Protein Structure and Function Practice Questions

Q: Who was awarded the Nobel Prize for determining the amino acid sequence of insulin?

Sanger. ***Sanger*** - **Frederick Sanger** was awarded the Nobel Prize in Chemistry in 1958 for his work on the **structure of proteins**, specifically for determining the **amino acid sequence of insulin**. - His method involved breaking down the protein into smaller fragments and then sequencing these fragments to reconstruct the entire protein structure. *Banting & Macleod* - **Frederick Banting** and **John Macleod** received the Nobel Prize in Physiology or Medicine in 1923 for the **discovery of insulin** itself. - Their work focused on isolating and demonstrating the therapeutic effects of insulin in treating diabetes. *Paul Berg* - **Paul Berg** was awarded the Nobel Prize in Chemistry in 1980 for his fundamental studies of the **biochemistry of nucleic acids**, particularly for his work on **recombinant DNA technology**. - His contributions were pivotal in the development of genetic engineering. *Charles Best* - **Charles Best** was a medical scientist who assisted Frederick Banting in the **discovery of insulin**. - While central to the discovery, he was not included in the Nobel Prize awarded to Banting and Macleod, though Banting shared his prize money with Best.

Q: A 60 year old lady is concerned about the wrinkles around her eyes. This is primarily due to alterations in

Collagen cross linking. ***Collagen cross linking*** - With aging, the **collagen fibers** in the skin undergo structural changes, including a decrease in efficient cross-linking. - This reduction in **collagen cross-linking** leads to a loss of skin elasticity and tensile strength, contributing to the formation of wrinkles. *Fibrillin* - **Fibrillin** is a glycoprotein that is essential for the formation of elastic fibers, not primarily collagen. - Defects in fibrillin are associated with conditions like **Marfan syndrome**, which affects connective tissue integrity but is not the primary cause of age-related wrinkles. *Collagenase* - **Collagenase** is an enzyme that breaks down collagen; an increase in its activity can contribute to collagen degradation. - While collagenase activity plays a role in skin aging, the *deficiency* or *defect* is not the primary cause of wrinkles, rather it is the overall degradation and altered structure of collagen. *Desmosine* - **Desmosine** is a unique amino acid that is part of **elastin fibers**, not collagen. - It is crucial for the elasticity of tissues but a defect in desmosine itself is not the direct cause of age-related wrinkles, which are more directly related to collagen structure.

Q: Which of the following is not a peptide/protein -

Glucocorticoids. ***Glucocorticoids*** - **Glucocorticoids** are **steroid hormones** derived from cholesterol, making them **lipids**, not peptides or proteins. - They exert their effects by binding to **intracellular receptors** to regulate gene expression. *Growth hormone* - **Growth hormone (GH)** is a **peptide hormone** produced by the anterior pituitary gland. - It plays a crucial role in **growth**, cell reproduction, and metabolism. *PTH* - **Parathyroid hormone (PTH)** is a **peptide hormone** secreted by the parathyroid glands. - It primarily regulates **calcium** and phosphate levels in the blood. *Insulin* - **Insulin** is a **peptide hormone** produced by the beta cells of the pancreatic islets. - Its main function is to regulate **glucose metabolism** by facilitating glucose uptake into cells.

Q: Guanidine group is present in

Arginine. ***Arginine*** - Arginine is a basic amino acid characterized by a **guanidinium group** at the end of its side chain. - The **guanidinium group** consists of three nitrogen atoms bonded to a central carbon atom, giving it a high pKa and making it positively charged at physiological pH. *Tryptophan* - Tryptophan contains an **indole ring** in its side chain, an aromatic heterocyclic organic compound. - It is known for being a precursor to neurotransmitters like **serotonin** and melatonin. *Proline* - Proline is unique among amino acids due to its **cyclic structure**, where the side chain is bonded to both the alpha-amino group and the alpha-carbon. - This forms a **pyrrolidine ring**, which imposes structural constraints on protein folding. *Tyrosine* - Tyrosine contains a **phenol group** in its side chain, which is an aromatic ring with a hydroxyl group attached. - It plays a crucial role as a precursor to several important neurotransmitters like **dopamine**, norepinephrine, and epinephrine.

Q: Which of the following hormones is an example of a peptide hormone?

Parathormone. ***Parathormone*** - **Parathormone**, also known as parathyroid hormone (PTH), is a **peptide hormone** secreted by the parathyroid glands. - It plays a crucial role in regulating **calcium and phosphate levels** in the blood. *Adrenaline* - **Adrenaline** (epinephrine) is a **catecholamine**, which is a type of amine hormone derived from the amino acid tyrosine. - It is involved in the "fight or flight" response, affecting the cardiovascular system and metabolism. *Thyroxine* - **Thyroxine** (T4) is a **thyroid hormone**, which is an amine hormone derived from tyrosine and iodine. - It is critical for regulating metabolism, growth, and development. *Cortisol* - **Cortisol** is a **steroid hormone**, synthesized from cholesterol in the adrenal cortex. - It is a glucocorticoid involved in stress response, metabolism, and immune function.

Q: A glycoprotein that promotes new attachment and increased cell proliferation is:

Fibronectin. ***Fibronectin*** - **Fibronectin** is a **glycoprotein** that plays a crucial role in **cell adhesion**, growth, migration, and differentiation by binding to integrins on the cell surface. - It promotes **new attachment** of cells to the extracellular matrix and can enhance **cell proliferation**. *Glycogen* - **Glycogen** is a branched polysaccharide of glucose that serves as the primary **storage form of glucose** in animals and fungi. - Its main function is energy storage, not cell attachment or proliferation. *Fibrin* - **Fibrin** is an insoluble protein formed from **fibrinogen** during blood coagulation, leading to the formation of a blood clot. - While it's involved in wound healing and provides a scaffold, its primary role is not to promote new cell attachment or proliferation in the general sense like fibronectin. *Glycosaminoglycan* - **Glycosaminoglycans (GAGs)** are unbranched polysaccharides that are often found covalently linked to proteins to form **proteoglycans**. - They contribute to the structural integrity of tissues, hydration, and can interact with growth factors, but their direct role in promoting new cell attachment and increased cell proliferation is less pronounced than that of fibronectin.

Q: In which of the following condition is SHBG synthesis decreased?

Increased androgen. ***Increased androgen*** - **Androgens** (e.g., testosterone, DHT) directly suppress the hepatic synthesis of **Sex Hormone-Binding Globulin (SHBG)**. - This leads to a higher proportion of **free, biologically active sex hormones** in circulation. - Conditions with excess androgens (e.g., PCOS, androgen therapy) show decreased SHBG levels. *Increased estrogen* - **Estrogens** have the opposite effect - they *increase* hepatic synthesis of **SHBG**. - This results in *lower* levels of free sex hormones in circulation. *Pregnancy* - During **pregnancy**, there is a significant *increase* in **estrogen** levels. - This surge in estrogen leads to a substantial *increase* in **SHBG** production (can increase 2-3 fold). *Hyperthyroidism* - **Hyperthyroidism** (excess thyroid hormone) *increases* hepatic protein synthesis including **SHBG**. - Conversely, hypothyroidism would decrease SHBG levels.

Q: Amino acid with its pKa value within physiological range is:

Histidine. ***Histidine*** - Histidine's side chain has a **pKa of 6.0**, which is very close to physiological pH (7.4), allowing it to act as both a **proton donor and acceptor** at physiological conditions. - This property makes histidine crucial for **enzyme catalysis** and maintaining **pH buffering** in various biological systems. *Arginine* - Arginine has a **pKa of 12.5**, which is significantly higher than physiological pH, meaning its side chain is almost always **protonated and positively charged** at physiological conditions. - Its high pKa makes it a strong base and less likely to buffer effectively within the physiological range. *Glycine* - Glycine is a **non-polar amino acid** with no ionizable side chain; its pKa values are for the **alpha-carboxyl** (around 2.34) and **alpha-amino** (around 9.60) groups. - While these groups are ionized at physiological pH, they are part of the peptide backbone in proteins and do not provide buffering capacity within the physiological range. *Lysine* - Lysine has a **pKa of 10.5**, which is also significantly higher than physiological pH, meaning its side chain is predominantly **protonated and positively charged** at this pH. - Like arginine, its high pKa makes it a strong base that does not readily buffer within the physiological pH range.

Q: The primary structure of a protein is determined by:

Amino acid sequence.. ***Amino acid sequence*** - The **primary structure** of a protein is defined as the **linear sequence of amino acids** connected by **peptide bonds**. - This sequence is determined by the **genetic code** (DNA → mRNA → protein) and dictates all higher-order structures. - The primary structure is the fundamental level of protein organization and determines the protein's unique properties and function. - Any change in the amino acid sequence (mutation) can alter protein function, as seen in diseases like sickle cell anemia (single amino acid substitution in hemoglobin). *Hydrogen bonds* - Hydrogen bonds are involved in **secondary structure** (α-helix and β-pleated sheet) and **tertiary structure** stabilization. - They form between the backbone carbonyl oxygen and amide hydrogen atoms, not determining the sequence itself. - While important for protein folding, they do not define primary structure. *Disulfide bonds* - Disulfide bonds (covalent bonds between cysteine residues) contribute to **tertiary** and **quaternary structure** stability. - They form after the protein is synthesized and help maintain the 3D conformation. - They are post-translational modifications, not determinants of the primary amino acid sequence. *Hydrophobic interactions* - Hydrophobic interactions are non-covalent forces that drive **tertiary structure** formation by causing nonpolar amino acids to cluster in the protein core. - They contribute to protein folding and stability but do not determine the sequence of amino acids. - These are weak interactions that occur after the primary structure is established.

Q: The shortest hormone is:

TRH. ***TRH*** - **TRH (Thyrotropin-Releasing Hormone)** is a **tripeptide**, meaning it is composed of only three amino acids (pyroGlu-His-Pro-NH2), making it the **shortest known hormone**. - Its primary function is to stimulate the release of **TSH (Thyroid-Stimulating Hormone)** and prolactin from the anterior pituitary. *Insulin* - **Insulin** is a **peptide hormone** composed of 51 amino acids (two chains linked by disulfide bonds). - It plays a crucial role in regulating **glucose metabolism** and is significantly larger than TRH. *Glucagon* - **Glucagon** is a **polypeptide hormone** consisting of 29 amino acids. - Its main function is to **raise blood glucose levels**, and while smaller than insulin, it is still much larger than TRH. *HCG* - **HCG (Human Chorionic Gonadotropin)** is a **glycoprotein hormone** composed of two subunits (alpha and beta) with a total of 237 amino acids. - It is involved in maintaining **pregnancy** and is a very large hormone compared to TRH.

Question 1

Who was awarded the Nobel Prize for determining the amino acid sequence of insulin?

Accepted Answer

Sanger

Answer

Banting & Macleod

Answer

Paul Berg

Answer

Charles Best

Question 2

A 60 year old lady is concerned about the wrinkles around her eyes. This is primarily due to alterations in

Accepted Answer

Collagen cross linking

Answer

Fibrillin

Answer

Collagenase

Answer

Desmosine

Question 3

Which of the following is not a peptide/protein -

Accepted Answer

Glucocorticoids

Answer

Growth hormone

Answer

PTH

Answer

Insulin

Question 4

Guanidine group is present in

Accepted Answer

Arginine

Answer

Tryptophan

Answer

Proline

Answer

Tyrosine

Question 5

Which of the following hormones is an example of a peptide hormone?

Accepted Answer

Parathormone

Answer

Adrenaline

Answer

Thyroxine

Answer

Cortisol

Question 6

A glycoprotein that promotes new attachment and increased cell proliferation is:

Accepted Answer

Fibronectin

Answer

Glycogen

Answer

Fibrin

Answer

Glycosaminoglycan

Question 7

In which of the following condition is SHBG synthesis decreased?

Accepted Answer

Increased androgen

Answer

Increased estrogen

Answer

Pregnancy

Answer

Hyperthyroidism

Question 8

Amino acid with its pKa value within physiological range is:

Accepted Answer

Histidine

Answer

Arginine

Answer

Glycine

Answer

Lysine

Question 9

The primary structure of a protein is determined by:

Accepted Answer

Amino acid sequence.

Answer

Hydrogen bonds.

Answer

Disulfide bonds.

Answer

Hydrophobic interactions.

Question 10

The shortest hormone is:

Accepted Answer

TRH

Answer

Insulin

Answer

Glucagon

Answer

HCG

Protein Structure and Function — MCQs

Protein Structure and Function — MCQs

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