Structural proteins give strength and support to tissues like tendons, ligaments and muscles. Which one of the following options does NOT primarily contain a structural protein?

Introduction:
Proteins in the body have many different roles. Some proteins act as enzymes, some function as hormones and others serve a structural role, providing strength and support to tissues such as bone, cartilage, tendons and muscles. This question asks you to identify which of the listed options does not primarily contain a structural protein but instead contains a different type of protein with another function.

Given Data / Assumptions:
- Examples given include tendons, ovalbumin, muscles and ligaments. - Structural proteins include collagen, elastin and contractile proteins like actin and myosin. - We assume normal human anatomy and standard biochemical classification of proteins. - The task is to single out the option where the main protein is not structural in function.

Concept / Approach:
Tendons and ligaments are dense connective tissues rich in collagen, the major structural protein that provides tensile strength. Muscles contain contractile proteins such as actin and myosin that enable movement and also have structural roles. Ovalbumin, on the other hand, is the main protein found in egg white and functions primarily as a storage protein for the developing embryo, not as a structural suport in body tissues. Therefore, ovalbumin is the correct option that does not mainly represent a structural protein in the context of human tissues.

Step-by-Step Solution:
Step 1: Identify the main protein components in each structure or substance mentioned. Step 2: Recall that tendons connect muscle to bone and are rich in the fibrous structural protein collagen. Step 3: Remember that ligaments connect bone to bone and are also composed mainly of collagen and elastin, both structural proteins. Step 4: Note that muscles are made of contractile proteins actin and myosin, which form structural filaments that generate force. Step 5: Recognise that ovalbumin is the primary protein in egg albumen (egg white) and functions as a nutrient and storage protein rather than a structural element in tissues. Step 6: Conclude that ovalbumin is the correct answer because it is not primarily a structural protein in the body.

Verification / Alternative check:
Biochemistry references classify proteins based on function into structural, catalytic, transport, regulatory and storage types. Collagen, elastin, keratin, actin and myosin are cited as classic structural proteins. Ovalbumin is listed as a storage protein in egg white, providing amino acids to the developing chick embryo. Human tissues such as tendons and ligaments are repeatedly described as collagenous structures, reinforcing that these are structural, while ovalbumin is not. This confirms that ovalbumin does not belong with the others in the structural protein category.

Why Other Options Are Wrong:
Tendons: Composed largely of collagen fibres arranged in parallel bundles; collagen is a key structural protein providing strength. Muscles: Contain actin and myosin filaments that form the structural units of muscle fibres (sarcomeres) and are essential for contraction. Ligaments: Made of dense regular connective tissue with collagen and elastin, giving structural support and stability to joints.

Common Pitfalls:
Because all options involve biological substances, some learners may think each must contain some structural protein and get confused. Others may not have encountered the term ovalbumin and may fail to recall that it is an egg white protein. A good strategy is to remember that tendons, ligaments and muscles are physical structures in the body, so their proteins are naturally structural or contractile, whereas ovalbumin is associated with egg nutrition rather than mechanical support in tissues.

Final Answer:
The option that does not primarily contain a structural protein is Ovalbumin.