3.3 and 3.4 - Carbohydrates Flashcards
What elements do carbohydrates contain?
Carbohydrates are molecules that contain only the elements carbon, hydrogen and oxygen.
The literal meaning ‘hydrated carbon’.
What are carbohydrates also known as?
Saccharides or sugars.
What is a single sugar unit called?
A monosaccharide.
Give three examples of monosaccharides.
Glucose, fructose and ribose.
How are two monosaccharides that are joined together called?
A disaccharide.
Give two examples of disaccharides.
Lactose and sucrose.
When two or more monosaccharides are joined together, what is that molecule called?
A polysaccharide.
Give three examples of polysaccharides.
Glycogen, cellulose and starch.
What is the chemical formula for glucose?
C6H12O6
What does it mean if a molecule, for example glucose, is called a hexose monosaccharide?
It means that it contains 6 carbon atoms.
What is the difference between alpha glucose and beta glucose?
The difference between the two is the positioning of the hydroxyl - OH - group. It is in opposite positions on carbon 1.
How are the carbons numbered in molecular structure diagrams?
They are numbered in a clockwise direction, with carbon 1 starting from the right, going to the left.
How are the glucose molecules soluble in water and polar?
It is due to the hydrogen bonding between the hydroxyl groups and water molecules.
Why is it important that glucose is soluble in water?
The solubility in water is important as it means that glucose can be dissolved in the cytosol of the cell.
What reaction takes place between two alpha molecules and how?
What is the bonding that takes place called?
A condensation reaction takes place between the two alpha glucose molecules when they are side by side.
The two hydroxyl groups interact, one on carbon 1 and one on carbon 4, and a covalent bond called a glyosidic bond is formed.
When this happens bonds are broken and new bonds are reformed in different places producing new molecules.
As it is a condensation reaction, a water molecule is produced as a result of this interaction.
Two hydrogen molecules are removed along with one oxygen molecule.
Name two pentose monosaccharides.
Ribose in RNA, and deoxyribose in DNA.
How is glucose made in plant cells?
Through photosynthesis.
What kind of energy store is glucose?
Chemical energy store.
What are the two polysaccharides found in starch, and what is the difference in their bonding?
Amylose and amylopectin
Amylose is bonded only by 1,4 glycosidic bonds.
WHEREAS,
Amylopectin is bonded by 1,4 glycosidic bonds, BUT, amylopectin has a branched structure occurring every 25 glucose subunits causing 1,6 glycosidic bonding.
What is the structure and properties relating to the structure of amylose?
Amylose is joined by 1,4 glycosidic bonds, and the angle of the bonding means that this long chain of glucose twists to form a helix.
This makes the polysaccharide more compact and much less soluble than the glucose used to make it.
What is the structure and properties relating to the structure of amylopectin?
Amylopectin also has 1,4 glycosidic bonding, but some glycosidic bonds are formed between carbon 1 and 6.
This occurs approximately every 25 glucose subunits.
This means amylopectin has a branched structure.
What is the functionally equivalent energy storage to starch used in animals and fungi called?
Glycogen
What is the energy store in plants called?
Starch
What is the structure of glycogen and how does it relate to its function?
Glycogen forms more branches than amylopectin, therefore making it more compact and much less space is needed for it to be stored.
The branching also means that there are a lot of free ends where glucose molecules can be added or removed.
What are the key properties of amylopectin and glucose?
They are insoluble, branched, compact.
How do animals and plants release glucose as energy?
They undergo hydrolysis reactions, which requires the addition of water molecules.
Hydrolysis is the reverse of a condensation reaction.
What is the reverse of a condensation reaction?
A hydrolysis reaction
What is the reverse of a hydrolysis reaction?
A condensation reaction?
Why are beta glucose molecules not able to join together in the way that alpha glucose molecules can?
Because the hydroxyl groups are too far to interact with each other.
How do beta glucose molecules get around the problem of the hydroxyl groups being too far to interact with each other?
Alternate beta glucose molecules are turned upside down.
Check page 49 of the kerboodle book for diagrams.
What is subsequently caused due to the turning of the beta glucose molecule?
When a polysaccharide is formed in this way it is unable to coil or form any branches.
A straight chain molecule called cellulose is formed.
Check page 49 of kerboodle for diagrams.
What bonds do cellulose molecules make between each other?
Hydrogen bonds
When cellulose molecules join together with hydrogen bonds, what do they form?
Microfibrils
When microfibrils join together, they form ________?
Macrofibrils
Macrofibrils join into what?
Fibres
What are the properties and uses of fibres?
Strong and insoluble
Used to make cell walls
Why is cellulose important in our diet?
Because it is very hard to break cellulose down to its monomers and forms the ‘roughage’ necessary for a healthy digestive system.
What is the food test for carbohydrates?
The Benedict’s test
What is the food test for starch?
The Iodine Test
What is the positive result for the iodine test for starch?
The solution goes for yellow-orange to blue-black.
What is the positive result for reducing sugars test?
A brick red precipitate is formed
What is the positive result for non-reducing sugars?
The solution stays blue after warming.
What is the process for the Benedict’s Test for carbohydrates?
- Sample in boiling tube
- Add equal part Benedict’s reagent solution
- Heat the mixture gently in a boiling water bath for 5 minutes
If the solution turns brick red, then the test for reducing sugars is positive, and if the solution stays blue, therefore it is positive for a non-reducing sugars test.
What is the process for the iodine test for starch?
Add a few drops of iodine solution dissolved in iodine potassium iodide solution and mix with the sample.
If the solution changes colour from yellow-brown to purple-black, then starch is present.
