Cell Structure and Function

Eukaryotic cell definition

a cell containing a true nucleus enclosed by a nuclear envelope and membrane-bound organelles

Main characteristic of eukaryotic cells

compartmentalisation with specialised membrane-bound organelles performing distinct functions

Difference between eukaryotic and prokaryotic cells

eukaryotes have nucleus and organelles; prokaryotes lack both

Compartmentalisation in eukaryotic cells

division of cellular processes into separate membrane-bound organelles for efficiency

Nucleus function

stores DNA, controls gene expression, DNA replication, transcription, and rRNA synthesis

Nuclear envelope function

double membrane that separates nuclear contents from cytoplasm

Nucleolus function

site of rRNA synthesis and ribosome assembly

Endoplasmic reticulum (ER) structure

branched membrane network continuous with nuclear envelope

Rough ER function

synthesis of membrane-bound, secretory, and lysosomal proteins

Smooth ER function

synthesis of lipids, phospholipids, fatty acids, cholesterol, and steroids

Golgi apparatus function

modifies, sorts, and packages proteins for secretion or transport

Golgi structure

stacked, disc-shaped membranous cisternae

Mitochondria function

ATP production and metabolic pathways (energy generation)

Mitochondria structure

double membrane with inner membrane folds (cristae) and matrix

Lysosome function

intracellular digestion of foreign materials and damaged organelles

Lysosome content

hydrolytic enzymes in acidic vesicles

Peroxisome function

detoxification and oxidation of very long-chain fatty acids and amino acids

Peroxisome enzyme example

catalase for hydrogen peroxide breakdown

Vacuole function

storage, autophagy, and transport (endocytosis/exocytosis roles)

Cytoskeleton definition

dynamic protein network providing structure, movement, and organisation in cells

Main cytoskeleton components

microfilaments, intermediate filaments, and microtubules

Microfilaments structure

thin actin filaments that are dynamic and flexible

Microfilament function

cell movement, shape changes, and contraction

Intermediate filaments structure

rope-like fibres such as keratin and spectrin

Intermediate filament function

mechanical strength and tissue integrity

Microtubules structure

hollow tubes made of tubulin, largest cytoskeletal filaments

Microtubule function

organelle transport, cell division, cilia and flagella movement

Motor proteins function

move along cytoskeleton transporting vesicles and organelles

Examples of motor proteins

kinesin, dynein, and myosin

Cell junction function

link cells together and connect cytoskeletons for structural and signalling roles

Tight junction function

seal cells to prevent leakage (linked to actin)

Adherens junction function

cell adhesion belt linked to actin cytoskeleton

Desmosome function

strong mechanical attachment linked to intermediate filaments

Hemidesmosome function

anchors cells to basement membrane via intermediate filaments

Gap junction function

allows cell communication via ions and small molecules

Integrin function

connects extracellular matrix to intracellular cytoskeleton

ECM definition

non-cellular network surrounding cells in connective tissues

ECM main components

fibres (collagen, elastic, reticular) and ground substance

Collagen fibre function

provides tensile strength and prevents tissue tearing

Elastic fibre function

allows stretch and recoil of tissues

Reticular fibre function

forms supportive framework in soft organs

Ground substance definition

gel-like ECM material filling space between cells and fibres

Glycosaminoglycans (GAGs) function

attract water and provide hydration and resistance to compression

Proteoglycan function

bind ECM components and provide structural support and signalling regulation

Fibronectin and laminin function

cell adhesion glycoproteins linking cells to ECM

ECM function overall

structural support, cell signalling, nutrient diffusion, and tissue organisation