3.3 Carbohydrates Flashcards
What elements do carbohydrates contain?
Hydrogen, carbon , oxygen
General formula for carbohydrates
Cx (H2O)y
What is a monosaccharide
A single sugar unit
What is a disaccharide
when 2 monosaccharides link together
Examples of monosaccharides
fructose, glucose, ribose, deoxyribose, galactose
Examples of disaccharides
maltose, sucrose, lactose
What is a polysaccharide
when many monosaccharides link together to form a polymer
Examples of polysaccharides
glycogen, cellulose, starch
What is the chemical formula for glucose
C6H12O6
How many carbons does the monosaccharide glucose contain
6
How is glucose a polar molecule
Due to hydrogen bonds that form between hydroxyl groups and water molecules (Oxygen = negative + Hydrogen = positive)
What are the two types of glucose?
Alpha
Beta
What is the difference between between the two types of glucose?
Order of H and OH is reversed at Carbon-1 on beta glucose
H, OH = alpha
OH, H = beta
What is the structure of maltose
2 alpha glucose monosaccharides join together to form a disaccharide
What type of reaction is the formation of maltose? Why?
Condensation because water is released when the glycosidic bond forms from the two OH bonds
What type of bond forms during the formation of maltose
Glycosidic bond between Carbon-1 and Carbon-4
What type of monosaccharides are fructose and galactose
Hexose monosaccharides
Where is fructose found
Naturally occurs in fruit
What is sucrose made from
Alpha glucose and fructose
What is lactose made from
Alpha glucose and galactose
Define pentose monosaccharides
sugars that contain 5 carbon atoms
Examples of pentose monosaccharides
Ribose and deoxyribose
Features of monosaccharides
Monomers
Simplest of sugars (sweet)
Soluble in water (polar so can form H bonds)
Chemical bonds contain a lot of energy (respiratory substrate)
Features of disaccharides
made of 2 monomers
tastes sweet
soluble
easily hydrolysed (broken down with water to its monosaccharides)
What are isomers
same chemical formula but different structure
Define glycosidic bonds
bonds between two monosaccharides and are a type of covalent bond
formed by one oxygen from the 2 OH bonds
What is starch used for?
Energy store in plants
What is glycogen used for?
Energy store in animals
What are the two types of starch called?
amylose
amylopectin
Features of amylose
alpha glucose
1-4 glycosidic bonds
twists to form a helix - more compact
further stabilised using hydrogen bonds
insoluble
Features of amylopectin
alpha glucose
glycosidic bonds form in condensation reactions (1-6) - more compact
branched structure due to 1-6 glycosidic bonds - every 25 units
most insoluble
Features of glycogen
forms more branches than amylopectin - more compact
branching means that there are many free ends where glucose molecules can be added or removed
insoluble
Why do animals need more glycogen than plants need starch?
Animals are mobile so require more glycogen when the energy is used up faster
Why is it important than glycogen has many free ends?
It speeds up process of storing and releasing molecules of glucose
Hydrolysis reactions to produce glucose:
Glucose stored until it is needed for respiration
To release it, starch or glycogen undergo hydrolysis reactions requiring the addition of water
Catalysed with enzymes - reverse of condensation reactions that produce glycosidic bonds
Features of cellulose
Insoluble
Beta glucose molecules
Join together but alternate being inverted to allow them to bond
Contain microfibrils
How are micro/macro fibrils made?
Hydrogen bonds with each layer of cellulose to form microfibrils which join together to form macrofibrils which combine to make FIBRES
Why are fibres important in cellulose of cell walls?
They are strong and essential when making cell walls
Also are an important part of our diet
Can humans digest beta glucose polysaccharides?
No as we don’t have the enzymes required to break them down
Why do beta glucose monomers alternate rotating 180 degrees to form glycosidic bonds?
Must rotate 180 degrees so the hydroxyl groups on Carbon 1 and Carbon 4 are close enough to react in a condensation reaction
Hydroxyl group is above ring in beta glucose if not inverted (too far away from other OH group)
Features of glucose:
Chemical formula C6H12O6
Monosaccharide with 6 carbons (hexose)
Polar
Soluble in water
Respiratory substrate
What is sucrose used for?
Form in which carbs are transported in plants
Glucose is too useful - would be used up too quickly
