chemicals of living things

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The Chemicals of Living Cells

©The Wellcome Trust

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Carbohydrates

Carbohydrates contain the elements carbon, hydrogenand oxygen

%amiliar carbohydrates are sugar  and starch

&lucose# fructose# maltose and sucrose are sugars

&lucose and fructose have the same formula# C6H12O6

'ucrose and maltose have the same formula# C12H22O11

Carbohydrates provide the main source of energy for 

respiration in living organisms

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Glucose C6H

12O

6

C

C

C

C

C

C

HO

HO H

HO H

H OH

H OH

H2OH

 A glucose molecule as a

 straight chain

) of the carbon atoms may

be arranged in a ring

This molecule is often represented

simply as a he"agon

C O

C C

C C

C

*

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Other carbohydrates$ molecules of glucose can

 +oin together to form amolecule of maltose

maltose

sucrose is formed when

a molecule of glucose anda molecule of fructose combine

Starch and cellulose are

formed from hundreds of glucose molecules +oined

to form a long chain

part of a starch

molecule

)

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Protein structure and shape

The way the amino acids +oin up# gives a protein molecule a

particular shape# which is different for every protein

Ser-Cyst-Val-ly-Ser-Cyst !la

  Val

Val-Cyst-Ser-!la-Ser-Cyst-ly

  Val- Cyst-!la-!la-Ser-ly

This is a small# imaginary protein molecule showing how

it ac4uires a shape

5igh temperatures or certain chemicals can cause the

protein molecule to lose its shape and its properties!

6

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Lipids

Lipids are fats and oils

They are made up from glycerol and fatty acids

."amples of fatty acids are stearic acid# oleic acid and

palmitic acid

stearic acid

oleic acid

palmitic acid

C

C

H

H2

H2 C

O

O

O

glycerol fatty acids

 A simple lipid

7

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Salts and water 

8n addition to proteins# carbohydrates and lipids# cytoplasm

contains salts and water 

Water makes up the bulk of cytoplasm

 All the chemical reactions in cytoplasm take place in

solution# i!e! in water 

Water itself takes part in many of these chemical reactions

'alts of sodium# potassium and calcium and many others

play an important part in these reactions

9

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Enzymes

.n2ymes are special proteins

They are present in the cytoplasm of all cells

They help to speed up the chemical reactions in the cell

There are hundreds of different en2ymes but each en2ymespeeds up only one kind of reaction

%or e"ample# glucose and fructose might +oin up slowly to

form sucrose

glucose0-"ructose

With the right en2yme present# the reaction happens faster

glucose0-"ructose

:-

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Enzyme action (1

.n2ymes are large protein molecules

Like all proteins# each en2yme molecule has a particular shape

This shape determines which chemical reaction the en2yme

can speed up

8n speeding up the reaction# the en2yme combines temporarily

with the substances it is acting on

 Any substance an en2yme acts on is called a substrate

::

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en2yme

substrate A

substrate ;

The substrate molecules fit the shape of the en2yme:$

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:

:*

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substrates combine temporarily with en2yme

en2yme +oins substrates together 

:*

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new compound released

 by en2yme

en2yme unchanged

and ready for 

ne"t reaction

:)

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!ifferent types of enzyme reaction

The last * slides show how an en2yme is involved incombining substrates to create a larger molecule

%or e"ample# the en2yme could be building up a sucrose

molecule from glucose and fructose

The ne"t se4uence shows how an en2yme can help to

break a large molecule into smaller molecules

%or e"ample an en2yme can split a sucrose molecule

into the smaller glucose and fructose molecules

:3

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ntermediate sta%e (1

substrate combines

temporarily with en2yme

en2yme will break

molecule here

:7

:9

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ntermediate sta%e ()

substrate splits and

separates from en2yme

:9

$-

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*inal brea$&down products

end0products

en2yme ready for 

 ne"t reaction

$-

$:

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Properties of enzymes

They always produce the same end products

 Although they take part in the reaction# they are not used up

;ecause en2ymes are proteins# they are denatured by heat

or some chemicals

.n2ymes can act on only one type of substrate

 <enaturing involves a change of shape in the en2yme molecule so that it cannot combine with the substrate

8ndividual en2ymes work best at a particular temperature

and p5 (acidity or alkalinity

$:

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#n$ymes can act on only one type o" substrate

this substrate cannot combine

with this en2yme

this substrate cannot combine

with this en2yme

$$

% t i th d t d $

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%ecause en$ymes are proteins, they are denatured

by heat or some chemicals

en2yme

denatured

by heat

denatured en2yme cannot combine with substrate

en2yme =

substrate

$

.>?@. ACT8B> $*

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1

glucose

molecules

.

1! A glucose molecule combines

with the active site on an en2yme

.>?@. ACT8B> $*

$)

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.

2 A region of the active site is still available

$)

$3

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part of starch

molecule

.

& Bne end of a growing starch

molecule combines with the

glucose molecule at the activesite

$3

$6

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.

' The growing starch molecule

breaks free from the en2yme whichis now free to repeat the reaction

$6

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$9

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+uestion 1

The correct formula for glucose is

(a) C:$5$$B::

(b) C)5:-B)

(c) C*57B*

(d) C35:$B3

$9

-

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+uestion )

Which is the most accurate description of a carbohydrate

 A carbohydrate contains

(a)  carbon and o"ygen

(b)  carbon# o"ygen and nitrogen

(c)  carbon# hydrogen and o"ygen

(d)  carbon and hydrogen

-

:

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+uestion ,

When two molecules of glucose combine# they form

(a)  maltose

(b)  sucrose

(c)  fructose

(d)  ribose

:

$

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+uestion -

Which is the most accurate description of a protein

,roteins contain

(a) carbon# hydrogen and o"ygen

(b) carbon# hydrogen# o"ygen and nitrogen

(c) carbon# hydrogen and nitrogen

(d) carbon# nitrogen and o"ygen

$

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+uestion .

Which statements are correct

,roteins are present in

(a)  cell membranes

(b)  cell walls

(c)  cytoplasm

(d)  nucleus

*

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+uestion /

5igh temperatures damage proteins by

(a)  decomposing them

(b)  changing their chemical composition

(c)  changing their shape

(d)  making them soluble

*

)

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+uestion 0

 A protein is made up of a series of 

(a)  glucose units

(b)  fatty acids

(c)  amino acids

(d)  carbohydrates

)

3

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+uestion

Lipids are made up of 

(a)  glycerol and amino acids

(b)  glycerol and fatty acids

(c)  protein and fatty acids

(d) starch and fatty acids

3

6

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+uestion 2

.n2ymes are

(a)  proteins

(b) lipids

(c)  carbohydrates

(d)  a combination of these

6

7

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+uestion 13

 An en2yme can

(a) change a reaction

(b) prevent a reaction

(c) slow down a reaction

(d) speed up a reaction

7

9

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+uestion 11

 A substrate is a substance which

(a) an en2yme acts on

(b)  is produced by an en2yme reaction

(c) is a particular kind of en2yme

(d)  is any chemical substance in a cell

9

*-

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+uestion 1)

 An en2yme can

(a) combine with different substrates

(b)  form different kinds of end0product

(c) function at temperatures above 9-oC

(d) speed up a reaction in the cytoplasm

*:

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+uestion 1,

The part of an en2yme which combines with the substrate

is called

(a)  the reaction centre

(b) the active site

(c) the action centre

(d) the reaction site

*$

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+uestion 1-

 After being e"posed to a high temperature an en2yme

cannot function because

(a)  it has been broken down

(b)  its shape has been changed

(c) its composition has been changed

(d) it cannot separate from its substrate

*$

*

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"4S5E6 

Correct

*

**

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"4S5E6 

*ncorrect