L2 Eukaryotic Organelles

Question 1

difference between prokaryotes and eurkaryotes

Answer 1

prokaryotes have no membrane bound organelles and nucleus while eukaryotes have

Question 2

definition of organelle

Answer 2

sub-cellular membrane-enclosed compartment that has a distinct structure, composition and function

(ribosome and centrosome are not organelles)

Question 3

major compartments of biological membrane

Answer 3

lipids:
- 50% in mass
- serve as barrier to prevent movement of hydrophilic materials in and out of organelles

proteins:
- 50% in mass
- contribute to functions of membrane

carbohydrates: to form polysaccharide chains

Question 4

properties of membrane lipids

Answer 4

classification: phosphoglyceride, sphingolipid, cholesterol

amphipathic: have both hydrophobic and hydrophilic regions (different from normal lipids like triacylglyerol which are just hydrophobic)

capable of self assembly: spontaneously form lipid bilayer in aqueous environment

Question 5

properties of membrane lipid bilayer

Answer 5

two leaflets: cytoplasmic (layer facing cytoplasm) and luminal/extracellular leaflet

impermeable to hydrophilic molecules

fluid in 2D: free diffusion within each leaflet but flip-flop is prohibited bc need to overcome high energy barrier

Question 6

what are the two classes of membrane proteins

Answer 6

integral (transmembrane):
- can be predicted by primary sequence of protein
- contain continuous stretch of hydrophobic amino acids (20a.a long, alpha helix)

peripheral:
- bind more loosely to membrane > dissociate more easily under harsh chemical conditions
- attach to integral proteins or lipids
- not permanently attached to membrane > cycle between cytosol and membrane depending on signals within cell

Question 7

how do detergents solubilise cell membranes

Answer 7

detergent is amphipathic

hydrophobic part insert into membrane > disrupt lipid-lipid interactions > displace phospholipid and cause breakdown

membrane proteins become coated with detergent > prevent aggregation

Question 8

properties of membrane carbohydrates

Answer 8

covalently attached to protein or lipid to form glycoprotein or glycolipid

asymmetrically localised: only located at extracellular space bc all enzymes involved in synthesis of these carbohydrate chains found only in extracellular space

Question 9

properties of endoplasmic reticulum

Answer 9

largest organelle

RER made up of membrane sheets (double membrane) while SER made up of membrane tubules (single membrane)

continuous membrane and luminal space > only one ER per cell

outer membrane of nuclear envelope continuous with RER

consist of ER exit site: place where proteins and lipids synthesised in ER packaged into transport vesicles for delivery to Golgi

Question 10

properties of nuclear envelope

Answer 10

double membrane

consist of nuclear pore:
- aqueous channel which is the only connection between nucleus and cytosol
- nuclear pore complex is a 8-fold rotational symmetry
- facilitates nucleocytoplasmic trafficking

Question 11

what happens during N-glycosylation in ER

Answer 11

process where carbohydrate is attached to nitrogen atom of an asparagine residue in protein > occurs when protein is being synthesised and folded in ER

Question 12

morphology and structure of Golgi complex

Answer 12

many mini stacks laterally connected by membrane

a mini stack:
- consist of 4-7 membrane sacs called cisternae
- polarised
- many budding profiles

Question 13

polarised structure of Golgi

Answer 13

cis Golgi network > cis cisterna > medial cisterna > trans cisterna > trans Golgi network

Question 14

properties of cilium

Answer 14

its a plasma membrane protrusion en-sheathing a bundle of microtubules

only present in animal cells

contains axoneme: bundle of microtubule which extends from basal body (centriole)