Carbohydrates Flashcards
All carbohydrates are either…
Monosaccharides disaccharides or polysaccharides
Monosaccharides are
Simple sugars with a general formula of (CH2O)n where n can be 3 to 7
Glucose
Is an important monosaccharide
It has a general formula of C6H12O6
It’s the main way in which carbohydrates are transported around the body
Two types of glucose
Alpha glucose and beta glucose
The only difference in their structure is that the OH is above carbon one in beta glucose rather below it
Fructose
Very soluble and is sweeter than galactose
It’s the main sugar found in fruits and nectar
Galactose
Not as soluble
Has and important role in the production of glycolipids and glycoproteins
Ribose
Structural isomer of rna
Has a H and OH group at carbon 2
Deoxyribose
Structural isomer if dna has two H atoms at carbon two
Disaccharides are
‘Double sugars’ they are formed when two monosaccharides are joined by a glycosdic bond by a condensation reaction
Maltose
(Malt sugar) is formed by two glucose molecules held together by an alpha 1-4 glycosidic bond
Sucrose
(Table sugar) formed together by a glucose and fructose molecule held together by an alpha 1-4 glycosidic bond
Lactose
(Milk sugar) formed by a glucose and galactose molecule held together by an alpha 1-4 glycosidic bond
Testing for monosaccharides and disaccharides: reducing sugars
Using the Benedicts test
This is when Benedicts solution is added to a food sample in a water bath
The colour will change depending on amount of reducing sugars from the lowest to highest being green, yellow,orange,brick red
Test for non reducing sugars (mono and do saccharides)
Eg sucrose
There is no direct test so we must hydrolise it by adding hydrochloric acid then neutralising it
You can then do the Benedicts test
What are polysaccharides
Polymers containing many monosaccharides linked by glycosidic bonds and formed by a condensation reaction
They can be used as energy stores or structural components in cells
Starch is
A polysaccharide made of many alpha glucose molecules
Has two structural units: amylose and amylopectin
It is insoluble compact and easily hydrolised to release energy
Amylose
Structural unit of starch
Contains glucose molecules joined by alpha 1-4 glycosidic bonds only
Has unbranded chains forming a compact helical structure which is held together by hydrogen bonds
Isomer is
The same molecule of something but a different arrangement
Amylopectin
Also contains 1-4 alpha glycosidic bonds
But it also has many more 1-6 glycosidic bonds creating a highly branched structure
Glycogen is
How carbohydrates are stored in animals and is stored as granules
Has a similar structure to amylopectin containing many alpha 1-6 bonds
It is less dense and more soluble indicating high metabolic requirements in animals
Cellulose is
A polysaccharide made of beta glucose molecules in a 1-4 glycosidic bond
It’s the main part of a plants cell wall
Hydrogen bonds give it great tensile strength
Every other glucose molecule is rotated 180 degrees so that the hydroxyl groups are adjacent to each other resulting in long unbranched chains
It’s strong structure prevents plant cells from bursting
Testing for polysaccharides (starch)
Iodine test
Few drops of iodine dissolved in potassium iodide solution to sample
If starch is present it will turn blue black colour
The colour changes due to the iodine molecules fitting through the gaps in the helical structure of amylose
This forms a poly iodide starch complex
Many alpha glucose molecules create
A helical structure (eg amylose)
Many beta glucose molecules create
A straight line (eg cellulose)
Give two reasons why poly a glucose polysaccharides are more suitable for energy strong compounds in cells
They are made of glucose which can be respired
Forms a compact shape which can be stored in cells
Too large to diffuse out of cells
Monomers
Monomers are the smaller units from which larger molecules are made
Polymers
Molecules made from a large number of monomers joined together
Condensation reactions
A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water
Monomer of protein
Amino acids
