# Bio tutorial questions

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### The mass number of an atom is 15, and its atomic number is 7. The atom probably has

8 neutrons in the nucleus. The atomic number (7) gives the number of protons, and the mass number is the number of protons plus neutrons

### Which statement is true of atoms?

Electrons determine the atom's size. With electrons on the surface, atoms repel one another when they come too close. Thus, electrons determine the space that an atom occupies.

### Dr. Jones says an atom has 3 electrons in the first shell and four electrons in the second shell. Someone should tell Dr. Jones that

the first shell shouldn't have 3 electrons.The first shell can only have 0, 1, or 2 electrons

### Which statement is true of the energy levels of electrons in shells

The valence shell has higher energy than other occupied shells. The outer occupied shell is the valence shell, and outer shells hold electrons at higher energy than inner shells

### An orbital is dumbbell-shaped. Which statement is most likely true

Only the second and higher shells have dumbbell-shaped orbitals. Each orbital can hold just two electrons, and the electrons move in unknown paths such that both electrons can be in one lobe at one moment, and in opposite lobes at the next moment

### Two atoms always represent the same element if they have

the same number of protons. The number of protons defines a chemical element

### An atom has 6 electrons, 6 protons, and 6 neutrons. You can tell that this atom belongs to the element _____ because _____________________

C; it has 6 protons.

### An atom has 8 protons, 8 neutrons, and 8 electrons. Another isotope of the same element might have

10 neutrons. Isotopes have the same number of protons; different numbers of neutrons

### Radioactive decay is likely to occur when

an atom has too many neutrons. The atomic nucleus becomes unstable if the ratio of protons to neutrons is too far from unity

### Which model most accurately represents the current view of the structure of the atom

probability model

Protons

### Covalent bonds hold atoms together because they

fill shells without giving atoms much charge, bring electrons closer to protons

4, 1, 2, 3

### An atom's atomic number is 7. Its valence is most likely

3. The neutral atom has 7 electrons. Two electrons fill the first shell, and 5 go into the second (valence) shell. The atom needs 3 more electrons to fill the valence shell.

### By making two covalent bonds, an O atom (with 8 protons) fills its valence shell. Why does the atom's charge stay close to zero

Shared electrons aren't always near oxygen

### In a double covalent bond, a carbon atom shares

electrons in 2 orbitals

### Two C atoms form a double bond. Each C is bound to two H atoms. Which statement is true

All the atoms lie in a plane

### Partial charges occur when

atoms share electrons unequally

2 electrons

### Which answer helps to explain why carbon atoms tend to make 4 covalent bonds?

The valence shell needs 8 electrons.

1

O,N,C,H

### Dr. Haxton says the O-O bond is polar and the C-C bond is nonpolar. A good student would say

Wrong again, Ralph. Both bonds are nonpolar

O-H

H-N

### Which item is based on differences in electronegativity between atoms

the organization of phospholipids into bilayers, The pairing of bases in DNA, The tertiary folding of proteins

### Compared to covalent bonds, ionic bonds

rely much less on electron-sharing

### A cation with two units of charge has 10 neutrons and 8 protons. The ion also has

6 electrons. The part with the two units of + charge is a cation; the part with the unit of - charge is an anion

True

electron-sharing

### When chemists and biologists want to show how atoms are bonded in a molecule, they usually use a

structural formula

### Polar attractions are

forces between atoms with partial charges, weaker than covalent bonds, important because they are numerous.

### Hydrogen bonds

can form between H and N

### Dr. Haxton told his class that a water molecule can make 4 hydrogen bonds, all of them in the same plane as the three atoms. What would a good student reply

Wrong! Two hydrogen bonds are not in the plane of the atoms

### Which statement is part of the explanation for water's high cohesion

Oxygen has four valence orbitals, Oxygen is much more electronegative than hydrogen.

### Despite its cohesion, water can flow because

hydrogen bonds break and re-form rapidly

### Which answer helps to explain how many hydrogen bonds a water molecule can form

Oxygen's valence shell has four orbitals

### Which statement must be mentioned in explaining why amphipathic molecules line up at a water surface

Polar groups attract one another

### Dissolving is best described as

a mingling of molecules and/or ions.

### Water is a source of ______________ for chemical reactions in cells

hydrogen and oxygen atoms

### Which statement is true of water's tensile strength?

It results from hydrogen bonding, It helps to pull water through plants, It involves both cohesion and adhesion

### Water has surface tension because ...

hydrogen bonds between surface water molecules resist being stretched.

### Which of the following helps most to explain why water has a high specific heat?

A water molecule can make 4 hydrogen bonds.

### Primary Protein Structure

sequence of amino acids in a protein

### Secondary Structure

describes the alpha-helices and beta sheets that are formed by hydrogen bonding between backbone atoms located near eachother in the poly peptide chain

### Tertiary Structure

a protein folds into a compact 3D shape stabilized by interactions between side chain R-groups of amino acids

### Quaternary

result of 2 or more protein subunits assembling to form a larger biologically active protein complex

proteins

an oxygen

### what part of an amino acid is always acidic

Carboxyl Functional group

Nucleotides

True

amino acids

peptide bonds

hydrogen bonds

peptide bonds

### When is an enzyme denatured

when it loses it's native conformation, and it's biological activity

### An enzyme is considered a catalyst because

speeds up chemical reactions without being used up

### an enzyme is considred specific because

it's ability to recognize the shape of a particular molecule

### A cofactor

binds to an enzyme and plays a role in catalysis

### Complex

When properly aligned, and enzyme and a substrate form an enzyme-substrate

### A substrate binds to the enzyme at the

active site, where the reaction occurs.

substrate

### Competitive inhibitor

has a structure that is so similar to a substrate that it can bond to the enzyme just like a substrate

### Non competitive inhibitor

binds to a site on the enzyme that is not the active site

### Irreversible inhibitor

forms a covalent bond with an amino acid side group within the active site, which prevents that substrate from entering the active site, or prevents catalytic activity

active site

### when the non competitive inhibitor is bonded to the enzyme

the shape of the enzyme is distorted

substrate

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