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Medical Biology > Topic1 : Endoplasmic Reticulum > Flashcards

Topic1 : Endoplasmic Reticulum Flashcards

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1
Q

What is an endoplasmic reticulum?

A

A network of membrane-enclosed tubules and sacs that extends from the nuclear membrane.
Or
A network of tubular and flat vesicular structures in the cytoplasm.

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2
Q

What is the ER important for?

A

Protein trafficking of cells.

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3
Q

Difference btwn RER and SER?

A

RER is covered by ribosomes and SER is not covered by ribosomes but is involved in lipid metabolism

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4
Q

How do proteins travel from ER?

A

By secretory vesicles.

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5
Q

ER structure.

A

The tubules and vesicles of the ER are interconnected with one another.

It is involved in the internal delivery system of the cell along with the Golgi body.

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6
Q

What is the function of SER in specialized cells?

A

1.lipid biosynthesis
2.lipid transport
3.steroid hormone synthesis
4. Muscle contraction
5.synapses
6. Metabolic functions

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7
Q

What is the primary role of the (SER) in terms of lipid biosynthesis?

A

The (SER) is responsible for the synthesis of various lipids, including:
cell membrane phospholipids.
Phosphogliserides.
cholesterol.
triglycerides.

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8
Q

Where does lipid biosynthesis occur within the (SER)?

A

Lipid biosynthesis takes place at the cytosolic part of the SER membrane, where specific enzymes catalyze the synthesis of lipids such as phospholipids, phosphoglycerides, cholesterol, and triglycerides.

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9
Q

Name one type of lipid synthesized by the (SER) that is essential for the structure of cell membranes?

A

Phospholipids are synthesized by the (SER) and are crucial for the structure of cell membranes.

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10
Q

What are the products of lipid biosynthesis catalyzed by enzymes in the cytosolic part of the SER membrane?

A

The products of lipid biosynthesis include:
cell membrane phospholipids.
phosphoglycerides.
cholesterol.
triglycerides.

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11
Q

How are lipids transferred from intestinal epithelial cells into the cell?

A

Through diffusion.

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12
Q

What happens to monoglycerides and fatty acids after being taken into the cell?

A

They are transferred into the (SER).

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13
Q

How are monoglycerides and fatty acids converted to triglycerides in the SER?

A

With the help of enzymes like Acyl-coA synthetase and acyl-transferase.

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14
Q

What is the next destination for triglycerides after their formation in the SER?

A

They are transferred to the Golgi apparatus to form apolipoproteins.

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15
Q

What is the final destination for lipids after being processed in the Golgi apparatus?

A

They are given to the lymphatic or blood circulation.

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16
Q

Where does steroid hormone biosynthesis from cholesterol primarily occur?

A

Steroid hormone biosynthesis from cholesterol occurs in the mitochondria and (SER) with the involvement of oxidative enzymes like CYP11A1.

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17
Q

Name the steroid hormone produced by Leydig cells in the testis.

A

Testosterone

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18
Q

From which cells and organ is progesterone produced?

A

the ovary Corpus luteum.

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19
Q

What is the source of aldosterone, a mineralocorticoid steroid hormone?

A

Aldosterone is produced from the (SER) in the adrenal glands.

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20
Q

What role does the Sarcoplasmic Reticulum (SR) play in muscle contraction?

A

The Sarcoplasmic Reticulum plays a role in the regulation of Ca2+ ions during muscle contraction.

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21
Q

What is the function of Ca2+-ATPase pumps in the membranes of the Sarcoplasmic Reticulum (SR)?

A

Ca2+-ATPase pumps in the SR membranes are responsible for regulating the levels of Ca2+ ions.

22
Q

Where is Ca2+ stored in the Sarcoplasmic Reticulum, and what happens to it upon stimuli?

A

Ca2+ is present in the (SER) and upon stimuli, it is secreted to the outside to join the muscle contraction process.

23
Q

What role does the (SER) play in the synapses of neurons?

A

The SER plays a role in the regulation of Ca2+ ions for the transfer of signals from the synapses in neurons.

24
Q

Where are many SER vesicles located in neurons?

A

at the axonal ends of neuron cells.

25
Q

What metabolic functions does the Smooth Endoplasmic Reticulum (SER) play in the liver?

A

In the liver, the SER is involved in bile and cholesterol synthesis, breakdown of glycogen (via glucose-6-phosphatase), and detoxification of drugs, hormones, and alcohol, facilitated by the P450 (Cyp) enzyme family.

26
Q

Name some enzymes associated with the metabolic functions of the SER in the liver.

A

Enzymes such as 11-β-hydroxylase, aldosterone synthase, 21-hydroxylase, aromatase, and 17-α-hydroxylase are involved in the metabolic functions of the SER in the liver.

27
Q

How can the Rough Endoplasmic Reticulum (RER) be visualized under a light microscope?

A

The RER can be visualized under a light microscope with basic dyes, eg. Nissl bodies in the perikaryon of neurons.

28
Q

Describe the arrangement of cisternae in the Rough Endoplasmic Reticulum (RER) under an electron microscope.

A

Under an electron microscope, the cisternae of the RER are parallel, connected with each other, and in close association with the nuclear envelope.

29
Q

In which type of cells is the Rough Endoplasmic Reticulum (RER) abundantly found?

A

The RER is abundantly found in cells that are actively engaged in protein production.

30
Q

Provide examples of cells that have abundant (RER) due to their involvement in protein synthesis.

A

Examples include :
acinar cells of the exocrine pancreas.
plasma cells synthesizing immunoglobulin(Ig) neurons with perikarya involved in neurotransmitter synthesis.
Lysosomal enzyme synthesizing macrophages.

31
Q

What is the most important function of the (RER) related to protein synthesis?

A

It’s role in vectorial protein synthesis.

32
Q

Name some types of proteins whose synthesis takes place in the ribosomes bound to the (RER).

A

Secretional proteins
Lysosomal proteins
Plasma membrane glycoprotein

33
Q

What is the ER retention signal in ER resident proteins, and where is it located?

A

ER resident proteins contain an ER retention signal of 4 specific amino acids at the C-terminus.

34
Q

What is the role of Protein Disulfide Isomerase (PDI) in the folding of ER resident proteins?

A

PDI oxidizes free sulfhydryl (SH) groups on cysteines to form disulfide bonds (S-S), allowing ER resident proteins to refold.

35
Q

How do BiP (Binding Protein) chaperone proteins contribute to the folding of ER resident proteins?

A

BiP chaperone proteins pull proteins posttranslationally into the ER through the translocator and assist with protein folding.

36
Q

How are most soluble and transmembrane proteins glycosylated in the ER?

A

They are glycosylated by the addition of an oligosaccharide to the amino acid Asparagine (Asn).

37
Q

Describe the precursor oligosaccharide in the glycosylation process of ER proteins.

A

The precursor oligosaccharide is linked to dolichol lipid in the ER membrane, and in a high-energy state is transferred to the polypeptide.

38
Q

How is the precursor oligosaccharide transferred to the polypeptide during glycosylation in the ER?

A

The transfer is facilitated by oligosaccharyl transferase and occurs almost as soon as the polypeptide enters the ER lumen.

39
Q

What happens to improperly folded ER proteins?

A

Improperly folded ER proteins are exported from the ER and degraded in the cytosol.

40
Q

How do misfolded proteins in the ER trigger a cellular response?

A

Misfolded proteins in the ER activate an “Unfolded Protein Response” (UPR), leading to increased transcription of ER chaperones and degradative enzymes.

41
Q

How are misfolded soluble proteins in the ER recognized and targeted for degradation?

A

Misfolded soluble proteins in the ER lumen are recognized and targeted to a translocator complex in the ER membrane.

42
Q

Describe the initial interactions of misfolded soluble proteins in the ER lumen.

A

In the ER lumen, misfolded proteins interact with chaperones, disulfide isomerases, and lectins.

43
Q

What happens after misfolded soluble proteins are targeted to the translocator complex?

A

They are exported into the cytosol through the translocator.

44
Q

What processes occur in the cytosol to misfolded soluble proteins?

A

In the cytosol, misfolded proteins are ubiquitylated, deglycosylated, and degraded in proteasomes.

45
Q

How do misfolded membrane proteins follow a similar pathway?

A

Misfolded membrane proteins follow a similar pathway but use a different translocator for export and degradation.

46
Q

What is the main organelle in the secretional pathway of eukaryotic cells?

A

The endoplasmic reticulum (ER) is the main organelle in the secretional pathway of eukaryotic cells.

47
Q

Name some components involved in managing ER stress.

A

Components include :
foldases (enzymes and molecules catalyzing folding). chaperones (aiding protein folding by preventing aggregation).
glycosylation enzymes (enzymes catalyzing oligosaccharide addition).

48
Q

What factors can cause misfolded or unfolded proteins in the endoplasmic reticulum (ER)?

A

Oxygen, glucose, pH, ATP, and Ca+2 levels are factors that can lead to misfolded or unfolded proteins in the ER, causing proteotoxicity or ER stress and impairing vital cell functions.

49
Q

What are some causes of ER stress?

A

• Aberration in protein glycosylation
• Decrease in disulphide bond formation
• Decrease in Ca+2 in ER lumen
• Disruption of protein transport from ER to Golgi

50
Q

What is the response to ER stress?

A

Cells try to prevent ER stress in 4 ways;
1. Induce the transcription of ER chaperons
2. Inhibate new protein synthesis
3. Send misfolded proteins to proteosomes
4. Cause Apoptotic cell death

Medical Biology (10 decks)

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