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FLC > Endoplasmic Reticulum > Flashcards

Endoplasmic Reticulum Flashcards

1
Q

Describe what the endoplasmic reticulum is?

A

Continuous network of tubules forming a net structure

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2
Q

What other structure is the ER continuous with?

A

The Nucleur membrane

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3
Q

What are the major functions of the ER?

A

Protein synthesis - folding & assembly of long peptide chains

Glycosylation - attachment of sugars to proteins

Multiprotein Complexes

Lipid Synthesis - initiated in ER, (choletserol, phospholipids etc.)

Ca2+ sequestration - storage of ca2+ in lumen

Detoxification - by cytochrome P450 enzymes

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4
Q

Explain how Detoxification works?

A

Cytochrome P450 enzymes convert (inactive) prodrugs -> active drugs

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5
Q

How does calcium sequestration occur?

A

Ca2+ conc. very low in cytoplasm
cell has to actively pump ca2+ out
acts as a secondary messenger

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6
Q

What equipment can be used to view Pancreatic Acinar Cells?

A

Electron microscope

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7
Q

Where are the enzymes stored in acinar cells?

A

In Secretory Vesicles

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8
Q

What is the function of the Acinar cells?

A

secrete enzymes which enter small intestine (food digestion etc.)

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9
Q

Describe the structure of the RER?

A

Bilayers with Ribosomes on the membrane with the lumen inside

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10
Q

Where are Acinar Cells found in the body?

A

Exocreatine Pancreas

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11
Q

What is the RER?

A

Rough endoplasmic reticulum

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12
Q

How and where are the enzymes released from acinar cells?

A

Vesicles fuse with membrane in lumen of ER to secrete enzymes

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13
Q

How are SER and RER interlinked?

A

They are both part of the same network of membranes - all one organelle

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14
Q

What is the role of Insulin?

A

Regulates Blood Glucose levels

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15
Q

Outline the stages of Co translational Targetting to the ER

A
  1. mRNA encodes protein requiring secretion from cell
    • when translation occurs, ribosome has to assemble on mRNA and begin protein synthesis at AUG initiation methionine
  2. At beginning of protein, a signal sequence is present (v. rich in hydrophobic amino acids)
    • the signal sequence is a distinctive amino terminal signal
  3. Signal recognised by Signal recognition Particle (SRP)
  4. SRP bind sto its receptor (SRP receptor)
  5. Binding causes SRP and its receptor to dissociate following GTP hydrolysis
  6. Ribosome now able to bind to Peptide translocation complex Sec61
  7. Translation occurs
  8. Newly synthesised peptide is threaded into ER lumen
  9. Signal sequence cleaved off by Signal Peptidase
  10. mature protein produced
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16
Q

Why do disulphide bonds only form in the ER and not the cytoplasm ?

A

Cytoplasmic proteins don’t have S-S bonds due to insufficient enzymes present to catalyse their formation

17
Q

Which proteins have their signal sequence cleaved?

A

All proteins synthesised in ER have their signal sequence cleaved off

18
Q

How are proteins transported from one organelle to another?

A

via Vesicular Transport

19
Q

Which proteins would require to be exported from the cell?

A

Golgi apparatus
Lysosomes
etc.

20
Q

How is the final structure of insulin produced?

A

Via cotranslational protein targetting (requiring further modifications)

21
Q

How does vesicular transport work?

A

Vesicles fuse with the largest membrane and secrete the protein contents

22
Q

Why are some proteins not exported from the nucleus?

A

If the protein fail to correctly undergo :
- Proteolysis
- Glycosylation
- Disulfide bond formation
- Folding
- assembly into protein complex
they will not be exported out of the nucleus

23
Q

What happens to mRNA encoding a protein that needs to be exported to somewhere else in the secretory pathway?

A

Requires cotranslational targetting to the ER

24
Q

Where does the central dogma occur?

A

Takes place in nucleus and products (RNA) exported to cytoplasm

25
Q

Describe how the final product insulin is formed

A
  1. Insulin secreted as Preproinsulin
  2. It’s signal sequence is cleaved off
  3. Proinsulin formed
  4. 3 Disulphide bonds form between Cysteine amino acids
  5. Proteolysis occurs cutting out C peptide from proinsulin
  6. 2 separate peptides left connected by disulphide bonds
  7. Mature insulin formed
26
Q

Give examples of proteins destined to remain inside the cell

A

cell organelles
- mitochondria
- peroxisomes
etc.

27
Q

Explain what occurs to mRNA encoding a protein destined for the cell’s cytoplasm?

A

mRNA will interact with ribosomes free in the cytoplasm for it’s translation to be completed

28
Q

What is the fate of proteins that are not exported from the nucleus?

A

They are degraded instead

29
Q

How many amino acids in preproinsulin?

A

110 amino acid protein

30
Q

Explain the term Central Dogma

A

RNA Pol. II catalyses RNA synthesis
Using DNA strand as template
Forming tRNA, mRNA, rRNA -> proteins

31
Q

What is the cisface of the golgi?

A

Side facing the ER - where proteins enter from

32
Q

What is between the stacks of membranes in the golgi ?

A

Cisternae

33
Q

Name two lipids synthesised at the golgi

A

Sphingomyelin and Glycosyleramide

34
Q

Where are lipids and proteins transported to from the golgi?

A
  • Secretory granules
  • Plasma membrane
  • Basolateral vs. aplical membranes
  • Endosomes
  • Lysosomes
35
Q

Describe the structure of the golgi apparatus

A

A series of different membrane stacks

36
Q

Which protein modifications take place at the Golgi?

A

Glycosidase / glycosystransferases
O-linked glycolyation
Sulfates
Proteases

37
Q

What occurs at the Golgi’s transface?

A

Vesicles leave the golgi from here

38
Q

What are the functions of the Golgi apparatus?

A
  • Protein modification
  • Lipid synthesis
  • Protein & Lipid sorting
39
Q

What happens at the cisternae?

A

Vesicles are formed

FLC (34 decks)

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