3.2.1.1 Structure of Eukaryotic Cells

eukaryotic cell

-DNA is contained in a nucleus and contains membrane-bound specialised organelles

-also means ‘true nucleus’

FEATURES + FUNCTIONS -cell-surface membrane

-’fluid mosaic’ phospholipid bilayer with extrinsic and intrinsic proteins embedded

functions = isolates cytoplasm from extracellular environment, is selectively permeable so controls transport of substances in and out of cell

-nucleus

surrounded by nuclear envelope - a double membrane

this has nuclear pores - allows molecules to enter and exit

contains nucleoplasm and histone proteins which wind around DNA as there is lots of it

contains nucleolus - manufactures ribosomal RNA and assembles ribosomes

contains chromosomes - consists of chromatin (protein-bound linear DNA) - controls protein synthesis

functions = stores genetic information, where DNA replication occurs, production of mRNA

-mitochondria

-has a double membrane (outer and inner), where inner is folded to form cristae (provides large surface area), inside the inner is matrix (contains enzymes, circular mitochondrial DNA and ribosomes)

function = site of aerobic respiration to produce ATP

-chloroplast

-surrounded by a double membrane, contains thylakoids (membrane-bound flattened discs) which contain chlorophyll, when stacked they form granum, contains stroma (fluid filled matrix), contains circular DNA, ribosomes and starch grains

function = site of photosynthesis to convert solar energy to chemical energy

exocytosis

the process of how proteins are exported from cells

-golgi apparatus

-consists of cisternae (stack of membrane-bounded, flattened sacs in cytoplasm)

functions = modifies proteins or triglycerides from rER for exocytosis, often adds proteins to triglycerides or carbohydrates to proteins to form glycoproteins

-once modified, they are packaged into golgi vesicles which transport them and fuse with the cell membrane and secrete the proteins by exocytosis

-lysosomes

-membrane-bound organelle that releases hydrolytic enzymes

functions = digests the contents of phagosomes from phagocytosis, destroys worn-out organelles, release enzymes by exocytosis

-ribosomes

-formed of protein and RNA and are free in the cytoplasm or attached to the ER

-eukaryotes contain 80S ribosomes

function = site of protein synthesis - large subunit: joins amino acids, small subunit: contains mRNA binding site

-rough endoplasmic reticulum (rER)

-consists of cisternae (stack of membrane-bounded, flattened sacs in cytoplasm) and has ribosomes attached to its surface

function = site of protein synthesis and transport to golgi apparatus

-smooth endoplasmic reticulum (sER)

-has no ribosomes on its surface

function = site of lipid and carbohydrate synthesis and also transport

-cell wall

-only in plant and fungi cells

-consists of polysaccharides = in plant, it consists of cellulose microfibrils and in fungi, it consists of chitin, has a middle lamella (thin layer that acts as boundary between adjacent cell walls)

functions = provides mechanical support and protection, prevents cell from bursting

-cell vacuole

-only in plant cells

-a sac bounded by a single membrane (tonoplast) containing cell sap (mineral salts, pigments, organic acids, etc)

functions = stores waste products, has low water potential so controls turgidity of cell, pigments can attract pollinators

complex multicellular organisms

-eukaryotic cells become specialised for specific functions

-specialised cells organised into tissues, tissues into organs, organs into systems