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VMC002 Foundation Evidenced
Based Bioveterinary Sciences

Chemistry 4

Learning Outcomes

• Catalysts and Enzymes

– Describe the basic structure of enzymes and how they work
– Define the role enzymes play in homeostasis
– Describe how different factors affect the rate of reactions

• Diffusion and Osmosis

– Define diffusion and osmosis. Describe the differences between them
– Define tonicity and explain how it is used to describe different relative

concentrations

• Acid Base balance

– Define pH and the difference between acids and bases
– Explain the difference between strong and weak acids and bases
– Describe why acid base balance is important for homeostasis

Catalysts and
enzymes

Catalysts

A substance that increases the rate
of a chemical reaction without
itself undergoing any permanent
chemical change

E.g. Catalytic converter uses
Platinum, Rhodium and Palladium
to reduce toxin gases in car
exhaust fumes

Enzymes

• Biological catalysts - Not used up in

the reaction or changed

• Reduce activation energy of a

reaction and make the transition state
more stable

• Increase reaction rate

• Can be anabolic (e.g. DNA

polymerase) or catabolic
(e.g.amylase)

What enzymes do

Globular proteins – specific
shape (tertiary structure) and
active site

Regulatory regions
(allosteric binding) , co-
factors and/or co-enzymes

Hold molecules together or
stress bonds to lower
Activation Energy

Models of enzyme action: Lock and Key

Recommend
watching Enzymes
(Bozeman
science) 12 mins

Models of enzyme action: Induced fit hypothesis

Induced-fit hypothesis

What are enzyme activators?

Some enzymes require the addition of a
non-protein substance called a Co-enzymes
or cofactors before they can catalyse a
reaction. There are two main types of
cofactor:

• cofactors – inorganic groups that are

permanently bound to the enzyme and so
are a type of prosthetic group. Common
examples include iron, zinc and copper.

• coenzymes – organic molecules that bind

only temporarily to the enzyme,
transferring a chemical group necessary
required for the reaction. Examples include
vitamin C and ATP.

vitamin C

What are enzyme inhibitors?

Substances that interfere with
enzyme activity

Can be reversible or irreversible
(e.g. many poisons and toxins)

Can be competitive (blocking the
active site) or non-competitive
(allosteric) if change the shape of
the active site by binding at a
different location

Reaction rate inhibition

Increasing substrate concentration will
only increase rate in competitive
inhibition, not allosteric.

Enzyme inhibition is important in
regulating metabolic pathways. The
final (end) product often acts as a
regulator of the pathway in a process
called end-product inhibition.

When the amount of end product is
high, it binds non-competitively to an
enzyme in the pathway, blocking
further production of itself.

Kinematics of enzyme-catalysed reactions

• During an enzyme-catalysed

reaction, substrate is converted to
product.

• The reaction rate is highest

initially, then plateaus off as it
reaches equilibrium.

• Reaction rate is how fast a reaction

occurs; a change in concentration
per unit time.

Rate of enzymatic-catalysed reactions

Factors affecting rate of reaction include

•

Enzyme concentration

•

Substrate concentration

•

Temperature

•

pH

Different enzymes function best at
different pH

Most function best around body
temperature, 38C and are denatured at
higher temperatures

Diffusion and
osmosis

Diffusion

The passive movement of particles from a region of
higher concentration to one of lower concentration
i.e. down a concentration gradient.

Multiple factors can affect its rate

concentration gradient

size of the molecules

temperature

Osmosis

Diffusion of water molecules

down the gradient of ‘water potential’.

Occurs when solutions with different
solute concentration are separated by a
semi-permeable membrane.

Only smaller water molecules can
diffuse across and equalize the solute
concentration.

Concentration and tonicity

Solution – mixture of a solute dissolved into a solvent.

Solute concentration is a measure of the amount of solute to volume
of solvent.

Tonicity - its solute concentration relative to that of another solution

Hypertonic - the solute concentration is greater

Hypotonic – the solute concentration is less

Animal cells have a salt concentration of 0.9 %,described as isotonic.

Acid base balance

Quick recap: Acids and Bases (2 mins)

Acid base balance - pH scale

pH is a measure on a logarithmic scale of the
acidity or alkalinity of a substance

Acids dissolve to give pH <7
•They are proton donors and will release
hydrogen ions (protons) in water

Alkalis dissolve to give a pH >7
•They are proton acceptors and form hydroxide
ions in solution

pH is defined as the concentration of hydrogen
ions in solution

Dissociation

Molecules split to become ionised in
solution.

– Complete
– Incomplete – equilibrium exists between

states

Strong acids e.g. Nitric, Sulphuric and
Hydrochloric acid are usually fully
dissociated
Weak acids exist in equilibrium that favours
their undissociated state

Strong bases e.g. Sodium hydroxide, are
usually fully dissociated
Weak bases exist in equilibrium that favours
their undissociated state

Examples of acids and bases:

Water

Water exists in a slightly dissociated state
equilibrium of dissociation is relatively constant. We describe
this as Kw, the dissociation constant of water

Hence an acid is more protonated than water, and a base is
less protonated than water

Buffers

• Maintain an approximate pH

• Acidic buffers are made from a weak acid (that dissociates poorly) and a salt

of the weak acid (that dissociates fully)

• Similarly basic buffers are made from a weak base

and a salt of the weak base

• Because there are two equilibriums in play, this results

in ‘mopping up’ of the Hydrogen or Hydroxide ions
and helps resist pH changes in.

• ‘Buffering capacity’ - important role in homeostasis

Acid-base homeostasis

• Minor changes in pH can have a devastating effect

• Animal bodies normal pH is 7.35-7.45

• Dealing with disturbance in acid-base balance

– Blood buffering capacity HCO−

3

– CO2 can be eliminated through the lungs. Fast but

not a long term option

– Kidneys secrete acid (H+) using buffers such as

ammonia, and reabsorb bicarbonate. Tight
physiological control, takes days.

• This is why respiratory and renal disease will cause

upsets in the body’s acid base balance, e.g. acidosis
or alkalosis in plasma pH

Acidosis and Alkalosis

Summary

Enzymes allow biochemical processes to take place in the
most energy efficient way.

Osmosis of water across a semi-permeable membrane is
essential for cell function

Homeostatic control is achieved by active management of
acid-base balance in the body, through buffers and
physiological mechanisms

Next steps

• Review the LabSci practical simulation

– Access through Blackboard