Biological molecules: carbohydrates Flashcards
what are carbohydrates?
molecules that only contain carbon, hydrogen and oxygen. Carbohydrates literally mean hydrated carbon (carbon and water). Carbohydrates are also known as saccharides.
sugars with six carbon atoms are called…
hexose sugars
What is a monosaccharide and name the four examples?
It is a single sugar unit. Examples: glucose, galactose, fructose and ribose.
why are monosaccharides polar and soluble?
because the OH group forms hydrogen bonds with the water molecules. This allows glucose to be dissolved in the cytosol.
what are pentose monosaccharides and name the example?
monosaccharides which contain 5 carbon atoms e.g ribose
what are the differences between the isomers of glucose?
the isomers of glucose is alpha glucose and beta glucose. If the carbon 1 hydroxyl points below the ring it is alpha glucose. If above, beta glucose.
how is the disaccharide, maltose made?
formed by two alpha glucose molecules
what is made when a disaccharide is formed from two monosaccharides?
water is made from a hydrogen from one of the monosaccharides and a hydroxyl group from the other. This is a condensation reaction.
what is the new chemical bond formed when monosaccharides join and what type of bond is it?
glycosidic bonds which is a covalent bond
How do you break glycosidic bonds?
by adding water, this is called hydrolysis.
How is the disaccharide, sucrose formed?
formed from monosaccharides, glucose and fructose
How is the disaccharide, lactose formed?
formed from monosaccharides, glucose and galactose
plant cells store glucose as… and what two molecules does it consist of?
starch. Starch consists of two molecules, amylose and amylopectin.
Describe the structure of amylose polysaccharide and what bonds occur?
- polymer of alpha glucose molecules joined by 1-4 glycosidic bonds.
- twists into a complex, compact helix with hydrogen bonds forming in between glucose molecules along the chain which stabilises the structure and is ideal for storage. This makes starch insoluble.
- unbranched
Describe the structure of amylopectin polysaccharide
- polymer of alpha glucose molecules joined by 1-4 glycosidic bonds
- have branches every 25-30 glucose molecules
- the branches are held by 1-6 glycosidic bond
As amylose and amylopectin are polysaccharides, they are too big to pass through the cell membrane therefore…
enzymes are used to break the glycosidic bonds which is a hydrolysis reaction. The enzymes act at the end of the molecules
animals store glucose as… and describe the structure
glycogen, which has the same structure as amylopectin but forms more branches than amylopectin. Major stores of glycogen is in the liver and muscle cells.
why can enzymes convert glycogen and amylopectin quickly into glucose?
Because as they have many branches, they have many ends which increases the rate as enzymes only work on the ends. Glycogen is quicker at converting as it has more branches, this is important as animals have a high rate of respiration.
what is the plant cell wall made of?
cellulose
what are the polysaccharides of alpha glucose?
amylose, amylopectin and glycogen
describe the structure of cellulose
- polymer of beta glucose molecules joined by 1-4 glycosidic bonds
- every second beta glucose is flipped upside down as hydroxyl groups are now close enough to react and form the glycosidic bond.
- unbranched
why is cellulose strong?
-as it is a straight chain, it allows the cellulose molecules to get close together. Therefore lots of hydrogen bonds form between neighbouring chain, making it strong and insoluble.
how does a microfibril develop into a fibre?
microfibrils join to make a macrofibril and macrofibrils join to make a fibre
why does cellulose need to be strong?
so they cell doesn’t burst.
how is glycogen adapted for food storage?
it is insoluble and it is compact so more can be stored in a less space
why is it important for a storage molecule to be insoluble and compact?
compact meaning more can be stored in a small area. Insoluble meaning it doesnt affect water potential
how does beta glucose differ from alpha glucose? (2marks)
OH and H are reversed (1) on the right carbon (1)
