BiochemistryBiochemistry

CarbohydratesCarbohydrates

Learning ObjectivesLearning Objectives

To understand the role of carbohydrates in To understand the role of carbohydrates in biology.biology.

To understand the logic of monomer, To understand the logic of monomer, isomer and polymer carbohydratesisomer and polymer carbohydrates

What is a carbohydrate?What is a carbohydrate? Carbohydrates are Carbohydrates are

‘sugars’‘sugars’ The name describes The name describes

the atoms they the atoms they contain: Carbon, contain: Carbon, Hydrogen and Hydrogen and OxygenOxygen

Glucose is the basic Glucose is the basic sugar made by plantssugar made by plants

The ratio of hydrogen The ratio of hydrogen to oxygen is always to oxygen is always 2:12:1

Shortcut to Biochemistry.lnk

Shortcut to Biochemistry.lnk

GlucoseGlucose CC66HH1212OO6 6 is made by is made by

photosynthesisphotosynthesis It is a simple sugar or It is a simple sugar or

‘monomer’.‘monomer’. The carbons are counted in The carbons are counted in

a clockwise direction, 1, 2, a clockwise direction, 1, 2, 3, 4, 5, 6.3, 4, 5, 6.

Most other more complex Most other more complex sugars are chains of thissugars are chains of this

Complex sugars have to be Complex sugars have to be broken back down to broken back down to glucose before they are glucose before they are absorbed in the small absorbed in the small intestine.intestine.

It is essential for respirationIt is essential for respirationSkeletal formula of glucose

FructoseFructose

Fructose is a monomer Fructose is a monomer carbohydrate found in carbohydrate found in fruits and honeyfruits and honey

It has the same formula It has the same formula as glucose but its as glucose but its structure is different: it is structure is different: it is an an isomerisomer of glucose of glucose

Monomer carbohydrates Monomer carbohydrates are also known as are also known as monosaccharidesmonosaccharides

Two kinds of glucoseTwo kinds of glucose

There are two types of glucose:There are two types of glucose:Alpha glucose with the OH group belowAlpha glucose with the OH group belowBeta glucose with the OH group above.Beta glucose with the OH group above.

Linking Sugar Monomers -Linking Sugar Monomers -DisaccharidesDisaccharides

Two conjoined Two conjoined monosaccharides monosaccharides form a disaccharideform a disaccharide

They conjoin by a They conjoin by a condensationcondensation reaction (a water reaction (a water molecule is lost)molecule is lost)

The ‘join’ is called a The ‘join’ is called a glycosidic linkglycosidic link

Maltose is two glucose molecules joined in a condensation reaction.For the glucose to be re-released water must be available.

SucroseSucrose

Sucrose is a very Sucrose is a very common disaccharide common disaccharide made from made from glucose glucose and and fructose.fructose.

It is the sugar sold in It is the sugar sold in the supermarketthe supermarket

It is commonly made It is commonly made in plants for transport in plants for transport in phloem.in phloem.

Sucrose is made from the joining of the isomers glucose and fructose.

Polymers (polysaccharides)Polymers (polysaccharides) Carbohydrate Monomers linked in a long chain Carbohydrate Monomers linked in a long chain

are known as polysaccharides.are known as polysaccharides. A common example in plants is A common example in plants is starchstarch, made , made

from long chains of alpha glucose.from long chains of alpha glucose. Amylose Starch forms alpha 1-4 glycosidic Amylose Starch forms alpha 1-4 glycosidic

links.links. Plants put monomers into long chains for storage Plants put monomers into long chains for storage

purposespurposes Starch doesn’t dissolve so doesn’t influence Starch doesn’t dissolve so doesn’t influence

water potential.water potential.

AmylopectinAmylopectin Amylopectin is a Amylopectin is a

combination of straight combination of straight chain 1,4 bonded glucosechain 1,4 bonded glucose

ANDAND 1, 6 bonded glucose 1, 6 bonded glucose

which causes branches which causes branches to formto form

It therefore forms many It therefore forms many branches providing many branches providing many ‘ends’‘ends’

Glycogen (animal starch)Glycogen (animal starch) The surplus glucose we eat is The surplus glucose we eat is

stored in the liver as the stored in the liver as the polysaccharide glycogenpolysaccharide glycogen

It’s essentially the same as It’s essentially the same as AmylopectinAmylopectin

Glycogen it forms branches Glycogen it forms branches as well as straight chains, this as well as straight chains, this is because 1, 6 links form as is because 1, 6 links form as well as 1, 4 links.well as 1, 4 links.

This makes it easy to break This makes it easy to break down quicklydown quickly

HydrolysisHydrolysisHydrolysis ‘water breaking’, is just the Hydrolysis ‘water breaking’, is just the

condensation reaction in reversecondensation reaction in reverseThe water molecule is added to the glycosidic The water molecule is added to the glycosidic

link to break the bond and re-form glucoseslink to break the bond and re-form glucoses It can occur in disaccharides or It can occur in disaccharides or

polysaccharidespolysaccharides

The disaccharide lactose broken by hydrolysis

CelluloseCellulose Plants also build starch Plants also build starch

chains into structures chains into structures such as cellulose.such as cellulose.

Beta glucose make Beta glucose make straight chainsstraight chains

These straight chains These straight chains linked top and bottom linked top and bottom by hydrogen bonds by hydrogen bonds form cellulose.form cellulose.

Cell walls are made of Cell walls are made of cellulose, these give cellulose, these give structure.structure.

 

CelluloseCellulose

QuestionsQuestions

Why are glucose and fructose described as Why are glucose and fructose described as monosaccharides?monosaccharides?

What is the sugar made in photosynthesis.What is the sugar made in photosynthesis. Name a disaccharide and say which monomers Name a disaccharide and say which monomers

it is made of.it is made of. Why is starch described as a polysaccharide?Why is starch described as a polysaccharide? What does the body do with surplus glucose?What does the body do with surplus glucose? Which polysaccharide is used as building Which polysaccharide is used as building

material by plants?material by plants?