A brief intro to Carbohydrates for AS Biologists

1. BiochemistryBiochemistry
CarbohydratesCarbohydrates

2. Learning ObjectivesLearning Objectives
 To understand the role of carbohydrates inTo 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

3. What is a carbohydrate?What is a carbohydrate?
 Carbohydrates areCarbohydrates are
‘sugars’‘sugars’
 The name describesThe name describes
the atoms theythe atoms they
contain: Carbon,contain: Carbon,
Hydrogen andHydrogen and
OxygenOxygen
 Glucose is the basicGlucose is the basic
sugar made by plantssugar made by plants
 The ratio of hydrogenThe ratio of hydrogen
to oxygen is alwaysto oxygen is always
2:12:1
Shortcut to Biochemistry.lnk
Shortcut to Biochemistry.lnk

4. GlucoseGlucose
 CC66HH1212OO66 is made byis made by
photosynthesisphotosynthesis
 It is a simple sugar orIt is a simple sugar or
‘monomer’.‘monomer’.
 The carbons are countedThe carbons are counted
in a clockwise direction,in a clockwise direction,
1, 2, 3, 4, 5, 6.1, 2, 3, 4, 5, 6.
 Most other more complexMost other more complex
sugars are chains of thissugars are chains of this
 Complex sugars have toComplex sugars have to
be broken back down tobe broken back down to
glucose before they areglucose before they are
absorbed in the smallabsorbed in the small
intestine.intestine.
 It is essential forIt is essential for
respirationrespirationSkeletal formula of glucose

5. FructoseFructose
 Fructose is a monomerFructose is a monomer
carbohydrate found incarbohydrate found in
fruits and honeyfruits and honey
 It has the same formulaIt has the same formula
as glucose but itsas glucose but its
structure is different: it isstructure is different: it is
anan isomerisomer of glucoseof glucose
 Monomer carbohydratesMonomer carbohydrates
are also known asare also known as
monosaccharidesmonosaccharides

6. 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 below
 Beta glucose with the OH group above.Beta glucose with the OH group above.

7. Linking Sugar MonomersLinking Sugar Monomers
-Disaccharides-Disaccharides
 Two conjoinedTwo conjoined
monosaccharidesmonosaccharides
form a disaccharideform a disaccharide
 They conjoin by aThey conjoin by a
condensationcondensation
reaction (a waterreaction (a water
molecule is lost)molecule is lost)
 The ‘join’ is called aThe ‘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.

8. SucroseSucrose
 Sucrose is a verySucrose is a very
common disaccharidecommon disaccharide
made frommade from glucoseglucose
andand fructose.fructose.
 It is the sugar sold inIt is the sugar sold in
the supermarketthe supermarket
 It is commonly madeIt is commonly made
in plants for transportin plants for transport
in phloem.in phloem.
Sucrose is made from
the joining of the isomers
glucose and fructose.

9. Polymers (polysaccharides)Polymers (polysaccharides)
 Carbohydrate Monomers linkedCarbohydrate Monomers linked
in a long chain are known asin a long chain are known as
polysaccharides.polysaccharides.
 A common example in plants isA common example in plants is
starchstarch, made from long chains, made from long chains
of alpha glucose.of alpha glucose.
 Amylose Starch forms alphaAmylose Starch forms alpha
1-4 glycosidic links.1-4 glycosidic links.
 Plants put monomers into longPlants put monomers into long
chains for storage purposeschains for storage purposes
 Starch doesn’t dissolve soStarch doesn’t dissolve so
doesn’t influence waterdoesn’t influence water
potential.potential.

10. AmylopectinAmylopectin
 Amylopectin is aAmylopectin is a
combination ofcombination of
straight chain 1,4straight chain 1,4
bonded glucosebonded glucose
 ANDAND
 1, 6 bonded glucose1, 6 bonded glucose
which causeswhich causes
branches to formbranches to form
 It therefore formsIt therefore forms
many branchesmany branches
providing many ‘ends’providing many ‘ends’

11. Glycogen (animal starch)Glycogen (animal starch)
 The surplus glucose we eatThe surplus glucose we eat
is stored in the liver as theis stored in the liver as the
polysaccharide glycogenpolysaccharide glycogen
 It’s essentially the same asIt’s essentially the same as
AmylopectinAmylopectin
 Glycogen it forms branchesGlycogen it forms branches
as well as straight chains,as well as straight chains,
this is because 1, 6 linksthis is because 1, 6 links
form as well as 1, 4 links.form as well as 1, 4 links.
 This makes it easy to breakThis makes it easy to break
down quicklydown quickly

12. HydrolysisHydrolysis
 Hydrolysis ‘water breaking’, is just theHydrolysis ‘water breaking’, is just the
condensation reaction in reversecondensation reaction in reverse
 The water molecule is added to the glycosidicThe 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 orIt can occur in disaccharides or
polysaccharidespolysaccharides
The disaccharide lactose broken by hydrolysis

13. CelluloseCellulose
 Plants also build starchPlants also build starch
chains into structureschains into structures
such as cellulose.such as cellulose.
 Beta glucose makeBeta glucose make
straight chainsstraight chains
 These straight chainsThese straight chains
linked top and bottomlinked top and bottom
by hydrogen bondsby hydrogen bonds
form cellulose.form cellulose.
 Cell walls are made ofCell walls are made of
cellulose, these givecellulose, these give
structure.structure.

14. CelluloseCellulose

15. QuestionsQuestions
 Why are glucose and fructose described asWhy 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 monomersName 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 buildingWhich polysaccharide is used as building
material by plants?material by plants?