Lecture 2: The Secretory Pathway in Eukaryotic Cells

Question 1

Molecules must be transported within and into/out of the cell. The molecules are parcelled in …

Answer 1

VESICLES

Question 2

Lysosome…

Answer 2

Contains digestive enzymes that break down cell parts or substances entering the cell by vesicles

Question 3

Smooth Endoplasmic reticulum..

Answer 3

Synthesises lipids and have various other functions

Question 4

Golgi apparatus…basic

Answer 4

modifies lipids and proteins from the ER; sorts and packages them into vesicles

Question 5

Rough Endoplasmic reticulum…

Answer 5

synthesises proteins and packages them into vesicles. (folding and assembly)

Question 6

In man, __ of genes that code for proteins that enter the __

Answer 6

1/3 & Endoplasmic reticulum

Question 7

______ must fold and be modified correctly in the __ before being transported via the ___ ____ to the cell surface or to lysosome/vacuoles

Answer 7

Polypeptides
ER
golgi apparatus

Question 8

Protein translocation via TRANSLOCAN pore

Answer 8

N-terminal signal peptide is removed while the new polypeptide is emerging into the ER lumen

Question 9

The ER lumen is specialised for:

Answer 9

folding, assembly, modification, quality control and recycling

Question 10

how do proteins enhance stability before secretion?

Answer 10

by undergoing processes such as glycosylation & disulphide bond formation

Question 11

Glycosylation:

Answer 11

process by which sugars are attached to proteins

Question 12

ER in cells is dynamic, movement is dependant on..

Answer 12

actin/myosin in plants and microtubules in animals

Question 13

The golgi apparatus…

Answer 13

the distribution, shipping (& manufacturing) department for many of the cells chemical products (proteins, carbohydrates and lipids).

Question 14

Vesicle traffic..

Answer 14

Transport vesicle with kinesin strand attached. ATP is required for every step, ATP –> ADP + Pi. Move along microtubule towards + end. A protein complex enables vesicles to dock and fuse wit their target membranes precisely.

Question 15

E.g. of protein type secreted via Golgi in vertebrates (Serum proteins)

Answer 15

E.g. = albumin

cellular site of synthesis: hepatocyte (liver)

Question 16

E.g. of protein type secreted via Golgi in vertebrates (extracellular matrix proteins)

Answer 16

E.g. Collagen

cellular site of synthesis: fibroblast

Question 17

E.g. of protein type secreted via Golgi in vertebrates (peptide hormone)

Answer 17

e.g. insulin

cellular site of synthesis: pancreatic B-islet cells

Question 18

E.g. of protein type secreted via Golgi in vertebrates (digestive enzymes)

Answer 18

E.g. trypsin, amylase

cellular site of synthesis: Pancreatic acini

Question 19

E.g. of protein type secreted via Golgi in vertebrates (milk proteins)

Answer 19

E.g. Casein, lactalbumin

cellular site of synthesis: mammary gland

Question 20

E.g. of protein type secreted via Golgi in vertebrates (Glycoprotein)

Answer 20

E.g. Mucus

cellular site of synthesis: widespread

Question 21

Role of ER and Golgi in MILK SECRETION

Answer 21

1. Transport of ions and water
2. SMOOTH ER: formation of cytoplasmic lipid vesicles & lipid secretion
3. ROUGH ER: synthesis of milk protein (casein) & vesicle delivery via Golgi. Synthesise of lactose from Glc & UDP - Gal occurs in Golgi.
4. Vesicular movement (immunoglobulins)

Question 22

UDP - Gal and Glc meanings

Answer 22

Uridine diphosphate galactose

Glucose

Question 23

Immunoglobulins..

Answer 23

any of a class of proteins present in the serum and cells of the immune system, which function as antibodies.

Question 24

Protein bodies:

Answer 24

Proteins stored for growth & development (eg. eggs)

Question 25

Plants store proteins in protein bodies (_______) to provide ______ for rapid growth &eg

Answer 25

vacuoles
C N & F
eg; Ricin from castor bean

Question 26

Castor bean seeds contain..

Answer 26

ricin (a lectin) a potent cytotoxin. Anti-herbivory

Question 27

Ricin stored in

Answer 27

protein bodies

Question 28

Castor bean: How does ricin work

Answer 28

inhibits protein synthesis by irreversibly inactivating eukaryotic ribosomes. When seed germinates, ricin is rapidly degraded.

Question 29

Castor bean: How is ricin synthesised and how does the plant avoid poisoning its own ribosomes

Answer 29

as proricin that contains both A and B chains. Proricin modified within the GOLGI, then transported to the PROTEIN BODIES. Ricin not catalytically active until proteolytically cleaved within the protein bodies - hence avoids poisoning

Question 30

Assassination with Ricin

Answer 30

Pellet from the tip of an umbrella that had some ricin on it was used to assassinate Giorgi Markov in 1978 - v little needed

Question 31

Understanding sub cellular targeting can help engineer _____ production in plants. E.g.

Answer 31

PROTEIN
Insulin;
-Demand for insulin will potentially double over next ten years.
-Insulin can form 0.24% of total seed protein in this ER-directed version of Arabidopsis.
- 0.4 Kg.ha-1 of insulin in safflower. 6,500 hectares of safflower insulin would meet world demand.

Question 32

Quality control in the ER

Answer 32

-Proteins that are recognised as being incompletely or incorrectly folded (e.g. mutants) are retained within the ER & targeted for degradation by lysosomes or proteasome.

Question 33

Chaperons:

Answer 33

are proteins that assist the correct intracellular folding and assembly of polypeptides.

Question 34

ERAD;

Answer 34

ER-associated protein degradation

Question 35

CFTR; and what does it do

Answer 35

Cystic Fibrosis transmembrane conductance regulator is a chloride ABC transporter.

Question 36

ER quality control & cystic fibrosis

Answer 36

• CFTR is a chloride ABC transporter
• Epithelia lining sweat gland ducts fail to take up Cl efficiently from the lumen
• Lack of CFTR allows accumulation of mucus, in the lungs & pancreas, so digestive enzymes cannot get into the intestine

Question 37

Onemutationcausingcysticfibrosis(70%ofsufferers) results in lack of

Answer 37

Phe508, but does NOT affect channel function (ability to take up Cl) –> SINGLE MUTATION.
-Quality control check in the ER: the mutant protein fails to leave the ER. - believes there is a mistake v. sensitive

Question 38

what cells are vacuoles and lysosomes present in

Answer 38

Plantandfungalcells,someprotist, animal and bacterial cells.

Question 39

Autophagy:

Answer 39

destruction of damaged or redundant cellular components in vacuoles

Question 40

Vacuole and lysosome jobs

Answer 40

Autophagy, lysis and recycling of mis‐ folded proteins

Question 41

Vacuole and lysosome volume in epidermal cells

Answer 41

99% volume

Question 42

Vacuole and lysosome volume in mesophyll cells

Answer 42

~70% volume

Question 43

What do vacuoles and lysosome store & isolate

Answer 43

• Storage of carbohydrates, organic acids, anthocyanins, seed storage proteins.
• Isolation of toxic substances(Na,Al).

Question 44

Are Vacuoles and lysosomes anti-herbivory?

Answer 44

YES; Tannins are the most abundant secondary metabolites made by plants, from 5‐10% dry weight of tree leaves. Cyanogenic glucosides. Ricin.

Question 45

Cyanogenic glucosides

Answer 45

Hydrogen cyanide is released from the cyanogenic glycosides when fresh plant material is macerated as in chewing, which allows enzymes and cyanogenic glycosides to come together, releasing hydrogen cyanide.

Question 46

Vacuoles and lysosomes maintain..

Answer 46

internal hydrostatic pressure (cell turgor)

Question 47

Cyanogenesis how many species and e,g,

Answer 47

3000 species including white clover, flax, almonds, sorghum, wild lima bean, and cassava. Anti herbivory.

Question 48

Cassava is a major source of…

Answer 48

calories for man in sub‐Saharan Africa.

Question 49

Where cassava and lima beans comprise the major item of the diet…

Answer 49

chronic cyanide poisoning exists.

Question 50

Sweet and bitter amount of HCN and lethal dose

Answer 50

Sweet cassava roots: < 50 mg.Kg‐ 1 FWt HCN
Bitter roots: 400 mg.Kg-1FWt.
Lethal dose is 0.5 - 3.5 mg.Kg-1 of body weight

Question 51

In Sorghum leaves what the cyanogenic glucoside called

Answer 51

dhurrin

Question 52

Cyanogenesis and compartmentation; Sorghum leaves

Answer 52

In Sorghum leaves, the cyanogenic glucoside, dhurrin, is isolated in the vacuoles of epidermal cells, whereas the β‐ glucosidase and α‐ hydroxynitrilases are present in the chloroplasts and cytosol, respectively, in the underlying mesophyll cells.

Question 53

The hydrolysis of dhurrin occurs only after

Answer 53

tissue disruption (by herbivory)

Question 54

Steps for Sorghum plant: Cyanogenic glucoside

Answer 54

Cyanogenic glucoside combines with Beta-glucosidase –> Alpha-hydroxynitrile. Combines with Alpha-hydroxynitrilises –> to give a KETONE and HCN

Question 55

Cyanogenesis in animals

Answer 55

• A few species of insects are able to synthesize cyanogenic glucosides.

Question 56

E.g. of cyanogenesis in animals Larvae

Answer 56

Larvae of the Burnet moth, Zygaena filipendulae, isolate cyanogenic glucosides from their food plants.
•Larvae store them in viscous droplets in cuticular cavities in the integument

Question 57

integument:

Answer 57

a tough outer protective layer

Question 58

E.g. of cyanogenesis in animals adults

Answer 58

AdultfemalesreleaseHCNaspheromoneto attract males. Females prefer to mate with males that have greater contents of cyanide. The males give cyanogenic glucosides to the females as a nuptial gift during mating. This extra HCN helps the females protect the eggs.