Biology: Metabolism, Photosynthesis, Cellular Respiration & DNA Replication

Metabolism

The sum of all chemical reactions in a living organism that maintain life.

Catabolism

The breakdown of complex molecules into simpler ones, releasing energy.

Anabolism

The building of complex molecules from simpler ones, requiring energy.

Free Energy

The energy available in a system to do useful work.

Endergonic

A reaction that requires an input of free energy (ΔG > 0).

Exergonic

A reaction that releases free energy (ΔG < 0).

Enzyme

A biological catalyst (usually a protein) that speeds up a specific reaction.

Catalyst

A substance that increases the rate of a chemical reaction without being consumed.

Competitive Inhibitor

A molecule that binds to an enzyme's active site and blocks the substrate.

Noncompetitive Inhibitor

A molecule that binds to a site other than the active site and changes the enzyme's shape.

Hydrolysis

The chemical breakdown of a compound by reaction with water.

Photosynthesis

The process by which plants convert light energy into chemical energy stored in glucose.

Autotroph

An organism that produces its own food from inorganic sources.

Photoautotroph

An organism that uses light energy to make its own food.

Heterotroph

An organism that obtains energy by consuming other organisms.

Chloroplast

The organelle in plant cells where photosynthesis occurs.

Chlorophyll

The green pigment in chloroplasts that absorbs light energy.

Light Reactions

The stage of photosynthesis that converts light energy into ATP and NADPH.

Dark Reactions (Calvin Cycle)

The stage of photosynthesis that uses ATP and NADPH to fix carbon into sugar.

Chemiosmosis

The use of a proton gradient across a membrane to drive ATP synthesis.

Carbon Fixation

The incorporation of CO₂ into organic molecules during the Calvin cycle.

Cellular Respiration

The process that breaks down glucose to produce ATP.

Redox Reaction

A chemical reaction involving the transfer of electrons.

Substrate-level Phosphorylation

Direct transfer of a phosphate group to ADP to form ATP.

Glycolysis

The breakdown of glucose into pyruvate, producing a net of 2 ATP and 2 NADH.

Electron Transport Chain

A series of membrane proteins that transfer electrons and pump protons.

Oxidative Phosphorylation

ATP production driven by the electron transport chain and chemiosmosis.

Fermentation

Anaerobic process that regenerates NAD⁺ so glycolysis can continue.

Transformation

The uptake of foreign DNA by a bacterial cell.

Bacteriophages (phages)

Viruses that infect and replicate within bacteria.

Double Helix

The twisted ladder structure of DNA formed by two complementary strands.

DNA Strand

One of the two polynucleotide chains that make up a DNA molecule.

Anti-parallel Strands

The two DNA strands run in opposite 5′→3′ directions.

Base Pairing

Complementary hydrogen bonding between A-T and G-C bases.

DNA Replication

The process of copying a DNA molecule.

Semiconservative Replication

Each new DNA molecule contains one original and one new strand.

Origin of Replication

The specific site where DNA replication begins.

Helicase

The enzyme that unwinds the DNA double helix.

RNA Primase

The enzyme that synthesizes short RNA primers to start DNA synthesis.

Topoisomerase

The enzyme that relieves supercoiling ahead of the replication fork.

Single Strand Binding Protein

Proteins that stabilize unwound single-stranded DNA.

Replication Forks

Y-shaped regions where the DNA helix is unwound for replication.

Template Strand

The DNA strand used as a pattern for synthesizing a complementary strand.

DNA Polymerase

The enzyme that adds nucleotides to a growing DNA strand.

Leading Strand

The continuously synthesized DNA strand in the 5′→3′ direction.

Lagging Strand

The discontinuously synthesized DNA strand made in short fragments.

Okazaki Fragments

Short DNA segments synthesized on the lagging strand.

Telomeres

Protective nucleotide sequences at the ends of eukaryotic chromosomes.

Telomerase

The enzyme that lengthens telomeres in certain cells.

Gene Expression

The process by which information from a gene is used to make a functional product.

Transcription

The synthesis of RNA from a DNA template.

Translation

The synthesis of a polypeptide using the information in mRNA.

mRNA

Messenger RNA that carries the genetic code from DNA to the ribosome.

rRNA

Ribosomal RNA that forms the structural and catalytic core of ribosomes.

tRNA

Transfer RNA that carries amino acids to the ribosome.

Ribosomes

Molecular machines that synthesize proteins.

Primary Transcript

The initial RNA product before processing.

Codon

A three-nucleotide sequence in mRNA that codes for an amino acid.

Reading Frame

The way nucleotides are grouped into consecutive codons.

RNA Polymerase

The enzyme that synthesizes RNA from a DNA template.

Promoter

A DNA sequence where RNA polymerase binds to start transcription.

Terminator

A DNA sequence that signals the end of transcription.

Transcription Unit

The stretch of DNA that is transcribed into an RNA molecule.

Transcription Factor

A protein that helps regulate the initiation of transcription.

TATA Box

A DNA sequence in many eukaryotic promoters that helps position RNA polymerase.

Poly-A Tail

A string of adenine nucleotides added to the 3′ end of eukaryotic mRNA.

RNA Splicing

The removal of introns and joining of exons in pre-mRNA.

Exons

Coding segments of a gene that are retained in mature mRNA.

Introns

Noncoding segments of a gene that are removed during RNA splicing.

Anti-Codon

The three-nucleotide sequence on tRNA that pairs with an mRNA codon.

Aminoacyl-tRNA Synthetase

The enzyme that attaches the correct amino acid to its tRNA.

Signal Peptide Sequence

A short amino acid sequence that directs a protein to a specific location.

Mutations

Permanent changes in the nucleotide sequence of DNA.

Cell Division

The process by which a parent cell divides into two or more daughter cells.

Stem Cells

Undifferentiated cells that can self-renew and differentiate into specialized cells.

Cell Cycle

The ordered sequence of events a cell goes through from formation to division.

Mitosis

The division of the nucleus that produces two genetically identical daughter nuclei.

Interphase

The phase of the cell cycle when the cell grows and replicates its DNA.

Mitotic Phase

The phase of the cell cycle that includes mitosis and cytokinesis.

Chromosome

A structure of DNA and proteins that carries genetic information.

Sister Chromatids

Identical copies of a chromosome joined at the centromere.

Cytokinesis

The division of the cytoplasm to form two separate daughter cells.

Cohesin

A protein complex that holds sister chromatids together.

Mitotic Spindle

The structure of microtubules that separates chromosomes during mitosis.

Centrosome

The microtubule-organizing center that forms the poles of the mitotic spindle.

Centromere

The region of a chromosome where sister chromatids are most tightly joined.

Nuclear Envelope

The double membrane that surrounds the nucleus.

Kinetochore

The protein structure on the centromere where spindle fibers attach.

Microtubule

A cytoskeletal polymer of tubulin that forms the mitotic spindle.

Hypothesis

A testable, tentative explanation for an observation.

Scientific Method

A systematic approach to investigating phenomena through observation, hypothesis, experimentation, and analysis.

Control Group

The group in an experiment that does not receive the experimental treatment.

Checkpoints

Control points in the cell cycle that ensure conditions are favorable before proceeding.

Cyclin-Dependent Protein Kinase

Enzymes that regulate the cell cycle when bound to cyclins.

Growth Factor

A signaling molecule that stimulates cell division and growth.

Anchorage Dependence

The requirement that a cell must be attached to a surface to divide.

Density-Dependent Inhibition

The phenomenon in which crowded cells stop dividing.

Proto-oncogene

A normal gene that can become an oncogene when mutated.

Oncogene

A mutated gene that promotes uncontrolled cell division.

Tumor Suppressor Gene

A gene that normally inhibits cell division or promotes DNA repair.