Carbohydrates

What are the functions of carbohydrates?
They are a source of energy; they store energy and they act as structural units.
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Describe the structure of a monosaccharide.
They can exist as straight chains or ring or cyclic forms; They have a backbone of single-bonded carbon with one double-bonded to an oxygen (a carbonyl group)
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Monosaccharides can have different numbers of carbon atoms. How many carbon atoms does a hexose sugar have? How many does a pentose sugar have? How many carbons does a tetrose sugar have? How many does a triose sugar have?
A hexose sugars have 6 carbon atoms, pentose sugars have 5, tetrose sugars have 4 and triose sugars have 3.
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Which monosaccharide sugars are monomers of more complex carbohydrates. They bond together to form disaccharides and polysaccharides.
Monosaccharide HEXOSE sugars are monomers of more complex carbohydrates. They bond together to form disaccharides and polysaccharides.
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In solution, how do triose and and tetrose sugars exist?
As straight chains.
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In what forms are hexose and pentose sugars more likely to be found?
In cyclic or ring form.
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What are isomers?
Molecules with the same formula but with there atoms arranged differently.
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In both straight-chain and cyclic forms, glucose can exist as a number of isomers. Describe these.
In straight-chain form, the -OH and -H group can be reversed. The ring shape is formed when oxygen (which is attached to carbon 5) bonds to carbon 1. The -OH and -H groups of carbon 1 can be above or below so there are two isomers α- and β- glucose.
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What do monosaccharides and dissacharides have in common?
They are both sweet and soluble.
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What are the most common disaccharides?
Maltose (malt sugar), lactose (milk sugar) and sucrose.
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How are disaccharides made?
When two monosaccharides join together through a glycosidic bond.
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What is a glycosidic bond?
One formed by a condensation reaction between two hydroxyl groups. A water molecule is removed and an oxygen atom acts as a link between the two monosaccharides.
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How is maltose made?
Two α-glucose.
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How is sucrose made?
An α-glucose and fructose.
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How is lactose made?
An α-glucose and a β-glucose.
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How is cellobiose made?
Two β-glucose.
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Is glucose a hexose or peontose sugar?
Hexose.
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Is (deoxy)ribose a hexose sugar or a pentose sugar?
Pentose.
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What is the difference between α-glucose and β-glucose?
The -H of carbon 1 of the α-glucose is on top while the -OH is on the bottom where as the opposite is true for β-glucose.
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What is the difference between ribose and deoxyribose?
The carbon 2 of ribose has a a -H and an -OH but deoxyribose carbon 2 only has -H.
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What is a homopolysaccharide?
A polysaccharide made entirely one kind of monosaccharide.
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What is a heteropolysaccharide?
A polysaccharide made of more than one monomer.
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Glucose is a source of energy as it is a r_______ in respiration.
REACTANT
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If you join glucose molecules into a polysaccharide you can create a store of....
energy.
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How do plants store energy?
As starch in the chloroplasts or in membrane-bound grains.
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How do humans store energy?
As glycogen in the muscle and liver cells.
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Why is it an advantage that glycogen and starch are compact?
They occur in dense granules in the cell and so don't occupy large amounts of space.
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Why is it an advantage that polysaccharides hold glucose in chains?
The glucose can easily be 'snipped off; the end of the chain by hydrolysis when needed for respiration.
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Branched chains tend to be more compact. What other advantage do they have?
More glucose can be 'snipped off' from the ends of all the different branches at the same time if there is a high demand for energy.
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Which enzyme is responsible for hydrolysing 1-4 glycosidic linkages? (the linkage between carbon 1 of one glucose and carbon 4 of another)
Amylase.
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Which enzyme is responsible for hydrolysing 1-6 glycosidic linkages?
Glucosidase.
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Why are polysaccharides less soluble than monosaccharides?
Because they are larger but also because regions that could hydrogen bond with the water are hidden inside the molecule. Sometimes amylose may even form a double helix with a hydrophobic external surface.
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Why is it a good thing that polysaccharides are less soluble than monosaccharides?
Because it means they don't dissolve in the cytoplasm and disrupt the water potential of the cell.
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What is amylose made from and where is it found?
It is a long chain of α-glucose with glycosidic bonds between carbons 1 and 4. It is found in plants.
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What shape does amylose coil into and how does it stay in place? What makes the molecule less soluble?
It coils into a spiral shape held together by the hydrogen bonds. Carbon 2 hydroxyl groups are inside the coil which allows hydrogen bonds to form and keep the spiral stable as well as making it less soluble.
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What is amylopectin made from and where is it found?
It is like amylose but with additional branches formed by glycosidic bonds between carbons 1 and 6. It is found in plants.
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What shape does amylopectin coil into?
It also coils into a spiral like amylose but with branches emerging from said spiral.
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What is glycogen made from and where is it found?
It is like amylopectin with glycosidic bonds between 1 and 4 as well as branches with 1 and 6.
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What is glycogens overall shape and how does this affect it?
the 1-4 bonded chains tend to be smaller than amylopectin and so they don't tend to coil. They have more branches so are more compact and easier to remove monomer units as there are more ends.
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What is cellulose made from and where is it found?
It is a homopolysaccharide made from chains of up to 15,000 β-glucose molecules. It forms the cell walls of plants.
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Cellulose is a tough, in_______ and f______.
Cellulose is a tough, INSOLUBLE, FIBROUS substance.
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Cellulose chains are straight and lay side by side unlike spiralling chains of α-glucose. Why is this?
Because it is made of β-glucose which has an inverted carbon 1. This and the β-1-4 bonding helps prevent spiralling.
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How does hydrogen bonding also help prevent cellulose spiralling?
Hydrogen bonds occur between rotated β-glucose within chains and between the β-glucose in different chains because the carbon 2 hydroxyl group sticks out. This provides additional strength to the whole structure.
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What are microfibrils and what do they do?
They are 60-70 cellulose chains bonded together and are about 10-30nm in diameter. Up to 400 of these microfibrils then bundle together into macrofibrils which embed in pectin and form plant cell walls.
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Micro and macrofibrils have a very high tensile strength which is a good property for cell wall material. Why do they have such a high tensile strength?
Because of the strength of the glycosidic bonds but also because of the hydrogen bonds between chains.
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Macrofibrils run in all directions, why is this a good property for cell wall material?
The criss-crossing provides extra strength.
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The Glycosidic bonds between the glucose molecules are hard to break. Most animals don't have an enzyme to catalyse the reaction. Why is this a good property for plant cell wall material?
It makes it hard to digest.
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What is the role of the plant cell wall?
To strengthen individual cells to support the plant as a whole; space between macrofibrils makes the cell wall fully permeable; high tensile strength stops the cell from bursting when turgid and increases support of the whole plant
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The macrofibrils structure can be reinforced with other substances e.g. cutin and suberin which block spaces in the wall and make it __________. Lignin does this in Xylem cells. Woody parts of tree trunks can also have extra thick cell walls, why?
Being reinforced or extra thick provides even more strength and support. The cutin, suberin and lignin can make the cell wall waterproof.
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Cotton is 90% cellulose, it also used for other things such as paper and cellophane, why is this?
Because of its structural strength.
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Peptidoglycan is another polysaccharide used for structures in bacteria. What structure does it form?
The cell wall of the bacteria.
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Other cards in this set

Card 2

Front

Describe the structure of a monosaccharide.

Back

They can exist as straight chains or ring or cyclic forms; They have a backbone of single-bonded carbon with one double-bonded to an oxygen (a carbonyl group)

Card 3

Front

Monosaccharides can have different numbers of carbon atoms. How many carbon atoms does a hexose sugar have? How many does a pentose sugar have? How many carbons does a tetrose sugar have? How many does a triose sugar have?

Back

Preview of the front of card 3

Card 4

Front

Which monosaccharide sugars are monomers of more complex carbohydrates. They bond together to form disaccharides and polysaccharides.

Back

Preview of the front of card 4

Card 5

Front

In solution, how do triose and and tetrose sugars exist?

Back

Preview of the front of card 5
View more cards

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