Key Concepts in Biology: Molecules to Gene Expression

Monomer

A small molecule that can bind to others to form a polymer.

Polymer

A large molecule made from many monomers joined together.

Condensation Reaction

A reaction where two molecules combine, releasing a molecule of water.

Hydrolysis Reaction

A reaction where a molecule is split into two by the addition of water.

Monosaccharide

The simplest form of carbohydrate, e.g., glucose.

Disaccharide

A carbohydrate composed of two monosaccharides, e.g., maltose.

Polysaccharide

A carbohydrate composed of many monosaccharides, e.g., starch.

Glycosidic Bond

A covalent bond formed between two monosaccharides during a condensation reaction.

Amino Acid

The building block of proteins, containing an amino group, carboxyl group, and R group.

Peptide Bond

A covalent bond formed between two amino acids during a condensation reaction.

Enzyme

A biological catalyst that speeds up chemical reactions without being consumed.

Active Site

The region on an enzyme where the substrate binds.

Substrate

The molecule upon which an enzyme acts.

Activation Energy

The minimum energy required to start a chemical reaction.

Denaturation

The alteration of a protein's structure, leading to loss of function.

DNA (Deoxyribonucleic Acid)

A molecule that carries genetic information.

RNA (Ribonucleic Acid)

A molecule involved in protein synthesis.

Nucleotide

The basic unit of nucleic acids, consisting of a sugar, phosphate group, and nitrogenous base.

Phosphodiester Bond

A bond linking nucleotides in a nucleic acid chain.

ATP (Adenosine Triphosphate)

The primary energy carrier in cells.

Prokaryotic Cell

A cell lacking a nucleus and membrane-bound organelles.

Eukaryotic Cell

A cell with a nucleus and membrane-bound organelles.

Plasma Membrane

A selectively permeable membrane surrounding the cell.

Nucleus

The organelle containing genetic material.

Mitochondrion

The site of aerobic respiration in cells.

Ribosome

The site of protein synthesis.

Endoplasmic Reticulum (ER)

A network of membranes involved in protein and lipid synthesis.

Golgi Apparatus

An organelle involved in modifying and packaging proteins.

Lysosome

An organelle containing digestive enzymes.

Cell Wall

A rigid structure providing support to plant cells.

Chloroplast

The site of photosynthesis in plant cells.

Vacuole

A storage organelle in plant cells.

Diffusion

The passive movement of particles from high to low concentration.

Osmosis

The diffusion of water across a selectively permeable membrane.

Active Transport

The movement of substances against a concentration gradient using energy.

Phagocytosis

The process by which cells engulf large particles.

Mitosis

A type of cell division resulting in two identical daughter cells.

Meiosis

A type of cell division producing gametes with half the chromosome number.

Surface Area to Volume Ratio

A factor affecting the rate of diffusion.

Gas Exchange Surface

A surface adapted for efficient gas exchange.

Trachea

The windpipe conducting air to the lungs.

Alveoli

Air sacs in the lungs where gas exchange occurs.

Ventilation

The movement of air into and out of the lungs.

Xylem

Vascular tissue transporting water in plants.

Phloem

Vascular tissue transporting sugars in plants.

Transpiration

The evaporation of water from plant leaves.

Stomata

Pores on leaf surfaces for gas exchange.

Haemoglobin

A protein in red blood cells that carries oxygen.

Oxyhaemoglobin

The complex formed when oxygen binds to haemoglobin.

Bohr Effect

The effect of carbon dioxide concentration on oxygen release from haemoglobin.

Gene

A sequence of DNA that codes for a polypeptide.

Allele

A different version of a gene.

Genotype

The genetic makeup of an organism.

Phenotype

The observable characteristics of an organism.

Homozygous

Having two identical alleles for a gene.

Heterozygous

Having two different alleles for a gene.

Dominant Allele

An allele that expresses its phenotype even in the presence of a recessive allele.

Recessive Allele

An allele that only expresses its phenotype when homozygous.

Codominance

A situation where both alleles contribute to the phenotype.

Locus

The specific location of a gene on a chromosome.

Mutation

A change in the DNA sequence.

Transcription

The process of copying DNA into RNA.

Translation

The process of assembling a protein from RNA.

Genetic Code

The set of rules by which information in DNA is translated into proteins.

Triplet Code

A set of three nucleotides coding for an amino acid.

Photosynthesis

The process by which plants convert light energy into chemical energy.

Chlorophyll

The pigment that absorbs light for photosynthesis.

Light-Dependent Reaction

The first stage of photosynthesis requiring light.

Light-Independent Reaction (Calvin Cycle)

The second stage of photosynthesis not requiring light.

Respiration

The process of releasing energy from glucose.

Glycolysis

The breakdown of glucose into pyruvate.

Krebs Cycle

A series of reactions generating energy through the oxidation of acetate.

Electron Transport Chain

A series of compounds transferring electrons to produce ATP.

ATP Synthase

An enzyme that synthesizes ATP.

Anaerobic Respiration

Respiration without oxygen.

Aerobic Respiration

Respiration with oxygen.

Net Primary Productivity (NPP)

The rate at which plants store energy.

Gross Primary Productivity (GPP)

The total rate of photosynthesis.

Trophic Level

A level in a food chain.

Decomposer

An organism that breaks down dead material.

Stimulus

A change in the environment.

Receptor

A cell or organ that detects stimuli.

Effector

A muscle or gland that brings about a response.

Reflex Arc

The pathway of neurons involved in a reflex.

Synapse

The junction between two neurons.

Neurotransmitter

A chemical messenger between neurons.

Resting Potential

The electrical potential of a neuron at rest.

Action Potential

A rapid change in membrane potential.

Depolarisation

A reduction in membrane potential making the inside of the neuron less negative.

Repolarisation

The return of the membrane potential to its resting state.

Refractory Period

A period following an action potential during which a neuron is unable to fire again.

All-or-Nothing Principle

A principle stating that if a stimulus is above a certain threshold, an action potential will occur; if not, it won't.

Hormone

A chemical messenger produced by glands and transported in the blood to target organs.

Second Messenger Model

A mechanism where a hormone binds to a receptor and triggers an intracellular response via a second messenger like cAMP.

Homeostasis

The maintenance of a stable internal environment within physiological limits.

Negative Feedback

A mechanism that restores conditions to their normal level.

Positive Feedback

A mechanism that increases the original change in conditions.

Glucoregulation

The control of blood glucose levels.

Glycogenesis

The conversion of glucose to glycogen.

Glycogenolysis

The breakdown of glycogen to glucose.