4.2 - The eukaryotic cell

Question 1

bacterium cell (4)

Answer 1

1. cell wall
2. cell membrane
3. DNA (not in nucleus)
4. flagellum

Question 2

animal cell (4)

Answer 2

1. fibroblast (DNA in nucleus)
2. mitochondria
3. many organelles
4. cytoskeleton

Question 3

plant cell (4)

Answer 3

1. cell wall
2. vacuole
3. chloroplasts
4. rigid

Question 4

features of eukaryotic nucleus (3)

Answer 4

1. nucleolus within nucleus produces ribosomal RNA
2. double membrane penetrated by pores (allow transport in/out)
3. ribosomes stud outer membrane

Question 5

nuclear pore complex

Answer 5

gate through which selected macromolecules and larger complexes can enter/exit

Question 6

protein nuclear localisation/export signals

Answer 6

signals in amino acid sequence, directs proteins to/out of nucleus

Question 7

which nuclear signal do mRNAs have?

Answer 7

nuclear export signal

Question 8

endoplasmic reticulum structure

Answer 8

1. membranous network
2. rough ER studded with ribosomes

Question 9

role of endoplasmic reticulum (rough and smooth)

Answer 9

rough - protein synthesis (translation)
smooth - synthesis/ modification of lipids and storage of Ca2+ ions used in intracellular signalling

Question 10

rough ER role in protein synthesis (3)

Answer 10

1. ribosomes enter lumen of rough ER
2. modified, re-folded and packaged into vesicles
3. transported in vesicles to other parts of endomembrane system (often golgi)

Question 11

golgi apparatus

Answer 11

involved in protein sorting and vesicle trafficking

Question 12

how does the golgi apparatus transport components of the cell?

Answer 12

transport vesicles bud from one membrane and fuse with another, carrying membrane components and soluble proteins between compartments of endomembrane system and plasma membrane

Question 13

endomembrane system

Answer 13

network of interconnected membranous organelles in eukaryotic cells

Question 14

plasma membrane

Answer 14

phospholipid bilayer

Question 15

exocytosis (2)

Answer 15

1. vesicle fuses with plasma membrane
2. releases content into cell’s surrounding

Question 16

endocytosis (2)

Answer 16

1. extracellular materials captured by vesicles that bud inward from plasma membrane
2. carried into cell
   (can be receptor-mediated)

Question 17

lysosomes

Answer 17

contain hydrolytic enzymes (promote hydrolysis)

Question 18

role of lysosomes (2)

Answer 18

1. each pathway leads to intracellular digestion of materials derived from a different source
2. phagosomes can fuse with lysosomes to release lysosome enzymes, killing pathogen

Question 19

vacuoles

Answer 19

1. found in many cells, some prokaryotic many eukaryotic
2. typically small, membrane bound storage compartments, variety of functions

Question 20

main purpose of plant cell vacuole (large, central vacuole)

Answer 20

maintain turgor pressure within cell (can be adjusted with water uptake/loss)

Question 21

eukaryotic cell: single membrane organelles (4)

Answer 21

1. endoplasmic reticulum
2. golgi apparatus
3. lysosome
4. vesicles

Question 22

eukaryotic cell: double membrane organelles (3)

Answer 22

1. nucleus
2. mitochondria
3. chloroplast

Question 23

fluid mosaic model

Answer 23

1. proteins can be embedded/associated with membrane
2. membrane proteins/phospholipids in outer membrane can be glycosylated (sugars attached)
3. these carbohydrates protect and lubricate cell (also role in cell recognition and adhesion)

Question 24

role of proteins in phospholipid bilayer

Answer 24

mitigate permeability and transfer information

Question 25

why are phospholipid bilayers usually electrically polarised?

Answer 25

ion gradients across membrane

Question 26

functions of phospholipid bilayer (5)

Answer 26

1. signalling 2. import/export 3. separating reactions 4. generating proton gradient for ATP synthesis 5. transmitting nerve signals etc

Question 27

amphipathic

Answer 27

phospholipid bilayer - hydrophilic head (phosphate group) and hydrophobic tail (fatty acids joined by glycerol)

Question 28

how do phospholipid bilayers form in aqueous environment?

Answer 28

1. phospholipids spontaneously form bilayers - hydrophobic core and hydrophilic surface/vesicles 2. nonpolar portions aggregate - fewer water molecules ordered (entropy increases) 3. hydrophobic effect powers membrane formation

Question 29

what forces stabilise phospholipid bilayer membrane?

Answer 29

van der waals between hydrophobic tails

Question 30

phosphatidylcholine (2)

Answer 30

1. major component of most eukaryotic membranes 2. head of choline + phosphate, 2 fatty acid chains linked by glycerol (many prokaryotes can't synthesise this lipid)

Question 31

what does the presence of C=C bonds introduce in phospholipid bilayers

Answer 31

create kinks in fatty acid tails

Question 32

role of cholesterol in phospholipid bilayer membrane (3)

Answer 32

1. can fill spaces between phospholipid molecules generated by kinks 2. "buffers" membrane fluidity 3. different effects depending on temperature

Question 33

archaeal membranes

Answer 33

better membrane stability by ether linkages and branching structures prevent hydrolysis and oxidation of membranes

Question 34

archaeal membrane composition

Answer 34

isoprenoid tetraethers with unique alcohols (differs from glycerol)

Question 35

what determines whether lipid bilayer is gel or fluid phase?

Answer 35

composition and temperature

Question 36

phospholipid bilayer gel phase

Answer 36

molecules cant move around

Question 37

phospholipid bilayer fluid phase

Answer 37

molecules can move around

Question 38

membrane more fluid-like or gel-like under physiological conditions?

Answer 38

fluid-like

Question 39

melting point

Answer 39

temperature at which membrane transitions from highly ordered to very fluid (dependant on length of fatty acids in membrane, lipid and degree of cis uncaturation)

Question 40

higher temp membrane requirements

Answer 40

need more long, saturated fatty acids

Question 41

lower temp membrane requirements

Answer 41

need more unsaturated fatty acids

Question 42

membrane permeability

Answer 42

permeable to small nonpolar molecules that can passively diffuse through. impermeable to polar molecules and ions

Question 43

passive diffusion

Answer 43

transport of solutes influenced by both concentration gradient and membrane potential

Question 44

where may passive diffusion occur

Answer 44

channels or transporters

Question 45

active transport

Answer 45

requires energy input to move against concentration gradient

Question 46

where can active transport be performed

Answer 46

transporters

Question 47

membrane fusion (2)

Answer 47

1. membranes can fuse without exposure of lipids to aqueous solvent (membrane faces conserved) 2. spontaneous or protein mediated

Question 48

what allows release of molecules such as neurotransmitters from cell?

Answer 48

fusion of internal membranes with plasma membrane