Greek Roots in Biology

Lipids

• Refers to a collection of organic molecules of varying chemical composition: fatty acids, glycerides, nonglyceride lipids, and complex lipids.
• Includes sterol derivatives.

Biological Functions of Lipids

• Energy source: each gram of fat releases 9 kcal of energy.
• Energy storage: in the form of triglycerides (TAG) in adipocytes.
• Cell membrane structural components: phosphoglycerides, sphingolipids, and steroids make up the basic structure of all cell membranes.
• Hormones: eicosanoids and steroid hormones.
• Vitamins: lipid-soluble vitamins (A, D, E, and K).
• Vitamin absorption: dietary fat serves as a carrier of lipid-soluble vitamins.
• Protection: fats as shock absorbers.
• Insulation: subcutaneous fat.

Eicosanoids

• Act as paracrine signals.
• Derived from arachidonic acid.
• Are drug targets.

Sterols and Derivatives

• Sterols are amphipathic (contain polar and nonpolar parts) and planar (flat).
• No rotation around carbon bonds.
• Cholesterol is a sterol derivative.
• Bile salts: derived from cholesterol, amphipathic, and enable fat absorption.

Synthesis of Lipids

• Lipids are built from acetate.
• Acetate is converted to Acetyl-Coenzyme A (Acetyl-CoA).
• Fatty acids and sterols are made from Acetyl-CoA.
• Fatty acids are built two carbons at a time.
• Palmitate is the precursor of fatty acids.
• Longer chain fatty acids are made by fatty acid elongation systems in the smooth ER.

Steroid Hormones

• Derived from sterol.
• Act as cellular messengers.
• Many drugs are steroid analogues.
• Examples: sex hormones (e.g., progesterone) and corticosteroids.

Vitamins

• Water-soluble vitamins: B class (1, 2, 3, 5, 6, 7, 9, 12) and C.
• Fat-soluble vitamins: A, D, E, and K.
• Vitamin A (Retinol): important in skin cells and vision.
• Vitamin D: made from 7-dehydrocholesterol, controls calcium metabolism.
• Vitamin K: used as an antidote against rat poison and as a treatment for anticoagulant overdose.

Cell Signalling

• Cell signalling is the communication between cells, involving a chemical messenger (signal/ligand) released by the signalling cell.
• The signal is detected by the responding cell (receptor), triggering intracellular reactions that influence the behaviour of the responding cell.

Tasks of Cell Communication

• Signal release: synthesis and excretion of the signalling molecule by the signalling cell.
• Signal detection: interaction of signal and receptor.
• Signal transduction: translation of detection to changes in cell physiology or gene expression.

Types of Signals

• Paracrine signals: act on a local set of cells.
• Autocrine signals: act on the secreting cell itself.
• Endocrine signals: long-range signals moving through the bloodstream.

Signalling and Control of Gene Expression

• Cell-cell signalling can change the repertoire of transcription factors in the responding cell, resulting in different gene expression.
• Some signals can form gradients, and cell fate depends on signal concentration.

Signal Entry into the Cell

• Two strategies for signal entry:
  • The signal can pass through the plasma membrane (e.g., nuclear receptors).
  • The signal can activate a membrane receptor (e.g., G protein linked receptors, Serine/threonine kinase receptors).

Nuclear Receptors

• Signals are steroids or retinoids.
• These signals can pass through the plasma membrane and encounter nuclear receptors in the cytoplasm.
• The receptor-ligand complex then enters the nucleus to activate genes.

Signalling through Nuclear Receptors

• Nuclear receptors like the glucocorticoid receptor are cytoplasmic proteins.
• In their inactive form, they are bound to Hsp chaperones.
• Ligand binding releases the Hsp, and the receptor-ligand complex moves to the nucleus to activate the transcription of target genes.

G-Protein Linked Receptors

• Transmembrane receptors are linked to a G-protein.
• Upon ligand binding, the G protein releases GDP and takes up GTP.
• Ga dissociates from Gbg and activates downstream 'second messengers' (e.g., cAMP).
• GTP is hydrolyzed to GDP, and Ga reassociates with Gbg.

Serine/Threonine Kinase Receptors

• Transmembrane receptors that bind the TGFb family of signals.
• Ligand brings together type I and type II receptors.
• Type II phosphorylates type I.
• Smads become phosphorylated and move into the nucleus to act as transcription factors.

Cell Signalling

• Cell signalling is the communication between cells, involving a chemical messenger (signal/ligand) released by the signalling cell.
• The signal is detected by the responding cell (receptor), triggering intracellular reactions that influence the behaviour of the responding cell.

Tasks of Cell Communication

• Signal release: synthesis and excretion of the signalling molecule by the signalling cell.
• Signal detection: interaction of signal and receptor.
• Signal transduction: translation of detection to changes in cell physiology or gene expression.

Types of Signals

• Paracrine signals: act on a local set of cells.
• Autocrine signals: act on the secreting cell itself.
• Endocrine signals: long-range signals moving through the bloodstream.

Signalling and Control of Gene Expression

• Cell-cell signalling can change the repertoire of transcription factors in the responding cell, resulting in different gene expression.
• Some signals can form gradients, and cell fate depends on signal concentration.

Signal Entry into the Cell

• Two strategies for signal entry:
  • The signal can pass through the plasma membrane (e.g., nuclear receptors).
  • The signal can activate a membrane receptor (e.g., G protein linked receptors, Serine/threonine kinase receptors).

Nuclear Receptors

• Signals are steroids or retinoids.
• These signals can pass through the plasma membrane and encounter nuclear receptors in the cytoplasm.
• The receptor-ligand complex then enters the nucleus to activate genes.

Signalling through Nuclear Receptors

• Nuclear receptors like the glucocorticoid receptor are cytoplasmic proteins.
• In their inactive form, they are bound to Hsp chaperones.
• Ligand binding releases the Hsp, and the receptor-ligand complex moves to the nucleus to activate the transcription of target genes.

G-Protein Linked Receptors

• Transmembrane receptors are linked to a G-protein.
• Upon ligand binding, the G protein releases GDP and takes up GTP.
• Ga dissociates from Gbg and activates downstream 'second messengers' (e.g., cAMP).
• GTP is hydrolyzed to GDP, and Ga reassociates with Gbg.

Serine/Threonine Kinase Receptors

• Transmembrane receptors that bind the TGFb family of signals.
• Ligand brings together type I and type II receptors.
• Type II phosphorylates type I.
• Smads become phosphorylated and move into the nucleus to act as transcription factors.

Learn how Greek roots like 'eikosi' and 'para' are used to describe biological concepts like eicosanoids, which are fatty acid derivatives with a 20-carbon chain.