Question

This is refering to Cell Biology:

Discuss how the common functions of proteins contribute to the different properties of a living cell

Discuss how covalent and non-covalent interactions contribute to the 3D conformation of a protein

How do the properties of the selectively-permeable cell membrane dictate which types of molecules cross the cell membrane?

Answer 1

Answer 1)

Protein functions

Function	Description	Example
Antibody	Antibodies bind to specific foreign particles, such as viruses and bacteria, to help protect the body.	Immunoglobulin G (IgG)
Enzyme	Enzymes carry out almost all of the thousands of chemical reactions that take place in cells. They also assist with the formation of new molecules by reading the genetic information stored in DNA.	Phenylalaninehydroxylase
Messenger	Messenger proteins, such as some types of hormones, transmit signals to coordinate biological processes between different cells, tissues, and organs.	Growthhormone
Structural component	These proteins provide structure and support for cells. On a larger scale, they also allow the body to move.	Actin
Transport/storage	These proteins bind and carry atoms and small molecules within cells and throughout the body.	Ferritin

ANSWER 2) Non covalent Interactions:

a)Van der Waals interactions: 'van der Waals interaction' are cohesive (attraction between like), adhesive (attraction between unlike) and/or repulsive forces between molecules. The 'van der Waals interaction' is not sufficiently informative or descriptive or specific. Here we avoid the term "van der Waals interaction" because it is not well-defined and does not decompose the interactions in a physically meaningful way.

b)Electrostatic interactions:

Electrostatic interactions are between and among cations and anions, species with formal charge of ...-2,-1,+1,+2... Electrostatic interactions can be either attractive or repulsive, depending on the signs of the charges. Like charges repel. Unlike charges attract.

c) Ion Pairs in Proteins: Ion Pairs, sometimes called Salt Bridges, are formed when the charged group of a cationic amino acid (like lysine or arginine) is around 3.0 to 5.0 Å from the charged group of an anionic amino acid (like aspartate or glutamate). The charged groups in an ion pair are generally linked by hydrogen bonds, in addition to electrostatic interactions.

d) Dipolar Interactions:

-Electronegativities:Electrons are not shared equally in a molecule with unlike atoms. The tendency of any atom to pull electrons towards itself, and away from other atoms, is characterized by a quantity called electronegativity. Fluorine is the most electronegative atom (4.0) and cesium is the least electronegative (0.7).

-Partial Charges:In a molecule composed of atoms of various electronegativities, the atoms with lowest (smallest) electronegativities hold partial positive charges (δ+) and the atoms with the greatest electronegativities hold partial negative charges (δ-). A greater difference in the electronegativities of two bonded atoms causes the bond between them to be more polar, and the partial charges on the atoms to be larger in magnitude.

-Dipole moments: The extent of charge separation within a molecule is characterized by the dipole moment μ. A dipole moment is determined by the magnitudes of the partial charges and by the distances between them.

Answer c)

Various types of transmembrane proteins provide facilitated diffusion or active transport for molecules that are not passively diffuse through the cell membrane. Primary active transport requires the cell to expend energy to move molecules through the cell membrane. Diffusion requires no energy from the cell to do so.

- Concentration: The primary determinant of whether a molecule will diffuse across a cell membrane is the concentration of the molecule on each side of the cell membrane. For example, the extracellular concentration of oxygen is higher than the intracellular concentration, which is why oxygen diffuses into the cell. Carbon dioxide diffuses out for similar reasons.

-Charge and polarity: An ion is an atom or molecule that has an outright charge, due to an imbalance between the number of protons and electrons. Polarity is an uneven distribution of charge across a molecule, with some partially positive and negative regions. Charged and polarized molecules dissolve in water, whereas uncharged molecules dissolve in lipids. The lipid tails in the cell membrane prevent charged and polarized molecules from diffusing through the cell membrane. However, some cells actively maintain an electric potential on either side of the cell membrane that can attract or repel ions and polarized molecules.

-Size:Some molecules are small enough to slip past the lipid tails, even if the molecules are polarized. For example, water is polarized, but small enough to freely diffuse across the cell membrane. This is also true of carbon dioxide, the byproduct of cellular metabolism. Oxygen molecules have no polarity and are also small enough to easily diffuse into the cell. Sugar molecules, which contain five or more carbon atoms, are both polar and too large to diffuse through the cell membrane and must travel through transmembrane proteins.