Chpt.’s 9 and 10
Metabolism
• Is the sum of all the chemical reactions that
take place in an organism
– E.g. growth, movement, repair, response, reproduction
• Cells need energy to maintain themselves
• Metabolism is how cells obtain and use
energy
• Energy can either be released or absorbed
– *Catabolic reactions breakdown complex
molecules to simpler forms. Release energy.
• E.g. respiration or digestion
– *Anabolic reactions convert simple molecules into
complex ones. Energy is consumed.
• E.g. photosynthesis or polypeptide formation
• Reactions take place in steps. These steps are
carefully controlled by the cell. The most important
controller of cellular reactions are enzymes
Sources of Energy
Solar
Energy
Cellular
Energy
Enzymes
• A catalyst is a substance that speeds up a reaction
without being used up
• Enzymes are catalysts made of protein
• Enzymes are biological catalysts that speed up
reactions without being used up
• Proteins are formed by joining a sequence of
amino acids
• The function of a protein is determined by
» its amino acid sequence
» its shape
• Enzymes are folded into globular shapes
• The 3D shape of an enzyme means it will fit and react only
with a substance that has a matching shape
• Anything that changes the shape of the enzyme will alter
the efficiency of the enzyme
» pH
» temperature
Enzyme action
• Substrate – substance which an enzyme reacts with.
• Product – substance(s) the enzyme forms.
• Active Site – part of the enzyme that combines with the
substrate.
• Enzymes have a specific shape which determines their
function.
• Enzyme reactions are reversible.
• This means any enzyme can be anabolic or catabolic
• Naming Enzymes – add ase to name of their substrate
Lipid (substrate)
Lipase (enzyme)
Inhibitors
• chemicals that attach to an enzyme and destroy its shape
i.e. denature enzyme
Advantages – some insecticides, drugs and
antibiotics act as inhibitors of enzymes not present
in humans, therefore can act on bacteria etc.
without harming humans e.g. Penicillin
Disadvantages – many nerve gases are inhibitors
that attach to enzymes involved in nerve impulse
transmission e.g.
cyanide – denatures enzyme involved in
respiration.
The Role of Enzymes
• Catabolic and anabolic enzymes – see handout
Factors affecting enzyme activity:
• All enzymes work best under ideal conditions –
optimal conditions – any change in these conditions
will slow down the rate of the reaction by changing the
enzymes effectiveness.
• Will be investigating two of these conditions:
- temperature
- pH values
Temperature
– Human enzymes work best at 37oC
– Plant enzymes work best at 20 – 30oC
• At very low temps cells freeze and enzymes can
not function
• At very hot temps enzymes lose their shape and
can not function (denatured above 50oC)
TEMPERATURE AND RATE OF ENZYME ACTION
pH
pH scale 0 to 14
Enzymes work in a very narrow pH range
Outside range activity falls rapidly
Optimal pH for most enzymes is pH 7
0
7
acid
neutral
14
base
Temp and pH effect on activity
Immobilised Enzymes
Bio-processing: is the use of enzyme controlled reactions
to produce a product
Traditionally micro-organisms such as bacteria and yeast
were used but since the 1900’s and especially since the
1950’s enzymes are being used.
Bio-processing can be used to produce a vast range of
products such as cheeses, beer, antibiotics, vaccines,
methane gas, food flavours, vitamins and perfumes
Immobilised Enzymes
• If enzymes are used freely dissolved in a vessel it can be
very wasteful as they are lost at the end of the process.
• To prevent this problem enzymes are often immobilised
or fixed.
• This means they are attached to each other or an inert
substance and can be used repeatedly i.e. Immobilised
enzymes.
How to Immobilise Enzymes
Physical methods:
Adsorption: where enzymes are physically attached to
inactive supports such as glass beads or cellulose particles.
Trapped in a gel: sodium alginate is commonly used. This
allows substrates in and products out but prevents the
enzyme from leaving the gel.
Enclosed by a membrane: when enzymes are kept within
a membrane.
How to immobilise enzymes
Chemical Methods :
Bonded to a support enzymes chemically bonded to a
support such as glass beads or ceramics.
Bonded to each other enzymes are chemically bonded to
each other.
Enzyme
bonded to a
support
Advantages of Immobilised Enzymes
• Efficiency of enzyme is not affected.
• Immobilised enzymes can be easily recovered from the
product so you can get a pure sample of product easily.
• Immobilised enzymes can be reused this cuts costs.
• Enzymes frequently become more stable when
immobilised.
Uses of Immobilised Enzymes
Immobilised glucose isomerase converts glucose to
fructose which is used to sweeten drinks.
Lactase converts lactose to sweeter sugars
glucose and galactose which are then used
by food manufacturers.
Penicillin acylase changes the structure of
penicillin to make more antibiotics that will
fight a wider range of bacteria.
The Active Site
The Active site is the part of the enzyme that combines
with the substrate.
The Active Site
Contrary to belief the active site is not a rigid shape that is
fixed to fit the substrate.
When the substrate enters the active site it causes (or
induces) it to change shape slightly.
The enzyme then fits more precisely around the substrate
this is known as the Induced Fit Model of enzyme action.
The Bean Bag Theory
The Induced Fit Model can be compared to the way
a bean bag will adapt to fit snugly around our body
shape when we sit in it.
Mechanism of Enzyme Action The Induced Fit Model
1. The substrate combines with the active site of the
enzyme
2. The active site is induced or caused to change shape
slightly.
Active Site
Enzyme
Substrate
3. Substrate and enzyme form an enzyme substrate
complex. The bonds in the substrate are altered so that
the substrate changes into the product(s).
Enzyme Substrate
complex
Substrate changed to products
which are released
4. The products leave the active site. The active site
returns to its original shape and is ready for a new
substrate molecule.
Products
Active Site
Enzyme
New Substrate
Induced fit theory
Denaturation
• When most proteins are heated above 40⁰C or treated
with certain chemicals or radiation they will gradually
lose their 3 dimensional shape.
• This means enzymes will not be able to form the enzyme
substrate complex.
• Denaturation: occurs when the shape of an enzyme is
changed and it loses its biological activity.
• Example: white of an egg is denatured when an egg is
boiled.
Energy Carriers
• Energy is essential for cell metabolism e.g.:
- Photosynthesis – energy in sunlight is used to
make food.
- Respiration – food is broken down to release
energy.
• ATP , NADP+ and NAD+ play a vital role in trapping
and transferring energy in cellular activities.
ADP and ATP
ADP:
• ADP is an abbreviation for Adenosine Diphosphate this
is a molecule found in the cells of all organisms.
• It is made of the base adenine , a 5 carbon sugar called
ribose and 2 phosphate groups
Unstable
Bond
Adenine
Adenosine
• ADP is a low energy molecule
Ribose
P
P
Diphosphate
ADP and ATP
ATP:
• If another phosphate is added to ADP it forms ATP
(Adenosine Triphosphate)
Unstable Bond
Adenine
Ribose
P
P
P
• Extra energy is also added as there is an extra bond
between the last two phosphate groups.
• Addition of a phosphate group like this is called:
Phosphorylation
• ATP is rich in energy and stores this energy carrying it
around in the cell i.e. Energy Carrier.
ADP and ATP
ATP:
• ATP cannot store energy for very long it breaks
down releasing energy and converting back to ADP.
• Energy released is used to carry out most of the
reactions in cells.
• Most cells release energy from ATP 10 million
times every second!
NADP+ and NADPH
NADP+:
• NADP+ is a low energy molecule involved in
photosynthesis.
• NADP+ can combine with 2 high energy electrons and a
proton (Hydrogen ion H+) to form NADPH.
NADP+ + 2 electrons + H+
(LOW ENERGY)
(HIGH ENERGY)
NADPH
(HIGH ENERGY)
• Addition of electrons like this is called - Reduction
• NADPH is a very high energy molecule. It’s energy is
used to form glucose in photosynthesis.
NADP+ and NADPH
NADPH:
• NADPH releases energy, in the form of two high –
energy electrons, and a proton when broken down
into NADP+.
NADPH
NADP+
(HIGH ENERGY)
(LOW ENERGY)
+ 2 electrons + H+
(HIGH ENERGY)
NAD+ and NADH
• NAD+ is used in respiration
• It can combine with 2 high energy electrons and a proton
to form NADH which is very high in energy.
• Remember P for photosynthesis, NADP+ is used in
photosynthesis NAD+ in respiration.