Chapter 3- 3.3- Carbohydrates Flashcards
What is a single sugar known as?
A monosaccharide. Examples include glucose, fructose, and ribose. When 2 monosaccharide link together they form polymer called a polysaccharide. Glycogen, cellulose, and starch are examples of polysaccharides
What is glucose an example of?
A hexose monosaccharide.
Glucose molecules are polar and soluble in water. This is due to the hydrogen bonds that from between the hydroxyl groups and water molecules. This solubility in water is important because it means glucose is dissolved in the cytosol of the cell.
What is the chemical formula for glucose?
C(6)H(12)O(6).
What are the 2 structural variations of the glucose molecule?
Alpha and beta glucose.
The variation is that the OH(hydroxyl) group on carbon 1 is in the opposition position (upside down).
What is a condensation reaction?
When two alpha molecules are side by side, two hydroxyl groups interact (react).
When this happens bonds are broken and new bonds reformed in different places producing a new molecule.
2 hydrogen atoms and 1 oxygen atom are removed from the glucose monomers and join to form a water molecule. A bond forms between carbons 1 and 4 on the glucose molecule and the molecules are now joined.
A covalent bond called a glycosidic bond is formed between two glucose molecules. The reaction is called a condensation reaction because a water molecule is formed as one of the products of the reaction.
Because in this reaction carbon 1 of one glucose molecule is joined to carbon 4 of the other glucose molecule, the bond is known as a 1,4 glycosidic.
In this reaction, the new molecule is called maltose. This is am example of disaccharide (a molecule made up of two monosaccharides).
What are some examples of other sugars that are also hexose monosaccharides?
Fructose and galactose are also examples of hexose monosaccharides.
Fructose naturally occurs in fruit, often in combination with glucose forming the disaccharide sucrose, commonly known as cane sugar or just sugar.
Galactose and glucose from the disaccharide lactose. Lactose is commonly found in milk and milk products.
Fructose is sweeter than glucose and glucose is sweeter than galactose.
Pentose monosaccharides are sugars that contain five carbon atoms. Two pentose sugars are important components of biological molecules- ribose is the sugar present in RNA nucleotides and deoxyribose is the sugar present in DNA nucleotides.
How many different polysaccharides are known collectively as starch?
Glucose made by photosynthesis in plants is stored as what?
Many alpha glucose molecules can be joined by glycosidic bonds to form two slightly different polysaccharides known collectively as starch.
Glucose made by photosynthesis in plant cells is stored as starch. It is a chemical energy store.
What is and how is amylose formed?
One of the polysaccharides in starch is called amylose.
Amylose I formed by alpha glucose molecules joined together only by 1-4 glycosidic bonds.
The angle of the bond means that this long chain of glucose twists to form a helix which I further stabilised by hydrogen bonding within the molecule.
This makes the polysaccharide more compact and much less soluble, than the glucose molecules used to make it.
What is the other type of starch other than amylose?
Another type of starch is formed when gylcosidic bonds form in condensation reactions between carbon 1 and carbon 6 on two glucose molecules.
The other starch polysaccharide is called amylopectin. Amylopectin is also made by 1-4 glycosidic bonds between alpha glucose molecules, but (unlike amylose) in amylopectin there are also some gylcosidic bonds formed by condensation reactions between carbon 1 and carbon 6 on two glucose molecules.
This means that amylopectin has a branched structure, with the 1-6 branching points occurring approximately once in every 25 glucose subunits.
What is the functionally equivalent energy storage molecule to starch in animals and fungi is called what?
Glycogen.
Glycogen forms more branches than amylopectin, which means it is more compact and less space is needed for it to be stored.
This is important as animals, are mobile, unlike plants.
The coiling or branching of these polysaccharides makes them very compact, which is ideal for storage.
The branching also means there are many free ends where glucose molecules can be added or removed.
This speeds up the processes of storing or releasing glucose molecules required by the cell.
So, the key properties of amylopectin and glycogen are that they are insoluble, branched, and compact.
These properties mean they are ideally suited to the storage roles that they carry out.
Explain what a hydrolysis reaction is.
To release glucose for respiration, starch or glycogen undergo hydrolysis reactions, requiring the addition of water molecules. The reactions are catalysed by enzymes. These are the reverse of the condensation reactions that form the glycosidic bonds.
Glucose is stored as starch by plants or glycogen by animals and fungi, until it is needed for respiration- the process in which biochemical energy in these stored nutrients is converted into a useable energy source for the cell.
What and how is cellulose formed?
Beta glucose molecules are unable to join together in the same way that alpha glucose molecules can. The hydroxyl groups on carbon 1 and carbon 4 of the two glucose molecules are too far from each other to react.
The only way that beta glucose molecules can join together and form a polymer is if alternate beta glucose molecules are turned upside down.
When a polysaccharide is formed from glucose in this way it is unable to coil or form branches. A straight chain is formed called cellulose.
Cellulose molecules make hydrogen bonds with each other forming micro fibrils. These micro fibrils join together forming macrofibrils, which combine to produce fibres.
These fibres are strong and insoluble and are used to make cell walls.
Cellulose is an important part of our diet, it is very hard to break down into its monomers and forms the “fibres” or “roughage” necessary for a healthy digestive system.
