Introduction: Principles of Biology

Introduction 22 March 2025 Name Structure Function Plasma Membrane Phospholipid bilayer with embedded protein Form barrier from external environment; regulates the passage of materials across the membrane (permeability) Nucleus Enclosed by double lipid lilayer nuclear envelop, contains chromosomes. Largest organelle Control centre of cell; directs synthesis of ribosomes and proteins; pores regulate movement of substances (eg protein and mRNA) in and out Nucleolus spherical structure found in the cell's nucleus rRNA production and transcription; assembly of small and large subunits of ribosomes Cytoplasm A gelatinous fluid inside the plasma membrane including the organelles but not the nucleus Supports organelles and other cellular components in the cell; act as a medium for transport Cytosol The fluid portion of the cytoplasm, made of water plus dissolved and suspended substances (ions, ATP, proteins, lipids) Platform for cellular functions Ribosomes Floating within cytoplasm or attached to cytoplasmic side of plasma membrane or endoplasmic reticulum Free in the cytoplasm: protein production (translation) to be used in within the cell Attached to the RER: protein production (translation) for secretion, use in lysosome or extracellular signalling Rough Endoplasmic Reticulum Continuous with nuclear envelope attached with ribosomes Production of secreted, membrane, organelle proteins Smooth Endoplasmic Reticulum Extends from the rough ER, lacks ribosomes Housing unit for proteins and enzymes (cell/tissue type specific); synthesizes lipids (including steroids and phospholipids); storage of cell-specific proteins Golgi apparatus A stack of 3-20 flattened membranous sacs called cisternae Modify, sort, package and transport newly synthesized proteins received from the RER using enzymes in each cisternae; formation of secretory vesicles Vesicle Membrane-bound sac Stores and transport substances Lysosomes Contains hydrolytic digestive enzymes Digests macromolecules and cell debris (recycling) (cell component- autophagy, entire cells- autolysis) Mitochondria With outer and inner mitochondrial membrane, with cristae; fluid filled interior cavity: mitochondrial matrix Generation of ATP through cellular respiration Cytoskeleton: Microfilaments Actin strands interwined; smallest Dynamic; bear tension and weight by Found around the periphery and lining the anchoring cytoskeleton to plasma membrane interior of cell proteins, and promote amoeboid motility if required; muscle contraction Cytoskeleton: Intermediate filaments Fibrous proteins (keratin) coiled into cables; found in the cytoplasm Act as scaffold for cellular organelles; cell tension and weight support; formation of nuclear lamina; less dynamic Cytoskeleton: Microtubules Tubular structure with central lumen, alpha and beta tubulin; biggest Extends from centriole into cytoplasm/nucleus Cell division; support and movement of cilia/flagella; guide movement of vesicle from golgi to membrane; cell shape support; dynamic