BM: Carbohydrates Flashcards
Why is life based on carbon?
Carbon readily forms bonds with other carbons.
This allows sequences of carbon to build up, forming ‘backbones’ upon which other molecules can attach.
Carbon-containing molecules are known as what?
Organic molecules.
What is a monomer?
A small, basic molecular unit.
A small, basic molecular unit, is also known as what?
A monomer.
Give examples of monomers?
Monosaccharides, amino acids and nucleotides.
Monosaccharides, amino acids and nucleotides are all examples of what?
Monomers.
What do all organisms on Earth contain?
A few carbon-based compounds that interact in similar ways.
What are polymers?
Large, complex molecules composed of long chains of monomers joined together.
What elements do all carbohydrates contain?
C, H and O.
What monomers are carbohydrates composed of?
Monosaccharides.
Give general properties of monosaccharides:
- Sweet- tasting
- Soluble
What is the general formula of monosaccharides?
‘n’ can be any number from 3 to 7.
Give examples of monosaccharides:
Glucose, fructose and galactose.
What is glucose?
A hexose sugar.
A monosaccharide with six carbon atoms in each molecule.
What are the two types of glucose?
Alpha - α
Beta - β
What are isomers?
Molecules with the same molecular formula as each other, but with atoms connected in different ways.
α - glucose and β - glucose are examples of what?
Glucose isomers.
Draw the structure of α - glucose:
Draw the structure of β - glucose:
What is a condensation reaction?
When two molecules join together with the formation of a new chemical bond and the release of a water molecule.
What is released when a glycosidic bond is formed?
A molecule of water.
How are monosaccharides joined?
Through condensation reactions.
What type of bond joins monosaccharides?
A glycosidic bond.
Give examples of disaccharides:
- Maltose
- Sucrose
- Lactose
How is the disaccharide maltose formed?
Two α - glucose molecules joined together via a condensation reaction.
How is a the disaccharide sucrose formed?
Via a condensation reaction between a glucose molecule and a fructose molecule.
How is the disaccharide lactose formed?
Via a condensation reaction between a glucose molecule and a galactose molecule.
How can polymers be broken down into monomers?
Through hydrolysis reactions.
What is a hydrolysis reaction?
A reaction that breaks the chemical bond between monomers using a water molecule.
What is the general term for monosaccharides and disaccharides?
Sugars.
How can all sugars be classified?
As either:
Reducing
or
Non-reducing
Reducing sugars are what?
All monosaccharides and some disaccharides.
All monosaccharides and some disaccharides are…
… reducing sugars.
What is reduction?
What does this mean a reducing sugar is?
Reduction is a chemical reaction involving the gain of electrons or hydrogen.
A reducing sugar is therefore a sugar that can donate electrons to another chemical, eg Benedict’s reagent.
What is the test for reducing sugars?
The Benedict’s test.
Describe the Benedict’s test for reducing sugars:
- Add Benedict’s reagent to the sample - ensure it is in excess.
- Heat it in a water bath that’s been brought to the boil.
- If the test’s positive a coloured precipitate will form:
- Blue - green - yellow - orange - red, depending on concentration of reducing sugar.
Draw a table of results for the reducing sugars test:
The higher the concentration of the reducing sugar, the further the colour change goes.
How would you get more accurate results in the reducing sugars test?
Filter the solution and weigh the precipitate.
How do you test for non-reducing sugars?
Eg, sucrose
- Break them down into monosaccharides
- Get a sample of the test solution
- Add dilute hydrochloric acid
- Carefully heat in a water bath that’s been brought to the boil
- Neutralise this with sodium hydrogencarbonate.
- Then, carry out the test for reducing sugars/Benedict’s test.
What is a positive result in the non-reducing sugars test?
A coloured precipitate will form - as with the reducing sugars test.
If the test’s negative, the solution will stay blue, which means the sample does not contain any sugar (either reducing or non-reducing).
What type of data does the Benedict’s test produce?
Semi-quantitative, so an approximate estimate of reducing sugar in the sample can be made.
Name three polysaccharides:
Starch, glycogen and cellulose.
What is starch?
A polysaccharide.
It is the main storage material in plants.
Where do plants get their energy from?
When they have excess of this, what do they do?
Get energy from glucose.
They store excess glucose as starch, which can be broken down when needed.
What is starch a made of?
Two polysaccharides of alpha-glucose.
Amylose and amylopectin.
What is amylose?
A long, unbranched chain of alpha-glucose.
Describe the shape of amylose and explain how this relates to its function:
- Coiled structure (due to the angles of the glycosidic bond).
- This makes it compact, so it is great for storage because you can fit a lot of it in a tight space.
What is amylopectin?
A long, branched chain of alpha-glucose.
Describe the shape of amylopectin and explain how this relates to its function:
- It has lots of side branches.
- These many side branches can all be acted on by enzymes simultaneously, meaning starch can be broken down for quick energy release.
Describe how the structure of starch makes it adapted to its function:
- Insoluble in water, so does not affect the water potential or cause cells to swell via osmosis.
- Large and insoluble so doesn’t diffuse out of cells.
- Compact (amylose) so lots can be stored in one place.
- When hydrolysed it forms alpha glucose, which is easily transported and readily used in respiration to make energy
- The branched form means it has many ends, which can be acted on enzymes simultaneously meaning glucose monomers are released rapidly
What is glycogen?
The main energy storage material in animals.
What is the test for starch?
Iodine test.
Describe how you would perform the iodine test for starch:
- Add iodine dissolved in potassium iodide solution to the test sample.
- Shake or stir.
What would a positive result be in the iodine test for starch?
When starch is present, the sample changes colour from browny-orange to a dark, blue-black colour.
Describe the structure of glycogen:
Alpha-glucose molecules joined by glycosidic bonds.
Very similar to amylopectin, however it is even more highly branched .
Where do animals get their energy from?
How do they store this when they have excess?
They get their energy from glucose.
When they have excess, they store it as glycogen.
Draw starch:
Draw glycogen:
How does the structure of glycogen mean it is adapted to its function?
- More highly branched than starch and has more ends that can be simultaneously acted on by enzymes
- So more rapidly broken down to form glucose monomers, that can be used in respiration.
- Important for animals which have higher metabolic and respiratory rates than plants, because they are more active.
- Insoluble and so tends not to draw water into cells by osmosis.
- Does not diffuse out of cells, and so is ideal for storage, as it is insoluble.
- Compact, so a lot can be stored in a small place.
What is cellulose?
The major component of cell walls in plants.
What is cellulose made of?
Long, unbranched chains of beta-glucose.
What forms when beta-glucose molecules bond?
Straight cellulose chains.
These run parallel to each other, allowing hydrogen bonds to form cross-linkages between adjacent chains.
These are known as microfibrils.
What are microfibrils?
Parallel chains of beta-glucose, joind via hydrogen bonds.
They group together to form fibres.
Draw cellulose:
What is the function of glycogen?
It is the stored version of glucose, which is used in animals to facilitate respiration.
What is the role of cellulose?
- Cellulose adds structure and rigidity to plants.
- Prevents plants cells from bursting as water enters via osmosis.
- It does this by exerting an inward pressure that stops any more water from entering
- So, living plant cells are turgid and push against each other
- This is important in making stems and leaves turgid, so that they provide the maximum surface area for photosynthesis.
- It can only be broken down by enzymes produced by certain bacteria or fungi
- So, only certain animals, like termites or cows (which harbour this bacteria in their gastrointestinal tracts) can digest and utilize cellulose as an energy source.
How does the structure of celluose relate to its function?
- Made of β-glucose so form long, straight, unbranched chains
- Chains run parallel to each other and are cross-linked by hydrogen bonds which add collective strength
- Molecules are grouped to form microfibrils, which are then grouped to form fibres, which provide even more strength.
