1 Flashcards
_____ is made of combinations of _____—substances such as hydrogen or carbon that cannot be broken down or interconverted by chemical means.
Matter
Elements
The smallest particle of an element that still retains its distinctive
chemical properties is an _____.
Atom
The characteristics of substances other than pure elements—including the materials from which living cells are made—depend on which atoms they contain and the way that these
atoms are linked together in groups to form______.
Molecules
Each ____ has at its center a dense, positively charged nucleus, which
is surrounded at some distance by a cloud of negatively charged _____, held in orbit by______ to the nucleus.
Atom
Electron
electrostatic attraction
The ____ consists of two kinds of subatomic particles: ________,
which are positively charged, and ______, which are electrically neutral.
Nucleus
Protons
Neutrons
The ______ of an element is determined by the number of protons
present in its atom’s nucleus. An atom of ______ has a nucleus composed of a single proton; so hydrogen, with an atomic number of 1, is the ______.
Atomic number
Hydrogen
Lightest element
The _____ carried by each proton is exactly______and______
to the charge carried by a single electron.
Electric charge
equal and opposite
the number of ___________ surrounding the nucleus is therefore _______ to the number of positively charged protons that the nucleus contains; thus the number of______ in an atom also equals the atomic number.
negatively charged electrons
Equal
electrons
_______ have essentially the same ___ as protons.
Neutrons
Mass
an element can
exist in several physically distinguishable but chemically identical forms, called _______, each having a different number of neutrons but the same number of protons.
isotopes
The number of electrons in an
atom is equal to the number of protons, so that the atom has no____.
net charge
_______ of almost all the elements occur naturally, including some that are unstable—and thus _______.
Multiple isotopes
radioactive
The_________ of an atom, or the ___________ of a molecule,
is its mass relative to the mass of a __________.
atomic weight
molecular weight
hydrogen atom
The mass of an atom or a molecule is generally specified in ______, one dalton being an atomic mass unit essentially equal to the mass of a hydrogen atom.
daltons
An individual carbon atom is roughly_______ in diameter, so it would take about ______of them, laid out in a straight line, to span a ______.
0.2 nm
5 million
millimeter
One proton or neutron weighs approximately_______.
1/(6 × 1023) gram.
This huge number, called _________, allows us to relate everyday quantities of chemicals to numbers of individual atoms or molecules. If
a substance has a molecular weight of _______of the substance will
contain_______.
Avogadro’s number
X, X grams
6 × 1023 molecules
The concept of_____ is used widely in chemistry as a way to represent the number of molecules that are available to participate in chemical reactions.
mole
there is a strict limit to the number of electrons that can be accommodated in an orbit of a given type, a so-
called_________.
electron shell
This electron exchange can be
achieved either by __________ from one atom to another or by _________ between two atoms. These two strategies generate the two types of ______ that can bind atoms strongly to one another
transferring electrons
sharing electrons
chemical bonds
an ________ is formed when electrons are donated by one atom to another
ionic bond
a ________ is formed when two atoms share a pair of electrons
covalent bond
Atoms can attain a more
stable arrangement of electrons in their_______ by interacting with one another.
outermost shell
The number of protons in
an atom determines its ______.
atomic number
An atom consists of a nucleus
surrounded by an _______.
electron cloud
A ______ is a cluster of atoms held together by ______, in
which electrons are_____ rather than transferred between atoms.
molecule
covalent bonds
shared
The________ form a cloud of negative charge that is densest between the two positively charged nuclei.
shared electrons
The attractive and repulsive forces are precisely in balance when these nuclei are separated by a characteristic distance, called the______.
bond length
Most covalent bonds involve the sharing of two electrons, one donated by each participating atom; these are called_______.
single bonds
________are shorter and stronger than single bonds and have a characteristic effect on the geometry of molecules containing them.
Double bonds
A _______ between two atoms generally allows the rotation of one part of a molecule relative to the other around the bond axis.
single covalent bond
A _________prevents
such rotation, producing a more rigid and _____________ of
atoms.
double bond
less flexible arrangement
Covalent bonds in which the electrons are shared unequally in
this way are known as________.
polar covalent bonds
A_______ (in the electrical sense) is one in which the positive charge is concentrated toward one atom in the molecule (the positive pole) and the negative charge is concentrated toward another atom (the negative pole).
polar structure
The tendency of an atom to attract electrons is called its_______, a property that was first described by the chemist_______.
electronegativity
Linus Pauling
________ is measured by the amount of energy that must be supplied to break the bond, usually expressed in units of either______ or_______.
Bond strength
kilocalories per mole (kcal/mole)
kilojoules per mole (kJ/mole)
A _______ is the amount of energy needed to raise the temperature of ________. Thus, if 1 kilocalorie of energy must be supplied to break 6 × 1023 bonds of a specific type (that is, 1 mole of these bonds), then the strength of that bond is _______.
kilocalorie
1 liter of water by 1°C
1 kcal/mole
________ is equal to about
4.2 kJ, which is the unit of energy universally employed by physical scientists and, increasingly, by cell biologists as well.
One kilocalorie
covalent bonds are normally broken only during specific chemical reactions that are carefully
controlled by highly specialized protein catalysts called_______.
enzymes
The resulting bonds, called _____, are usually formed between atoms that can attain a completely filled outer shell most easily by _______ electrons to—or ______ electrons from—another atom, rather than by sharing them.
ionic bonds
donating
accepting
Positive ions are called ______
and negative ions are called ______.
cations
anions
In aqueous solution, ionic bonds are ________ than the covalent bonds that hold atoms together in molecules.
10–100 times weaker
the electrical attraction between
them can establish a weak bond called a_______. These bonds are ______ than covalent bonds and are easily broken by random thermal motions.
hydrogen bond
much weaker
______ are not limited to water. In general, a hydrogen bond
can form whenever a positively charged H atom held in one molecule by a polar covalent linkage comes close to a negatively charged atom—
typically an oxygen or a nitrogen—belonging to another molecule
Hydrogen bonds
substances that contain polar bonds and can form hydrogen bonds also mix well with water. Such substances are termed _________, meaning that they are ________. A large proportion of the molecules in the aqueous environment of a cell fall into this category, including sugars, DNA, RNA, and a majority of proteins.
hydrophilic
“water-loving”
________molecules, by contrast, are uncharged and form few or no hydrogen bonds, and they do not dissolve in water.
Hydrophobic (“water-fearing”)
________ are individually quite weak, their energies can sum to create an effective force between two molecules.
noncovalent bonds
What are the noncovalent bonds
hydrogen bonds
Electrostatic attractions
van der Waals attraction
hydrophobic force
_______ are strongest when the atoms involved are fully charged, as are Na+ and Cl– ions. But a ________ can occur between molecules that contain polar covalent bonds.
Electrostatic attractions
weaker electrostatic attraction
__________, comes into play when any two atoms approach each other closely. These nonspecific interactions spring from fluctuations in the distribution of electrons in every atom, which can generate a transient attraction when the atoms are in very close proximity. These weak attractions occur in all types of molecules, even those that are nonpolar and cannot form ionic
or hydrogen bonds.
van der Waals attraction
a _______ is generated by a pushing of nonpolar surfaces out of the hydrogen-bonded water network, where they would otherwise physically interfere with the highly favorable interactions between water molecules.
hydrophobic force
Hydrophobic forces play an important part in promoting molecular interactions—in particular, in building _______, which are constructed largely from _____ with long hydrocarbon tails.
cell membranes
lipid molecules
Substances that release protons when they dissolve in water, thus forming H3O+, are termed ______.
Molecules that accept protons when dissolved in water are called ______.
acids
bases
The interior of a cell is kept close to neutral by the presence of _______:
mixtures of weak acids and bases that will adjust proton concentrations around pH 7 by releasing protons (acids) or taking them up (bases) when ever the pH changes.
buffers
______ is outstanding among all the elements in its ability to form
large molecules.
Carbon
carbon-containing compounds are called _______. By contrast, all other molecules, including water, are said to be ______.
organic molecules
inorganic
The small organic molecules of the cell are carbon compounds with
molecular weights in the range _______ or so carbon atoms.
100–1000 that contain up to 30
Some are used as ________ to construct the cell’s polymeric ________—its proteins, nucleic acids, and large polysaccharides.
monomer subunits
macromolecules
What are the four main families of small organic molecules in cells.
Sugars, fatty acids, amino
acids, and nucleotides
Sets of molecules with the same chemical formula but different structures are called _____, and mirror-image pairs of such molecules are called______.
isomers
optical isomers
_______ can be linked by covalent bonds—called ________—to form larger ________.
Monosaccharides
glycosidic bonds
carbohydrates
________ linked
together make a ______, such as sucrose, which is composed of
a _____ and a _____ unit.
Two monosaccharides
disaccharide
glucose
fructose
Larger sugar polymers range from the _______ (trisaccharides, tetrasaccharides, and so on) up to
giant _______, which can contain thousands of _________ (monomers).
oligosaccharides
polysaccharides
monosaccharide subunits
A bond is formed between an –OH group on one sugar and an –OH group on another by a ________, in which a molecule of water is expelled as the bond is formed.
condensation reaction
The bonds created by all of these condensation reactions can
be broken by the reverse process of______, in which a molecule of
water is consumed.
hydrolysis
________, which synthesize larger molecules from smaller subunits, are energetically unfavorable;__________, which break down larger molecules
into smaller subunits, are energetically favorable.
condensation reactions
hydrolysis reactions
The ________ has a central role as an energy source for cells. It is broken down to smaller molecules in a series of reactions, releasing energy that the cell can harness to do useful work.
monosaccharide glucose
Cells use simple polysaccharides composed only of glucose units—principally ______ in animals and _____ in plants—as long-term stores of glucose, held in reserve for energy production.
glycogen
starch
The most abundant organic molecule on Earth—the _____ that forms
plant cell walls—is a polysaccharide of glucose.
cellulose
Another extraordinarily abundant organic substance, the ____ of insect exoskeletons and fungal cell walls, is also a polysaccharide.
chitin
Smaller oligosaccharides can be covalently linked to proteins to form ______, or to lipids to form _____, which are both found in cell membranes.
glycoproteins
glycolipids
A ______ molecule, such as _____, has two chemically distinct regions. One is a long ________, which is hydrophobic and not
very reactive chemically. The other is a _________, which behaves as an acid (carboxylic acid):
fatty acid
palmitic acid
Hydrocarbon chain
Carboxyl group
Molecules—such as fatty acids—that possess both hydrophobic
and hydrophilic regions are termed _______.
amphipathic
The hydrocarbon tail of palmitic acid is _______: it has _______
between its carbon atoms and contains the maximum possible number of hydrogens.
saturated
no double bonds
Some other fatty acids, such as oleic acid, have _________, with one or more double bonds along their length.
unsaturated tails
Fatty acids have both
________ and _______ components.
hydrophobic and hydrophilic
Fatty acids are stored in the _____ of many cells
in the form of fat droplets composed of _______ compounds made of three fatty acid chains covalently joined to a ______.
cytoplasm
triacylglycerol molecules
glycerol molecule
________ are the animal fats found in meat, butter, and cream, and the plant oils such as corn oil and olive oil.
Triacylglycerols
______ are loosely defined as molecules that are insoluble in
water but soluble in fat and organic solvents such as _______. They typically contain ________, as in the fatty acids, or multiple linked aromatic rings, as in the ______.
Lipids
benzene
long hydrocarbon chains
steroids
The most unique function of fatty acids is in the establishment of the _____, the structure that forms the basis for all cell membranes.
lipid bilayer
_____ are small organic molecules with one defining property: they all possess a carboxylic acid group and an amino group, both attached
to a ________ atom.
Amino acids
central α-carbon
Cells use amino acids to build _______—polymers made of amino acids, which are joined head-to-tail in a long chain that folds up into a three-dimensional structure that is unique to each type of protein.
proteins
The covalent bond between two adjacent amino acids in a protein chain is called a ______, and the resulting chain of amino acids is therefore also known as a
________.
peptide bond
polypeptide
Sugars Are both Energy Sources and Subunits of _______
Polysaccharides
Fatty Acid Chains Are Components of _________.
Cell Membranes
Amino Acids Are the Subunits of ________.
Proteins
Nucleotides Are the Subunits of ___ and ___.
DNA and RNA
DNA and RNA are built from subunits called ________.
nucleotides
Nucleotides
consist of a ________-containing ring compound linked to a ________ that has one or more ________ groups attached to it.
Nitrogen
five-carbon sugar
phosphate
The sugar can be either ribose or deoxyribose. Nucleotides
containing ribose are known as ________, and those containing deoxyribose are known as _________.
ribonucleotides
deoxyribonucleotides
There is a strong family resemblance between the different nucleotide bases. Cytosine (C), thymine (T), and uracil (U) are called _______, because they all derive from a six-membered pyrimidine ring; guanine (G) and adenine (A) are _______, which bear a second, A five-membered ring fused to the six-membered ring.
pyrimidines
purines
A base plus its sugar (without any phosphate group attached) is called a ________.
nucleoside
the _________ known as ____________, or ____, participates in the ______ in hundreds of metabolic reactions.
ribonucleoside triphosphate
adenosine triphosphate
ATP
transfer of energy
_____ is formed
through reactions that are driven by the energy released from the break
down of foodstuffs. Its three phosphates are linked in series by two ______________.
ATP
phosphoanhydride bonds
Rupture of these phosphate
bonds by hydrolysis releases large amounts of useful energy, also known as _________.
free energy
Nucleotides also have a fundamental role in the storage and retrieval of
biological information. They serve as ________ for the construction of ________—long polymers in which nucleotide subunits are
linked by the formation of covalent __________ between the
phosphate group attached to the sugar of one nucleotide and a hydroxyl group on the sugar of the next nucleotide.
building blocks
nucleic acids
phosphodiester bonds
Polysaccharides, proteins, and nucleic acids are made from _________.
monomeric subunits
