Aim: explore and the structure and function of enzymes Objectives: List the main properties of enzymes Explain the terms active site, specificity and catalysts Discuss how enzyme activity is affected by temperature and pH

1. Jorge Melo

2. Phosphate
Group
O 5
Nitrogenous
base
O=P-O CH2 (A, G, C, or T)
O
O
N
C4 Sugar
(deoxyribose)
C1
C3 C2

3. 5 O 3
3 O
P 5 P
5 O
1 G C 3
2
4 4
2 1
3 5
O
P P
5
T A 3
O
O
5
P 3 P

4.  Double helix
 Antiparallel (5’-3’)
(3’-5’)
 Complementary rule
 Chargaff’s rule
 A-T
 C-G
 Hydrogen bonds

5.  The sugars
 Uracil instead of thymine
 RNA –usually single stranded

7.  mRNA
 rRNA
 tRNA

8.  DNA double helix unwind (helicase)
 RNA polymerase
 Ligase

9.  Helicase
 RNA
Transcription polymer
ase
 Ligase
Translation
 tRNA

11.  Name given to some stretches of DNA and
RNA that encode for a peptide
Stands for:
Ribonucleic acid

12.  I am important to life
 I am affected by temperature
 I am a globular molecule
 I am involved in biochemical reactions
 I am involved in the breakdown of molecules
 I am an Enzyme

13.  Aim: explore and the structure and
function of enzymes
 Objectives:
 List the main properties of enzymes
 Explain the terms active site, specificity and
catalysts
 Discuss how enzyme activity is affected by
temperature and pH

14.  Enzymes: facts and functions
 Enzymes: chemical structure
 Enzymes: properties
 Names of enzymes
 How enzyme works (theories)
 Activation energy and Rate of reaction
 The effect of temperature and pH on the enzyme

15.  Enzymes are chemicals that control
the reactions in cells.
 They are the caretakers of cells and
tissues.
 They make sure that cell chemistry
is kept in good shape.
 Each one has a particular job to do.

16.  Clear the fat out the blood stream after a meal
 Detection of glucose level in the body
 Break down the alcohol in beer or wine (liver)

17.  Thousands of chemical reactions take place in
the body every second.
 These make up the metabolism.
 Enzymes control the metabolism by
determining when and how chemical reactions
take place.

18.  Enzymes are catalysts that speed up the rate of
metabolic reactions.
 These reactions will take place without
enzymes, but they would take years rather
milliseconds.

19.  Which of the following reactions break
molecules down and which build molecules
up?
 A glycogen molecule formed from glucose
molecules.
 The digestion of starch to maltose.
 Urea formed from ammonia and carbon
dioxide.

20.  Example of a reaction that you already know:
Enzyme Enzyme
Hydrolysis Condensation

21.  globular proteins.
 long chains of amino acids.
 In a globular protein, the amino acid chain is
folded and wound into a spherical or globular
shape.

22. Enzyme
Tertiary
structure

23.  Specific three-dimension shape (tertiary
structure)
 This is Important: if it is altered , the enzyme cannot
function
 Three dimension shape is maintained by
hydrogen bonds and ionic forces

24.  Specific.
 Not used up in reactions.
 Combine to form enzyme/substrate
complexes.
 Only small amount of enzyme needed

25.  Are fast acting – high turnover number.
 Affected by temperature and pH.
 Some only able to work if a cofactor is present.
 Can be slowed down or stopped by inhibitors.

26.  Each enzyme can only catalyse one particular
reaction.
 This is because an enzyme can only react with a
specific substrate molecule.
 Amylase can only catalyse the hydrolysis of
starch into smaller disaccharide maltose
molecules.
 This is because amylase can only react with
starch molecules.

27.  An enzyme acts on a chemical known as a
substrate and the new substance that is formed
is the product
Enzyme
 Substrate product
 The name of the enzyme often comes from
substituting or adding -ase in the name of the
substrate

28.  The name of an enzyme comes from the
particular substance on which it acts.
 Lactase acts on the milk sugar lactose.
 Amylase works on starch – proper name
amylose.
 Cellulase breaks down cellulose.

29. Enzyme Substrate Reaction catalysed
Maltase Maltose Hydrolysis of maltose
to glucose
Amylase Amylose Hydrolysis of starch
to maltose
Alcohol Alcohol Removal of hydrogen
dehydrogenase from alcohol
DNA Ligase DNA Joining together 2
DNA strands
RNA polymerase Nucleotides that make Synthesis of mRNA to
RNA DNA molecule
Glycogen synthetase Glucose Polymerisation of
glucose into glycogen
ATPase ATP Synthesis or splitting
of ATP

30.  Which substrate do you think each of these
enzymes acts upon?
 Sucrase.
 Lipase.
 Protease.

32.  There are two models that explain how
enzymes work:
 1. Lock and Key theory
 2. Induced fit theory

33. Substrate Products
Enzyme
Substrate
complex
Activation
site
Enzyme Enzyme

34.  This attempts to explain why enzymes are
specific.
 They are large molecules, usually much bigger
than their substrates.
 Only a relatively small part comes into contact
with the substrate.

36.  This is called the active site.
 Only 3-12 aa make the active site, but its shape
is an exact fit for the substrate.
 The substrate is the key that fits the enzymes
lock.

37.  The two molecules form a temporary structure
called an enzyme/substrate complex
 The products are formed at the active site
 They then no longer fit and are repelled
 The active site is then free to react with more
substrate

39. Catabolic reaction: certain enzyme break a
substrate down into two or more products
Enzyme
Substrate
Products
Enzyme

40. Anabolic reaction: certain enzyme bond tow or
more substrates together to assemble one
product
Substrates Enzyme
Product
Enzyme

42.  The active site is a cavity of a particular shape
 Initially the active site is not the correct shape in
which to fit the substrate
 As the substrate approaches the active site, the site
changes and this results in it being a perfect fit
 After the reaction has taken place, and the
products have gone, the active site returns to its
normal shape

43.  Most reactions in cells
would be very slow
without enzymes.
 The substrate may not
be converted into the
product unless it is
given extra energy.
 Heating the particles
would increases their
kinetic energy and
they move about more
quickly.

44.  This means that
there is greater
chance of
collisions.
 The rate of reaction
then increases.

45. The energy needed to
start a chemical reaction
It can be thought of as an
energy barrier to get over
before the reaction can get
underway.
This energy can be
supplied in the form of
heat.
But this is not practical in
living systems.

46.  By lowering the activation energy of a reaction, the
enzyme provides a different pathway for the reaction.
 By lowering the activation energy, enzymes reduce the
input of energy needed.
 This allows reactions to take place at the at the lower
temperatures found in the cells of organisms.

49.  The factors that affect enzyme activity also affect the
functions of the cell and ultimately the organism
 enzymes are proteins and their functions is therefore
altered by:
 Temperature
 pH
 Substrate concentration
 Enzyme concentration
 Cofactors
 inhibitors

50.  Work in pairs and think about how are the
enzymes affected with the temperature and pH

51.  High temp. reactions tend to take place faster (more
kinetic energy)
 However if temp. is too high the enzyme may lose
their shape
 Bonds that old the tertiary structure of the enzyme
molecule on shape tend to break
 When the active site of the enzyme loses its shape it is no
longer able to bond to the substrate
 Enzyme denatured
 Irreversible reaction

52.  The temperature at which the enzyme works
most rapidly is called optimum temperature
 OT for plant enzymes
 25 C
 OT for Human body
 37 and 40 C
 OT some bacteria
 80 C

53.  Can have a direct effect on the bonding
responsible for holding the enzyme molecule in
its precise three-dimensional shape. If the
active site is changed then enzyme action will
be affected
 Each enzyme has an optimum pH
 Extremes of pH can denature enzymes and
stop them from functioning as catalysts

56.  Six facts about enzymes
 Enzymes are globular proteins
 They reduce the activation energy needed for a reaction
to proceed and produce products
 Enzymes have a region called an active site. The site is
the "lock" into which a substrate "key" fits.
 The enzyme then fits closely around the substrates. This
is called induced fit.
 Enzyme activity is affected by substrate type,
temperature, pH and substrate concentration.