Carbohydrates Flashcards
What elements do carbs contain ?
C, H, O
What’s the general formula of carbs ?
Cx(H2O)y
What are monosaccharides ?
Simplest form of carbohydrates which cannot be hydrolysed to any simpler carbs
What is the general formula of monosaccharides ?
(CH2O)n
- can range from 3-7 carbons long
- have a carbonyl group and multiple hydroxyl groups attached
What are the different types of monosaccharides ?
Aldoses and ketones
Open chain and ring form
a-isomer (alpha) and ß-isomer (beta)
What is the difference between aldoses and ketoses?
Aldoses (aldehyde sugar) - have carbonato group attached at the end of the carbon chain (-CHO)
Ketoses (ketone sugar) - have carbonyl group within the carbon skeleton (C=O)
What’s the most common type of carbon skeletons in monosaccharide ?
Pentose (5C) and hexose (6C)
Is open chain or ring form the most usual forms and why?
In aqueous solutions, pentose and hexose form stable ring structures which are the usual forms (due to the bond angle between carbon atoms)
What is a pyranose ring?
A six membered ring in hexoses (6C) which are aldoses
- the first carbon atom combines with oxygen on carbon atom 5
- eg. Glucose
- count carbon starting from the C after oxygen, count clockwise
What is a furanose ring ?
Five membered ring in hexoses (6C) which are ketoses
- the carbonyl group of Caron atom 2 reduces the -OH group on carbon 5
- eg. Fructose
- count carbon starting from the carbon in CH2OH on top, count anticlockwise
What are the two ring forms that glucose exists in ?
a (alpha) and ß (beta)
Alpha - the -OH group on carbon 1 projects below the ring
Beta - the -OH group on carbon 1 projects above the ring
(Carbon 1 is the first carbon atom to the right of the oxygen in the ring, count clockwise)
What are the properties of monosaccharides ?
- sweet
- crystalline in appearance
- readily soluble in water (-OH groups form H bond with water)
- all are reducing sugars (have the ability to reduce Cu2+ in benedict’s reagent to Cu+ which results in formation of Cu2O, brick red ppt)
What are disaccharides made of ?
2 monosaccharides joined by glycosidic bonds
What are the three disaccharides ?
Lactose - glucose + galactose
Maltose - glucose + glucose
Sucrose - glucose + fructose
What is the name of the reaction in which disaccharides are formed from monosaccharides and vice versa ?
Disaccharides from monosaccharides - condensation, a single H2O molecule is lost
Disaccharides split into monosaccharide - hydrolysis, addition of water
What are monosaccharides in disaccharides / once they are linked called ?
Residue
Which of the three disaccharides is non-reducing ?
Sucrose
What bond is formed between two monosaccharides ?
Glycosidic bond
What are the properties of disaccharides ?
Sweet
Crystalline in appearance
Readily soluble in water
Can be hydrolysed to a monosaccharide under certain condition
What are the two methods in which a disaccharide can be hydrolysed into a monosaccharide ?
Chemical method - incubating the disaccharide with dilute acid at 100ºC
Enzymatic method - incubating the disaccharide with an enzyme at room temperature
( sucrose : sucrase, invertase | Maltose : Maltase | lactose : lactase )
What is maltose and where can it be found ?
A breakdown product during starch digestion by amylases
It occurs commonly in animals and germinating seeds
Characteristics of lactose ?
Exclusively found in milk (milk sugar)
Is slowly digested so gives a steady release of energy
Characteristics of sucrose ?
Cane sugar
Most plentiful disaccharide in nature
Most commonly found in plants
Why is sucrose commonly found in plants ?
Good transport sugar - highly soluble
Good storage sugar - chemically unreactive
What are macromolecules ?
Polymers with a few hundred to a few thousand monosaccharides joined together by glycosidic bonds
Characteristic of polysaccharides ?
Macromolecules
Insoluble in water due to its big size
Chain can be branched or unbranched
What are the two groups of polysaccharides ?
Storage polysaccharides
Structural polysaccharides
What are the two storage polysaccharides ?
Starch - amylose + amylopectin
Glucose
What is an example of a storage polysaccharide ?
Cellulose
Characteristics of starch ?
Polymer of a-glucose
Found in most parts of plants in the form of small granules - Serves as an energy store formed from excess glucose produced during photosynthesis
What are the two substances that starch is made up of ?
Amylose and amylopectin
What is the structure of amylose ?
a-glucose residues joined together by (a 1-4 glycosidic bonds) with bond angle of 109º causing the polymer to form a helix (like loops)
The -OH on carbon 2 of each glucose residue projects into the middle of the spiral
What residues make up amylose ?
a-glucose residues
What bond is in amylose ? bond angle ?
a 1-4 glycosidic bond \
109º
How does amylose hold its helical shape?
The -OH groups on each carbon 2 pointing inside the helix forms H bonds with each other, stabilising the shape of the polymer
Characteristic of amylopectin
a-glucose residues joined by either (a 1-4 glycosidic bonds) or (a 1-6 glycosidic bonds)
Multi-branched compact polymer
Why is amylopectin branched while amylose is not ?
The formation of the (a 1-6 glycosidic bond) in amylopectin puts a branch point into the polymer making it branched
How is both amylose and amylopectin compact ?
Amylose - coiled up into a compact helical shape
Amylopectin - branched to form a closely packed brush shape
Characteristics of glycogen
Major polysaccharide storage material in animals and fungi (mainly stored in liver and muscles)
Exist as granules usually associated with the smooth endoplasmic reticulum
What type of monosaccharide is glycogen made up of ?
a-glucose
Structure and bonding in glycogen ?
Branched
a-glucose residues bonded by (a 1-4) and (a 1-6) glycosidic bonds
What are the differences between glycogen and amylopectin ?
Glycogen has shorter chains an is more highly branched
Why is glycogen highly branched ?
It has multiple ends where enzymes can cleave off glycogen molecules resulting in quick release of many glucose
Characteristics of cellulose
Most abundant organic molecule on earth
A structural component of all plant cell walls
Type of residue in cellulose and bond formed
ß-glucose linked by ß 1-4 glycosidic bonds
How is the ß 1-4 bond formed between the residues ?
Every alternate ß–glucose residue is flipped upside down (180º) so that the -OH groups are lined up to form the bonds
Formation of cellulose from ß-glucose chains
- -OH groups project outwards form each chain in all directions and form H bonds with neighbouring chains (cross-linking binds the chains rigidly together)
- The chains are aggregated into bundles to form cellulose micelles (~40 chains)
- The micelles are embedded in other polysaccharides and arranged in larger bundles to form microfibrils (3.5nm in diameter)
- Microfibrils combine to form macrofibrils
Where is cellulose formed and assembled ?
NOT the Golgi apparatus
Made by specific enzyme on the cell surface membrane
What are the five structures of storage molecules (which can be related to properties) ?
Large molecule
Composed of many a-glucose monomers
Compact shape
Stable
Organisation of chain
How does being a large molecule enable starch and glycogen to be storage molecules ?
Large thus insoluble in water making them an ideal storage material as it has little effect on the water potential of the cell - can be stored in large quantities in cell
How is starch and glycogen insoluble even when they have -OH groups to form H bonds with water ?
The molecule is so large that there are not enough H bonds between the -OH groups and water to dissolve the entire macromolecule
Is starch or glycogen less soluble in water ?
Starch
Why is starch less soluble in water than glycogen ?
Tight spirals of amylopectin in starch reduce the ability of -OH groups interacting with water molecules
While glycogen is branched thus -OH groups more exposed
How does being composed of many a-glucose monomers enable starch and glycogen to be storage molecules ?
Starch and glycogen act as large store of carbon (building blocks) and energy (respiratory substrate broken down in the process of respiration)
How does having a compact shape enable starch and glycogen to be storage molecules ?
Compact and ideal for storage as many glucose residues can be stored in a small volume within the cell - saves space
(Compact due to the helical coils formed)
How does being stable enable starch and glycogen to be storage molecules ?
Most -OH groups of glucose residues are projected into the interior of the helices
-OH groups form H bonds with each other to stabilise the shape
How does organisation of chains enable starch and glycogen to be storage molecules ?
Organisation : Starch and glucose are not cross-linked to form a bundle
Can be readily hydrolysed to release their monomers when required
How is starch readily hydrolysed ?
The (a 1-4) glycosidic bonds of amylose and amylopectin can be easily hydrolysed by enzymes present in plants and most organisms
The (a 1-4) glycosidic bonds create many branch points which increases the SA for enzyme action, allowing many enzymes to hydrolyse amylopectin at the same to release many glucose molecules
How is glycogen readily hydrolysed ?
The (a 1-4) glycosidic bond can be easily hydrolysed by enzyme glycogen phosphorylase to form glucose-1-phosphate molecules (the phosphate group must be removed so that glucose can leave the cell)
The (a 1-6) glycosidic bonds creates many branch points which allows many enzymes to hydrolysed it at the same time, releasing many glucose molecules
What are the structures of cellulose (that can be linked to properties)?
Large molecule
Straight chain
Effective inter-chain bonding
Microfibrils and macrofibrils
How does being a large molecule enable cellulose to be a structural molecule ?
Large therefore insoluble in water therefore an ideal structural material as it will remain intact in the presence of water to provide structural support to the plant cells
How does being a straight chain enable cellulose to be a structural molecule ?
Straight chain due to every alternate ß-glucose residue being flipped upside down to form (ß 1-4) glycosidic bonds which are not easliy hydrolysed so cellulose is stable which is important for serving structural function
How does effective inter-chain bonding enable cellulose to be a structural molecule ?
Cross-linking between the -OH groups of neighbouring chains binds the chains rigidly together conferring great tensile strength and inelastic nature
How does microfibrils and macrofibrils enable cellulose to be a structural molecule ?
Association of chains into microfibrils and macrofibrils resulting high tensile strength which translates further into mechanical strength
- allows cellulose cell wall to withstand stress and prevents cell from bursting when water enters by osmosis
- cellulose cell wall helps determine shape of cells
Microfibrils and macrofibrils are not easily broken down
