dense than water = buoyancy of aquatic animals e.g grey seal
Describe what an Amphiphatic molecule is and name one example.
A molecule with both hydrophobic and hydrophilic regions
• Phospholipids
Phospholipids and triglycerides are NOT polymers. Explain why (1)
They are not made from a small repeating unit (monomers)
• They are MACROMOLECULES
Describe the structure and functions of starch
Storage polymer of a-glucose in plant cells
• insoluble = no osmotic effect on cells
• large = does not diffuse out of cells made from amylose:
1,4 glycosidic bonds
and amylopectin:
• 1,4 & 1,6 glycosidic bonds
• helix with intermolecular branched = many terminal
H-bonds = compact
ends for hydrolysis into glucose
