3.1.2 Carbohydrates Flashcards
What are the monomers of a carbohydrate called?
Monosaccharides
What is a carbohydrate?
A molecule made up of carbon, hydrogen and oxygen
What are the three main functions of a carbohydrate?
Energy (for respiration)
Structural (e.g. cell walls)
Storage
What is a monomer?
A subunit (individual smaller molecules) that form polymers when put together in chains
Give three examples of a monosaccharide.
Glucose, galactose and fructose
What type of reaction forms a disaccharide?
Condensation
What type of bond is formed in a condensation reaction?
Glycosidic bond
How are disaccharides formed?
The condensation of two monosaccharides
How is maltose formed?
The condensation of two glucose molecules
How is sucrose formed?
The condensation of a glucose and fructose molecule
How is lactose formed?
The condensation of a glucose and galactose molecule
What are the two isomers of glucose?
Alpha and beta
What is the name for a “OH” group?
Hydroxyl group
What is the order of the hydroxyl groups in alpha glucose?
Down
Up
Down
Down
What is the order of the hydroxyl groups in beta glucose?
Down
Up
Down
Up
How are polysaccharides formed?
By the condensation of many glucose units
Name two polysaccharide formed by the condensation of alpha glucose?
Glycogen
Starch
How is the polysaccharide cellulose formed?
Condensation of beta glucose
What’s the general formula of a monosaccharide?
(CH2O)n
What makes glucose a hexose sugar?
It has 6 carbon molecules
What is the formula of glucose?
C6H12O6
Where can cellulose be found?
Cell wall
What makes cellulose useful for its function?
Beta glucose is bonded by a condensation reaction to form glycosidic bonds between each unit (alternate upside down upright)
These straight chains of beta glucose are linked by many weak hydrogen bonds which forms a strong bond as there are so many
These form microfibrils which form fibres to make up cellulose
The strength means it’s useful in cell walls because when the cell becomes turgid it won’t burst due to the strength
Describe starch?
Alpha glucose 1-4 and 1-6 Energy store In plants Compact Large surface area
Describe glycogen?
Alpha glucose 1-4 and 1-6 Energy store In animals Compact Large surface area (branched) Insoluble
Describe cellulose?
Beta glucose 1-4 Makes up cell wall Strong Rigid/flexible In plants
Why is glycogen useful in animal cells?
Glycogen is branched so glucose can be made at a faster rate
More ends are worked on by enzymes simultaneously
Animals need more glucose for respiration as they’re more active that plants
Name a reducing sugar?
Glucose
What is the test for reducing sugars?
Add Benedict’s reagent to the sample
Heat the mixture in a water bath until a change is seen
Brick-red precipitate indicated the presence of a reducing sugar
(Stays blue otherwise)
Name a non-reducing sugar?
Sucrose
What is the test for a job reducing sugar?
Benedict’s reagent to sample Heat in water bath Observe no change (blue) Add hydrochloric acid to sample Heat in water bath Add sodium hydrogencarbonate to the tube Add Benedict’s again Observe a brick red precipitate in the presence of a non-reducing sugar.
What property of carbon atoms allowed sequences of various lengths to be built?
They readily form bonds with other carbon atoms
What is the collective name for carbon containing molecules?
Organic molecules
Why is life based on a small number of chemical elements?
In living organisms there are relatively few atoms that attach to carbon
In the general formula for a monosaccharide what is the value of n?
Anything from 3 to 7
What is a reducing sugar?
A sugar that can donate electrons (or reduce) to another chemical
(When tested for they donate to Benedict’s reagent)
Why is the bonding of two monosaccharides called a condensation reaction?
A molecule of water is removed
What is the hydrolysis of a disaccharide?
Addition of water that causes breakdown into two monosaccharides (under suitable conditions)
Why is sodium hydrocarbonate added when testing for non-reducing sugars?
To neutralise the hydrochloric acid previously added which hydrolysed any disaccharides into their monosaccharides
What makes polysaccharides suitable for storage?
They are very large molecules which makes them insoluble
Where is starch found?
In plants in the form of small granules
Eg starch grains in chloroplasts
How is starch tested for?
Add potassium iodide solution
Shake or stir
Changes blue-black in the presence of starch
What is a benefit of starch being insoluble?
It doesn’t affect water potential
So water is not drawn into the cells by osmosis
What is the benefit of starch being made of alpha glucose?
When hydrolysed it forms alpha glucose
This is easily transported
And readily used in respiration
Why it the branched form of starch effective is glucose release?
There are more ends
More ends can be acted on by enzymes simultaneously
Glucose monomers released rapidly
Where are the two main places glycogen is stored as small granules?
Muscles
Liver
