Carbohydrates Flashcards
How are polymers made?
By linking identical or similar subunits, monomers, to form straight or branched chains
How do the small molecules join together?
In a condensation reaction, so called because a water molecule is released as the two molecules combine in the reaction. Addition of water in a hydrolysis reaction splits the molecule.
What are monosaccharides?
Single sugar units with the general formula (CH2O)n, where n is the number of carbon atoms in the molecule
How many carbon atoms do monosaccharides have?
Between 3 and 7 carbon atoms, the most common number is 6. For example, glucose, galactose and fructose all contain 6 and are known as hexose sugars.
What is the structure of a hexose sugar molecule?
It has a ring structure formed by 5 carbons and an oxygen atom; the sixth carbon projects above or below the ring. The carbon atoms in the molecule are numbered, starting with 1 on the extreme right. The side branches project above or below the ring, and their position determines the type of sugar molecule and its properties.
What do monosaccharides do?
They provide a rapid source of energy. They are readily absorbed and require little or, in the case of glucose, no change before being used in cellular respiration
What is glucose?
Glucose is important as the main sugar used by all cells in respiration. Starch and glycogen are polymers made up of glucose subunits joined together. When starch or glycogen is digested, glucose is produced. This can be absorbed and transported in the bloodstream to cells.
Draw the structure of glucose
What is galactose?
Galactose occurs in our diet mainly as part of the disaccharide sugar lactose, which is found in milk. Notice that the -OH groups on carbon 1 and carbon 4 lie on the opposite side of the ring compared with their position in glucose.
Draw the structure of galactose
What is fructose?
Fructose is a sugar which occurs naturally in fruit, honey and some vegetables. It’s sweetness attracts animals to eat the fruits and so help with seed dispersal.
Draw the structure of fructose
What are disaccharides?
Two single sugar units can join together and form a disaccharide in a condensation reaction releasing a water molecule
What is the bond that forms between the two sugar units?
Glycosidic bond
Draw the condensation reaction of maltose
What is sucrose?
Sucrose, formed from glucose and fructose, is the usual form in which sugar is transported around the plant
Draw the structure of sucrose
What is maltose?
Maltose, formed from two glucose molecules, is the disaccharide produced when amylase breaks down into starch. It is found in germinating seeds such as barley as they break down their starch stores to use for food.
Draw the structure of maltose
What is lactose?
Galactose and glucose make up lactose, the sugar found in milk
Draw the structure of lactose
How can the glycosidic bond in a disaccharide be split?
Hydrolysis, this is the reverse of condensation: water is added to the bond and the molecule splits into two
When does hydrolysis of carbohydrates take place?
When carbohydrates are digested in the gut and when carbohydrate stores in a cell are broken down to release sugars
How are polysaccharides and disaccharides digested?
They have to be digested into monosaccharides before being absorbed, which takes some time, so the monosaccharides are released more slowly
