Biological molecules - CARBOHYDRATES Flashcards
How does a condensation reaction between two monosaccharides form a glycosidic bond?
A water molecule is released and a covalent bond between one O and a carbon (4) is formed
What are monomers?
Monomers are the smaller units from which polymers are made
What are polymers?
Polymers are (often chains) made up of many monomers
Name examples of monomers
Monosaccharides, amino acids and nucleotides
What are some common disaccharides?
Sucrose, lactose and maltose
How are common disaccharides formed?
By the condensation of two monosaccharides
How is maltose formed?
By the condensation of two α-glucose molecules
How is sucrose formed?
By the condensation of a glucose molecule and a fructose molecule
How is lactose formed?
By the condensation of a glucose molecule and a galactose molecule
How are glycogen and starch formed?
By the condensation of α-glucose (alpha glucose)
How is cellulose formed?
By the condensation of β-glucose (beta glucose)
How can we test for reducing sugars and non reducing sugars?
Benedict’s solution: heat in a water bath at 80-85 degrees celsius for 5 minutes; (REDUCING SUGARS) colour change from blue - brick red, yellow, green/(NON_REDUCING SUGARS) add HCl + heat, then add sodium hydrogencarbonate to neutralise, then Benedict’s solution and heat - colour change to brick red
How can we test for starch?
Iodine solution: colour change from orange/brown - blue/black
What is the molecular formula for carbohydrates?
Cn(H2O)n
Molecular formula of general name ‘triose’?
C3H6O3
Molecular formula of general name ‘pentose’ and example?
C5H10O5 - ribose
Molecular formula of general name ‘hexose’ and examples?
C6H12O6 - glucose (α & β), fructose, galactose
What is an isomer?
Same molecular formula but different displayed/structural formula
What does ABBA stand for and how can we use it?
‘Alpha below’ and ‘Beta above’
In an α-glucose, the OH is below the 1st carbon.
In a β-glucose, the OH is above the 1st carbon.
Key characteristics of condensation and hydrolysis reactions? (In terms of: water, covalent bonds and size)
CONDENSATION
water - released
covalent bond - form glycosidic bonds
size - larger
HYDROLYSIS
water - used
covalent bond - broken
size - smaller but more of them
Why are sugars soluble?
They have the ability to form hydrogen bonds between the solute (glucose) and water (solvent)
What polymers of alpha glucose can be formed?
Animals & funghi: GLYCOGEN
Plants: STARCH (amylose and amylopectin)
Describe Amylose
Monomer: α-glucose
Covalent bonds: α 1,4 glycosidic
Structure : Spiral, coiled, α-helix
Function: Stores glucose for use in respiration
Describe Amylopectin
Monomer: α-glucose
Covalent bonds: α 1-4 AND 1-6 glycosidic bonds
Structure: relatively few 1-6 bonds, branched, crystalline
Function: Stores glucose for use in respiration
Describe Glycogen
Monomer: α-glucose
Covalent bonds: α 1-4 AND 1-6 glycosidic bonds
Structure: More branches than amylopectin, spherical
Function: Stores glucose for use in respiration
Structure to function of amylose, amylopectin and glycogen?
1) Insoluble - doesn’t affect the water potential and cause water to move by osmosis
2) Large molecules - cannot diffuse across cell membrane and be lost from cell
3) Branched or coiled - more compact, so more can fit in the cell
4) Polymer of α-glucose - respiratory substrate
5) Highly branched - allows rapid hydrolysis to provide glucose for respiration (ONLY GLYCOGEN)
Describe Cellulose
Monomer: β-glucose
Covalent bonds: β 1-4 glycosidic bonds
Structure: Straight, unbranched chain that form fibrils
Function: Cell wall
Structure to function of cellulose?
1) H bonds - Produce high tensile strength, so cell walls are flexible
2) Straight chains - form fibrils, which are stronger
3) Offset ends of chains - strengthens the fibre to prevent breaking
BENEDICT’S TEST - Why do you repeat the test for a reducing sugar using distilled water?
To provide us with a control experiment - so we can compare and check that the heat is not causing the reagent to change colour
BENEDICT’S TEST - Why did you initally test sucrose without the treatment with hydrochloric acid and sodium hydrogencarbonate?
To test and see if sucrose is a reducing sugar (it is not!)
BENEDICT’S TEST - Why did you heat the sucrose with hydrochloric acid at the start of the test for non-reducing sugars? Explain the reactions occurring during this part of the experiment
HCl and heat hydrolyses the sucrose without an enzyme, breaking the glycosidic bonds
BENEDICT’S TEST - Why is sodium hydrogencarbonate added to the tube before testing with Benedict’s solution?
The sodium hydrogencarbonate neutralises the acidic solution so the Benedict’s can react
BENEDICTS’S TEST - How could you modify the procedure to determine the amount of glucose in a solution?
Use a colorimeter
BENEDICT’S TEST - How could you improve the validity of the experiment?
1) Filter twice - the remaining Cu2O will affect absorbance
2) Cuvette volume - affect absorbance - measure volume
3) Volume measurement - air bubbles/meniscus ; smallest syringe for the volume
4) Reaction didn’t stop at 5 minutes - delays in filtering as it was still hot; put in ice bucket
Where would you identify maltose?
Germinating seeds as it is the intermediate stage of polysaccharide digestion
starch -> maltose + glucose
Where would you identify lactose
Milk sugar - produced in lactation in mammals
Where would you identify sucrose?
Transport in the phloem - allows for specialist transport proteins
