First-year courses · Sciences

Biology: cell and molecular biology

Cell structure, membranes and transport, DNA replication, transcription, translation, enzymes, respiration and the cell cycle in first-year biology flashcards.

45 cards6 topicsAbout 20 minutes a roundTypical first-year introductory biology, cellular and molecular term

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About this deck

First-year biology usually splits into a cells-and-molecules term and an evolution-and-ecology term; this deck covers the first. It includes prokaryotic and eukaryotic cells and their organelles, the fluid mosaic membrane and how substances cross it, DNA structure and semiconservative replication, transcription, RNA processing and translation, mutations and a first look at gene regulation, enzymes and energy, cellular respiration and photosynthesis, and the cell cycle with mitosis and meiosis.

Grade 12 biology and chemistry give enough background. It helps to remember what hydrogen bonds and polar versus nonpolar molecules are, because membrane transport and DNA base pairing both depend on them.

Biology exams test both vocabulary and processes. For vocabulary cards, give the definition and one example before flipping. For process cards (replication, translation, glycolysis), try to narrate the steps in order, naming the enzyme or location at each step; if you stall, that tells you exactly what to review. A useful trick is to explain a card to an imaginary classmate in under twenty seconds. When the tags feel familiar, shuffle them all so you practise switching between structure and process questions.

Common mistakes: writing DNA or RNA sequences without labelling 5' and 3' ends, or pairing them in the same direction rather than antiparallel; saying that DNA polymerase can start a new strand on its own (it needs a primer); and mixing up mitosis and meiosis, especially which one separates homologous chromosomes (meiosis I). Students also often state that plants do photosynthesis instead of respiration, when plant cells do both.

Before you start: Grade 12 biology and chemistry (or equivalents).

All 45 cards

Cover the definitions with a sheet of paper and test yourself, or use the study modes above.

Cells and organelles

Prokaryotic versus eukaryotic cells: Prokaryotes (bacteria, archaea) lack a nucleus and membrane-bound organelles; eukaryotes (animals, plants, fungi, protists) have both and are usually much larger.Example: E. coli has its chromosome in a nucleoid region; a liver cell keeps DNA in a nucleus.
Nucleus: The double-membrane organelle that holds a eukaryotic cell's chromosomes; nuclear pores control traffic, and the nucleolus builds ribosome subunits.Example: mRNA is made here and exported through pores to the cytoplasm.
Ribosome: A complex of rRNA and proteins that translates mRNA into protein; free in the cytosol or bound to the rough ER. Not surrounded by a membrane.Example: Bacterial versions (70S) differ from eukaryotic (80S), which is why some antibiotics target them.
Endoplasmic reticulum: A membrane network continuous with the nuclear envelope: the rough region (with ribosomes) makes secreted and membrane proteins; the smooth region makes lipids and detoxifies.Example: Liver cells have abundant smooth ER for detoxifying drugs.
Golgi apparatus: Stacked membrane sacs that modify, sort and package proteins and lipids from the ER into vesicles for their destinations.Example: Adds carbohydrate tags to proteins before secretion.
Lysosome: A membrane-bound sac of acidic hydrolytic enzymes that digests worn-out organelles, macromolecules and engulfed material (mainly in animal cells).Example: White blood cells use them to destroy engulfed bacteria.
Mitochondrion: Double-membrane organelle where pyruvate oxidation, the citric acid cycle and oxidative phosphorylation produce most of the cell's ATP; has its own DNA.Example: Muscle cells contain many of them.
Chloroplast: Double-membrane plant and algal organelle containing chlorophyll in thylakoids, where photosynthesis converts light energy into chemical energy.Example: Light reactions occur in thylakoid membranes; the Calvin cycle in the stroma.
Endosymbiotic theory: The idea that mitochondria and chloroplasts descend from free-living prokaryotes engulfed by an ancestral host cell.Example: Evidence: both have their own circular DNA, 70S-type ribosomes and double membranes.
Cytoskeleton: A network of protein fibres (microfilaments, intermediate filaments, microtubules) that gives shape, anchors organelles and moves materials and cells.Example: Microtubules form the mitotic spindle.

Membranes and transport

Fluid mosaic model: Description of cell membranes as a fluid phospholipid bilayer with proteins, cholesterol and carbohydrates scattered through it and able to move laterally.Example: Membrane proteins tagged with dyes spread evenly after two cells fuse.
Simple diffusion: Net movement of molecules from higher to lower concentration without energy input or a transport protein; works for small nonpolar molecules.Example: O2 and CO2 cross membranes this way.
Osmosis: Diffusion of water across a selectively permeable membrane toward the side with higher solute concentration.Example: A red blood cell in pure water swells and may burst.
Tonicity: How a surrounding solution affects cell volume: hypertonic (more solute outside, cell shrinks), hypotonic (less solute outside, cell swells), isotonic (no net change).Example: 0.9% saline is isotonic to human cells.
Facilitated diffusion: Passive movement down a concentration gradient through channel or carrier proteins, for ions and polar molecules that cannot cross the bilayer.Example: Glucose enters many cells through GLUT carrier proteins.
Active transport: Movement of a substance against its concentration gradient using energy, usually ATP, through a pump protein.Example: The Na+/K+ pump moves 3 Na+ out and 2 K+ in per ATP.

DNA and replication

Nucleotide: The monomer of nucleic acids: a five-carbon sugar (deoxyribose or ribose), a phosphate group and a nitrogenous base.Example: DNA bases: A, T, G, C; RNA uses U instead of T.
DNA double helix: Two antiparallel strands with sugar-phosphate backbones outside and paired bases inside: A with T (2 hydrogen bonds), G with C (3 hydrogen bonds).Example: 5'-ATGC-3' pairs with 3'-TACG-5'.
Chargaff's rules: In double-stranded DNA, the amount of A equals T and G equals C, because of complementary base pairing.Example: DNA that is 20% A is also 20% T, leaving 30% G and 30% C.
Semiconservative replication: Each new DNA double helix contains one original (parent) strand and one newly made strand.Example: Shown by the Meselson-Stahl experiment with heavy and light nitrogen.
DNA polymerase: Enzyme that builds new DNA by adding nucleotides to the 3' end of an existing strand, so synthesis runs 5' to 3'; it needs a primer and proofreads errors.Example: It cannot start a strand from nothing; primase supplies an RNA primer.
Leading and lagging strands: At a replication fork, one strand is made continuously toward the fork (leading); the other is made in short Okazaki fragments away from it (lagging).Example: Ligase seals the gaps between Okazaki fragments.
Replication enzymes: Helicase unwinds the helix, topoisomerase relieves twisting ahead of the fork, primase lays RNA primers, polymerase extends and ligase joins fragments.Example: Single-strand binding proteins keep separated strands from re-pairing.

Gene expression

Central dogma: The usual flow of genetic information: DNA is transcribed into RNA, which is translated into protein.Example: Retroviruses are an exception: reverse transcriptase makes DNA from RNA.
Transcription: Synthesis of RNA from a DNA template by RNA polymerase, starting at a promoter; the RNA matches the coding strand except U replaces T.Example: Template 3'-TACGGA-5' gives mRNA 5'-AUGCCU-3'.
RNA processing: In eukaryotes, pre-mRNA gets a 5' cap and a 3' poly-A tail, and introns are removed by splicing before export from the nucleus.Example: Alternative splicing lets one gene code for several proteins.
Genetic code: The set of rules linking mRNA codons (three-base words) to amino acids: 64 codons, 61 for amino acids and 3 stops; it is redundant but not ambiguous.Example: AUG codes for methionine and starts translation; UAA, UAG and UGA stop it.
Translation: Protein synthesis at the ribosome: tRNAs bring amino acids matching each codon, and peptide bonds join them until a stop codon is reached.Example: mRNA 5'-AUG GCU UAA-3' gives Met-Ala, then stops.
tRNA: A small folded RNA that carries a specific amino acid and has an anticodon that base-pairs with an mRNA codon.Example: Anticodon 3'-UAC-5' pairs with codon 5'-AUG-3' and carries methionine.
Point and frameshift mutations: A point mutation changes one base (silent, missense or nonsense); inserting or deleting bases not in multiples of 3 shifts the reading frame and garbles the rest of the protein.Example: Sickle cell anemia results from a single missense change (Glu to Val).
Lac operon: A bacterial gene cluster for lactose use, switched off by a repressor bound to the operator; lactose (as allolactose) releases the repressor so genes are transcribed.Example: Without lactose present, E. coli does not waste energy making lactose enzymes.

Metabolism and energy

ATP: Adenosine triphosphate, the cell's main short-term energy carrier; hydrolysis of its terminal phosphate releases energy that drives other reactions.Example: ATP to ADP + Pi releases about 30.5 kJ/mol under standard conditions.
Enzyme: A biological catalyst, usually a protein, that speeds a reaction by lowering its activation energy; substrates bind at its active site.Example: Catalase breaks down hydrogen peroxide into water and oxygen.
Competitive versus noncompetitive inhibition: A competitive inhibitor binds the active site and can be outcompeted by more substrate; a noncompetitive one binds elsewhere and lowers maximum rate regardless of substrate.Example: Methanol poisoning is treated with ethanol, which competes for the same enzyme.
Cellular respiration overview: Aerobic breakdown of glucose: C6H12O6 + 6 O2 gives 6 CO2 + 6 H2O, yielding roughly 30 to 32 ATP per glucose.Example: Stages: glycolysis, pyruvate oxidation, citric acid cycle, oxidative phosphorylation.
Glycolysis: Splitting of one glucose into two pyruvate in the cytosol, with a net gain of 2 ATP and 2 NADH; needs no oxygen.Example: It occurs in nearly every living cell.
Citric acid cycle: Series of reactions in the mitochondrial matrix that fully oxidizes acetyl-CoA to CO2, producing NADH, FADH2 and a little ATP (or GTP).Example: Per glucose (two turns): 6 NADH, 2 FADH2, 2 ATP, 4 CO2.
Oxidative phosphorylation: The electron transport chain passes electrons from NADH and FADH2 to O2, pumping H+ across the inner mitochondrial membrane; H+ flowing back through ATP synthase makes most ATP.Example: Cyanide blocks the chain, halting ATP production.
Fermentation: Regeneration of NAD+ without oxygen so glycolysis can continue, producing lactate (animals, some bacteria) or ethanol and CO2 (yeast).Example: Sprinting muscles produce lactate when oxygen delivery falls short.
Photosynthesis: Conversion of light energy to chemical energy: light reactions make ATP and NADPH and release O2; the Calvin cycle uses them to fix CO2 into sugar.Example: 6 CO2 + 6 H2O + light gives C6H12O6 + 6 O2.

Cell cycle and division

Cell cycle: The repeating sequence of a dividing cell: interphase (G1, S where DNA replicates, G2) followed by the mitotic phase (mitosis and cytokinesis).Example: Most of a typical cell's time is spent in interphase.
Mitosis: Nuclear division producing two genetically identical nuclei; stages are prophase, prometaphase, metaphase, anaphase and telophase.Example: In anaphase, sister chromatids separate to opposite poles.
Meiosis: Two divisions that turn one diploid cell into four haploid, genetically different cells; the first division separates homologous chromosomes and the second separates sister chromatids.Example: Human gametes have 23 chromosomes, not 46.
Crossing over: Exchange of segments between non-sister chromatids of homologous chromosomes during prophase I of meiosis, creating new allele combinations.Example: Together with independent assortment, it explains why siblings differ.
Cell cycle checkpoints: Control points (G1, G2 and spindle checkpoints) where the cell checks DNA integrity and chromosome attachment before continuing; failures can lead to cancer.Example: The p53 protein can halt the cycle at G1 if DNA is damaged.