AS Biology: Units 2 & 3

Revision Session 1: Carbohydrates

OBJECTIVES

Reaffirm knowledge on structure of carbohydrates

Have an opportunity to ask teacher any questions about things

not understood

Success criterion

Correctly answer questions and carry out tasks relating to

carbohydrate structure

STARTER

In pairs – list 10 words you can remember that

link with the topic of carbohydrate structure

1 to start you off....’monosaccharide’

REVISION – COMES FROM YOU

These sessions are aimed at giving you time to

work over the areas you want to practice and

ask questions about anything you don’t

understand

Most of the action will come from you – not the

teacher!

PHONE A FRIEND

What do you remember about carbohydrates?

Tell us one quick fact, then nominate someone else

to give us a fact

Starting with.....

Making Polymers

Many organic molecules, includingcarbohydrates, are made up of individualmolecules called monomers.

The carbon atoms of these monomers jointo form longer chains called polymers.Polymers are made up of repeatedmolecules called monomers.

Biological molecules like carbohydrates andproteins are often polymers.

Most of these polymers are made up ofjust four elements: carbon hydrogen,oxygen and nitrogen.

Carbohydrates

• Carbohydrates are carbon molecules (carbo)combined with water (hydrate). Some moleculesare small while others are large.

• These are all examples of sugars (saccharides).

• Where there is only one sugar it is called amonosaccharide.

• Two monosaccharides can join together to form adisaccharide.

• Many monosaccharide units can join together toform polysaccharides.

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• Carbohydrates are carbon molecules (carbo)combined with water (hydrate). Some moleculesare small while others are large.

• These are all examples of sugars (saccharides).

• Where there is only one sugar it is called amonosaccharide.

• Two monosaccharides can join together to form adisaccharide.

• Many monosaccharide units can join together toform polysaccharides.

MONOSACHARIDES

Have between 3 and 7 carbon molecules

The name/number is a bit of a give away:

Triose

Hexoses (e.g. Glucose, fructose, galactose)

Pentose (e.g. Ribose) etc.....

JOINING UP AND BREAKING UP

Monosaccharides join together in a glycosidic

bond

H2O is released = condensation reaction

The opposite (bond breakage) = hydrolysis

reaction = H20 is added

FORMATION OF GLYCOSIDIC BOND BY

REMOVAL OF WATER (CONDENSATION

REACTION)

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C

C

C

C

C

CH2OH

OH

OH

OH

OH

H

H

H

H

HO

1

23

4

5

6

H2O

α glucose fructose

Water

CH2O

HC C

C

OH

OH

OH H

H

H

O1

2

3 4

5

6CH2OH

C

FORMATION OF GLYCOSIDIC BOND BY

REMOVAL OF WATER (CONDENSATION

REACTION)

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C

C

C

C

C

CH2OH

OH

OH

OOH

H

H

H

H

HO

1

23

4

5

6

CH2O

HC C

C

OH

OH H

H

H

O1

2

3 4

5

6CH2OH

C

1-2 Glycosidic

bond

Sucrose+ H2O Water

ALPHA AND BETA GLUCOSE

Use your sheets of paper to cut out the

molecular diagram and add the H—OH the

correct way around

Which way around is alpha and which is beta?

Have a go at using your card cut outs

REDUCING AND NON-REDUCING SUGARS

REDUCING SUGARS = all monosaccharides and some

disaccherides (e.g. Maltose)

Benedict’s test (orange brown colour) – receives the

electrons

NON-REDUCING SUGARS = Most disaccharides

Do not turn Benedict’s reagent orange brown

To test – first break down into monosaccharides (by

adding HCL) then do Benedict’s test (if turns orange

brown – shows non-reducing sugars were present

TASK 1 - 5 MINUTES

Think of a questions about carbohydrates that

you need to know but don’t know the answer to

In pairs – ask the other person your question

(i.e. Swap questions)

The other person must TELL you the answer to

the question

Take 2-3 minutes to look up the answer if you

can’t answer your partner’s question straight

away

WORKSHEETS

1) Carry out the ―If this is the answer what is the

question‖ worksheet

2) Carbohydrates ―test‖

3) Exam paper questions

Use the books provided to find the answers

Shout if you need help!

PLENARY

Carbohydrates scrabble – use as many words

relating to this morning’s work as you can

Useful summary website on macromolecules to note down before you leave:

www.mansfield.ohio-state.edu/~sabedon/campbl05.htm