Carbohydrates Flashcards
What are carbohydrates
Molecules that only contain the elements carbon, hydrogen and oxygen
What are carbohydrates also known as
Saccharides or sugars
What’s a single sugar unit known as
Monosaccharide- like glucose, fructose and ribose.
What’s a disaccharide
When two monosaccharides link together- like lactose and sucrose
What are polysaccharides
When two or more(usually many more) monosaccharides are linked-like glycogen, cellulose and starch.
What is glucose
A monosaccharide- six carbons= hexose monosaccharide
What’s a molecular structure diagram
Carbons are numbered clockwise beginning with the carbon to the right of the oxygen atom within the ring
Two forms of glucose
Alpha(OH below) and beta(OH above)- OH(hydroxyl) group on carbon 1 is in opposite positions.
Properties of glucose molecules
Polar and soluble in water-due to hydrogen bonds that between hydroxyl groups and water molecules. This solubility in water is important, because it means glucose is dissolved in the cystol of the cell.
What’s a condensation reaction
When two alpha glucose molecules are side by side, two hydroxyl groups interact (react). When this happens bonds are broken and new bonds reformed in different places producing new molecules. Two hydrogen atoms and an oxygen atom are removed from the glucose monomers and join to form a water molecule. A bond forms between carbon 1 and 4.
What bond forms between glucose molecules
Covalent bond called a glycosidic bond is formed. Called a condensation reaction because a water molecule is formed as one of the products of reaction. Known as 1,4 glycosidic bond.
What’s maltose
Two glucose reacted- example of disaccharide- molecule made up of two monosaccharides
What’s fructose
Naturally occurs in fruit, often in combination with glucose forming the disaccharide sucrose.
What do galactose and glucose form
The disaccharide lactose-found in milk. - galactose and fructose are also hexose monosaccharides
What are pentose monosaccharides
Sugars that contain five carbon atoms. Ribose is the sugar present in RNA nucleotides and deoxyribose is the sugar present in DNA nucleotides
What is starch
Chemical energy store in plants- lots of glucose molecules
What’s amylose
Formed by alpha glucose molecules joined by 1,4 glycosidic bonds. Angle of this bond means long chain twists to form a helix which is 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.
How is amylopectin formed
When glycosidic bonds form in a condensation reaction between carbon 1 and carbon 6 on two glucose molecules. Amylopectin is also made up of 1-4 glycosidic bonds between alpha glucose molecules but there are also 1,6 formed by condensation reactions. This means that amylopectin has a branched structure, with the 1,6 branching points occurring approximately once in every 25 glucose subunits.
What is glycogen
The functionally equivalent energy storage molecule to starch in animals and fungi. Glycogen forms more branches than amylopectin, which means it is more compact and less space is needed for it to be stored.
Why do animals need glycogen to be compact
Mobile, 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.
Key properties of glycogen and amylopectin
Insoluble, branched and compact.
What reaction does starch or glycogen undergo to release glucose
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.
Why are beta glucose unable to react in same way alpha glucose can
Hydroxyl groups on carbon 1 and 4 are too far away 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
What is cellulose
Made up of beta glucose- when a polysaccharide is formed from glucose in this way it is unable to form branches. A straight chain molecule is formed called cellulose.
