1.12, 1.13: Monosaccharides, disaccharides & polysaccharides

spec point

What type of substances are carbohydrates?

organic

What does it mean that carbohydrates are organic substances?

contains carbon and at least one hydrogen

What are the molecules in carbohydrates?

Carbon, hydrogen, oxygen

What are the three main groups of carbohydrates?

monosaccharides

disaccharides

polysaccharides

What are monosaccharides?

the monomers of carbohydrate
they are simple carbohydrates
they are sugars

Monosaccharides can join together to make…

carbohydrate polymers

What are the names of the different types of monosaccharides formed from molecules with varying numbers of carbon atoms?

triose (3C)

pentose (5C)

hexose (6C)

What type of sugar is glucose?

a hexose sugar

What type of structure do the six carbons that make up glucose form?

a ring structure

• carbons 1-5 form a ring, while carbon 6 sticks out above the ring

What are the two forms of glucose?

alpha (α)

beta (β)

Difference between alpha and beta glucose

• alpha glucose has the H above carbon 1 and the OH group below

  • alpha has the H above

• beta glucose has the H below carbon 1 and the OH group above

  • beta has the H below

What is the main function of monosaccharides?

to store energy within their bonds

When the bonds are broken during ___________, ______ is released

respiration

energy

How is the structure of glucose related to its function as the main energy store for animals and plants?

• it is soluble so can be transported easily

• it has many covalent bonds which store energy

Monosaccharides can combine through ____________ reactions to form larger carbohydrates

condensation

Some monosaccharides are used to form long, structural ______, which can be used as ________ _______ in some cell types

fibres

cellular support

To make monosaccharides more suitable for storage, they are bonded together to form…

disaccharides and polysaccharides

How are disaccharides and polysaccharides formed?

two hydroxyl groups (OH) on different monosaccharides interact to form a strong covalent bond called a glycosidic bond

What are the names of the two types of glycosidic bonds?

1,4 glycosidic bonds

1,6 glycosidic bonds

Difference between 1,4 and 1,6 glycosidic bonds

1,4: The OH groups are located on carbon 1 of one monosaccharide and carbon 4 of the other

1,6: The OH groups are located on carbon 1 of one monosaccharide and carbon 6 of the other

What type of reaction are glycosidic bonds formed by, and what does this mean?

condensation reaction
- every glycosidic bonds results in one water molecule being released

How is the disaccharide maltose formed?

two alpha glucose molecules joined by a 1,4 glycosidic bond

How is the disaccharide sucrose formed?

glucose + fructose joined by a 1,4 glycosidic bond

How is the disaccharide lactose produced?

glucose + galactose joined by a 1,4 glycosidic bond

How is a glycosidic bond broken?

when water is added in a hydrolysis reaction

Examples of hydrolytic reactions

digestion of food in the alimentary tract

breakdown of stored carbohydrates in muscle and liver cells

Function of disaccharides

to provide the body with a source of quick-release energy

- disaccharides are made up of two sugar molecules so they’re easily broken down by enzymes in the digestive system into their respective monosaccharides and then absorbed into the bloodstream

Solubility of disaccharides in water (and explanation)

easily soluble
- there is a large number of hydroxyl groups which form hydrogen bonds with the water molecules when dissolved in aqueous solutions

Sweetness of disaccharides and monosaccharides

both have a sweet taste
- e.g. sucrose = table sugar

Examples of polysaccharides

starch
glycogen
cellulose

Define polysaccharides

carbohydrate polymers which are made of repeated chains of many monosaccharides joined by glycosidic bonds in a condensation reaction

Categories of polysaccharides

branched or unbranched

straight or coiled

Branched vs unbranched polysaccharides

being branched increases the rate at which a polysaccharide can be broken down

What are straight polysaccharides more suitable for?

constructing cellular structures e.g. cellulose

What are coiled polysaccharides more suitable for?

being coiled makes a molecule more compact and suitable for storage
e.g. amylose in starch

Examples of storage polysaccharides

• starch

• glycogen

Example of structural polysaccharide

• cellulose

Why are starch and glycogen useful as storage polysaccharides?

• they are compact so large quantities can be stored

• they are insoluble so will have no osmotic effect, (unlike glucose which would increase the solute concentration of a cell and cause water to move in by osmosis)

Starch is the storage polysaccharide of…

plants

How is starch stored inside plant cells?

as granules

Plants make _______ during photosynthesis and the molecules of _______ are joined to make the polysaccharide starch

glucose

How many different polysaccharides is starch constructed from?

two

What are the two polysaccharides for starch?

amylose

amylopectin

Shape/structure of amylose

• unbranched

• helix-shaped chain forming a spiral shape

• 1,4 glycosidic bonds between α-glucose molecules

Benefits of the structure of amylose

the helix shape enables it to be more compact and thus more can be stored

Structure/shape of amylopectin

• branched molecule

• 1,4 glycosidic bonds and 1,6 glycosidic bonds between α-glucose molecules

Benefits of structure/shape of amylopectin

• branches result in many terminal glucose molecules that can be easily hydrolysed for use during cellular respiration or added to for storage

Glycogen is the storage polysaccharide of…

animals and fungi

Structure/shape of glycogen

• highly branched (even more than amylopectin)

• not coiled

• contains both 1,4 and 1,6 glycosidic bonds

• glycogen is compact

Benefits of shape/structure of glycogen

• branching provides more terminal glucose molecules
  - these can either be added to or removed by hydrolysis
  - this allows the quick storage or release of glucose to suit the demands of the cell
  → this is essential in animal cells as animals are very metabolically active

• glycogen being compact means that much can be stored in a small space
  - liver and muscle cells have a concentration of glycogen, present as visible granules
  → this enables a high cellular respiration rate

Summary of storage polysaccharides table

Summary of types of carbohydrates table

Where is cellulose found?

plant cell walls

What monomers and bonds is cellulose made from?

beta glucose + inverted beta glucose joined by a 1,4 glycosidic bond

Bundles of 60-70 straight, unbranched cellulose molecules can lie ________ to form cellulose ____________

parallel
microfibrils

Microfibrils are held together by…

hydrogen bonds between the hydroxyl (-OH) groups in neighbouring chains to produce a strong structure

Microfibrils are stuck together by…

a polysaccharide ‘glue’ made from short branched polysaccharides called hemicelluloses and pectins

Function of cellulose

• main structural component of cell walls due to its strength which is the result of the many hydrogen bonds

• the high tensile strength of cellulose allows it to be stretched without breaking, making it possible for cell walls to withstand turgor pressure