2.3 Carbohydrates and lipids Flashcards
What are carbohydrates?
-Organic compounds with the general formula C x (H 2 O) y.
-They form the most important source of energy in the body.
How can carbohydrates be classified?
-Monosaccharides, disaccharides, and polysaccharides.
-Monosaccharides and disaccharides are both considered sugars, which are polar and soluble in water.
-Polysaccharides are macromolecules resulting from the polymerization (condensation) of sugars and are not soluble in water.
What are monosaccharides?
-The simplest types of carbohydrates.
-The number of carbon atoms can range from three to seven.
-The carbons are joined to a hydroxyl group (-OH).
Examples of monosaccharides
Ribose, glucose, fructose and galactose.
Monosaccharides act as ___
Monomers to make larger complex carbohydrate molecules.
Two monosaccharide monomers are linked together by a ___
Condensation reaction which forms a glycosidic bond producing a disaccharide, releasing one water molecule.
What do several monomer units linked together form?
A polysaccharide.
What is a condensation reaction?
-A reaction in which two smaller organic molecules combine to form a larger molecule and a molecule of water or some other simple molecule.
-The reaction opposite to condensation is called hydrolysis.
-This is a chemical reaction in which water is used to break down the bonds of big compounds.
To avoid confusing condensation and hydrolysis, think about the following ideas.
-Condensation is just like the formation of condensation (water droplets) on a cold window: water droplets are produced.
-Hydrolysis is the opposite of condensation. It is when water (‘hydro’) is added and used to break up (‘lyse’) a polymer, a disaccharide or a dipeptide into smaller monomers.
Diagram showing monosaccharides and condensation reactions. (Two monomers of glucose forming the disaccharide maltose and water in a condensation reaction.)
What is glucose?
A monosaccharide.
What two forms does glucose exist in?
-D-glucose and L-glucose.
-They are isomers meaning they have the same chemical formula but a slightly different arrangement of the atoms.
-Furthermore, there are two forms of the D-glucose, α-D-glucose, and β-D-glucose.
-These differ in the placement of the -OH group on carbon 1.
Diagram of Alpha-D-glucose
Diagram of Beta-D-glucose
What form of glucose does this diagram show?
Alpha-D-glucose
What form of glucose does this diagram show?
Beta-D-glucose
Glucose is often drawn in an abbreviated form where the ____
The carbon atoms are omitted.
What are polysaccharides?
Polysaccharides are large molecules, such as cellulose, glycogen and starch.
What is the function of glycogen?
It is a storage substance in animals and fungi.
Plants store ___ in their roots and stems.
Starch
Examples of disaccharides
-Sucrose
-Maltose
-Lactose
What are the monomers of sucrose?
Glucose and fructose
What are the monomers of maltose?
Glucose (2 units)
What are the monomers of lactose?
Glucose and galactose
Examples of polysaccharides
-Starch
-Glycogen
-Cellulose
What are the monomers of starch?
Glucose
What are the monomers of glycogen?
Glucose
What are the monomers of cellulose?
Glucose
How is maltose formed?
By joining two glucose molecules in a condensation reaction.
Cellulose is a polysaccharide made up of ___
Numerous glucose molecules joined together
What is the name of the reaction in which monomers are joined together and form a polymer?
Condensation reaction
What is the role of polysaccharides in the supply and storage of energy?
-In plants, starch is used to store energy; this becomes very obvious if you consider potatoes and other tubers.
-Starch is made up of a mixture of two polysaccharides, namely amylose and amylopectin.
-In the case of animals, glycogen is the carbohydrate used to store energy
What functions do polysaccharides have other than supplying and storing energy?
-They can also be used as a structural component.
-For instance, cellulose present in plant cell walls gives the walls extra strength and protects the cell from over-expanding and bursting, as well as storing enough energy to be a source for biofuels.
What is the similarities and differences between starch and cellulose?
They are both made up of the same monomer- glucose- but they differ in the arrangement of glucose molecules and the position of the glycosidic bonds.
Structure of glucose monomers in starch and cellulose molecules.
-In starch molecules, all glucose monomers are oriented in the same direction.
-In contrast, cellulose molecules are made up of glucose monomers that rotate 180 degrees around the backbone chain.
-In starch, the arrangement of glucose molecules can be linear, which is called amylose, or branched, which is called amylopectin.
Diagram showing the differences between the amylose and amylopectin structure, two different forms of starch.
In what form of starch is the arrangement of glucose molecules linear?
Amylose (alpha glucose monomers form a helix)
In what form of starch is the arrangement of glucose molecules branched?
Amylopectin
What is the function of hydrogen bonds between glucose subunits?
To stabilize the structure of starch, cellulose, and glycogen.
Polarity and solubility in water of monosaccharides.
Monosaccharides are polar and soluble in water.
Polarity and solubility in water of disaccharides.
Disaccharides are polar and soluble in water.
Polarity and solubility in water of polysaccharides.
Not all are polar and soluble in water.
Examples of monosaccharides
-Glucose
-Ribose
-Fructose
-Galactose
Examples of disaccharides
-Maltose
-Lactose
-Sucrose
Examples of polysaccharides
-Glycogen
-Cellulose
-Starch
Sources of fructose and galactose
-Fructose is a sugar found in fruits and honey.
-Galactose is a sugar in milk.
Sources of maltose, sucrose, and lactose
-Maltose (glucose + glucose) is found in grains.
-Sucrose (glucose + fructose) is found in sugar cane and sugar beets.
-Lactose (glucose + galactose) is found in mammalian milk.
Sources of cellulose, starch, and glycogen
-Cellulose is the structural component of plant cell walls.
-Starch forms energy stores in plants (e.g potatoes and cassava).
-Glycogen is the storage form of carbohydrate. It is found in animals in the liver and muscles
Key facts about the utilization of starch in industry.
1) Starch is a polymer made up of glucose monomers. Glucose monomers can form a long, unbranched chain known as amylose or a branched-chain called amylopectin. A starch molecule consists of both forms: unbranched amylose and branched amylopectin.
2) Amylopectin gives starch its characteristic stickiness. This is very useful in the food, paper, and chemical industries, where it is used to make a paste, glue (adhesive), or lubricant.
3) Amylopectin makes up 80% of the starch content in potatoes. A genetically modified potato that predominantly produces amylopectin starches (useful for adhesive making), has been produced and approved for cultivation.
What is the function of cellulose in plants?
Formation of cell walls.
Starch consists of both ____
Branched and unbranched chains of glucose monomers.