human higher bio

Stem cells

Unspecialised cells that can reproduce themselves by repeated mitosis while remaining undifferentiated, and can differentiate into specialised cells of various types when required by the multicellular organism.

Somatic cells

Any body cells not involved in reproduction that originate from stem cells; they divide by mitosis to maintain a diploid chromosome number of $46$ ($23$ homologous pairs) and form various body tissues.

Epithelial tissue

Tissue consisting of a single layer or multiple layers of cells that covers both internal and external body surfaces, such as the skin and the linings of the cheek, oesophagus, and blood vessels.

Connective tissue

Body tissue containing large amounts of extracellular material in the spaces between cells; this material can be solid (as in bone), fibrous or gelatinous (as in cartilage), or liquid (as in blood).

Muscle tissue

Tissue composed of cells capable of contraction to create movement, categorised into three types: skeletal, smooth, and cardiac.

Nerve tissue

Tissue composed of a network of neurons that receive and transmit nerve impulses, along with glial cells that support and maintain the neurons.

Germline cells

Cells located in the testes and ovaries that can divide by mitosis to produce diploid germline cells, or by meiosis to produce haploid sex cells (gametes).

Gametes

Sex cells produced by germline cells undergoing meiosis that contain a haploid number of $23$ single chromosomes.

Meiosis

A form of cell division in germline cells consisting of two successive divisions—the first separating homologous pairs of chromosomes, and the second separating chromatids—resulting in haploid gametes with $23$ single chromosomes.

Germline mutation

A mutation occurring within germline cells that is passed on to the next generation.

Cellular differentiation

The process by which unspecialised cells become specialised in structure and biochemical properties by expressing only a small fraction (about $3\text{--}5\text{\%}$) of their genes that code for the proteins required by that specific cell type.

Pluripotent

The developmental potential of embryonic stem cells from the very early embryo, in which all genes can be switched on, allowing them to differentiate into all the cell types that make up an individual.

Embryonic stem cells

Pluripotent cells derived from the very early embryo (blastocyst) capable of differentiating into any cell type of the individual.

Tissue stem cells

Multipotent stem cells found in specific tissues (such as the skin and red bone marrow) involved in growth, repair, and renewal of cells within that particular tissue type.

Multipotent

The limited differentiation potential characteristic of tissue stem cells, in which many genes are already switched off, restricting differentiation exclusively to cell types found within that specific tissue.

Red bone marrow stem cells

Multipotent tissue stem cells that undergo mitosis and differentiation to produce all varieties of blood cells (including red blood cells, platelets, phagocytes, and lymphocytes).

Cancer cells

Cells that divide excessively by mitosis because they fail to respond to regulatory signals and cell cycle controls, forming a mass of abnormal cells.

Tumour

A mass of abnormal cells formed as a result of excessive and uncontrolled cell division.

Benign tumour

A non-cancerous mass of abnormal cells that remains confined as a discrete group in one place within normal tissue.

Malignant tumour

A cancerous tumour whose cells lose surface molecules that keep them attached to the original group, allowing them to break off, enter the circulatory system, and spread through the body.

Secondary tumours

New tumours formed (seeded) in distant parts of the body after malignant cells break away from the primary tumour and travel through the circulatory system.

Carcinogens

Cancer-causing agents—such as the chemical compounds found in cigarette smoke or ionising ultraviolet radiation—that increase the risk of cancer by inducing cellular mutations.

Cellular Respiration

A series of metabolic pathways in living cells that release energy from a foodstuff (usually glucose) and regenerate the high-energy compound adenosine triphosphate ($\text{ATP}$).

Adenosine Triphosphate (ATP)

A high-energy molecule acting as the energy currency of the cell, composed of adenosine and three inorganic phosphate groups ($P_i$), which releases immediate energy when its terminal phosphate bond is broken.

Phosphorylation

An enzyme-controlled process in which a phosphate group is added to a molecule (such as $\text{ADP} + P_i \rightarrow \text{ATP}$), or transferred from ATP to a reactant to make it more reactive and energised.

Glycolysis

The breakdown of glucose into two $3\text{C}$ pyruvate molecules in the cell cytoplasm; it does not require oxygen and yields a net gain of ATP via energy investment and energy pay-off phases.

NAD

A hydrogen carrier coenzyme that binds hydrogen ions and electrons released by dehydrogenase enzymes during glycolysis and the citric acid cycle, becoming reduced to form $\text{NADH}$.

Mitochondrial Matrix

The fluid-filled interior compartment of a mitochondrion that contains enzymes and serves as the site for the citric acid cycle.

Cristae

The folds of the inner mitochondrial membrane where the electron transport chain takes place.

Citric Acid Cycle

A cyclic series of enzyme-controlled reactions in the mitochondrial matrix where $2\text{C}$ acetyl CoA combines with $4\text{C}$ oxaloacetate to produce $6\text{C}$ citrate, generating ATP, releasing $\text{CO}_2$, and producing NADH.

Acetyl Coenzyme A (Acetyl CoA)

A compound formed in the mitochondrial matrix when pyruvate is broken down into a $2\text{C}$ acetyl group and combines with coenzyme A, entering the citric acid cycle.

Oxaloacetate

The $4\text{C}$ compound in the citric acid cycle that combines with $2\text{C}$ acetyl CoA to form $6\text{C}$ citrate and is regenerated at the completion of the cycle.

Electron Transport Chain

A series of carrier proteins embedded in the inner mitochondrial membrane that transport electrons from NADH, using released energy to pump hydrogen ions ($H^+$) across the membrane into the intermembrane space.

ATP Synthase

An enzyme embedded in the inner mitochondrial membrane that rotates as hydrogen ions diffuse back into the matrix, catalysing the synthesis of ATP from ADP and $P_i$.

Oxygen (Respiration)

The final hydrogen and electron acceptor in the electron transport chain, which combines with hydrogen ions and electrons to produce water.

Fermentation

Anaerobic respiration occurring in the cytoplasm where only glycolysis proceeds, converting pyruvate into lactate in muscle cells to regenerate NAD and producing a net yield of $2\,\text{ATP}$.

Oxygen Debt

The cumulative demand for oxygen built up during vigorous exercise as lactate accumulates in muscles; repaid after exercise when aerobic energy converts lactate back to pyruvate and glucose in the liver.

Slow Twitch Muscle Fibres (Type 1)

Skeletal muscle fibres that rely predominantly on aerobic respiration; they contract slowly, sustain contractions longer, possess many mitochondria, a dense blood supply, high myoglobin content, and store fats as fuel.

Fast Twitch Muscle Fibres (Type 2)

Skeletal muscle fibres that generate ATP primarily through glycolysis; they contract rapidly, fatigue quickly, have fewer mitochondria, a lower blood supply, and store glycogen and creatine phosphate.

Myoglobin

An oxygen-storing protein found in high concentrations within slow twitch muscle fibres.

DNA Nucleotide

The basic building block of DNA, consisting of a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases (adenine, thymine, guanine, or cytosine).

Antiparallel

The structural arrangement of the two complementary strands in a DNA double helix running in opposite directions, one running from $3'$ to $5'$ and the other from $5'$ to $3'$.

DNA Polymerase

The enzyme that synthesizes new DNA strands by adding complementary nucleotides exclusively to the deoxyribose ($3'$) end of an existing strand or primer.

Helicase

The enzyme that unwinds the double helix and breaks the weak hydrogen bonds between base pairs, separating DNA strands at the replication fork.

Primer (Replication)

A short sequence of nucleotides complementary to the $3'$ end of a parent DNA strand that is required for DNA polymerase to initiate synthesis of a new strand.

Leading Strand

The strand of DNA replicated continuously towards the replication fork in the $5'$ to $3'$ direction.

Lagging Strand

The strand of DNA replicated discontinuously in fragments working away from the replication fork, with each fragment initiated by its own primer.

DNA Ligase

The enzyme that joins the fragments of the lagging strand together during DNA replication.

Polymerase Chain Reaction (PCR)

An in vitro technique used to amplify specific target sequences of DNA through repeated automated thermal cycles of heating and cooling in a thermal cycler.

Taq Polymerase

A heat-tolerant DNA polymerase enzyme used in PCR that synthesizes complementary DNA strands at temperatures between $70^\times\text{C}$ and $80^\times\text{C}$.

Gene Expression

The process by which information stored in DNA sequences is transcribed and translated into proteins, with only a fraction of genes expressed in any given cell.

RNA (Ribonucleic Acid)

A single-stranded nucleic acid composed of nucleotides containing a ribose sugar, a phosphate group, and the bases adenine, uracil, guanine, and cytosine.

RNA Polymerase

The enzyme responsible for transcription that binds to the gene's promoter region, unwinds DNA, and adds RNA nucleotides in a $5'$ to $3'$ direction to make the primary transcript.

Introns

Non-coding regions of a primary mRNA transcript that are removed during RNA splicing.

Exons

Coding regions of a gene that remain in the mature mRNA transcript after splicing and are translated into protein.

RNA Splicing

The process where non-coding introns are cut out from the primary transcript and coding exons are joined together to form a mature mRNA transcript.

Codon

A sequence of three consecutive nucleotides on an mRNA molecule that codes for a specific amino acid.

Transfer RNA (tRNA)

An RNA molecule folded into a three-dimensional shape by hydrogen bonds that carries a specific amino acid to the ribosome and features an exposed anticodon triplet.

Anticodon

A triplet of bases on a tRNA molecule complementary to a specific codon on the mRNA strand.

Ribosome tRNA Binding Sites

The three specialized sites on a ribosome: Site P (holds the tRNA carrying the growing polypeptide), Site A (holds the incoming tRNA with its amino acid), and Site E (releases discharged tRNA).

Alternative RNA Splicing

A process where different combinations of exons from the same primary RNA transcript are included or excluded, allowing multiple distinct mature mRNAs and protein isoforms to be produced from one gene.

Fibrous Proteins

Proteins arranged in long strand-like structural shapes, with examples including collagen and keratin.

Globular Proteins

Proteins folded into spherical shapes, examples of which include enzymes, antibodies, and hormones.

Conjugated Proteins

Proteins with a spherical shape that incorporate another non-protein chemical group, such as haemoglobin containing a haem group.

Missense Mutation

A single nucleotide substitution that causes one codon to code for a different amino acid, resulting in a protein that may be non-functional or have minor functional change.

Nonsense Mutation

A single nucleotide substitution that converts a codon into a premature stop codon, terminating translation early and producing an abnormally shortened protein.

Splice-site Mutation

A mutation occurring at intron-exon boundaries that creates or destroys splicing codons, causing introns to be retained or exons to be omitted from mature mRNA (e.g. Beta-thalassemia).

Frameshift Mutation

A mutation caused by the insertion or deletion of nucleotides that shifts the reading frame, altering all subsequent triplet codons and drastically changing protein structure.

Genome

The complete hereditary genetic information of an organism that is encoded within its DNA.

Human Genome Project

A collaborative scientific effort completed in April 2003 aimed at sequencing the $3\text{ billion}$ bases and identifying the approximately $100{,}000$ genes that compose human DNA.

Bioinformatics

The discipline combining computer technology, molecular biology, and statistical analysis to organize, store, search, and analyse enormous volumes of genetic and protein sequence data.

Pharmacogenetics

The study of how an individual's genetic makeup affects their response to drugs, enabling personalized dosages and identification of patients at risk of side effects.

Personalised Medicine

Medical care tailored to an individual's specific genome to provide the right drug, for the right disease, at the right time, and with the right dosage while minimizing toxicity.

Metabolic Pathway

A sequence of enzyme-controlled chemical reactions that changes one metabolite into another, with each step controlled by a gene-coded enzyme.

Anabolism

Biosynthetic metabolic pathways that build complex molecules from simpler ones, requiring an input of energy (e.g., joining amino acids to make protein).

Catabolism

Degradation metabolic pathways that break down complex molecules into simpler ones, releasing energy (e.g., glucose oxidation during respiration).

Activation Energy

The initial energy required to break chemical bonds and initiate a reaction; enzymes act by lowering this energy threshold.

Active Site

The specific region on an enzyme molecule where substrate molecules bind and undergo a chemical reaction.

Induced Fit

The mechanism whereby an enzyme active site slightly changes its shape to closely fit and bind the substrate.

Competitive Inhibitor

A substance chemically similar to the substrate that binds directly to the active site and blocks substrate binding; its inhibitory effect is overcome by increasing substrate concentration.

Non-Competitive Inhibitor

A substance that attaches to a site other than the active site, altering the shape of the active site so that the substrate cannot bind; its effect cannot be reversed by increasing substrate concentration.

Feedback Inhibition

A regulatory mechanism where the final product of a metabolic pathway builds up and binds to an enzyme early in the pathway (such as enzyme 1), slowing down the entire pathway by negative feedback.