Carbs & Lipids Flashcards
What is a monomer?
A monomer is a smaller/repeating molecule from which larger molecules called polymers are made.
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. (3)
- Long, straight, unbranched chains of Beta glucose
- (Joined by) many weak hydrogen bonds
- Form microfibrils / macrofibrils
- Provide rigidity/support/strength
Give one feature of starch and explain how this feature enables it to act as a storage substance.
- Helical so compact
- Insoluble so no osmotic effect/does not leave cell/does not affect water potential
- Large molecule/long chain so does not leave cell / contains large number of glucose units
- Branched chains so rapid hydrolysis to remove glucose for respiration
Hydrogen bonds are important in cellulose molecules. Explain why.
- Holds chains together, forming microfibrils
- Providing strength/rigidity (to cellulose/cell wall)
- Weak hydrogen 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
- Joined by glycosidic bond
- Added to polypeptide in Golgi
Describe how the student would show that reducing sugars were present in a solution.
- Add Benedict’s
- Heat to 95°C
- Red/orange/yellow/green precipitate (shows reducing sugar present)
Describe how you would test a sample of food for the presence of starch.
- Add potassium iodide (KI) solution to the food sample
2. Blue/black/purple indicates starch is present
Describe how you would test a liquid sample for the presence of a lipid and how you would recognise a positive result.
- (Mix/shake sample) with ethanol, then water and shake
2. Cloudy white / milky (emulsion)
Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid?
- Double bond(s)
- Between carbon atoms within the hydrocarbon chain
Describe how an ester bond is formed in a phospholipid molecule.
- Condensation (reaction) OR loss of water
- Between glycerol and fatty acid
Some seeds contain lipids. Describe how you could use the emulsion test to show that a seed contains lipids. (3)
- Crush/grind
- With ethanol/alcohol, to dissolve the lipid
- Then add water then shake
- Forms a white emulsion/goes white
What are the differences between a triglyceride and a phospholipid?
- Fatty acid removed
- Replaced with a phosphate group
Compare and contrast the structure and properties of triglycerides and phospholipids
- BOTH contain ester bonds
- BOTH contain glycerol
- Fatty acids on BOTH may be saturated or unsaturated
- BOTH are insoluble in water
- BOTH contain C,H and O, BUT phospholipids also contain P
- Triglyceride has 3 fatty acids BUT phospholipids have 2 fatty acids plus a phosphate group
- Triglycerides are hydrophobic/non-polar BUT phospholipids have hydrophilic and hydrophobic region
- Phospholipids form micelle/bilayer BUT triglycerides don’t.
Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample.
Lipid:
1. Add ethanol/alcohol then add water and shake/mix.
2. White/milky emulsion
Non-reducing sugar:
1. Do Benedict’s test and stays blue/negative
2. Boil with acid then neutralise with alkali
3. Heat with Benedict’s and becomes red/orange precipitate
Amylase:
1. Add biuret reagent and becomes purple
2. Add starch, leave for a time, test for reducing sugar/absence of starch
