Carbohydrates Flashcards
How many carbons does a hexose have and what is it a form of?
6 carbons
form of glucose
What are carbohydrates made out of?
Carbon and water
What is the general formula of carbohydrates?
Cn(H2O)n
Name the three carbohydrate groups
Monosaccharides
Disaccharides
Polysaccharides
What are the properties of monosaccharides?
Colourless, crystalline solids, soluble in water (OH groups), single aldehyde or ketone group
What makes up a disaccharide and how are they made?
2 monosaccharides and formed by condensation reaction (removal of H2O)
What is a polysaccharide?
Polymers of monosaccharides
What are the two forms of polysaccharides?
Homopolysaccharides and heteropolysaccharides
Name three carbohydrate functions
Energy storage/supply
structural functions
signalling (between and within cells)
What are the 2 structural forms of carbohydrates?
Fischer projections - 2D, linear
Ring (cyclic structure)
What are the 3 monosaccharide groups?
Ketone (C-O)
Aldehyde (COH)
Hydroxyl (OH)
What is isomerism?
Atomic arrangements within the molecule that can significantly affect the function
What is a chiral centre?
Carbon atoms that have 4 different chemical groups attached
What is an enantiomer?
When molecules have the same functional group but one is a mirror image of the other
What is D configuration in an enantiomer in a Fischer projection?
If the OH group is to the right of the last chiral centre carbon
What is L configuration in an enantiomer in a Fischer projection?
If the OH group is to the left of the last chiral centre carbon
What is D configuration in a ring enantiomer?
If the oxygen bond to the last chiral centre carbon is at the right
What is the L configuration in a ring enantiomer?
If the oxygen bond to the last chiral centre carbon is at the left
Where does an epimer occur?
Where functional groups are arranged differently at one or more chiral centres (not mirror images)
What happens when a molecule is dextrorotatory?
It rotates light clockwise
How are dextrorotatory molecules denoted?
(+)
Where do anomers occur?
Only in rings
What is an anomeric carbon?
Ones involved in hemiacetal or hemiketal bonding during ring formation
Where do anomeres occur?
Only in rings
What does alpha mean when denoted on an anomer for hexose?
carbon 6 and new hydroxyl group (OH) are on opposite sides of rings
What does beta mean when denoted on an anomer for hexose?
carbon 6 and new hydroxyl group (OH) are on the same side of the ring
What does “pyran” mean?
six in the ring
What does “furan” mean?
five in the ring
What group are aldohexoses predominantly part of?
Pyranose
What group are ketohexoses predominantly part of?
furanose
Where do conformers occur?
only for rings
What causes puckered conformations?
strain
What are the 2 conformations that rings flip between?
“boat” and “chair”
What test can be use to detect monosaccharides?
Benedict’s test for reducing sugars - precipitated as insoluble red
What can you do to detect monosaccharides?
Oxidation - only free aldehyde/ketone groups can be oxidised, afterwards the monosaccharide can reduce the metal ions
When is an O-glycosidic bond formed in a disaccharide?
When an anomeric carbon of one monosaccharide binds to oxygen from hydroxyl group of another sugar
Why does the glycosidic bond name contain alpha or beta?
If the monosaccharide is either alpha or beta
Can a glycosidic bond be hydrolysed?
Yes at low pH acids but not by bases
When does an N-glycosidic bond occur?
when an anomeric carbon of a sugar joined to a nitrogen atom in glycoproteins and nucleotides
Name some important disaccharides
Maltose: glucose + glucose
Lactose: galactose + glucose
Sucrose: glucose + fructose
Trehalose: energy storage compound in some insects, bacteria and fungi
What do glycosidic linkages form?
polysaccharides
What is a homopolysaccharide?
contain a single type of monosaccharide and used in energy storage/structural components
What is a heteropolysaccharide?
contain 2 or more different monosaccharides
What are the functions of a heteropolysaccharide?
Structural
cell-cell signalling
Name a polysaccharide and what its made out of
Starch - mixture of amylose and amylopectin
What are some biological functions of starch?
In plants: stored form of glucose
In animal diets: amylase hydrolyses alpha bond releasing maltose which is converted to glucose by maltase
Name 2 polysaccharides for structure?
Cellulose and chitin
Where is peptidoglycan found?
In the cell wall of Gram-positive and negative bacteria
What are the functions of peptidoglycan?
provides strength and rigidity to the cell wall
What is agar made out of?
mixture of heteropolysaccharides (agarose and agaropectin)
