Inglês para Bioquímica: Vocabulário e Frases Essenciais

"polypeptide chain"

a long, unbranched chain of amino acids linked by peptide bonds, forming the primary structure of proteins

"The polypeptide chain folds spontaneously into its native three-dimensional conformation."

"phospholipid bilayer"

the double-layered membrane structure made of phospholipid molecules with hydrophilic heads facing outward and hydrophobic tails facing inward

"The cell membrane's phospholipid bilayer acts as a selective barrier for ion transport."

"nucleotide"

the monomer unit of nucleic acids, consisting of a nitrogenous base, a five-carbon sugar, and a phosphate group

"Each nucleotide in a DNA strand is connected to the next via a phosphodiester bond."

"glycosidic bond"

the covalent bond linking a carbohydrate molecule to another group, such as a second sugar in a disaccharide

"Cellulose differs from starch in that its glucose units are linked by beta-1,4 glycosidic bonds."

"fatty acid"

a carboxylic acid with a long aliphatic chain, either saturated or unsaturated, serving as a key component of lipids

"Omega-3 fatty acids are essential because the human body cannot synthesise them de novo."

"ATP (adenosine triphosphate)"

the primary energy currency of the cell, releasing energy upon hydrolysis of its terminal phosphate bond

"The hydrolysis of ATP to ADP releases approximately 30.5 kJ/mol under standard conditions."

"disulfide bridge"

a covalent bond formed between two cysteine residues in a protein, stabilising its tertiary or quaternary structure

"The disulfide bridges in insulin help maintain the correct folding of its two chains."

"chromatin"

the complex of DNA and proteins (mainly histones) that constitutes chromosomes within the eukaryotic cell nucleus

"Chromatin remodelling complexes alter histone–DNA contacts to regulate gene accessibility."

"Michaelis constant (Km)"

the substrate concentration at which the reaction rate is half its maximum value, a measure of enzyme–substrate affinity

"A low Km indicates that the enzyme reaches half-maximal velocity at a low substrate concentration."

"turnover number (kcat)"

the maximum number of substrate molecules converted to product per active site per unit time

"Carbonic anhydrase has an exceptionally high kcat of around 10⁶ reactions per second."

"allosteric regulation"

the modulation of enzyme activity by molecules binding to sites other than the active site, inducing conformational changes

"Phosphofructokinase undergoes allosteric regulation by ATP, which acts as an inhibitor at high concentrations."

"competitive inhibition"

inhibition in which the inhibitor competes with the substrate for the same active site, raising apparent Km without changing Vmax

"Malonate is a classic example of competitive inhibition of succinate dehydrogenase."

"cofactor"

a non-protein chemical compound or metal ion required for enzyme catalytic activity

"Zinc acts as a cofactor for carbonic anhydrase, directly participating in the catalytic mechanism."

"active site"

the specific region of an enzyme where the substrate binds and the chemical reaction takes place

"Mutations in the active site residues typically abolish catalytic activity entirely."

"catalytic efficiency"

the ratio of kcat to Km, representing how effectively an enzyme converts substrate to product at low concentrations

"Diffusion-limited enzymes approach the theoretical maximum for catalytic efficiency."

"substrate specificity"

the ability of an enzyme to select and bind only particular substrates among many possible molecules

"The high substrate specificity of restriction enzymes makes them essential tools in molecular cloning."

"glycolysis"

the metabolic pathway that converts glucose into two pyruvate molecules, yielding a net gain of 2 ATP and 2 NADH

"Glycolysis occurs in the cytoplasm and does not require molecular oxygen."

"citric acid cycle"

also called the Krebs cycle; a series of chemical reactions used to generate energy through the oxidation of acetyl-CoA

"One turn of the citric acid cycle produces 3 NADH, 1 FADH₂, and 1 GTP."

"oxidative phosphorylation"

the metabolic pathway in which cells use enzymes to oxidise nutrients, releasing energy used to produce ATP

"Oxidative phosphorylation takes place on the inner mitochondrial membrane and accounts for most cellular ATP production."

"gluconeogenesis"

the synthesis of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids

"Gluconeogenesis is activated during fasting to maintain blood glucose levels for the brain."

"beta-oxidation"

the catabolic process by which fatty acid molecules are broken down in the mitochondria to generate acetyl-CoA

"Each cycle of beta-oxidation shortens the fatty acid chain by two carbons and produces one NADH and one FADH₂."

"anabolism"

the metabolic processes that construct complex molecules from simpler ones, requiring energy input

"Protein synthesis is a key anabolic process that requires a constant supply of amino acids and ATP."

"catabolism"

the metabolic breakdown of complex molecules to release energy, often producing smaller building-block molecules

"During prolonged exercise, catabolism of muscle glycogen provides glucose for continued ATP synthesis."

"metabolic flux"

the rate of turnover of molecules through a metabolic pathway at steady state

"Flux control analysis revealed that hexokinase exerts significant control over glycolytic flux in erythrocytes."

"transcription"

the process by which the information in a DNA strand is copied into a complementary RNA molecule by RNA polymerase

"Transcription is initiated when transcription factors recruit RNA polymerase II to the promoter region."

"translation"

the process by which ribosomes synthesise a protein from an mRNA template, reading codons to add amino acids

"Translation begins at the AUG start codon and terminates when a stop codon enters the ribosomal A site."

"gene expression"

the process by which genetic information is used to produce a functional gene product, such as a protein or RNA

"Differential gene expression allows a single genome to give rise to hundreds of distinct cell types."

"splicing"

the post-transcriptional process of removing introns from a pre-mRNA molecule and joining the exons together

"Alternative splicing can generate multiple protein isoforms from a single gene."

"epigenetic modification"

heritable changes in gene expression that do not involve alterations to the DNA sequence itself, such as DNA methylation and histone acetylation

"Histone H3K27 trimethylation is an epigenetic modification associated with stable gene silencing."

"codon"

a sequence of three nucleotides in mRNA that specifies a particular amino acid or a stop signal during translation

"The genetic code is degenerate, meaning that most amino acids are encoded by more than one codon."

"plasmid"

a small, circular, double-stranded DNA molecule distinct from chromosomal DNA that can replicate independently in a host cell

"Recombinant plasmids carrying the gene of interest are introduced into bacteria by transformation."

"PCR (polymerase chain reaction)"

a technique used to amplify a specific DNA sequence through repeated cycles of denaturation, annealing, and extension

"Quantitative PCR allows researchers to measure gene expression levels in real time."

"receptor tyrosine kinase"

a transmembrane receptor that, upon ligand binding, phosphorylates tyrosine residues on target proteins to activate downstream signalling

"The epidermal growth factor receptor is a prototypical receptor tyrosine kinase linked to cell proliferation."

"second messenger"

a small intracellular signalling molecule that relays a signal received by a cell surface receptor to its downstream effectors

"cAMP functions as a second messenger, activating protein kinase A following beta-adrenergic receptor stimulation."

"phosphorylation cascade"

a series of sequential protein phosphorylation events that amplify and propagate a signal inside the cell

"The MAPK phosphorylation cascade translates extracellular growth signals into changes in gene expression."

"G-protein coupled receptor (GPCR)"

a large class of cell surface receptors that activate intracellular G-proteins upon ligand binding, triggering downstream effects

"Approximately one-third of all modern drugs target G-protein coupled receptors."

"ligand"

a molecule that binds specifically to a receptor or other binding site, triggering a biological response

"Insulin acts as a ligand for the insulin receptor, initiating glucose uptake in muscle and adipose cells."

"apoptosis"

programmed cell death characterised by specific cellular changes including chromatin condensation, DNA fragmentation, and formation of apoptotic bodies

"Dysregulation of apoptosis is a hallmark of cancer, often caused by overexpression of anti-apoptotic Bcl-2 proteins."

"protein kinase"

an enzyme that transfers phosphate groups from ATP to specific amino acids in target proteins, altering their activity

"Cyclin-dependent kinases are protein kinases that regulate key transitions in the cell cycle."

"signal transduction"

the process by which a chemical or physical signal is transmitted through a cell via molecular pathways to produce a response

"Impaired signal transduction through the insulin pathway leads to type 2 diabetes."

"gel electrophoresis"

a technique that separates macromolecules such as DNA, RNA, or proteins by size as they migrate through a gel matrix under an electric field

"SDS-PAGE gel electrophoresis is used to separate denatured proteins according to their molecular weight."

"Western blot"

a technique that uses antibodies to detect specific proteins after they have been separated by gel electrophoresis and transferred to a membrane

"The Western blot confirmed that treatment with the inhibitor reduced phosphorylation of the target protein."

"ELISA (enzyme-linked immunosorbent assay)"

a plate-based assay technique designed to detect and quantify proteins, antibodies, or antigens using enzyme-linked antibodies

"The ELISA results showed a threefold increase in cytokine levels following stimulation."

"spectrophotometry"

a technique that measures the absorption of light by a solution at specific wavelengths to determine the concentration of a substance

"Protein concentration was determined by Bradford spectrophotometry using a bovine serum albumin standard curve."

"centrifugation"

a technique that uses centrifugal force to separate components of a mixture based on differences in density

"Differential centrifugation was used to isolate mitochondria from the cell homogenate."

"chromatography"

a laboratory technique for separating mixtures based on differential movement through a stationary phase under the influence of a mobile phase

"Size-exclusion chromatography was used to purify the recombinant protein from bacterial lysate."

"mass spectrometry"

an analytical technique that measures the mass-to-charge ratio of ions to identify and quantify molecules in a sample

"Tandem mass spectrometry enabled the identification of post-translational modifications on the purified enzyme."

"immunoprecipitation"

a technique used to isolate a specific protein from a solution using an antibody that specifically binds to that protein

"Co-immunoprecipitation demonstrated a direct physical interaction between the two signalling proteins."