Carbohydrates Flashcards
What are carbohydrates?
Carbohydrates are a group of molecules containing carbon, hydrogen and oxygen.
They are a hydrated carbon.
Carbohydrates are also part of other molecules, such as nucleic acids and glycolipids.
What are the functions of carbohydrates?
They acts as a source of energy e.g. glucose.
They acts as a store for energy e.g. starch and glycogen.
They act as structural units e.g. cellulose in plants and chitin in insects.
What are the three types of Carbohydrates?
Monosaccharides, Disaccharides and Polysaccharides
What are Monosaccharides?
- They are the simplest carbohydrates
- They provide a source of energy because they have a large number of carbon-hydrogen bonds
- They are sugars
- They are soluble in water and insoluble in non-polar solvents
- They have a backbone of single-bonded carbon atoms, with one double-bonded to an oxygen atom to form a carbonyl group.
- An example is glucose and fructose
What are Disaccharides?
- They are sweet and soluble.
- The most common are maltose, sucrose and lactose.
- Disaccharides are made when two monosaccharides join together. There are lots of different combinations:
a-glucose + a-glucose –> maltose
a-glucose + fructose –> sucrose
b-galactose + a-glucose –> lactose
b-glucose + b-glucose –> cellobiose - They form by condensation reactions to form a glycosidic bond.
- Disaccharides are broken into monosaccharides by a hydrolysis reaction.
What is the function of a-glucose?
It is an energy source. Component of starch and glycogen, which acts as energy stores.
Type of sugar= Hexose
What is the function of b-glucose?
Energy source, component of cellulose, which provides structural support in plant cell walls.
Type of sugar= Hexose
What is the function of Ribose?
Component of ribonucleic acid (RNA), ATP and NAD.
Type of sugar= Pentose
What is the function of deoxyribose?
Component of deoxyribonucleic acid (DNA).
Type of sugar= Pentose
What are Polysaccharides?
Polysaccharides are polymers made of monosaccharides bonded together. They are made from one type of monosaccharides called homopolysaccharides.
Example= Amylose, Amylopectin and Glycogen
What is the equation for respiration?
Glucose + Oxygen –> Carbon Dioxide + Water
Why are polysaccharides good energy stores?
Glycogen and starch are compact, which means that they do not occupy a large amount of space. They both occur in dense granules within the cell.
Polysaccharides hold glucose molecules in chains, so they can easily be ‘snipped off’ from the end of the chain by hydrolysis when required for respiration. Hydrolysis reactions are always catalyse by enzymes.
Some chains are unbranched (amylose) and some are branched (amylopectin and glycogen). Branched chains are more compact, but it is more likely for glucose molecules to be snipped off by hydrolysis when lots of energy is required quickly.
Polysaccharides are less soluble in water than monosaccharides. This is because of their size and because the hydrogen bonds are hidden.
What is Amylose?
It is in plants.
This is a long chain of a-glucose molecules. It has glycosidic bonds between carbons 1 & 4.
Amylose coils into a spiral shape, with hydrogen bonds holding the spiral in place. Hydroxyl groups on carbon 2 are situated on the inside of the coil, making the molecule less soluble and allowing hydrogen bonds to form to maintain the coil’s structure.
What is Amylopectin?
It is in plants.
It has glycosidic bonds between carbons 1 and 4 but in addition it has branches formed by glycosidic bonds between carbons 1 and 6.
Amylopectin also coils into a spiral shape, held together with hydrogen bonds, but with branches emerging from the spiral.
What is Glycogen?
It is in animals.
This molecule is like amylopectin with glycosidic bonds between carbon 1 and 4, and branches formed by glycosidic bonds between 1 and 6.
The 1-4 bonded chains tend to be smaller than in amylopectin, so glycogen has less tendency to coil. However, it does have more branches, which makes it more compact and it is easier to remove monomer units as there are more ends.
