Carbohydrates Flashcards
Carbohydrates
Molecules that consist only of carbon, hydrogen and oxygen and are made of long chains of sugar units called saccharides
Glucose
A monosaccharide containing six carbon atoms in each molecule and is the main substrate for respiration
What type of sugar describes glucose?
Hexose sugar
What are the two isomers of glucose?
Alpha glucose and beta glucose
How are the two isomers of glucose linked together?
They contain the same atoms but they are arranged in a different way
What are three examples of common monosaccharides?
Glucose, galactose and fructose
What are the typical characteristics of common monosaccharides?
They are sweet tasting and are soluble substances
What is the general formula of monosaccharides?
(CH20)n where n is any number from three to seven
What types of bonds are in glycogen molecules?
1-4 and 1-6 glycosidic bonds
Why do glycogen and amylopectin have a large number of side branches?
To allow energy to be released quickly as enzymes can act simultaneously on the branches
Why do glycogen and starch have a large but compact shape?
To maximise the amount of energy it can store
Why are glycogen and starch molecules insoluble?
To make sure it won’t affect the water potential of cells and so cannot diffuse out of cells
What are the two components of starch?
Amylose and amylopectin
Amylose
An unbranched chain of glucose molecules that are joined by 1-4 glycosidic bonds
What are the characteristics of amylose?
It is coiled and a very compact molecule storing a lot of energy
Amylopectin
A branched-chain of glucose molecules that are joined by 1-4 and 1-6 glycosidic bonds
What is cellulose composed of?
Long, unbranched chains of beta glucose, which are joined by glycosidic bonds
Microfibrils
Strong threads that are made of long cellulose chains running parallel to each other that are joined together by hydrogen bonds forming strong cross-linkages
How do cellulose molecules stop cell walls from bursting under osmotic pressure?
Cellulose molecules exert inward pressure that stops the influx of water meaning that the cells stay turgid and rigid and maximising the surface area
Which carbohydrates are reducing sugars?
All monosaccharides and some disaccharides
What colour is benedict’s reagent?
Blue
What colour shows a positive result for reducing sugars in the benedict’s test?
Brick red colour
Which carbohydrates are non-reducing sugars?
All polysaccharides and some disaccharides
Why is dilute hydrochloric acid added in the non-reducing sugar biochemical test?
To hydrolyse the disaccharides and polysaccharides into their monosaccharides
Why is sodium hydrogen carbonate added in the non-reducing sugar biochemical test?
To neutralise the test tube as benedict’s reagent will not work in acidic conditions
What colour is iodine in potassium iodide?
Orange-brown colour
What colour shows a positive result for starch in the iodine test?
Blue-black colour
