carbs & lipids Flashcards
what is a monomer ?
a monomer is a smaller / repeating) unit / molecule from which larger molecules / 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/strength/support
give one feature of starch and explain how this feature enables it to act as a storage
substance
helical / spiral So compact / tightly packed / can fit (lots) into a small space
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/cellulose molecules together/forms cross links between chains/cellulose molecules/forms 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/range/yellow/green precipitate (shows reducing sugar present);
describe how you would test a sample of food for the presence of starch.
- (mix / shake sample) with ethanol, then water and shake
- cloudy White / milky (emulsion)
omega-3 fatty acids are unsaturated
what is an unsaturated fatty acid?
double bond(s)
(bonds) 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 of 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 are also contain P
triglyceride has three fatty acids and phospholipids have two fatty acids plus phosphate group
triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region
phospholipids form monolayer/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 OR Add ethanol/alcohol and shake/mix then pour into/add water
2. white/milky emulsion OR emulsion test turns white/milky
non-reducing sugar
3. do Benedict’s test and stays blue/negative
4. boil with acid then neutralise with alkali
5. heat with Benedict’s and becomes red/orange (precipitate)
amylase
6. add biuret (reagent) and becomes purple/violet/mauve/lilac
7. add starch, (leave for a time), test for reducing sugar/absence of starch
A student carried out the Benedict’s test
suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution
- filter and dry (the precipitate)
- find mass/weight
What is a polymer? (1)
Polymers are large molecules made from joining 3 or more similar monomers together
What is a condensation reaction? (1)
removal of one water molecule which forms a bond
SPEC - joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water.
What is a hydrolysis reaction? (1)
addition of one water molecule to break a bond
SPEC - breaks a chemical bond between two molecules and involves the use of a water molecule.
Give 2 examples of monomers (2)
Alpha/Beta glucose
Nucleotides
Amino acids
Give 2 examples of polymers (2)
Nucleic Acids
Cellulose
Starch
Protein
Name the bond formed between two monosaccharides within a condensation reaction (1)
Glycosidic bond
Draw the structure of alpha glucose (1)
Draw the structure of beta glucose (1)
https://www.aqa.org.uk/subjects/science/as-and-a-level/biology-7401-7402/subject-content/biological-molecules/carbohydrates
Which monosaccharides form maltose and which enzyme is used to hydrolyse maltose? (2)
Alpha Glucose and Alpha
Glucose
Enzyme - Maltase
Which monosaccharides form lactose and which enzyme is used to hydrolyse lactose? (2)
Alpha Glucose and Galactose
Enzyme - Lactase
Which monosaccharides form sucrose and which enzyme is used to hydrolyse sucrose? (2)
Alpha Glucose and Fructose
Enzyme - Sucrase
Give three features of starch and explain how these enable it to act as a storage substance. (3)
Helical so compact
Insoluble so doesn’t affect water potential
Large molecule so does not leave cell
Branched chains (1:4 and 1:6 glycosidic bonds) so rapid hydrolysis to remove glucose for respiration
Describe how a student would show that a non-reducing sugar is present in the solution (5)
Complete Benedict’s test and observe negative
result
Add HCI to sugar solution AND heat to 95C
Neutralise with alkali
Add equal volume of Benedict’s solution
Heat again to 95C
Red/Orange/Green PRECIPITATE formed
What is a triglyceride made from and what bond is formed between them? (1)
3 fatty acids bonded via an ester bond to one glycerol molecule
What is a saturated fatty acid? (1)
Do not have double bonds between carbon atoms within the hydrocarbon chain
Explain how the digestion of starch in the small intestine leads to an increase in the
concentration of glucose in the blood. Details of co-transport are not required. (3)
Starch is hydrolysed by amylase
Produces glucose
Small enough to cross the gut wall into the blood
Describe the structure of glycogen (2)
- Polymer of alpha glucose
- joined by glycosidic bonds
Suggest how glycogen acts as a store of energy (2)
- Hydrolysed
- Glucose used in respiration
What are monosaccharides
are the monomers from which larger carbohydrates are made. Glucose, galactose and fructose are common monosaccharides.
What does the condensation of two monosaccharides form
Disaccharides
What are the 3 disaccharides
Maltose
Sucrose
Lactose
How is maltose the disaccharide formed
Formed by condensation of two glucose molecules
How is sucrose the disaccharide form
Formed by condensation of a glucose molecule and a fructose molecule
How is the lactose disaccharide formed
Formed by a condensation of a glucose molecule and a glucose molecule
What are the two isomers of glucose
a-glucose
β-glucose
What are polysaccharide’s
Polysaccharides are formed by the condensation of many glucose units
What does the condensation of a-glucose
lead to
Glycogen and starch
What does the condensation of β-glucose lead to
Cellulose
What are 2 groups of lipids
Triglycerides
Phospholipids
How are triglycerides formed
By the condensation of one molecule of glycerol & 3 molecules of fatty acid
What forms an ester bond
A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond
The R-group of a fatty acid can be what
Saturated or unsaturated
What happens in a phospholipid
One of the fatty acids of a triglyceride is substituted by a phosphate-containing group
