3.3 Carbohydrates Flashcards
what is in carbohydrates and what’s the general ratio
general ratio = Cx(H20)y and contains oxygen, carbon and hydrogen.
Literally means ‘hydrated carbon’.
What are …saccharides
Carbohydrates are also known as saccharides or sugars.
Single sugar = monosaccharide (glucose, fructose, ribose).
2 monosaccharides = disaccharide (lactose, sucrose)
When 2 or more link together, they form a polysaccharide (glycogen, cellulose, starch).
What is the formula and properties for glucose
The basic building blocks/or monomers, of some biologically important large carbohydrates are glucose molecules.
Have the chemical formula C6H12O6.
Glucose molecules are polar and soluble in water - due to hydrogen bonds that form between hydroxyl groups and water molecules.
Solubility is important because it means it can dissolve in the cytosol of the cell.
What are condensation reactions
When a reaction takes place to join 2 molecules, whilst losing water.
When 2 alpha glucose molecules are next to each other, 2 hydroxyl groups interact (react) because the OH’s are next to each other.
Bonds break as a result and new bonds reform in different places producing more molecules.
2 hydrogens and an oxygen atom are removed from the glucose monomers and joint to form a water molecule, therefore, called a condensation reaction.
A bond forms between carbons 1 and 4 on the glucose molecules and the molecules are now joined.
A covalent bond called a GLYCOSIDIC BOND is formed between 2 glucose molecules. The reaction is a condensation one because a water molecule is a product.
Because carbon 1 an carbon 4 joined, this specific reaction is called a 1,4 glycosidic bond.
Forms MALTOSE, a disaccharide.
What are hexose sugars
Sugars that have 6 carbons
Fructose and galactose = hexose monosaccharides
FRUCTOSE occurs naturally in fruit, and combines WITH GLUCOSE = sucrose (disaccharide/normal sugar)
GALACTOSE + GLUCOSE = lactose (disaccharide/found in milk and dairy products).
Fructose is sweeter than glucose and glucose is sweeter than galactose.
What are pentose sugars
Pentose monosaccharides are sugars that contain 5 carbons.
2 pentose sugars are biologically important components of molecules - RIBOSE is the sugar present in RNA nucleotides
DEOXYRIBOSE is the sugar in DNA nucleotides.
What is the structure of starch and glycogen
Many alpha glucose molecules can be joined by glycosidic bonds to form slightly different polysaccharides known as STARCH.
Glucose made by photosynthesis in plant cells is stored as starch; chemical energy store.
One of the polysaccharides in starch is AMYLOSE.
Amylose is formed by alpha glucose molecules joined together by 1.4 glycosidic bonds.
The angle of the bond means that this long chain of glucose twists to form a helix which is stabilised by hydrogen bonding with the molecule. = polysaccharide is more compact and much less soluble than the glucose molecules used to make it.
Another type of starch is formed when glycosidic bonds form in condensation reactions between carbon 1 and 4 on 2 glucose molecules = AMYLOPECTIN
Difference between amylose and amylopectin = in amylopectin there are also some glycosidic bonds formed when condensation reaction between carbon 1 and 6.
Means that amylopectin has branched structure with the 1-6 branching points occurring approx. once in every 25 glucose subunits.
The functionally equivalent energy storage molecule to starch in animals and fungi is GLYCOGEN.
Forms more branches than amylopectin so more compact; good because animals are mobile.
Branching also means there are many free end for glucose molecules to be added or removed which speeds up storing or releasing glucose molecules required by cell.
What are Hydrolysis Reactions
Glucose is stored by plants or glycogen by animals and fungi until it’s needed for respiration.
To release glucose for respiration, starch or glycogen undergo HYDROLOYSIS REACTIONS, requiring water molecules.
The reactions are catalysed by enzymes and are the reverse of the condensation reactions that form the glycosidic bonds.
What is the structure of cellulose
A straight chain molecule is formed called CELLULOSE.
Beta glucose molecules are unable to join together in the same way alpha molecules can because the hydroxyl groups don’t line up so they can be near and react together. Therefore, every other beta molecule is flipped upside down.
When a polysaccharide is formed from glucose in this way, it’s unable to coil or form branches. Cellulose molecules make hydrogen bonds with each other forming microfibrils.
Microfibrils join together to form macrofibrils which combine to produce cellulose fibres.
These fibres are strong and insoluble and used to make cell walls; important for our digestive system, and hard o break down into monomers.
What are the 2 variations of glucose and what’s the structural differences between them?
Alpha and Beta
In it’s ring diagram, Alpha has the hydroxyl group (OH) at the bottom of Carbon 1, while Beta glucose has OH at the top of Carbon 1.
If glucose has 6 carbons, what is it
hexose monosaccharide
