Lecture 9. Synthesis and Packaging of Signaling Molecules for Release

Question 1

How does the secretory system function ?

Answer 1

Through the use of vesicular transport

Question 2

What is vesicular transport ?

Answer 2

When transport vesicles carry soluble proteins and membranes between compartments

Question 3

What did Pallad show us ?

Answer 3

How proteins move through at a subcellular level

Question 4

What is sec 1 protein essential for ?

Answer 4

Vesicles fusing with a membrane which is called Munc 18

Question 5

What can vessels with sec 1 do ?

Answer 5

Carry a full cargo intended for the cell surface but cannot merge with it and releases their contents

Question 6

What does sec 7 do ?

Answer 6

Causes a huge swelling in the golgi network that prevents vesicles from forming

Question 7

What happened when sec 1 and sec 7 are crossed ?

Answer 7

The swellings still formed but vesicles were not produced.

This tells us that vesicles production was downstream or later in the process than swelling formation

Question 8

What do proteins destined for the membrane or secretory pathway have ?

Answer 8

A signal sequence on the nascent polypeptide

Question 9

What does having a signal sequence on the nascent peptide target the proteins for ?

Answer 9

Binding with the protein signal recognition particle

Question 10

How many particles does the signal recognition particle contain ?

Answer 10

6

Question 11

What is the function of the signal recognition particle ?

Answer 11

Binds to the signal sequence and take it to the endoplasmic reticulum

Question 12

What happens once the signal recognition particle has bound the signal sequence ?

Answer 12

It is recognised by the signal recognition particle receptor protein which is in the membrane of the rough endoplasmic reticulum

Question 13

What happens when the signal recognition receptor protein complex binds ?

Answer 13

It directs the nascent protein into the lumen of the endoplasmic reticulum

Question 14

Where does the signal peptide go through ?

Answer 14

The translocator complex

Question 15

What happens when the signal peptide goes through the translocator complex ?

Answer 15

The signal peptidase cleaves off the signal peptide which is left in the membrane and the mature protein is cleaved off and liberated into the endoplasmic reticulum

Question 16

What is the function of sugars that bind to the protein as it emerges into the endoplasmic reticulum ?

Answer 16

Regulate protein folding

Question 17

What are the chaperone proteins that recognise the sugar binding ?

Answer 17

Calnexin and calreticulin

Question 18

What are calnexin and calreticulin specialised to do ?

Answer 18

Recognise when the sugars are being cleaved off and therefore retain the protein in the endoplasmic reticulum until the protein is correctly folded

Question 19

What is the signal that protein folding is complete ?

Answer 19

Once the sugar residues have been cleaved off

Question 20

What do exit signal proteins do ?

Answer 20

Recognise the released proteins with some specificity and begin to form vesicles

Question 21

What is the function of coat protein complex coated vesicles ?

Answer 21

They are structurally important in organising the form of the vesicle

Question 22

What can the vesicle coated with COPII do once it forms the vesicular tubule structure ?

Answer 22

Can bud off

Question 23

How does the vesicle coated with COPII travel ?

Answer 23

In an antergrade fashion along the microtubule

Question 24

What do vesicles coated with COPII use to walk and carry the cargo ?

Answer 24

Motor proteins like kinesin

Question 25

What is vesicle coated with COPII targeted according to ?

Answer 25

What they are coated in to move towards the golgi network

Question 26

In the golgi apparatus, what are vesicles sorted into ?

Answer 26

Cis-cisterna, trans-cisterna and the trans-golgi network

Question 27

What labels the layers in the stack in the golgi ?

Answer 27

Different enzymes or substances

Question 28

What happens to the vesicles after they have gone through several processes in the golgi?

Answer 28

Proteins are sorted into new vesicles which bud off from the trans golgi network to the final destination in the cell

Question 29

How does insulin messenger RNA go from the ribosome to the endoplasmic reticulum ?

Answer 29

Translator complex

Question 30

What is insulin synthesised as ?

Answer 30

Pre pro insulin

Question 31

What does pre pro insulin have that targets it to the signal recognition complex ?

Answer 31

A signal sequence

Question 32

What part of the pre pro insulin gets cleaved off in the endoplasmic reticulum ?

Answer 32

The signal sequence

Question 33

Once the signal sequence is cleaved from the pre pro insulin how many amino acids remain ?

Answer 33

76

Question 34

What happens after pre pro insulin cleavage ?

Answer 34

It starts to fold but three disulphide bonds form which keep the a and b parts of the peptide together

Question 35

What is between the a and b peptide ?

Answer 35

The c peptide

Question 36

What is the structure of the c peptide ?

Answer 36

It remains continuous with the a and b peptides because of the pair of basic amino acids at both ends

Question 37

What does endopeptidase do ?

Answer 37

Cleaves at two positions and release the c peptide

Question 38

What does carboxypeptidase do ?

Answer 38

Cleaves off the basic amino acids. This occurs in the secretory vesicle

Question 39

What is the result of carboxypeptidase cleavage ?

Answer 39

A and b chain dimer with disulphide bonds

Question 40

Where is insulin initially packaged ?

Answer 40

Into immature secretory granules emanating from the trans golgi network

Question 41

What is step 1 on granule maturation ?

Answer 41

Acidification of the granule lumen via the activation of proton pumps lower the luminal pH. This is the optimal pH for activation of proteases and consequent conversion of proinsulin to insulin and C-peptide through proteolysis by endoproteases, followed by the trimming of the carboxyl termini carboxypeptidase E

Question 42

What is step 2 on granule maturation ?

Answer 42

In the presence of calcium and zinc, it forms hexamers and effectively crystallises forming electron dense cores

Question 43

What is step 3 on granule maturation ?

Answer 43

Fusion using SNARE complexes, vesicles fuse with the target membrane. Through synaptotagmin binding of incoming calcium, vesicle contents are released

Question 44

What does mature insulin wait for to be released ?

Answer 44

Metaboli signals to exocytosed from the cell into circulation

Question 45

What are the two stages of beta cell release of insulin ?

Answer 45

1. Rapidly released in response to increased blood glucose levels 2. There is a sustained slow release of newly formed vesicles triggered independently of sugar

Question 46

How is insulin released from secretory cells ?

Answer 46

Calcium dependent exocytosis

Question 47

How is calcium influxed ?

Answer 47

Comes through voltage dependent calcium channels

Question 48

How is calcium released for the endoplasmic reticulum ?

Answer 48

By ryanodine receptors

Question 49

How is insulin secreted ?

Answer 49

Via the fusion of a vesicle filled with a plasma membrane

Question 50

Why is the fusion of a vesicle with a plasma membrane electron dense ?

Answer 50

They are basically crystallised hexamers of insulin, which are cross-linked by aldehyde fixation

Question 51

What is a neuron ?

Answer 51

A highly specialised structure with branched dendrites for receiving signals from other neurons and a long highly specialised axon which conveys messages from this cell to another

Question 52

What is the axon end called ?

Answer 52

A presynaptic terminal

Question 53

What does the presynaptic vesicle contain ?

Answer 53

Secretory vesicles

Question 54

What is the long stretch of axon between cell bodies and the presynaptic terminal coated with ?

Answer 54

Myelin

Question 55

What is the function of myelin ?

Answer 55

Insulates the axon and allows electrical conductance to flow more rapidly down the axon

Question 56

What makes myelin ?

Answer 56

Oligodendrocytes

Question 57

What are astrocytes responsible for ?

Answer 57

Neurotransmitter reuptake, insulation/isolation, migration, synaptic plasticity

Question 58

Where are astrocytes found ?

Answer 58

Brain

Question 59

What are microglia ?

Answer 59

Immune function scavengers with possible roles in synaptic regulation

Question 60

What is the neuron composed of ?

Answer 60

Cell body, axon and synapse

Question 61

What is neurotransmission?

Answer 61

The conversion of an electrical signal to a chemical signal down the axon, that allows the signal to pass from one cell to the next

Question 62

Where does the conversion of the electrical signal to a chemical signal occur ?

Answer 62

The synaptic cleft

Question 63

Where is acetylcholine released from ?

Answer 63

The vagus nerve

Question 64

Where does acetylcholine act on ?

Answer 64

Receptors in the heart

Question 65

How does the noradrenaline speed up the heart rate ?

Answer 65

Through the accelerator nerve

Question 66

Where is the post synaptic density found ?

Answer 66

Specialised structure on a spine on a cell

Question 67

What does the post synaptic density receive ?

Answer 67

The synaptic enervation

Question 68

When do post synaptic density release the neurotransmitter ?

Answer 68

With elevated levels of calcium

Question 69

What is one of the key differences of the post synaptic neurons ?

Answer 69

They release substances that are not protenatious

Question 70

What are some examples of neurotransmitters ?

Answer 70

1. Biogenic amines 2. Amino acid neurotransmitters 3. Others

Question 71

What is the four criteria for designation as a neurotransmitter ?

Answer 71

1. Synthesis in neuron 2. Verifiable release from neuron 3. Effect on post-synaptic neuron via a specific post synaptic receptor 4. Appropriate termination mechanism

Question 72

What are catecholamines ?

Answer 72

Neurotransmitters that are derived from tyrosine

Question 73

What is the structure of a catecholamine ?

Answer 73

The catechol ring structure and the amine group

Question 74

How is DOPA formed ?

Answer 74

In the cytoplasm, tyrosine hydroxylase hydroxylates tyrosine by adding an OH to the catechol ring

Question 75

How is dopamine formed from DOPA ?

Answer 75

DOPA decarboxylase decarboxylates DOPA

Question 76

How is noradrenaline formed from dopamine ?

Answer 76

Dopamine beta hydroxylase adds a hydroxyl group to the beta carbon of dopamine

Question 77

What is a major driving of parkinsons ?

Answer 77

Loss of cells that makes dopamine

Question 78

Where are amine neurotransmitter synthesised enzymatically ?

Answer 78

In the cytosol

Question 79

Where is amine neurotransmitters packaged into vesicles ?

Answer 79

Synaptic vesicles

Question 80

What are the two key proteins that small vesicles are specialised by ?

Answer 80

1. Vesicular neurotransmitter transporter | 2. A vesicular ATPase which pumps H+ into the lumen

Question 81

What are the two linked but distinct processes that are involved in the packaging of synaptic vesicles ?

Answer 81

1. Vesicular ATPase pumps H+ into the vesicle against the concentration gradient and therefore require ATP hydrolysis 2. A vesicular neurotransmitter transporter, transports neurotransmitters into vesicles against the concentration gradient by harnessing the power provided by the flow of H+ ions, down the concentration gradient out of the vesicle

Question 82

What do all four types of neurotransmitter transporters contain ?

Answer 82

12 membrane spanning regions called transmembrane domains

Question 83

What are the four types of neurotransmitter transporters ?

Answer 83

1. VMAT 2. VaChTs 3. VGAT 4. VGLUT

Question 84

What are VMATs ?

Answer 84

Amine transporters that transport biogenic amines all positively charged at neutral pH and require outward movement of 2H+

Question 85

How is vesicle packaged ?

Answer 85

Using neurotransmitter transporters