(9) Examples of different functions of proteins e.g. how are they used in the human body

As already mentioned, protein molecules adopt a very specific folded 3D shape in order to be able to carry out their specific function - so what are these functions?

Every protein has its own unique shape to for its specific structure and function in an organism.

These proteins may end up in muscle cells, brain cells, enzyme catalysts, haemoglobin molecules etc.

BUT, note that proteins, particularly enzymes, are involved in building up non-protein molecules e.g. fats, cell walls, glycogen etc.

 

(a) Enzymes are biological catalysts that control most chemical reactions in living organisms.

Reminder: Enzymes have active sites of a specific shape that connect with substrate molecules, and this allows them to catalyse a specific chemical reaction in the biochemistry of living organisms.

Enzymes are physiologically active proteins.

The 'key and lock' mechanism of how an enzyme works - the correct 3D structure is crucial and that depends on the sequence and interconnection of the amino acids.

The crucial 3D protein structure of an enzyme, and denaturing effect e.g. from a high temperature or wrong pH.

 

(b) Many tissues are built of proteins e.g. collagen a strong structural protein (triple helix of polypeptides )that strengthens connective tissue like ligaments and cartilage of muscle systems of the joints.

Elongated muscle cells made from the protein actin - forming the filaments in muscles.

The strong fibres of our hair are made from the fibrous protein keratin.

These particular tissues are partially built from structural proteins.

 

(c) Carrier molecules like haemoglobin (conveys oxygen to cells) are also based on protein molecules.

Other carrier protein molecules assist in active transport, conveying molecules and ions in and out of cells against the natural descending diffusion gradient.

 

(d) Some antibodies are protein molecules.

The shape of the antibody protein must match the antigen of a pathogen e.g. of a virus.

These particular antibodies are physiologically active proteins.

See notes on Keeping healthy - defence against pathogens and infections

 

(e) Many hormones are protein molecules e.g. insulin, the hormone released into the blood from the pancreas, controls blood sugar levels.

The shape of the insulin molecule must match the shape of its receptor molecule.

These particular hormones are physiologically active proteins.

(Note there are many hormones which are NOT proteins e.g. some hormones involved in the menstrual cycle.)

 

(f) The liver is one of the most important sites for the assimilation of amino acids to synthesise proteins.

The liver makes many different protein molecules, including plasma proteins, e.g. fibrinogen protein is involved with blood clotting. See notes on blood circulation

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Key points about proteins - uses and function

Based on the syllabus-specifications for students taking the AQA, Edexcel and OCR GCSE level biology examinations (~US grades 9-10).

Proteins: Uses and Importance in Understanding the Human Body

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1. What Are Proteins?

Proteins are large, complex molecules essential for life.

They are made up of amino acids linked by peptide bonds, and their function depends on their shape, which can be affected by temperature and pH.

• Structure: Made up of long chains of amino acids folded into specific shapes.

• Types: Structural proteins, enzymes, transport proteins, hormones, antibodies, and contractile proteins.

• Importance: Essential for growth, repair, metabolism, and maintaining bodily functions.

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2. Six Essential Uses of Proteins in the Human Body

Function	Examples	Importance
Structural	Collagen (skin, tendons), Keratin (hair, nails)	Provides strength and support to tissues.
Enzymatic	Amylase, DNA polymerase	Speeds up biochemical reactions (biological catalysts).
Transport	Haemoglobin, membrane proteins	Haemoglobin carries oxygen in the blood; membrane proteins transport substances in/out of cells.
Hormonal	Insulin, glucagon	Regulates body functions, such as blood sugar levels.
Defensive	Antibodies (immunoglobulins)	Helps fight infections and recognize pathogens.
Contractile	Actin & Myosin (muscles)	Enables muscle contraction and movement.

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3. How Proteins Are Made

Proteins are produced through protein synthesis, a two-step process:

1. Transcription – DNA is copied into mRNA in the nucleus.

2. Translation – Ribosomes read mRNA and link amino acids together to form a protein.

Proteins are coded by genes, and mutations in DNA can lead to faulty proteins, affecting health (e.g., sickle-cell anaemia).

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4. Proteins in Nutrition and Deficiency Diseases

• Essential amino acids must be obtained from food (meat, dairy, legumes).

• Protein deficiency can lead to conditions like kwashiorkor, causing swollen bellies and stunted growth.

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5. Protein-Related Laboratory Tests

Biuret Test (GCSE-required practical)

1. Add Biuret reagent (NaOH + CuSO₄).

2. Positive result: Purple/lilac colour.

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6. Real-World Applications of Protein Science

• Monoclonal antibodies in vaccines and cancer treatments.

• Enzymes in industry (biological washing powders, lactose-free dairy).

• Genetic engineering (bacteria producing human insulin for diabetics).

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Other points - exam tips

• Learn examples of proteins by function (exam questions often ask for named examples).

• Understand how shape affects function (enzyme active sites, haemoglobin structure).

• Link genes to proteins (mutations → faulty proteins → diseases).

• Be prepared to describe and explain practical tests (Biuret test).

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Summary of learning objectives and key words or phrases

Know and be able to explain a variety of examples different types of proteins and their varied functions such as antibodies, enzyme catalysts, hormones, muscle tissue fibres tissues, carrier molecules in active transport.

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