ILTS Science: Biology (239) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Cell membrane structure

A phospholipid bilayer with hydrophilic heads facing aqueous environments and hydrophobic tails inward, studded with proteins and cholesterol; it is selectively permeable and described by the fluid mosaic model.

Osmosis

The net diffusion of water across a selectively permeable membrane from a region of lower solute concentration to higher solute concentration, driven by the water potential gradient until equilibrium is reached.

Mitochondrial function

The organelle where pyruvate oxidation, the Krebs cycle, and oxidative phosphorylation occur; the inner membrane folds into cristae bearing the electron transport chain and ATP synthase.

Ribosome role

The ribonucleoprotein machine that translates mRNA codons into polypeptide chains; free ribosomes make cytosolic proteins while rough-ER-bound ribosomes make secreted and membrane proteins.

Enzyme active site

The region of an enzyme that binds substrate and stabilizes the transition state, lowering activation energy; its shape and chemistry determine substrate specificity and catalytic rate.

ATP hydrolysis

Cleavage of the terminal phosphate bond of ATP releases energy and yields ADP plus inorganic phosphate; this exergonic reaction powers endergonic cellular work such as transport and synthesis.

Glycolysis summary

A cytosolic pathway that splits one glucose into two pyruvate molecules, netting two ATP and two NADH; it occurs with or without oxygen and is the first stage of cellular respiration.

Krebs cycle

A mitochondrial matrix cycle that oxidizes acetyl-CoA, producing NADH, FADH2, ATP, and carbon dioxide; it completes the oxidation of carbon derived from carbohydrates, fats, and proteins.

Electron transport chain

A series of inner-mitochondrial-membrane protein complexes that pass electrons from NADH and FADH2 to oxygen, pumping protons to build a gradient that drives ATP synthase.

Light reactions

Thylakoid membrane reactions that split water, release oxygen, and produce ATP and NADPH using energy captured by photosystems; these products fuel the Calvin cycle.

Calvin cycle

The stroma-based cycle in which the enzyme rubisco fixes carbon dioxide onto ribulose bisphosphate, and ATP and NADPH reduce the product to form sugar.

DNA replication

Semiconservative synthesis in which each parental strand templates a new strand; helicase unwinds, primase lays primers, DNA polymerase extends 5' to 3', and ligase seals nicks.

Transcription

RNA polymerase reads the DNA template strand and builds a complementary mRNA 5' to 3'; in eukaryotes the transcript is processed with a cap, poly-A tail, and splicing.

Translation

Ribosomes read mRNA codons in the 5' to 3' direction while tRNAs bring complementary anticodons and amino acids; the chain grows until a stop codon triggers release.

Mutation types

Substitution changes one base, which may be silent, missense, or nonsense; insertion or deletion shifts the reading frame and usually alters all downstream amino acids.

Mendel's law of segregation

The two alleles of a gene separate during meiosis so that each gamete receives only one allele; their random rejoining at fertilization restores pairs in offspring.

Independent assortment

Alleles of genes on different chromosomes are distributed to gametes independently of one another during meiosis, producing genetic variety in offspring.

Incomplete dominance

A heterozygote shows an intermediate phenotype between the two homozygotes, as in pink snapdragon flowers from red and white parents; neither allele fully masks the other.

Codominance

Both alleles are expressed fully and simultaneously in the heterozygote, as in AB blood type, where both A and B antigens appear on the red blood cells.

Sex-linked inheritance

Genes on the X chromosome affect males and females differently; males are hemizygous and express recessive X-linked traits far more often than females.

Hardy-Weinberg equations

Allele frequencies sum as p plus q equals one; genotype frequencies follow p squared plus 2pq plus q squared equals one, describing a non evolving population at equilibrium.

Natural selection

Differential survival and reproduction of individuals whose heritable traits better suit the environment, gradually shifting allele frequencies in the population across generations.

Genetic drift

Random change in allele frequencies due to chance, strongest in small populations; bottleneck and founder effects are examples that reduce genetic diversity.

Reproductive isolation

Any barrier preventing members of different populations from interbreeding, such as geographic separation, timing of breeding, or hybrid inviability; it defines biological species.

Binomial nomenclature

A two-part scientific name in which the capitalized genus precedes the lowercase specific epithet, both italicized, giving every species a unique universal label.

Trophic levels

Feeding positions in a food chain: producers, primary consumers, secondary consumers, and decomposers; energy decreases at each transfer, typically to about ten percent.

Carrying capacity

The maximum population size an environment can sustain given available resources; logistic growth levels off at this value, unlike exponential growth.

Symbiosis types

Mutualism benefits both partners, commensalism benefits one while the other is unaffected, and parasitism benefits one at the other's expense; all describe close long-term interactions.

Negative feedback loop

A control mechanism in which a change in a variable triggers a response that reverses the change, restoring a set point such as blood glucose or body temperature.

Osmolarity regulation

Osmoreceptors detect blood solute concentration, prompting ADH release to increase water reabsorption in the kidney and concentrate urine, maintaining fluid balance.

Gel electrophoresis

A technique that separates DNA fragments by size in an electric field; negatively charged DNA migrates toward the positive electrode, with smaller fragments moving farther.

Polymerase chain reaction

Repeated cycles of denaturation, primer annealing, and extension by Taq polymerase that amplify a target DNA sequence exponentially in vitro.