Diagnostic Biochemistry and Haematology – Week 3
Lecture – Proteins: Structure, function, and Clinical Applications
Learning Outcomes
1. Understand protein formation from gene transcript
2. Structure of proteins – 4 levels of structure
3. Biological function of proteins
4. Proteins in Clinical Applications – proteins in disease
The Anatomy of an Amino Acid
• Amino acids consist of four components attached
to a central carbon, the alpha carbon.
• These components include a
hydrogen atom, a carboxyl
group, an amino group, and
a variable R group
(or side chain).
• Differences in R groups
produce the 20 different
amino acids.
• Carboxyl group → acidic part of the amino acid
• Glycine is the simplest AA
• The R group makes the difference between AA
Essential, Nonessential, and Conditional
Amino Acids
Essential:
Must be consumed in the diet
Nonessential:
Can be synthesised in the body
Conditionally essential:
Cannot be synthesised due to illness or lack of
necessary precursors
• Premature infants lack sufficient enzymes
needed to create arginine
• Essential AA → cannot be synthesised by
the human body through synthesis
pathways
a) Histidine one thought essential only for
Infants. Small amounts required in adulthood
b) Conditional essential if inadequate precursors or inadequate enzymes for bioavailability
1
, Four Stages of Protein Structure
• Primary → sequence of the amino
acids
• Secondary → formation of alpha or
beta helix → binds between carboxyl
and amino group
• Tertiary structure → formation of
polypeptide chains → beta sheets
and helixes combined
• Proteins and especially globular
proteins are made up of these three
dimensional structures
A protein’s function depends on its specific conformation
Protein function depends on its ability to recognise and bind to other molecules:
• Antibodies bind to particular foreign substances that fit their binding sites.
• Enzyme recognize and bind to specific substrates, facilitating a chemical reaction.
• Neurotransmitters pass signals from one cell to another by binding to receptor sites on
proteins in the membrane of the receiving cell.
• Proteins have to bind to other molecules or proteins to cause a reaction, physiological
change, synthesis of molecules, speeding or slowing down chemical reactions etc
• Neuromuscular junction → proteins are essential for signal transduction
• Even a slight change in primary structure can affect a protein’s conformation and ability to
function.
• In individuals with sickle cell disease, abnormal haemoglobins, oxygen-carrying proteins,
develop because of a single amino acid substitution.
• These abnormal haemoglobins crystallise, deforming the red blood cells and leading to clogs
in tiny blood vessels.
• Sickle cell disease → abnormal haemoglobin due to single AA substitution in the primary
structure of the protein
• The sickled haemoglobin →
reside 6 was replaced by valine
which results in the abnormal
structure
2
Lecture – Proteins: Structure, function, and Clinical Applications
Learning Outcomes
1. Understand protein formation from gene transcript
2. Structure of proteins – 4 levels of structure
3. Biological function of proteins
4. Proteins in Clinical Applications – proteins in disease
The Anatomy of an Amino Acid
• Amino acids consist of four components attached
to a central carbon, the alpha carbon.
• These components include a
hydrogen atom, a carboxyl
group, an amino group, and
a variable R group
(or side chain).
• Differences in R groups
produce the 20 different
amino acids.
• Carboxyl group → acidic part of the amino acid
• Glycine is the simplest AA
• The R group makes the difference between AA
Essential, Nonessential, and Conditional
Amino Acids
Essential:
Must be consumed in the diet
Nonessential:
Can be synthesised in the body
Conditionally essential:
Cannot be synthesised due to illness or lack of
necessary precursors
• Premature infants lack sufficient enzymes
needed to create arginine
• Essential AA → cannot be synthesised by
the human body through synthesis
pathways
a) Histidine one thought essential only for
Infants. Small amounts required in adulthood
b) Conditional essential if inadequate precursors or inadequate enzymes for bioavailability
1
, Four Stages of Protein Structure
• Primary → sequence of the amino
acids
• Secondary → formation of alpha or
beta helix → binds between carboxyl
and amino group
• Tertiary structure → formation of
polypeptide chains → beta sheets
and helixes combined
• Proteins and especially globular
proteins are made up of these three
dimensional structures
A protein’s function depends on its specific conformation
Protein function depends on its ability to recognise and bind to other molecules:
• Antibodies bind to particular foreign substances that fit their binding sites.
• Enzyme recognize and bind to specific substrates, facilitating a chemical reaction.
• Neurotransmitters pass signals from one cell to another by binding to receptor sites on
proteins in the membrane of the receiving cell.
• Proteins have to bind to other molecules or proteins to cause a reaction, physiological
change, synthesis of molecules, speeding or slowing down chemical reactions etc
• Neuromuscular junction → proteins are essential for signal transduction
• Even a slight change in primary structure can affect a protein’s conformation and ability to
function.
• In individuals with sickle cell disease, abnormal haemoglobins, oxygen-carrying proteins,
develop because of a single amino acid substitution.
• These abnormal haemoglobins crystallise, deforming the red blood cells and leading to clogs
in tiny blood vessels.
• Sickle cell disease → abnormal haemoglobin due to single AA substitution in the primary
structure of the protein
• The sickled haemoglobin →
reside 6 was replaced by valine
which results in the abnormal
structure
2
