3.1.2 Carbohydrates Flashcards
What are monosaccharides?
Monomers from which larger carbohydrates are made. They are soluble
What are three examples of monosaccharides?
Glucose, galactose, fructose
How is a glycosidic bond formed?
Through a condensation reaction between two monosaccharides
What are disaccharides?
Formed by the condensation of two monosaccharides
What is maltose?
A disaccharide formed by condensation of two glucose molccules
What is sucrose?
A disaccharide formed by condensation of a glucose molecule and a fructose molecule
What is lactose?
A disaccharide formed by condensation of a glucose molecule and a galactose molecule
What are the two glucose isomers?
α-glucose, β-glucose
How does α-glucose and β-glucose differ?
α-glucose - H above, OH below
β-glucose - H below, OH above
What are polysaccharides?
Formed by the condensation of many glucose units. They are insoluble
Which polysaccharides are formed by the condensation of α-glucose?
Glycogen, starch
Which polysaccharides are formed by the condensation of β-glucose
Cellulose
Why is dilute hydrochloric acid added into food sample of non-reducing sugar?
It will hydrolyse any disaccharide present into its constituent monosaccharides by breaking its glycosidic bonds
Why is sodium hydrogen carbonate solution (NaHCO3) added to hydrochloric acid (HCl)?
Benedict’s reagent will not work in acidic conditions - needs to be neutralised
What is the test for reducing sugar?
1.Combine equal quantities of test solution and Benedict’s reagent in a test tube
2. Heat in water bath at 80°C
3. Observe change in colour and opacity of solution - indicates concentration of reducing sugar: Green(least), Yellow, Orange, Brick Red(most)
Why is non-reducing sugar not detected by Benedict’s reagent?
They do not change colour of Benedict’s reagent as they have a lack of reducing parts - used in making glycosidic bond
How to detect non-reducing sugars?
It must be hydrolysed into its monosaccharide components (reducing sugar) by hydrolysis as they do not change the colour of Benedict’s reagent
When do you do a non-reducing sugar test?
When results for Benedict’s reagent is negative
What is the test for non-reducing sugar?
- Hydrolyse the glycosidic bond with warm dilute hydrochloric acid
- Neutralise with sodium hydrogen carbonate
- Perform a Benedict’s test again
What is the structure of amylose?
A straight chain, unbranched polymer of glucose units bound by (α1-4) glycosidic bond
What are the main two components of starch?
Amylose and amylopectin
Which type of glucose is amylose and amylopectin made of?
α-glucose
What secondary structure does amylose form?
α-helices
What is the structure of amylopectin?
A branched chain polymer with α1-4 glycosidic bonds, and occasional α1-6 bonds in order to create branches
Why is the rate of hydrolysis of amylopectin faster?
It has branches which increases surface area
What is the test for starch?
- Add iodine/ potassium iodide
- Observe change in colour: Yellow to Blue/Black
How does iodine indicate the presence of starch?
Iodine passes through the helix structure of amylose, which change the chemical properties of the helix, causing a different colour of light to reflect
What is the structure of glycogen?
It is a macro molecule with 1-4 and 1-6 glycosidic bonds from α-glucose
What is the difference in structure between starch and glycogen?
Glycogen has more frequent branching than starch - more surface area as demand in energy is more in animals for movement
What is the structure of cellulose?
It is a straight chain polymer of β-glucose monomers
How does fibres formed from cellulose give plant cell wall its strength
Cellulose molecules join to make microfibres through hydrogen bonds
Microfibres group into fibres
The arrangement of OH group of β-glucose on either side of chain allows for hydrogen bonds to form between adjacent chains above and below
All the hydrogen bonds have collective strength
How does cellulose make plant cell walls permeable?
Fibres are laid down in layers which are arranged at 90°to form sheet-like structure - cross-hatches which they are holes between chains
