BE Abitur Bio 3. PF key terms

Protein that speeds up a biochemical reaction by lowering its activation energy, without being consumed. Its shape determines which substrate fits, so temperature, pH and inhibitors affect its activity.

Energy barrier that must be overcome before a reaction proceeds. Enzymes reduce this barrier by stabilising the transition state, so reactions run faster at body temperature.

Property of an enzyme that binds only substrates fitting its active site, like a key in a lock. This selectivity keeps metabolic pathways ordered and prevents unwanted side reactions.

Model describing the fit between enzyme active site and substrate. The induced-fit extension adds that the active site adjusts slightly on binding, which explains better how catalysis is triggered.

Inhibition in which a molecule resembling the substrate occupies the active site. Raising substrate concentration can outcompete it, so maximum reaction rate is reached but more substrate is needed.

Inhibition at a site other than the active site, changing enzyme shape so the substrate no longer binds well. It cannot be overcome by adding more substrate and is typical of metabolic feedback control.

Loss of a protein's functional three-dimensional structure by heat, extreme pH or chemicals. Hydrogen bonds and other weak interactions break, so the enzyme or transport protein stops working, often irreversibly.

Four-level organisation of a protein: amino acid sequence, local folds such as helices, overall three-dimensional shape, and assembly of several chains. Shape at levels three and four determines function.

Covalent bond joining the carboxyl group of one amino acid to the amino group of the next, releasing water. Repeated peptide bonds form the polypeptide backbone of every protein.

Building block of proteins with an amino group, a carboxyl group and a variable side chain. Twenty standard types differ in side chain properties, which drives folding and function.

Adenosine triphosphate, the universal energy currency of cells. Cleaving its terminal phosphate releases usable energy for synthesis, transport and movement; it is regenerated by respiration.

Sequence of reactions in the cytoplasm that splits glucose into two pyruvate molecules, yielding a small net gain of ATP and reduced electron carriers. It works with or without oxygen.

Cyclic mitochondrial pathway that oxidises acetyl groups from pyruvate to carbon dioxide, producing reduced electron carriers and a little ATP. It feeds electrons into the respiratory chain.

Series of membrane protein complexes in mitochondria that pass electrons to oxygen and pump protons. The resulting proton gradient drives ATP synthase, giving most cellular ATP.

ATP synthesis driven by a proton gradient across a membrane. Protons flow back through ATP synthase, and this flow rotates the enzyme so it joins ADP and phosphate.

Anaerobic breakdown of glucose in which pyruvate is converted to lactate or ethanol and carbon dioxide, regenerating an electron carrier so glycolysis can continue. ATP yield is small.

Reaction that consumes more energy than it releases, so it does not run spontaneously. In cells it is coupled to ATP cleavage or another exergonic process to make it possible.

Process in chloroplasts converting light energy into chemical energy: water is split, oxygen released, and carbon dioxide fixed into sugar. It supplies the organic matter and oxygen that respiration depends on.

Light-dependent stage at the thylakoid membrane. Photosystems absorb light, split water, produce oxygen and reduce electron carriers, while a proton gradient drives ATP synthesis.

Light-independent stage of photosynthesis in the stroma, where the enzyme rubisco fixes carbon dioxide onto a five-carbon sugar. Using ATP and reduced carriers, it regenerates the acceptor and releases sugar.

Green pigment in thylakoid membranes that absorbs mainly red and blue light and reflects green. Absorbed energy excites electrons that start the light reaction.

Semiconservative copying of DNA before cell division. The double helix unwinds, each strand templates a new one, and enzymes add complementary nucleotides, so each daughter molecule keeps one old strand.

Rule that adenine pairs with thymine and guanine with cytosine in DNA, held by hydrogen bonds. It guarantees faithful copying and underlies the stability of the double helix.

Enzyme-driven synthesis of an RNA copy from a DNA template in the nucleus. RNA polymerase reads one strand, and the resulting messenger RNA carries the coding information to the ribosome.

Assembly of a polypeptide at the ribosome according to messenger RNA codons. Transfer RNAs deliver matching amino acids, and peptide bonds are formed until a stop codon ends the process.

Mapping from nucleotide triplets to amino acids, read in non-overlapping groups. It is nearly universal and degenerate, meaning several codons specify the same amino acid.

Heritable change in DNA sequence, such as substitution, insertion or deletion. Effects range from none to loss of protein function, and germline mutations can be passed to offspring.

Nuclear division producing two genetically identical daughter nuclei. Chromosomes condense, align and are pulled apart, followed by cytokinesis; it serves growth and repair in multicellular organisms.

Two successive divisions that halve the chromosome number and produce four genetically varied cells. Crossing over and independent chromosome assortment create new allele combinations in gametes.

Exchange of matching chromosome segments between homologous chromosomes during the first meiotic division. It recombines alleles and increases genetic variation among the resulting gametes.

Ordered sequence of interphase growth and DNA duplication followed by mitotic division. Checkpoints verify DNA integrity and chromosome attachment, and loss of control can lead to uncontrolled proliferation.

Principles of inheritance: alleles separate during gamete formation, and different genes are inherited independently. They explain predictable ratios in crosses of homozygous parents.

The particular combination of alleles an organism carries for a gene or set of genes. It is written as letter pairs and, together with environmental effects, produces the observable phenotype.

Observable characteristics of an organism, resulting from its genotype interacting with environmental influences. It is what a cross or a diagnostic test can actually measure.

Quantitative study of reaction rate as a function of substrate concentration, pH or inhibitor presence. Michaelis-Menten analysis gives maximum rate and the half-saturation constant used to compare enzymes.

End product of a pathway inhibits an earlier enzyme, usually allosterically, slowing its own production. This negative feedback keeps metabolite levels stable and avoids wasteful synthesis.