BIO 150 Chapter 2

Give an example that illustrates how a molecule's shape can determine its biological function?

A molecule has a characteristic size and shape, which are key to its function in the living cell. Molecular shape is crucial: It determines how biological molecules recognize and respond to one another with specificity. The role of molecular shape in brain chemistry illustrates how biological organization leads to a match between structure and function, one of biology's unifying themes: Endorphins are signaling molecules made by the pituitary gland that bind to the receptors, relieving pain and producing euphoria during times of stress. Opiates have shapes similar to endorphins and mimic them by binding to endorphin receptors in the brain. That is why opiates and endorphins have similar effects.

What biological application can radioactive isotopes be used for?

A radioactive isotope is one in which the nucleus decays spontaneously, giving off particles and energy. When the radioactive decay leads to a change in the number of protons, it transforms the atom to an atom of a different element. Radioactive isotopes are often used as diagnostic tools in medicine.

How are two isotopes of an element similar? How are they different?

All elements of a particular element have the same number of protons, but some atoms have more neutrons than other atoms of the same element and therefore have greater mass. These different atomic forms of the same element are called isotopes of the same element. They are similar in that they have the same number of protons but a different in that they have a different number of neutrons.

How does kinetic energy differ from potential energy?

An atom's electrons vary in the amount of energy they possess. Energy is defined as the capacity to cause change for instance, by doing work. Potential energy is the energy that matter possess because of its location or structure. For example, water in a dam has potential energy because of its altitude. Kinetic energy, in contrast, is the energy that matter possess because of its motion.

Why do electrons in the first electron shell or orbital have less potential energy than electrons located in higher electron shells or orbitals?

An electron's energy level is correlated with its average distance from the nucleus.

How are elements different from compounds? How are they similar?

An element is a substance that cannot be broken down to other substances by chemical reactions. A compound is a substance consisting of two or more different elements combined in a fixed ratio. Two elements can combine to become a compound while two compounds cannot combine to become an element.

What does it mean to say an interaction has reached chemical equilibrium?

As products accumulate, collisions resulting in the reverse reaction become more frequent. Eventually, the forward and reverse reactions occur at the same rate, and the relative concentrations of products and reactants stop changing. The point at which the reactions offset one another exactly is called chemical equilibrium.

How does the atomic number of an atom differ from its mass number?

Atoms of the various elements differ in their number of subatomic particles. All atoms of a particular element have the same number of protons in their nuclei. This number of protons, which is unique to that element, is called the atomic number and is written as a subscript to the left of the symbol for the element. Atomic number= number of protons = number of electrons in a neutral atom (unless otherwise indicated, an atom is neutral in electrical charge) We can deduce the number of neutrons from a second quantity, the mass number, which is the total number of protons and neutrons in the nucleus in the neutron Mass number= number of protons + neutrons Number of neutrons= mass number - atomic number

How do non-polar covalent, polar covalent, and ionic bonds differ? What is the basis for this difference?

In a covalent bond between two atoms of the same element, the electrons are shared equally because the two atoms have the same electronegativity. Such a bond is called a non-polar covalent bond. Polar covalent bonds in contrast, is a type of chemical bond in which a pair of electrons is unequally shared between two atoms. In polar covalent bonds, the electrons are not shared equally because one atom spends more time with the electrons than the other atom. In some cases, two atoms are so unequal in their attraction for valence electrons that the more electronegative atom strips an electron completely away from its partner. The two resulting oppositely charged atoms (or molecules) are called ions. A positively charged ion is called a cation, while a negatively charged ion is called an anion. Because of their opposite charges, cations and anions attract each other; this attraction is called an ionic bond.

What are the four elements that make up 96% of living matter? Why do you think these four elements dominate biological systems?

Just four elements- oxygen (O), carbon (C), hydrogen (H), and nitrogen make up approximately 96% of living matter. Of the 92 natural elements, about 20-25% are essential elements that an organism needs to live a healthy life and reproduce. This may offer an explanation as to why these four elements dominate biological systems.

How does the atomic weight of an atom differ from its mass number?

Neutrons and protons each have a mass very close to 1 dalton, so the mass number is close to, but slightly different from, the total mass of an atom, called its atomic mass (atomic weight). For example the mass number of sodium (Na) is 23, but its atomic mass is 22.9898 daltons.

How can the atomic number and mass number of an atom be used to determine the number of neutrons it possess?

Number of Neutrons= mass number - atomic number

How do neutrons differ from protons?

Protons are electrically charged (each proton has one unit of electrical charge). A neutron is electrically neutral

How do hydrogen bonds differ from Van Der Waals interactions?

When a hydrogen atom is covalently bonded to an electronegative atom, the hydrogen atom has a partial positive charge that allows it to be attracted to a different electronegative atom nearby. This attraction between a hydrogen and an electronegative atom is called a hydrogen bond. Even a molecule with non-polar covalent bonds may have positively and negatively charged regions. Electrons are not always evenly distributed; at any instant, they may accumulate by chance in one part of a molecule or another. The results are ever-changing regions of positive and negative charge that enable all atoms and molecules to stick to one another. These are called Van der Waals interactions. They are individually weak and occur only when atoms and molecules are very close together.

Why is it that strong covalent bonds and weak bonds are both essential in living organisms?

in organisms, most of the strongest chemical bonds are covalent bonds, which link atom's to form a cells molecules.