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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
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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
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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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*ncorrect