Protein Functions: Fibrous and Globular Proteins

Flashcards covering the structure, function, associated diseases, and regulatory mechanisms of fibrous proteins (collagen, keratin) and globular proteins (hemoglobin, myoglobin, albumin) from the lecture notes.

What is the most abundant protein in the human body?

Collagen

What type of protein is collagen?

A fibrous protein

What characteristic motif does collagen contain in its triple helical region?

GXY motif

Where is collagen translated and matured within the cell?

Translated on rough endoplasmic reticulum and matures in Golgi

What initiates the formation of the triple helix in procollagen?

The C-terminal propeptide in the rough ER

How are collagen fibrils primarily stabilized?

By lysin crosslinking (covalent bonds) and additional proteins

What medical condition results from a lack of vitamin C, leading to reduced proline hydroxylation in collagen?

Scurvy

What inherited disorder is caused by mutations in type I collagen, resulting in weak bones and irregular connective tissue?

Osteogenesis Imperfecta

What are keratins?

Extracellular insoluble proteins (hair and nails) and intracellular fibrous proteins (part of the cytoskeleton)

What is the tertiary structure of keratin?

α-helical

What condition results from mutations in epidermal keratin genes KRT5 or KRT14, making skin prone to blistering?

Epidermolysis bullosa

What is the major form of human adult hemoglobin (HbA1) composed of?

Two α and two β chains (α2β2)

What is the main function of hemoglobin in red blood cells?

To deliver O2 from lungs to peripheral tissues

How does hemoglobin's quaternary structure compare to myoglobin's?

Hemoglobin has a unique quaternary structure, while myoglobin is monomeric

Where is myoglobin primarily expressed, and what is its role?

Highest expression in striated muscle and cardiomyocytes; transports O2 from capillaries to mitochondria

How does the oxygen affinity of myoglobin compare to hemoglobin?

Myoglobin has a higher O2 affinity than hemoglobin

What type of oxygen binding behavior does hemoglobin exhibit?

Cooperative binding of oxygen, indicated by sigmoidal behavior

What are the two conformational states of hemoglobin related to oxygen binding?

T (tense) state for deoxyhemoglobin and R (relaxed) state for oxyhemoglobin

How does low pH affect hemoglobin's affinity for oxygen?

Low pH reduces Hb affinity to O2

What molecule produced in RBCs reduces hemoglobin's affinity to O2?

2,3-bisphosphoglycerate (2,3-BPG)

What impact does carbon monoxide (CO) have on hemoglobin?

CO binds Hb with about 240 times greater O2 affinity than O2, forming carboxyhemoglobin (COHb)

How is CO2 transported from peripheral cells to the lungs?

Primarily as bicarbonate

What is the mutation responsible for HbS (sickle cell hemoglobin) and its biochemical change?

Glu-6 β → Val mutation, causing cellular crystallization of oxygenated protein

What benefit do individuals heterozygous for HbS gain?

They are resistant to malaria and asymptomatic under normal conditions

What is the most abundant protein in blood serum?

Albumin

What type of protein is albumin?

A globular protein

What are the main functions of albumin?

Antioxidant, maintains oncotic pressure, and binds/transports fatty acids, hormones, and other metabolites

What conditions can lead to a reduction in serum albumin levels?

Hepatic disease, malnutrition (e.g., Kwashiorkor), renal loss (chronic kidney disease), burns, and sepsis