10 - Eukaryotic structure and function* Flashcards
Multicellular forms of eukaryotic organisms
vertebrate and invertebrate animals, plants, algae and some fungi
Unicellular forms of eukaryotic organisms
protists (protozoa, microalgae), yeasts, many other fungi
what do all eukaryotic cells have in common
- membrane-delimited nuclei
- membrane-bound, compartmentalised organelles that perform specific functions
- intracytoplasmic membrane complex serves as transport system
- more structurally complex and generally larger than bacterial or archaeal cells
different ways of protection and retention of cell contents
- Plasma membrane
- Cell wall
- Glycocalyx
- Cytoplasm and cytoskeleton
Plasma membrane
- All eukaryotic cells have plasma membranes
- Similar in structure and function to that of prokaryotes
- Retains cell contents
- Controls exchange with the external environment
- Consists of a phospholipid bilayer with sphingolipids and sterols that effect permeability and transport
- Heterogenous with lipid rafts
Cell wall
Only plants, algae, fungi and some stages of parasites have cell walls.
Animal, protozoan and other eukaryotic cells lack cell walls and have less rigid cell shapes
What is the composition of eukaryotic cell walls
- Different to prokaryotes
- Plants: cellulose
- Fungi: Chitin, glycans, protein
- Algae: Pectins, cellulose
How is cell shape maintained in a cell membrane
- Chemicals (sterols) embedded in plasma membrane (lipid rafts)
- The cytoskeleton (network of flexible fibres and microtubules)
- Some protists have a thin protein ‘pellicle’ layer supporting the membrane
Glycocalyx
- Gel like external cell coating
- Usually carbohydrate
- Anchored to membrane
Functions of glycocalyx
- Strengthens cell surface
- Helps attach cells together
- Cell-cell recognition/signalling
- Protection
Cytoplasm
Complex structure of liquid component with structural framework that support the various different organelles
Cytoskeleton
The cytoskeleton is a scaffold within the cytoplasm that is composed of three types of filaments providing structural integrity and transport
3 filaments of the cytoskeleton
- Actin filaments (microfilaments)
- Intermediate filaments
- microtubules
Structures that control cell activities and processes
The nucleus and ribosomes
The nucleus
Cell control centre determining cellular activities, most prominent organelle. Information for cell control is encoded on numerous long, linear DNA chromosomes.
Nuclear envelope
A double membrane system that encloses the nucleus
Pores allow exchange with cytoplasm (eg movement of ribosome subunits)
Ribosomes
- Found in both eukaryotic and prokaryotic cells
- Eukaryotic cells have both 70S and 80S ribosomes (prokaryotic just 70S)
- 70S inside organelles (mitochondria, chloroplasts)
- 80S free in cytoplasm or rough ER
- Sites of protein synthesis
Structures that generate energy
Mitochondria and chloroplasts
Mitochondria
- Generate ATP (plasma membrane in prokaryotic)
- Smooth outer membrane and highly convoluted inner membrane (cristae)
- Fluid matrix contains all the chemicals necessary to make ATP from nutrient chemicals in cell
- Have 70S ribosomes and their own circular DNA, divide independently of cell
Chloroplasts
- Sunlight used to convert CO2 and water to ATP for cell use
- Double outer membrane enclosing thylakoids (Light harvesting pigments)
- 70S ribosomes, their own circular DNA, and divide independently of the cell
Constraints imposed by increasing cell size
- S/V ratio
- Chemical diffusion rates
- Chemical concentration rates
Surface to volume ratio
- Cells need a sufficient S/V ratio to enable nutrient uptake and waste removal that meets cell needs
- As cells get bigger, increase in V outstrips increase in S
- Exchange becomes limiting
Chemical diffusion rates
- Prokaryotes rely on diffusion of chemicals throughout the cytoplasm
- Diffusion takes longer with increasing cell size and hence increased diffusion distance
Chemical concentration
- Prokaryotes rely on random chemical collisions
in the cytoplasm - To maintain chemical concentrations, 8 times more chemical must be made for every doubling in size
- Manufacturing chemicals puts a big energy drain on cells
- Eukaryotic cells keep chemicals concentrated in packages within organelle
Two organelles that are essential network elements
- Rough endoplasmic reticulum (Construction of proteins and post transcriptional modification)
- Smooth endoplasmic reticulum (mainly protein and glycoprotein construction)
- Golgi apparatus
Endoplasmic reticulum
- A continuous, interconnected network of membrane tubes and flattened sacs spreading the cytoplasm
- Involved in protein and lipid synthesis
- Transports materials through the cell
- Rough ER is studded on its outer surface with ribosomes
- Proteins may be for: Membrane synthesis, Export from the cell or Transport within the cell
Golgi apparatus
- GA prepares materials for secretion
- ER buds off ‘transitional vesicles’ for transport of ER products to the GA
- Consists of stacked membrane sacs
- ER products are further modified in the GA for specialised use by the cell (e.g. addition of polysaccharides or lipids)
Products of the GA
- Glycocalyx
- Cell wall/membrane repair kits
- Digestive or degradative enzymes
- Antibodies and receptors
Functions of flagella and cilia
- Find food/prey/new hosts
- Orientate in the environment
- aid dispersal
- enable mating
Flagella and cilia
- Similar structure and action
- Extensions of the plasma membrane
- Cilia are shorter
- Both whip like and beat to move cell along
- Movement driven by sliding of microtubules in extended section (causes wave like movement)
how to eukaryotic flagella differ from prokaryotic flagella
prokaryotic flagella are rigid protein spirals and their action occurs by rotation
Name one other type of cell movement
Amoeboid movement
Lysosomes
- membrane bound bodies
help destroy/digest intracellular components
