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Cellular Biology and Biochemistry > Getting to the cell surface > Flashcards

Getting to the cell surface Flashcards

1
Q

Describe organelles present in the secretory pathway

A

Endoplasmic reticulum
Gogli apparatus
Endosomes
Vesicles

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2
Q

Are all proteins trafficked through the secretory pathway exported?

A

No

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3
Q

What proteins are exported?

A

Hormones
Enzymes
Extracellular matrix proteins

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4
Q

What proteins aren’t exported?

A

Incorporated into the membrane
Channels and transporters
Receptors
Cell adhesion molecules

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5
Q

Where are proteins synthesised?

A

Ribosomes of the rough endoplasmic reticulum

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6
Q

What are signal peptides?

A 
Trigger transfer
15-20 amino acids long
At the N-terminal end
Hydrophobic
Cleaved upon transit across the membrane
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7
Q

Where are signal peptides for multi-pass membrane spanning proteins?

A

Internal

Not cleaved

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8
Q

How do proteins cross the endoplasmic reticulum membrane?

A

Signal recognition particle recognises the signal peptide
Signal recognition particle binds to the signal peptide, pausing translation
Signal recognition particle binds to receptor in the membrane
Signal peptide is inserted into the translator
Translation continues and polypeptide chain is through the membrane
Signal recognition particle and receptor dissociate
The signal peptide is cleaved and protein is released into the ER lumen

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9
Q

What cleaves the signal peptide?

A

Signal peptidase

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10
Q

What are the main events that happen in the endoplasmic reticulum?

A 
Signal peptide is cleaved
Protein is glycosylated
Protein is folded
Disulfide bonds form
Multimerisation can occur
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11
Q

What is N-glycosylation?

A

Most soluble and membrane spanning proteins are glycosylated

A preformed oligosaccharide (14 sugars) is transferred from dolichol to the new protein

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12
Q

What catalyses N-glycosylation?

A

Oligosaccharyl transferase

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13
Q

How do proteins leave the endoplasmic reticulum?

A

Vesicles containing soluble/membrane bound proteins bud from the ER and transit to the cis face of the Golgi

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14
Q

Describe the Golgi body

A

Comprises of flattened membrane compartments called cisternae
Each Golgi stack has two faces, the cis face and trans face
Two networks: the cis Golgi network and the trans Golgi network
Proteins arrive in vesicles at the cis face and leave in vesicles from the trans face

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15
Q

What are the two types of N-linked oligosaccharides?

A

Complex oligosaccharides

High mannose oligosaccharides

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16
Q

What are complex oligosaccharides?

A

Generated when the original N-linked oligosaccharide is trimmed and further sugars added

17
Q

What are high mannose oligosaccharides?

A

Original N-linked oligosaccharide is trimmed and further mannose residues added

18
Q

What is O-glycosylation?

A

Occurs when sugar residues are added to serine or threonine

Added by glycosyl transferases

19
Q

What are proteoglycans?

A

Contain glycosaminoglycan chains
Unbranched polysaccharide chains composed of repeating disaccharide units
Special link tetrasaccharide is added to serine

20
Q

What is the constitutive secretory pathway?

A

Operates continuously
Default pathway
Supplies the plasma membrane with newly synthesised membrane spanning proteins
Soluble proteins are continually secreted from the cell via this pathway

21
Q

What is the regulated secretory pathway?

A

Some proteins are sorted into secretory granules where they are stored until required
Release is triggered by an extracellular signal
Vesicle fuses with plasma membrane and releases its content

22
Q

What is the purpose of protein glycosylation?

A

Promotes protein folding
Aid cell recognition processess
Important in inflammatory response
Protect the cell

23
Q

How are enzymes transported to lysosomes?

A

Lysosomal enzymes enter the secretory pathway and transported to lysosomes in vesicles
Their sorting signal is mannose-6-phosphate

24
Q

How are proteins transported to the nucleus?

A

Nuclear localisation signals direct proteins to the nucleus

Runs of 5 or more basic amino acids anywhere in the protein sequence

25
Q

How are proteins transported to the mitochondria?

A

Mitochondrial signal sequences direct proteins to mitochondria
These are amphipathic helices at the N-terminus of mitochondrial proteins

26
Q

Which proteins do not enter the secretory pathway and why?

A

Nuclear and mitochondrial proteins

They are synthesised in cytoplasmic ribosomes

Cellular Biology and Biochemistry (22 decks)

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