Protein Functin

• A molecule that binds to a protein is called a ligan
• Ligand binding is often coupled to conformational changes
• Hemoglobin and myoglobin both use heme to bind
• In myoglobin, one oxygen binds to iron, and the other hydrogen bonds with histidine
• Hemoglobin has 4 subunits and is a tetromer
• myoglobin is a monomer and has one subunit
• myoglobin lacks a quaternary structure
• Ion pairs stabilize the T-state of deoxy-hemoglobin
• For effective transport of oxygen, affinity must vary with pO2
• conformational change of the T-and R-state is triggered by oxygen binding
• cooperativity is positive homotropic regulation
• CO2 binds to the N-terminus of hemoglobin and becomes a carboxylate
• the formation of a carboxylate yields a proton that can contribute to the Bohr effect
• the carbamate formed during CO2 export forms salt bridges that stabilize the T-state
• 2,3-Bisphosphoglycerate regulates O2 binding
• 2,3-Biphospholycerate is a negative heterotropic regulator of hemoglobin
• The small, negatively charged 2,3-BSC binds to the positively charged central cavity of hemoglobin and stabilizes the T-state
• 2,3-BPG allows for O2 release in the tissues and adaptation to changes in altitude
• The cellular immune system destroys infected host cells with the help of macrophages, killer T cells, and inflammatory T cells
• The humoral immune system targets extracellular pathogens, recognizes foreign proteins, and makes soluble antibodies
• key players in the humoral immune system include B-lymphocytes and helper-T cells
• antibodies are composed of two light chains and two heavy chains
• light chains have one constant and one variable domain
• heavy chains have three constant and one variable domain
• variable domains of each chain make up the antigen binding site and are hypervariable, which confers antigen specificity
• antigens bind to the Fab region
• the Fc region binds receptors on immune cells
• myosin is composed of two heads and two supercoiled alpha helices
• myosin has two heavy chains and four light chains
• F-actin is composed of G-actin subunits
• myosin is anchored to the M disk
• actin is anchored to the Z-disk
• Myosin thick filaments slide along actin thin filaments
• filament length does not change
• sarcomere length decreases because overlap increases
• actomyosin cycle is composed of steps including ATP binding causing dissociation, ATP hydrolysis causing conformational change, myosin head attaching to actin filament releasing Pi, and power stroke, which causes a conformational change that releases ATP
• muscle contraction is regulated by the release of Ca2_