10 - Eukaryotic structure and function*

Question 1

Multicellular forms of eukaryotic organisms

Answer 1

vertebrate and invertebrate animals, plants, algae and some fungi

Question 2

Unicellular forms of eukaryotic organisms

Answer 2

protists (protozoa, microalgae), yeasts, many other fungi

Question 3

what do all eukaryotic cells have in common

Answer 3

• 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

Question 4

different ways of protection and retention of cell contents

Answer 4

• Plasma membrane
• Cell wall
• Glycocalyx
• Cytoplasm and cytoskeleton

Question 5

Plasma membrane

Answer 5

• 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

Question 6

Cell wall

Answer 6

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

Question 7

What is the composition of eukaryotic cell walls

Answer 7

• Different to prokaryotes
• Plants: cellulose
• Fungi: Chitin, glycans, protein
• Algae: Pectins, cellulose

Question 8

How is cell shape maintained in a cell membrane

Answer 8

• 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

Question 9

Glycocalyx

Answer 9

• Gel like external cell coating
• Usually carbohydrate
• Anchored to membrane

Question 10

Functions of glycocalyx

Answer 10

• Strengthens cell surface
• Helps attach cells together
• Cell-cell recognition/signalling
• Protection

Question 11

Cytoplasm

Answer 11

Complex structure of liquid component with structural framework that support the various different organelles

Question 12

Cytoskeleton

Answer 12

The cytoskeleton is a scaffold within the cytoplasm that is composed of three types of filaments providing structural integrity and transport

Question 13

3 filaments of the cytoskeleton

Answer 13

• Actin filaments (microfilaments)
• Intermediate filaments
• microtubules

Question 14

Structures that control cell activities and processes

Answer 14

The nucleus and ribosomes

Question 15

The nucleus

Answer 15

Cell control centre determining cellular activities, most prominent organelle. Information for cell control is encoded on numerous long, linear DNA chromosomes.

Question 16

Nuclear envelope

Answer 16

A double membrane system that encloses the nucleus

Pores allow exchange with cytoplasm (eg movement of ribosome subunits)

Question 17

Ribosomes

Answer 17

• 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

Question 18

Structures that generate energy

Answer 18

Mitochondria and chloroplasts

Question 19

Mitochondria

Answer 19

• 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

Question 20

Chloroplasts

Answer 20

• 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

Question 21

Constraints imposed by increasing cell size

Answer 21

• S/V ratio
• Chemical diffusion rates
• Chemical concentration rates

Question 22

Surface to volume ratio

Answer 22

• 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

Question 23

Chemical diffusion rates

Answer 23

• Prokaryotes rely on diffusion of chemicals throughout the cytoplasm
• Diffusion takes longer with increasing cell size and hence increased diffusion distance

Question 24

Chemical concentration

Answer 24

• 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

Question 25

Two organelles that are essential network elements

Answer 25

- Rough endoplasmic reticulum (Construction of proteins and post transcriptional modification) - Smooth endoplasmic reticulum (mainly protein and glycoprotein construction) - Golgi apparatus

Question 26

Endoplasmic reticulum

Answer 26

- 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

Question 27

Golgi apparatus

Answer 27

- 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)

Question 28

Products of the GA

Answer 28

- Glycocalyx - Cell wall/membrane repair kits - Digestive or degradative enzymes - Antibodies and receptors

Question 29

Functions of flagella and cilia

Answer 29

- Find food/prey/new hosts - Orientate in the environment - aid dispersal - enable mating

Question 30

Flagella and cilia

Answer 30

- 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)

Question 31

how to eukaryotic flagella differ from prokaryotic flagella

Answer 31

prokaryotic flagella are rigid protein spirals and their action occurs by rotation

Question 32

Name one other type of cell movement

Answer 32

Amoeboid movement

Question 33

Lysosomes

Answer 33

- membrane bound bodies help destroy/digest intracellular components