Carbohydrates Flashcards
What is the function of carbohydrates?
To provide energy. This can be immediately (e.g. glucose) or as stored energy (e.g. glycogen in animals and starch in plants).
What are the 3 broad groups carbohydrates can be split into?
Monosaccharides, disaccharides, and polysaccharides
What is the general formula for monosaccharides?
Cn(H2O)n
What properties must a substance have to be classed as a sugar?
- Must dissolve in water
- Must be crystalline
- Must be sweet to taste
Are all monosaccharides classed as sugars?
Yes
What is the general name for monosaccharides containing:
a) 3 carbons
b) 5 carbons
c) 6 carbons
a) triose
b) pentose
c) hexose
Give an example of a 3 carbon sugar
G3P
How is sucrose formed?
A condensation reaction between alpha glucose and fructose
What hydrolyses sucrose?
Sucrase
Give 3 examples of disaccharides
Maltose, sucrose, and lactose
What kind of bond forms between sugars in a condensation reaction?
A glycosidic bond
How is maltose formed?
From a condensation reaction between two alpha glucose molecules
What hydrolyses maltose?
Maltase
How do two alpha glucose molecules bond to form maltose?
There is a reaction between the hydroxyl group of Carbon 1 of one molecule and Carbon 4 of the other molecule (be careful to specify C1 of one molecule and C4 of another)
Is the bond formed in the condensation reaction of alpha glucose above or below the plane of the ring?
Below
Give the two functions of polysaccharides
1) Energy storage
2) Structure in the form of cellulose in plant cell walls or chitin in insect wings and fungi walls
In what form is energy stored in:
i) plant cells
ii) animal cells
i) Starch
ii) Glycogen
Why are polysaccharides not classed as sugars? (3 reasons)
- They do not taste sweet
- They are not crystalline
- They do not dissolve in water
What are the three physical properties of both starch and glycogen that make them excellent storage molecules?
- They are insoluble in water
- They form very compact molecules
- They can be easily hydrolysed to release a glucose
(i) How does Starch and glycogen’s insolubility in water make them good storage molecules?
(ii) What would happen if they were soluble in water?
(i) They do not dissolve and therefore do not affect the water potential of cells
(ii) They would dissolve and change the water potential of the cell, causing water to move into the cell by osmosis and cause cell damage
Why is the ability to form compact molecules favourable for a storage molecule?
A lot of the molecules can fit into a small space, meaning more efficient storage
Why is it beneficial that starch and glucose can be easily hydrolysed?
Easy hydrolysis means that both starch and glycogen can provide a readily available source of glucose for respiration and so provide quick release energy.
What reacts to form glycogen?
Alpha glucose
What type of bonding occurs in glycogen? Why?
1,4 and 1,6 glycosidic bonding
- This allows for branching so each molecule has many ends where glucose can be added
- This means glycogen is a more compact molecule
- This means more terminal glucose molecules that can be simultaneously hydrolysed
What are the two components of starch?
Amylose and Amylopectin
i) What happens to the shape of amylose once it has been formed?
ii) What shape does this give it?
iii) What causes this change in shape to occur?
i) It coils
ii) Giving a helical shape
iii) Hydrogen bonds form within the coil
i) Which molecules make up amylose?
ii) What kind of bonding links these together?
iii) Therefore what kind of molecules is produced?
i) Alpha-glucose
ii) 1,4 glycosidic bonds
iii) Linear
i) What molecules make up amylopectin?
ii) What kind of bonding is present in amylopectin?
iii) Therefore which molecule is amylopectin similar to?
i) Alpha-glucose
ii) 1,4 and 1,6 glycosidic bonds
iii) Glycogen
i) How can the presence of starch be tested for?
ii) What is observed if starch is present?
iii) Why does this occur?
i) Potassium iodide solution is added
ii) The solution will go from being orange/brown to black/blue
iii) The iodine sits in the coils of the amylose component of starch, this complex appears blue/black
Where is cellulose found?
In plant cell walls
What is the monomeric unit of cellulose?
Beta glucose
What is the difference between alpha and beta glucose?
The OH group on Carbon 1 is above the plane of the ring in beta glucose but below the plane of the ring in alpha glucose
i) What bonding is present in cellulose?
ii) What issue arises with this bonding?
iii) Therefore what must happen to allow the bonding to occur?
i) 1, 4 glycosidic bonds between beta glucose molecule ii) The hydroxyl groups lie on different planes of the ring iii) Every other beta glucose must be rotated 180 degrees relative to the previous beta glucose
What are the monomeric units of sucrose?
Alpha glucose and fructose
Are all monosaccarides reducing sugars?
Yes
Are all disaccharides reducing sugars?
No, only some are
Give an example of a non-reducing sugar
Sucrose
Give an example of a reducing sugar
Maltose or lactose
Give an example of a 5 carbon sugar
Ribose or deoxyribose
Give an example of a 6 carbon sugar
Glucose or fructose or galactose
What type of reaction is the breakdown of maltose by maltase?
Hydrolysis
What is produced by the hydrolysis of maltose?
Two alpha glucose molecules
What is a reducing sugar?
Sugars that donate electrons resulting in the reduction of another molecule
