Definitions Flashcards
(335 cards)
1
Q
Absolute configuration
A
The nomenclature system used for the three-dimensional arrangement of atoms in
isomers; the most common systems are D/L and (R)/(S).
2
Q
Acetal
A
A carbon atom bonded to an alkyl group, two - OR groups, and a hydrogen.
3
Q
Acetyl-CoA
A
An important metabolic intermediate that links glycolysis and B-oxidation to the citric acid cycle; can also be converted into ketone bodies.
4
Q
Activation
A
The conversion of a biomolecule to its active or usable form, such as activation of tRNA with an amino acid or activation of a fatty acid with CoA to form fatty acyl-CoA .
5
Q
Activation energy
A
The energy required to change the state of a molecule or group of molecules to the transition state; the energy required for a reaction to occur.
6
Q
Active site
A
The catalytically active portion of an enzyme.
7
Q
Active transport
A
The movement of a molecule against its concentration gradient with energy investment; primary active transport uses ATP, whereas secondary active transport
uses a favorable transport gradient of a different molecule.
8
Q
Activity
A
The measure of the catalytic activity of an enzyme, also called the velocity or rate. It is often measured as a vmax and may be analyzed after protein isolation.
9
Q
Activity analysis
A
The determination of the enzymatic activity of an isolated protein by interaction with a substrate; usually colorimetric in nature.
10
Q
Adenosine triphosphate (ATP)
A
The primary energy molecule of the body; it releases energy by breaking the bond with the terminal phosphate to form ADP and inorganic phosphate.
11
Q
Adipocyte
A
A cell specializing in fat storage.
12
Q
Aerobic respiration
A
A collection of energy-producing metabolic processes that require oxygen, including the citric acid cycle, electron transport chain, and oxidative phosphorylation.
13
Q
Agglutination
A
Clumping of particles caused by the binding of antibody to target antigen.
14
Q
Aldose
A
A sugar in which the highest order functional group is an aldehyde; can be categorized by number of carbons (triose, tetrose, pentose, hexose, etc.).
15
Q
Allosteric enzymes
A
Enzymes that experience changes in their conformation as a result of interactions at sites other than the active site, called allosteric sites; conformational changes may increase or decrease enzyme activity.
16
Q
Alpha helix
A
An element of secondary structure, marked by clockwise coiling of amino acids around a
central axis.
17
Q
Alternative splicing
A
The production of multiple different but related mRNA molecules from a single primary transcript of hnRNA.
18
Q
Amino acid
A
A dipolar compound containing an amino group (- NH2) and a carboxyl group (-COOH).
19
Q
Amphipathic
A
Having both hydrophilic and hydrophobic regions.
20
Q
Amphoteric
A
The ability to act as an acid or base.
21
Q
Amplification
A
Increased transcription (and translation) of a gene in response to hormones, growth factors, and other intracellular conditions.
22
Q
Anabolism
A
The series of metabolic processes that result in the consumption of energy and the synthesis of molecules.
23
Q
Anaerobic respiration
A
The series of energy-producing metabolic processes that do not require oxygen, including glycolysis and fermentation.
24
Q
Anomers
A
A subtype of epimers in which the chiral carbon with inverted configuration was the carbonyl carbon (anomeric carbon).
25
Antibody
A specialized protein molecule produced by lymphocytes for interaction with antigens; antibodies consist of two heavy and two light chains that have constant and variable regions. Antibodies, also called immunoglobulins, are mediators of the immune response.
26
Anticodon
A three-nucleotide sequence on a tRNA molecule that pairs with a corresponding mRNA codon during translation.
27
Antigen
The region of a molecule that interacts with an antibody; in most cases, antigens are proteins.
28
Apoenzyme
An enzyme devoid of the prosthetic group, coenzyme, or cofactor necessary for normal activity.
29
Apolipoproteins
Protein molecules responsible for the interaction oflipo- proteins with cells and the transfer of lipid molecules between lipoproteins; also called apoproteins.
30
Aromaticity
The ability ofa molecule to delocalize pi electrons around a conjugated ring, creating exceptional stability.
31
Basal metabolic rate
The amount of energy consumed in a given period of time by a resting organism.
32
Beta-oxidation
The catabolism of fatty acids to acetyl-CoA.
33
Beta-Pleated sheet
An element of secondary structure, marked by peptide chains lying alongside one another, forming rows or strands.
34
Bile
A mixture of salts, pigments, and cholesterol that acts to emulsify lipids in the small intestine.
35
Binding proteins
Proteins that transport or sequester molecules by binding to them. Binding proteins have affinity curves for their molecules of interest.
36
Bioenerggetics
Biochemistry of the energy involved in bond interactions in biological organisms.
37
Biosignaling
The process by which cells receive and act on messages.
38
Cahn-Ingold-Prelog system
The system used to name isomers ((E) vs. (Z); (R) vs. (S)), based on the atomic numbers of their substituents and their orientation in three-dimensional space.
39
Bradford protein assay
A colorimetric method of determining the concentration of protein in an isolate against a protein standard; relies on a transition of absorption between bound and unbound Coomassie Brilliant Blue dye.
40
Calorimeter
A device for measuring the heat change during the course of a reaction.
41
Carboxylation
The addition of carboxylic acid groups to a molecule.
42
Carotenoids
A group of molecules that are tetraterpenes (made of eight isoprene units).
43
Catabolism
The series of metabolic processes that result in the release of energy and the breakdown of molecules.
44
Catalyst
A substance or enzyme that increases the rate of a reaction by lowering activation energy. Catalysts are not consumed during the catalyzed reaction.
45
Catalytic efficiency
The ratio of kcat/Km· Catalytic efficiency is directly related to efficiency of enzyme function.
46
Catecholamines
Mediators of the sympathetic nervous system and adrenal gland; include epinephrine and norepinephrine.
47
Cell adhesion molecules
Specialized structural proteins that are involved in cell-cell junctions as well as transient cellular interactions; common cell adhesion molecules are cadherins, integrins, and selectins.
48
Cellulose
A homupciysaccharide of glucose, and the main structural component of plants. Cellulose is indigestible for humans.
49
Central dogma of molecular biology
The major steps in the transfer of genetic information, from transcription of DNA to RNA to translation of that RNA to protein.
50
Centrifugation
The process of separating components on the basis of their density and resistance to flow by spinning a sample at very high speeds; the highest density materials form
a solid pellet and the lowest density materials remain in the supernatant (liquid portion).
51
Centromere
The area of a chromosome where sister chromatids are joined; it is also the point of attachment to the spindle fiber during mitosis and meiosis.
52
Ceramide
The simplest sphingolipid, with a single hydrogen as its head group.
53
Cerebroside
A sphingolipid containing a carbohydrate as a head group.
54
Chaperones
Proteins that assist in protein folding during posttranslational processing.
55
Chargaff's rule
DNA from any source should have a 1: 1 ratio of pyrimidine to purine bases, with adenine equal to thymine and cytosine equal to guanine.
56
Chemiosomtic coupling
The utilization of the proton-motive force generated by the electron transport chain to drive ATP synthesis in oxidative phosphorylation.
57
Chiral
Describes a molecule with a nonsuperirnposable mirror image.
58
Chiral center
A carbon atom bonded to four different substituents; a chiral compound must have at least one chiral center.
59
Cholesterol
A molecule containing four linked aromatic rings; cholesterol provides both fluidity and stability to cell membranes and is the precursor for steroid hormones.
60
Chromatid
Each of the two chro- mosomal strands formed by DNA replication in the S phase of the cell cycle, held together by the centromere. Identical pairs of chromatids are referred to as sister chromatids.
61
Chromatography
The process of separating molecules by their interactions with a stationary phase and mobile phase; most chromatograpic methods rely on the chemical similarity of molecules, with the exception of size-exclusion chromatography.
62
Chromosome
A filamentous body found within the nucleus of a eukaryotic cell or nucleoid region of a prokaryotic cell, composed of DNA.
63
Citric acid cycle
A metabolic pathway that produces GTP, energy carriers, and carbon dioxide as it burns acetyl-CoA; also called the Krebs cycle or tricarboxylic acid (TCA) cycle; can share
intermediates with many other meta- bolic processes including fatty acid and cholesterol synthesis, gluconeogenesis, amino acid metabolism, and others.
64
Closed system
A system capable of exchanging energy, but not matter, with the environment.
65
Coding strand
The strand of DNA that is not used as a template during transcription; also called the sense strand.
66
Codon
A three-nucleotide sequence in an mRNA molecule that pairs with an appropriate tRNA anticodon during translation.
67
Coenzyme
An organic molecule that helps an enzyme carry out its function.
68
Cofactor
An inorganic molecule or ion that helps an enzyme carry out its function.
69
Colligative properties
Physical properties that change according to the concentration of solutes, but not their identity. Colligative properties
include vapor pressure depression, boiling point elevation, freezing point depression, and osmotic pressure.
70
Colloid
A mixture composed of large molecules of one substance suspended within another substance.
71
Competitive inhibition
A decrease in enzyme activity that results from the interaction of an inhibitor with the active site of an enzyme; competitive inhibition can be overcome by addition of excess substrate.
72
Condensation reaction
A reaction in which the removal of a water molecule accompanies the formation of a bond; also called a dehydration reaction.
73
Conformational coupling
A less-accepted mechanism of ATP synthase activity in which the protons cause a conformational change that releases ATP from ATP synthase.
74
Conjugated protein
A protein that derives part of its function from covalently attached molecules (prosthetic groups).
75
Cooperativity
The interaction between subunits of a multi-subunit protein in which binding of substrate to one subunit increases the affinity of other subunits for the substrate;
unbinding of substrate from one unit decreases the affinity of other subunits for the substrate.
76
Corepressor
A species that binds with a repressor, allowing the complex to bind to the operator region of an operon, stopping transcription of the relevant gene.
77
Cristae
The infoldings of the inner mitochondrial membrane that increase the surface area available for electron transport chain complexes.
78
C-terminus
The free carboxyl end of a polypeptide.
79
Dalton (Da)
Molar mass unit used for
protein molecular weight. One amino
acid weighs approximately I00 Da, or 100 g/mol.
80
Degeneracy
A characteristic of the genetic code, in which more than one codon can specify a single amino acid.
81
Denaturation
The loss of secondary, tertiary, or quaternary structure in a protein, leading to loss of function.
82
Deoxyribonucleic acid (DNA)
A nucleic acid found exclusively in the nucleus that codes for all of the genes necessary for life; transcribed to mRNA and always read 5' to 3'.
83
Desmosomes
Cell-cell junctions that anchor layers of epithelial cells to one another.
84
Disastereomers
Compounds with at least one-but not all-chiral carbons in inverted configurations; differ in physical properties.
85
Diprotic
Containing two hydrogens (acid), or being able to pick up two hydrogens (base).
86
Disulfide bond
A covalent interaction between the -SH groups of two cysteine residues; an element of tertiary and quaternary structure.
87
Edman degradation
A stepwise process for determining the amino acid sequence in an isolated protein.
88
Electrochemical gradient
An uneven separation of ions across a biological membrane, resulting in potential energy.
89
Electrophoresis
The process of separating compounds on the basis of size and charge using a porous gel and an electric field; protein electrophoresis generally uses polyacrylamide, while nucleic acid electrophoresis generally uses agarose.
90
Elongation
The three-step cycle that is repeated for each amino acid being added to a protein during translation.
91
Emulsification
The mixing of two normally immiscible liquids.
92
Enantiomers
Compounds that are nonsuperimposable mirror images; have the same physical and chemical properties except for rotation of plane-polarized light and interaction with a chiral environment.
93
Endocytosis
The transport ofmolecules into a cell through the invagination of cell membrane and the formation ofa vesicle; phagocytosis is the endocytosis ofsolid, pinocytosis is the endocytosis of liquid
94
Endothermic reaction
A reaction that requires heat (positive deltaH).
95
Enhancer
A collection of several response elements that allow for the control of one gene's expression by multiple signals.
96
Enthalpy
The overall change in heat of a system during a reaction.
97
Entropy
The disorder of a system; systems in which entropy is increased are generally favored.
98
Enzyme
A biological molecule with catalytic activity; includes many proteins and some RNA molecules. Enzymes are specified for target substrate molecules.
99
Enzyme-linked receptor
A transmembrane protein that displays catalytic activity in response to ligand binding.
100
Epimers
A subtype of diastereomers that differ in absolute configuration at exactly one chiral carbon.
101
Euchromatin
The looser, less-dense collections of DNA that appear light colored under a microscope; transcriptionally active.
102
Exocytosis
The transport of molecules out of a cell by release from a transport vesicle; the vesicle fuses to the cell membrane during secretion
103
Exon
A portion ofhnRNA that is spliced with other exons to form mature mRNA.
104
Exothermc reaction
A reaction that releases heat (negative delta H)
105
Facilitated diffusion
The movement of solute molecules across the cell membrane down their concentration gradients through a transport protein or channel; used for ions and large or polar molecules.
106
Fatty acid
A monocarboxylic acid without additional substituents; fatty acids may be saturated (all single bonds) or unsaturated (contain at least one double bond); natural fatty acids are in the cis conformation.
107
Feedback inhibition
The inhibition of an enzyme by its product (or a product further down a metabolic pathway); used to maintain homeostasis.
108
Feed-forward activation
The stimulation of an enzymme by an intermediate that precedes the enzyme in a metabolic pathways.
109
Fermentation
The conversion of pyruvate to either ethanol and carbon dioxide (yeast) or lactic acid (animal cells); doe snot require oxygen,
110
FIbrous protein
A protein composed of long sheets or strands, such as collagen.
111
Fischer projection
A method of drawing organic molecules in which horizontal lines are coming out of the page (wedges) and vertical lines are going into the page (dashes).
112
Flavin adenine dinuclleotide (FAD)
An energy carrier that accepts electrons and feeds them into the electron transp0rt chain.
113
Falvorprotein
A protein bonded to FAD.
114
Fluid mosaic model
The representation of the plasma membrane as a dynamic phospholipid bilayer with interactions of cholesterol, proteins, and carbohydrates.
115
Frameshift mutation
A change in DNA in which the reading frame of the codoris in mRNA is shifted due to the insertion or deletion of nucleotides (other than in multiples of three).
116
Fructose
A monosaccharide found predominantly in fruit and honey.
117
Furanose
A five-membered ring sugar.
118
G protein-coupled receptors
A special class of membrane receptors with an associated GTP-binding protein; activation of a G protein-coupled receptors involves dissociation and GTP hydrolysis,
119
Galactose
A monosaccharide found predominantly in dairy.
120
Ganglioside
A sphingolipid with a head group containing an oligosacchande and one or more
N-acetylneuraminic acid (NANA) molecules.
121
Gap junctions
Cell-cell junctions that allow for the passage of small molecules between adjacent cells.
122
Gene
A unit of DNA that encodes a specific protein or RNA molecule.
123
Globoside
A sphingolipid with multiple carbohydrate groups attached as a head group.
124
Globular protein
A protein with a roughly spherical structure, such as myoglobin.
125
Glucagon
A mediator of glucose relea that is secreted by pancreatic alpha-cells; rises in response to low blood glucose.
126
Glucogenic
Describes amino acids that can be converted into intermedi ates that feed into gluconeogenesis; a except leucine and lysine.
127
Gluconeogenesis
The production of glucose from other biomolecules; carried out by the liver and kidney.
128
Glucose
The primary monosaccharide used for fuel by all cells of the body, with the formula C6 Hl2 06.
129
Glycerol
A three-carbon alcohol that serves as the backbone for glyerophospholipids, sphingolipids, and triacylglycerols.
130
Glycerophospholipid
Also referred to as a phosphoglyceride; a lipid containing a glycerol backbone with a phosphate group, bonded by ester linkages to two fatty acids.
131
Glycogen
A branched polymer of glucose that represents a storage form of glucose.
132
Glycogenesis
The synthesis of glycogen granules.
133
Glycogenolysis
The breakdown of glycogen granules.
134
Glycolysis
The breakdown of glucose to two molecules of pyruvate, with the formation of energy carriers (NADH); occurs under both aerobic and anaerobic conditions.
135
Glycosidic linkage
The bond between the anomeric carbon of a sugar and another molecule.
136
Glycosphingolipid
A sphingolipid with a head group composed of sugars; includes cerebrosides and globosides.
137
Glycosylation
The addition of sugars to a molecule.
138
Haworth projection
A method for depicting cyclic sugars as planar rings with -OH groups sticking up or down from the plane of the sugar.
139
Hemiacetal
A carbon atom bonded to an alkyl group, an -OR group, an -OH group, and a hydrogen.
140
Hemiketal
A carbon atom bonded to two alkyl groups, an -OR group, and an -OH group.
141
Hess's law
A relationship that states that the total change in any state func- tion is the same regardless of the path taken or the number of steps, and is equal to the difference between initial and final values of that state function .
142
Heterochromatin
The tightly coiled DNA that appears dark colored under a microscope; transcriptionally inactive.
143
Heterogeneoud nuclear RNA (hnRNA)
The precursor to processed mRNA; converted to mRNA by adding a poly-A tail and S' cap and splicing out introns.
144
Hill's coefficient
A quantitative measure of cooperative binding effects in enzymes.
145
Histone
A structural protein about which DNA is coiled in eukaryotic cells. Histone association with DNA can be altered by acetylation ofhistone proteins or methylation of the DNA strand.
146
Holoenzyme
An enzyme that has already bound a required prosthetic group, coenzyme, or cofactor.
147
Homeostasis
The stable internal state of an organism; homeostasis is not synonymous with equilibrium.
148
Homogenization
The process of breaking cell membranes and creating a uniform mixture of cell components for further separation; may be accomplished chemically or physically.
149
Hormone-sensitive lipase
The enzyme responsible for the mobili- zation of fatty acids from adipocytes; responds to a decrease in insulin levels.
150
Huckel's rule
One condition for aro- maticity, which states the compound must have 4n +2 (where n is any integer) pi electrons.
151
Hybridization
In research techniques involving DNA, the joining of complementary base pair sequences.
152
Hydrolase
An enzyme that catalyzes the cleavage of a molecule with the addition of water.
153
Hydrolysis
Breaking a covalent bond with the assistance of a water molecule.
154
Hydrophilic
Being attracted to water; describes polar and charged compounds and those that can participate in hydrogen bonding.
155
Hydrophobic
Being repelled by water; describes nonpolar, uncharged compounds (usually lipids or certain R groups of amino acids).
156
Hypertonic
A solution that has a greater concentration than the one to which it is being compared.
157
Hypotonic
A solution that has a lower concentration than the one to which it is being compared.
158
Induced fit model
The best-supported of the most prominent theories of enzyme specificity; states that the enzyme and substrate experience a change in conformation during binding to increase complementarity. Usually contrasted with the lock and key theory.
159
Inducible system
An operon that requires an inducer to remove a repressor protein from the operator site to begin transcription of the relevant gene.
160
Initiation
The start of translation, in which the small subunit of the ribo- some binds to the mRNA molecule, and the first tRNA (methionine or N-formylmethionine) is bound to the start codon (AUG).
161
Insulin
The primary mediator of car- bohydrate metabolism that is secreted by pancreatic, B-cells; rises in response to high blood glucose.
162
Internal energy
The sum of all of the different interactions between and within atoms in a system; vibration, rotation, linear motion, and stored chemical energies all contribute.
163
Intron
A portion of hnRNA that is spliced out to form mRNA; remains in the nucleus during processing.
164
Ion channels
Proteins that form a pore through the membrane in which they are embedded.
165
Irreversible inhibition
A decrease in enzyme activity that results from the interaction of an inhibitor that binds permanently at either the active site or an allosteric site; in laboratory settings, irreversible inhibitors are sometimes called suicide substrates.
166
Isoelectric focusing
A specialized method of separating proteins by their isoelectric point using electrophoresis; the gel is modified to possess a pH gradient.
167
Isoelectric point (pI)
The pH at which an amino acid is predominantly in zwitterionic form.
168
Isoform
A slightly different version of the same protein, often specific to a given tissue.
169
Isomerase
An enzyme that catalyzes the constitutional or stereochemical rearrangement of a molecule.
170
Isotonic
A solution that has the same concentration as the one to which it is being compared.
171
Jacob-Monod model
The description of the structure and function of operons in prokaryotes, in which operons have structural genes, an operator site, a promoter site, and a regulator gene.
172
Kcat
Rate of catalytic conversion of substrate. This value gives the number of substrate molecules turned over per enzyme molecule per second.
173
Ketal
A carbon atom bonded to two alkyl groups and two -OR groups.
174
Ketogenesis
The synthesis of ketone bodies from the metabolic products of B-oxidation or amino acid metabolism; occurs under conditions of starvation.
175
Ketogenic
Describes amino acids that can be converted into ketone bodies.
176
Ketolysis
The breakdown of ketone bodies for use as acetyl-CoA.
177
Ketose
A sugar in which the highest- order functional group is a ketone; can be categorized by number of carbons (triose, tetrose, pentose, hexose, and so on).
178
Kinase
A specific transferase protein that catalyzes the movement of a phos- phate group, generally from ATP, to a molecule of interest.
179
Km
The concentration ofsubstrate at which an enzyme runs at half its maximal velocity; a measure of enzyme affinity (the higher the Km, the lower the affinity).
180
Lactose
A disaccharide composed of glucose and galactose.
181
Lariat
The lasso-shaped structure formed during the removal of introns in mRNA processing.
182
Ligase
An enzyme that catalyzes the synthesis of large polymeric biomolecules, most commonly nucleic acids.
183
Lipid
A molecule that is insoluble in water and soluble in nonpolar organic solvents.
184
Lipoprotein
The transport mechanism for lipids within the circulatory and lymphatic systems; includes chylomicrons and VLDL, which transport triacylglycerols; and HDL, IDL, and LDL, which transport cholesterol and
cholesteryl esters.
185
Lock and key theory
One of the two most prominent theories of enzyme specificity; states that the enzyme and the substrate have a static but comple- mentary state. Less supported than the induced fit model.
186
Lyase
An enzyme that catalyzes the cleavage or synthesis of a molecule without the addition or loss of water.
187
Maltose
A disaccharide composed of two glucose molecules.
188
Matrix
The contents of the inner mitochondrial membrane; includes soluble enzymes of the electron transport chain and mitochondrial DNA.
189
Membrane
In cell biology, a double layer of phospholipids and proteins that forms the boundaries of cells and organelles within cells.
190
Membrane recpetors
Transmembrane protein molecules that act enzymatically or as ion channels to participate in signal transduction.
191
Messenger RNA (mRNA)
The strand of RNA formed after transcription of DNA; transfers to the cytoplasm to be translated.
192
Micelle
A collection of fatty acid or phospholipid molecules oriented to minimize free energy through hydrophobic and hydrophilic interactions; generally a sphere with a hydrophobic core and hydrophilic exterior.
193
Migration velocity
the velocity at which a compound moves through a gel during electrophoresis.
194
Missense mutation
A mutation in which one amino acid is substituted for by a different amino acid.
195
Mitochondria
The organelle responsible for aerobic respiration, generating ATP from the breakdown products of other biomolecules and energy carriers reduced in various metabolic pathways; contains an inner and outer membrane.
196
Mixed inhibition
A decrease in enzyme activity that results from the interaction of an inhibitor with an allosteric site; mixed inhibitors bind to free enzyme and to substrate-bound enzyme with different affinities. They cannot be overcome by addition of substrate and impact both Km and vmax·
197
Molten globules
Intermediate states in the folding of a protein.
198
Monocistronic
The coding pattern of eukaryotes in which one mRNA molecule codes for only one protein.
199
Monoprotic
Containing only one hydrogen (acid), or being able to pick up only one hydrogen (base).
200
Monosaccharide
A single sugar monomer; common examples are glucose, galactose, and fructose.
201
Motor proteins
Proteins that are involved in cell motility through interactions with structural proteins; motor proteins have ATPase activity and include myosin, kinesin, and dynein.
202
Mutarotation
The rapid interconversion between different anomers ofa sugar.
203
Negative control
In prokaryotic genetics, an operon that requires the binding of a protein to decrease transcription.
204
Nicotinamide adenine dinucleotide (NAD+)
An energy carrier that accepts electrons and feeds them into the electron transport chain.
205
Nicotinamide adenine dinucleotide phosphate (NADP+)
An electron donor produced in the pentose phosphate pathway that is involved in biosynthesis, oxidative stress, and immune function.
206
NMR spectroscopy
A method of determining molecular structure that uses the relative position of carbons and hydrogens determined by the rel- ative shielding and spins of electrons observed when molecule is exposed to a magnetic field.
207
Noncompetitive inhibition
A decrease in enzyme activity that results from the interaction of an inhibitor with an
allosteric site; noncompetitive inhibitors bind equally well to free enzyme
and to the substrate-bound enzyme. They
cannot be overcome by addition of substrate.
208
Nonsense mutation
A mutation in which a coding codon is changed to a stop codon. Also called a truncation mutation.
209
Nonemplate synthesis
The method of "de novo" synthesis oflipids and carbohydrates that relies on gene expression and enzyme specificity rather than the genetic template of DNA or RNA.
210
N-terminus
The free amino end of a polypeptide.
211
Nuclear pore
A hole in the nuclear envelope that permits the entrance and exit of substrates.
212
Nucleoside
Molecule composed of a pentose bound to a nitrogenous base at the C-1' position of the sugar.
213
Nucleotide
Molecule composed of one or more phosphate groups bound to the C-5' position of a nucleoside.
214
Nucleotide excision repair
Method for removing thymine dimers from DNA strands via a cut-and-patch process.
215
Okazaki fragments
Small strands formed on the lagging strand during DNA synthesis due to the unidirectional nature of DNA synthesis.
216
Oncogenes
Mutated genes that cause cancer.
217
Open system
A system capable of exchanging both matter and energy with the environment.
218
Operator site
A component of the operon in prokaryotes; a nontranscribable region of DNA that is capable of binding a repressor protein.
219
Operon
In prokaryotes, a cluster of genes transcribed as a single mRNA that can be regulated by repressors or inducers, depending on the system.
220
Opsonization
The marking of a pathogen by an antibody for later destruction.
221
Origiens of replication
Sites at which DNA unwinds to allow replication of new DNA. Generation of new DNA in both directions occurs at origins of replication, resulting in replication forks.
222
Osmosis
The simple diffusion of water.
223
Osmotic pressure
The pressure necessary to counteract the effect of an osmotic gradient against pure water; one of the colligative properties.
224
Oxidative phosphorylation
The transfer of a phosphate group, gener- ally to ATP that is powered by a gradient formed by oxidation-reduction reactions; occurs in the mitochondria.
225
Oxidoreductase
An enzyme that catalyzes an oxidation-reduction reaction, often using an electron carrier as a cofactor.
226
Pancreatic lipase
The primary enzyme involved in the digestion of lipids.
227
Pancreatc proteases
The enzymes that are primarily responsible for the digestion of proteins in the small intestine; they include trypsin,
chymotrypsin, and carboxypeptidases
A and B, and are secreted as zymogens.
228
Paracellular transport
The transport of matenals through the interstitial space without interactions with the cytoplasm or cell membrane.
229
Passive transport
The movement of a molecule down its concentration gradient without energy investment; includes simple and facilitated diffusion and osmosis.
230
Pentose phosphate pathway
A metabolic process that produces NADPH and ribose 5-phosphate for nucleotide synthesis.
231
Peptide
A molecule composed of more than one amino acid residue; can be subdivided into dipeptides (two amino acids), tripeptides (3), oligo- peptides (up to 20), and polypeptides (more than 20).
232
Peptide bond
An amide bond between the carboxyl group of one amino acid and the amino group of another amino acid.
233
Phospholipid
A lipid containing a phosphate and alcohol (glycerol or sphingosine) joined to hydrophobic fatty acid tails.
234
Phosphorylation
The placement of a phosphate group onto a compound.
235
pKa
The pH at which half of the molecules of a given acid are deprotonated; [HA]= [A-].
236
Point mutation
The substitution of one nucleotide for another in DNA.
237
Polarity
An uneven sharing of electrons in a molecule, creating a slightly positive side and a slightly negative side.
238
Polycistrnic
The coding pattern of prokaryotes, in which one mRNA may code for multiple proteins.`
239
Polymerase chain reactcion
An automated process to produce copies of a DNA sequence without use of bacteria for amplification.
240
Polyprotic
Containing more than one hydrogen (acid), or being able to pick up more than one hydrogen (base).
241
Polysaccharide
A long chain of monosaccharides linked by glycosidic bonds; can be divided into homopolysaccharides (only one type of monosaccharide is used) and heteropolysaccharides (more than one type of monosaccharide is used).
242
Positive control
In prokaryotic genetics, an operon that requires the binding of a protein to increase transcription.
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Postrandial state
State shortly after eating characterized by increased anabolism and fuel storage. Also referred to as the absorptive or well-fed state.
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Prenylation
The addition of lipid groups to a molecule.
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Primary structure
The linear sequence of amino acids in a polypeptide.
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Prometer region
The portion of DNA upstream from a gene; contains the TATA box, which is the site where RNA polymerase II binds to start transcription.
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Prostaglandin
A group of 20-carbon molecules that are unsaturated carboxylic acids derived from arachidonic acid; act as paracrine or autocrine hormones.
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Prosthetic group
A cofactor or coenzyme that is covalently bonded to a protein to permit its function. Proteins with lipid, carbohydrate, and nucleic acid prosthetic groups are referred to as lipoproteins, glycoproteins, and nuceloproteins, respectively.
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Protein
A molecule made up of at least one chain of amino acids joined by peptide bonds.
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Proteinogenic
The ability of certain (20) amino acids to be integrated into proteins.
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Proton-motive force
The proton concentration gradient across the inner mitochondrial membrane that is created in the electron transport chain and used in oxidative phosphorylation.
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Purine
Nitrogen-containing base
found in nucleotides possessing a two-
ring structure. The purines are adenine and guanine.
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Pyranose
A six-membered ring sugar.
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Pyrimidine
Nitrogen-containing base found in nucleotides possessing a onering structure. The three pyrimidines are cytosine, thymine, and uracil.
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Pyruvate
An important metabolic intermediate that can feed into the citric acid cycle, fermentation, or gluconeogenesis.
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Q cycle
The shuttling of electrons between ubiquinol and ubiquinone in the inner mitochondrial membrane as a part of Complex Ill's function.
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Quaterny structure
The interaction between different subunits of a multi-subunit protein; stabilized by R group interactions.
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Reaction coupling
The tendency of unfavorable biological reactions to occur concurrently with favorable reactions, often catalyzed by a single enzyme.
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Reading frame
In translation, the three nucleotides that make up a codon.
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Recombiant DNA
DNA that has been formed by combining genetic material from multiple sources in a laboratory.
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Reducing sugar
A sugar that can reduce other compounds and can be detected by Tollens' or Benedict's reagent.
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Regulator gene
In an operon, the gene that codes for the repressor protein.
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Release factor
The protein that binds to the stop codon during termination of translation.
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Renaturation
The regaining of the correct secondary, tertiary and quaternary structure after denaturation of a protein.
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Replisome
Set of specialized proteins that assist DNA polymerase during replication.
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Repressible system
An operon that requires a repressor to bind to a corepressor before binding to the operator site to stop transcription of the relevant gene.
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Repressor
For enzymes, an inhibitor of enzyme action; for operons, a species that binds to the operator region to stop transcription of the relevant gene.
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Resiratory control
The coordinated regulation of the different aerobic metabolic processes.
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Respiratory quotient
A numerical representation that can be used to determine the mest prevalent type of biomolecule being used in metabolism; the ratio of carbon dioxide produced to oxygen consumed.
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Respirometry
A method of measuring metabolism through the consumption of oxygen.
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Resting membrane potential
The electrical potential that results from the unequal distribution of charge around the cell membrane; resting membrane potential characterizes a cell that has not been stimulated.
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Restriction enzyme
Enzymes that recognize palindromic double- stranded DNA sequences and cut through the backbone of the double helix at those locations.
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Ribonucleic acid (RNA)
A nucleic acid found in both the nucleus and cytoplasm and most closely linked with transcription and translation, as well as some gene regulation.
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Ribosomal RNA (rRNA)
The structural and enzymatic RNA found in ribosomes that takes part in translation.
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Ribosome
Organelle composed of RNA and protein; it translates mRNA during protein synthesis.
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Ribozyme
An RNA molecule with enzymatic activity.
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Saponification
The reaction between a fatty acid and a strong base, resulting in a negatively charged fatty acid anion bound to a metal ion; creates soap.
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Saturation
The presence or absence of double bonds in a fatty acid; saturated fatty acids have only single bonds, whereas unsaturated fatty acids, have at least one double bond.
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Secondary structure
The local structure of neighboring amino acids; most common are alpha-helices and B-pleated sheets.
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Sequencing
Determining the order of amino acids in a polypeptide, or of nucleotides in a nucleic acid.
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Shine-Dalgarno Sequence
The site of initiation of translation in prokaryotes.
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Shuttle mechanism
A method of functionally transferring a compound across a membrane without the actual molecule crossing; common examples are the glycerol 3-phosphate shuttle and malate-aspartate shuttle.
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Sialic acid
The common name of N-acetylneuraminic acid (NANA), which is the terminal portion of the head group in a ganglioside.
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Side chain
The variable component of an amino acid that gives the amino acid its identity and chemical proper- ties; also called an R group.
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Silent mutation
A mutation in the wobble position of a codon or non-coding DNA that leads to no change in the protein produced during translation.
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Simple diffusion
The movement ofsolute molecules through the cell membrane down their concentration gradients without a transport protein; used for small, nonpolar, lipophilic molecules and water.
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Single-strand DNA-binding protein
Proteins that bind to unraveled DNA strands to prevent reassociation of DNA or degradation of DNA during replication events.
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Small nuclear ribonucleoproteins (snRNPs)
The protein portion of the spliceosome complex.
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Small nuclear RNA (snRNA)
The RNA portion ofthe spliceosome complex.
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Sodium-potassium pump
An ATPase that exchanges three sodium cations for two potassium cations; responsible for maintaining cell volume and the resting membrane potential.
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Solvation layer
The layer of solvent particles that interacts directly with the surface of a dissolved species
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Sphingolipid
A lipid containing a sphingosine or sphingoid backbone, bonded to fatty acid tails; include ceramide, sphingomyelins, glycosphingolipids, and gangliosides.
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Spingomyelin
A sphingophospholipid containing a sphingosine backbone and a phosphate head group.
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Spliceosome
The apparatus used for splicing out introns and bringing exons together during mRNA processing.
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Starch
A branched polymer of glucose used for energy storage in plants; common examples are amylose and amylopectin.
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Start codon
The first codon in an mRNA molecule that codes for an amino acid (AUG for methionine or N-formylmethionine).
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Stereoisomers
Compounds that have the same chemical formula and backbone, differing only in their spatial orientation; also called optical
isomers.
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Steroid
A derivative of cholesterol.
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Stop codon
The last codon of translation (UAA, UGA, or UAG); release factor binds here, terminating translation.
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Structural proteins
Proteins that are involved in the cytoskeleton and extracellular matrix; they are generally fibrous in nature and include collagen, elastin, keratin, actin, and tubulin.
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Structural gene
Within an operon, the region that codes for the protein of interest.
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Substrate
The molecule upon which an enzyme acts.
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Substrate-level phosphorylation
The transfer of a phosphate group from a high-energy compound to ATP or another compound; occurs in glycolysis.
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Sucrose
A disaccharide composed of glucose and fructose.
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Supercoiling
Wrapping of DNA on itself during replication, characterized by torsional stress and potential for strand breakage.
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Surfactant
A compound that lowers the surface tension between two solutions, acting as a detergent or emulsifier.
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TATA box
The site of binding for RNA polymerase II during transcription; named for its high concentration of thymine and adenine bases.
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Tautomerization
The rearrangement of bonds within a compound, usually by moving a hydrogen and forming a double bond.
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Telomere
Repeating unit at the end of DNA that protects against the loss of information with repeated DNA replication.
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Template strand
The strand of DNA that is transcribed to form mRNA; also called the antisense strand.
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Termination
The end of translation, in which the ribosome finds a stop codon and release factor binds it, allowing the peptide to be freed from the ribosome.
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Terpene
A class of lipids built from isoprene moieties; have carbon groups in multiples of five.
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Terpenoid
A terpene derivative that has undergone oxygenation or rearrangement of the carbon skeleton.
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Tertiary structure
The three-dimensional shape of a polypeptide, stabilized by numerous interactions between R groups.
315
Thyroid hormones
The primary permissive metabolic hormones involved in the regulation of the basal metabolic rate.
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Tight junction
Cell-cell junctions that prevent the paracellular transport of materials; tight junctions form a collar around cells and link cells within a single layer.
317
Titration
A laboratory technique in which a solution of unknown concentration is mixed with a solution of known concentration to determine the unknown concentration.
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Transcellular transport
The transport of materials through the cell; requires interaction with the cytoplasm and may require transport proteins.
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Transcription
The production of an mRNA molecule from a strand of DNA.
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Transcription factors
Proteins that help RNA polymerase II locate and bind to the promoter region of DNA.
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Transfer RNA (tRNA)
A folded strand of RNA that contains a three-nucleotide anticodon that pairs with an appropriate mRNA codon during translation and is charged with the corresponding amino acid.
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Transferase
An enzyme that catalyzes the transfer of a functional group.
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Translation
The production of a protein from an mRNA molecule.
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Triaclyglycerol
A glycerol molecule esterified to three fatty acid molecules; the most common form of fat storage within the body.
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Uncompetitive inhibition
A decrease in enzyme activity that results from the interaction with an inhibitor at the allosteric site; uncompetitive inhibi- tors bind only to the substrate-bound enzyme and cannot be overcome by addition of substrate.
326
UV spectroscopy
A method of determining the concentration of protein in an isolate by comparison against a protein standard; relies on the presence of aromatic amino acids. It can also be used with nucleic acids and other compounds.
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Van't Hoff factor
The number of particles obtained from a molecule when dissociated in solution.
328
Vitamin
An organic essential coenzyme that assists an enzyme in carrying out its action.
329
vmax
Maximum velocity for a given quantity of enzyme. vmax occurs when the enzyme is fully saturated.
330
Watson-Crick model
This model proposed the structure of DNA as a double stranded helix.
331
Wax
A high-melting point lipid com- posed of a very long chain alcohol and a very long chain fatty acid.
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Wobble
The third nucleotide of a codon that often plays no role in specifying an amino acid; an evolutionary development designed to protect against mutations.
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X-ray crystallography
A method of determining molecular structure using apparent bond angles and diffraction and refraction of X-rays.
334
Zwitterion
A molecule that contains charges, but is neutral overall. Most often used to describe amino acids.
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Zymogen
An enzyme that is secreted in an inactive form and must be activated by cleavage; common examples are digestive enzymes.
