Chapter 2: Chemical Components of Cells Flashcards
chemistry of life is based overwhelmingly on carbon compounds, the study of which is known as _________.
organic chemistry
chemistry of life depends almost exclusively on chemical reactions that take place in _______.
watery, or aqueous, environment
molecules made of many chemical subunits linked end-to- end.
polymers
The ________ of an atom, or the _________ of a molecule, is its mass relative to the mass of a hydrogen atom.
atomic weight or molecular weight
An individual carbon atom is roughly ____ in diameter.
0.2 nm
allows us to relate everyday quantities of chemicals to numbers of individual atoms or molecules.
Avogadro’s number
Living things, however, are made of only a small selection of these elements:
- Carbon
- Hydrogen
- Nitrogen
- Oxygen (constitute 96% of any organism’s weight)
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
Matter is made of combinations of _______.
elements
substances such as hydro- gen or carbon that cannot be broken down or interconverted by chemical means.
elements
The smallest particle of an element that still retains its distinctive chemical properties is an ______.
atom
Each atom has at its center a dense, positively charged nucleus, which is surrounded at some distance by a cloud of negatively charged _____.
electron
held in orbit by electrostatic attraction to the nucleus
electron
The nucleus consists of two kinds of subatomic particles:
protons and neutrons
are positively charged
protons
are electrically neutral
neutrons
The ________ of an element is determined by the number of protons present in its atom’s nucleus.
atomic number
The electric charge carried by each proton is exactly __________ to the charge carried by a single electron.
equal and opposite
the number of ______ in an atom also equals the atomic number.
electrons
_________ have essentially the same mass as protons.
Neutrons
Neutrons contribute to the __________ of the nucleus: if there are too many or too few, the nucleus may disintegrate by radioactive decay.
structural stability
an element can exist in several physically distinguishable but chemically identical forms, called ______.
isotopes
A ________ is X grams of a substance, where X is the molecular weight of the substance.
mole
A mole will contain
______ molecules of the substance.
6 × 10^23
1 mole of carbon weighs _____.
12 g
1 mole of glucose weighs ______.
180 g
1 mole of sodium chloride weighs ____.
58 g
Multiple isotopes of almost all the elements occur ______.
naturally
The mass of an atom or a molecule is generally specified in ______.
daltons
There are about ___ naturally occurring elements, each differing from the others in the number of protons and electrons in its atoms.
90
(true or false) The Outermost Electrons Determine How Atoms Interact
True
______ are in continuous motion around the nucleus, but motions on this submicroscopic scale obey different laws from those we are familiar with in everyday life.
Electrons
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
The electrons closest on average to the positively charged nucleus are attracted ______ to it and occupy the inner, most tightly bound shell.
most strongly
This innermost shell can hold a maximum of ________.
two electrons.
The arrangement of electrons in an atom is most _______ when all the electrons are in the most tightly bound states that are possible for them.
stable
two types of chemical bonds:
ionic bonds and covalent bonds
is formed when electrons are donated by one atom to another
an ionic bond
is formed when two atoms share a pair of electrons
a covalent bond
a cluster of atoms held together by covalent bonds.
molecule
(true or false) The hydrogen molecule is held together by a covalent
bond.
true
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
In living organisms, covalent bonds are normally broken only during specific chemical reactions that are carefully controlled by highly specialized protein catalysts called _____.
enzymes
are usually formed between atoms that can attain a completely filled outer shell most easily by donating electrons to—or accepting electrons from—another atom, rather than by sharing them.
ionic bonds
Positive ions
cations
Negative ions
anions
In aqueous solution, ionic bonds are _______ weaker than the covalent bonds that hold atoms together in molecules.
10–100 times
When a positively charged region of one water molecule comes close to a negatively charged region of a second water molecule, the electrical attraction between them can establish a weak bond called a ________.
hydrogen bond
These bonds are much weaker than covalent bonds and are easily broken by random thermal motions.
hydrogen bonds
Such substances are termed _____, meaning that they are “water-loving.”
hydrophilic
molecules in the aqueous environment of a cell fall into the hydrophilic category:
- sugars
- DNA
- RNA
- majority of proteins
“water-fearing”
Hydrophobic
are uncharged and form few or no hydrogen bonds, and they do not dissolve in water.
Hydrophobic
are strongest when the atoms involved are fully charged, as are Na+ and Cl+ ions.
Electrostatic attractions
a weaker electrostatic attraction can occur between molecules that contain ________.
polar covalent bonds
A third type of noncovalent bond, called a ______, comes into play when any two atoms approach each other closely.
van der Waals attraction
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.
van der Waals attraction
In an aqueous environment, 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 cell membranes, which are constructed largely from __________ with long hydrocarbon tails.
lipid molecules
Length and Strength of COVALENT
- 0.10 nm
- 377 [90] kJ/mole (in vacuum and water)
Length and Strength of Noncovalent: IONIC BOND
- 0.25 nm
- 335 [80] kJ/mole (in vacuum)
- 12.6 [3] kJ/mole (in water)
Length and Strength of Noncovalent: HYDROGEN BOND
- 0.17 nm
- 16.7 [4] kJ/mole (in vacuum)
- 4.2 [1] kJ/mole (in water)
Length and Strength of Noncovalent: VAN DER WAALS
- 0.35 nm
- 0.4 [0.1] kJ/mole (in vacuum)
- 0.4 [0.1] kJ/mole (in water)
proton can dissociate from its original partner and associate instead with the oxygen atom of the water molecule, generating a _____.
hydronium ion
Substances that release protons when they dissolve in water, thus forming H3O+, are termed ______.
acids.
logarithmic scale
pH scale
Pure water has a pH of ___ and is thus neutral—that is, neither acidic (pH <7) nor basic (pH >7).
7.0
Molecules that accept protons when dissolved in water are called _____.
bases
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
carbon-containing compounds
organic molecules
all other molecules, including water, are said to be ______.
inorganic molecules
The small organic molecules of the cell are carbon compounds with molecular weights in the range _________ that contain up to 30 or so carbon atoms.
100–1000
Some are used as _______ subunits to construct the cell’s polymeric macromolecules
monomer
its proteins, nucleic acids, and large polysaccharides.
macromolecules
Nearly ______ different kinds of small organic molecules have been detected in the well-studied bacterium Escherichia coli.
4000
Broadly speaking, cells contain four major families of small organic molecules:
the sugars, the
fatty acids, the amino acids, and the nucleotides
small organic building blocks of the cell —> larger organic molecules of the cell
SUGARS –> POLYSACCHARIDES, GLYCOGEN, AND STARCH (IN PLANTS)
FATTY ACIDS –> FATS AND MEMBRANE LIPIDS
AMINO ACIDS –> PROTEINS
NUCLEOTIDES __> NUCLEIC ACIDS
The simplest sugars.
monosaccharides
Sets of molecules with the same chemical formula but different structures are called ____.
isomers
mirror-image pairs of such molecules are called
optical isomers
Monosaccharides can be linked by covalent bonds—called ________ —to form larger carbohydrates.
glycosidic bonds
Two monosaccharides linked together make a
disaccharide
Larger sugar polymers range from the _______ (trisaccharides, tetrasaccharides, and so on) up to giant _____, which can contain thousands of monosaccharide subunits (monomers).
- oligosaccharides
- polysaccharides
is used to refer to molecules made of a small number of monomers, typically 2 to 10 in the case of oligosaccharides.
oligo
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
The monosaccharide ____ has a central role as an energy source for cells.
glucose
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
chitin
Smaller oligosaccharides can be covalently linked to proteins to form ______.
glycoproteins,
A fatty acid molecule, such as ______, has two chemically distinct regions.
palmitic acid
The hydrocarbon tail of palmitic acid is _______: it has no double bonds between its carbon atoms and contains the maximum possible number of hydrogens.
saturated
Molecules—such as fatty acids—that possess both hydrophobic and hydrophilic regions are termed _______.
amphipathic
Some other fatty acids, such as oleic acid, have _______ tails, with one or more double bonds along their length.
unsaturated
Fatty acids are stored in the cytoplasm of many cells in the form of fat droplets composed of ________ molecules.
triacylglycerol
compounds made of three fatty acid chains covalently joined to a glycerol molecule
triacylglycerol
loosely defined as molecules that are insoluble in water but soluble in fat and organic solvents such as benzene
lipids
the structure that forms the basis for all cell membranes
lipid bilayer
These thin sheets, which enclose all cells and surround their internal organelles, are composed largely of _______.
phospholipids
are small organic molecules with one defining property: they all possess a carboxylic acid group and an amino group, both attached to a central α-carbon atom
Amino acids
Cells use amino acids to build
proteins
polymers made of amino acids
proteins
The covalent bond between two adjacent amino acids in a protein chain is called a
peptide bond
the resulting chain of amino acids is therefore also known as a
polypeptide
are formed by condensation reactions that link one amino acid to the next
Peptide bonds
Nucleotides containing ribose are known as _____, and those containing deoxyribose are known as ______.
- ribonucleotides
- deoxyribonucleotides.
participates in the transfer of energy in hundreds of metabolic reactions.
adenosine triphosphate, or ATP
is formed through reactions that are driven by the energy released from the break- down of foodstuffs
ATP
long polymers in which nucleotide subunits are linked by the formation of covalent phosphodiester bonds
nucleic acid
are constructed simply by covalently linking small organic monomers, or subunits, into long chains, or polymers
macromolecules
The vast majority of the dry mass of a cell consists of macromolecules
mainly polysaccharides, proteins, and nucleic acids (DNA and RNA)
forms when two atoms come very close together and share one or more of their outer-shell electrons.
covalent bond
Carbon and hydrogen together make stable compounds (or groups) called
hydrocarbons
These are nonpolar, do not form hydrogen bonds, and are generally insoluble in water.
C-H Compounds
the bonding electrons move within the molecule, stabilizing the structure by a phenomenon called ______.
resonance
The –OH is called a ______ group.
hydroxyl
The C = O is called a _____ group.
carbonyl
The –COOH is called a __________ group.
carboxyl
are formed by combining an acid and an alcohol.
Esters
are formed by combining an acid and an amine.
amides
Inorganic phosphate is a stable ion formed from
phosphoric acid
can form between a phosphate and a free hydroxyl group
Phosphate esters
are often covalently attached to proteins in this way.
Phosphate groups
Substances that release hydrogen ions (protons) into solution are called
acids.
Many of the acids important in the cell are not completely dissociated, and they are therefore
weak acids
_______ occur both between
fully charged groups (ionic bond) and between partially charged groups on polar molecules.
Electrostatic attractions
