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MCP Unit 1 > Organelles 3 > Flashcards

Organelles 3 Flashcards

1
Q

Functions of the Golgi

A
  • Sorting and dispatching station for proteins and lipids made in ER
  • Modification of N-linked oligosaccharide chains on glycoproteins made in ER
  • Synthesis of O-linked oligosaccharides on proteins and lipids made in ER
  • Sythesis of glycosaminoglycan chains on core proteins of proteoglycans
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2
Q

Structure of Golgi

A
  • Flattened membrane-bounded cisternae stacked together (3-20 per golgi) stack
  • Cis face (entry face) is adjacent to the ER
  • Trans face (exit face) points toward the plasma membrane
  • Network of interconnected tubular and cisternal structures from the cis and trans golgi networks at either end of the stack
  • Typically located near the cell nucleus
  • Number of golgi stacks per cell depends on the cell type
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3
Q

Cis Golgi network

A

Sorts proteins that need to be returned to the ER (have an ER retention signal)

Signal binds a specific receptor in Cis golgi network transport vesicles that return to the ER

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4
Q

Trans Golgi network

A

Sorts proteins destined for lysosomes or regulated secretion from those that will continue to the plasma membrane via the default pathway

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5
Q

Modification of N-linked Oligosaccharides in the Golgi

A
  • Glycosidases can remove sugars
  • Glycosyl transferases can add sugars
  • Degree of modification can vary (3 classes: High mannose, complex, hybrid)
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6
Q

O-linked glycosylation in the Golgi

A
  • Covalent attachement of oligosaccharides to the OH groups of serine or threonine residues in proteins.
  • Sugars are added to proteins one at a time
  • Sugars are added post-translationally with the use of specific glycosyltransferases
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7
Q

Proteoglycans

A
  • Typically contain more than 95% carbohydrate by mass and a small core protein.
  • Carbohydrate portion always consists of glycosaminoglycan chains which are linear polymers of a repeating disaccharide unit that are hundreds of sugars long
  • High density of negative charges due to carboxyl and sulfate groups
  • Attract water well (form gels and lubricants)
  • Come in a variety of sizes with varying numbers and types of glycosaminoglycans attached (most link to a serine residue)
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8
Q

6 classes of glycosaminoglycans

A 
Chondrotin sulfate
Dermatan sulfate
Keratan sulfate
Heparin
Heparin sulfate
Hyaluronate
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9
Q

Synthesis of proteoglycans

A
  • Occurs in the golgi
  • Core protein is synthesized in the ER and then transported to the golgi
  • In the golgi a series of different glycosyltransferases act sequentially to build the 4 sugar linker region on the serine of the core protein
  • Repeated action of two specific glycosyltransferases adds the sugars of the repeating disaccharide unit one at a time to build the glycosaminoglycan
  • Additional enzymes modify the sugars as the chain is elongating
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10
Q

Lysosomal hydrolases

A

Proteases and glycosidases

Degrade glycoproteins and proteoglycans in the lysosomes

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11
Q

Endoglycosidases

A

Remove carbohydrates from the protein in glycoproteins and proteoglycans

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12
Q

Proteases

A

Cleave the protein component of glycoproteins and proteoglycans into amino acids that can be reused by the cell.

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13
Q

Glycosidases

A

Specific glycosidases act on each glycosidic bond in serial fashion in reverse order to that in which they were added

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14
Q

Glycoprotein

A

Any protein with one or more covalently bound carbohydrate units that do not contain a serial repeat unit; typically, but not always, they are mostly protein with a little carbohydrate attached.

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15
Q

Proteoglycan

A

Any protein with one or more covalently bound glycosaminoglycan chains; typically, but not always, they are mostly carbohydrate with a very small core protein.

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16
Q

Biological functions of glycoproteins

A
  • Extracellular matrix (structure/support)-collagen, fibrin
  • Hormones- FSH, CG
  • Lubrication and protection- mucins, mucus secretions of GI
  • Enzymes- proteases, glycosidases, hydrolases
  • Immunologic molecules- immunoglobulins, complement, interferon
  • Cell surface antigens- ABO blood group antigens
  • Plasma proteins- blood clotting factors

-Glycocalyx- thick layer of carbohydrate on cell surface

17
Q

Mucins

A
  • Viscous glycoproteins composed of 80% carb by mass
  • Mostly O-linked
  • Rod shaped with central region of Ser and Thr (for O-linking)
  • Important for mucus in epithelial surfaces
  • Polymerization and high density of carbs allows the glycoproteins to generate a hydrated gel
18
Q

A blood allele

A

Encodes a transferase that transfers an N-acetyl galactosamine
-Codominant with B allele

19
Q

B blood allele

A

Encodes a transferase that transfers a galactose
Differs from A allele by only 4 aa
Codominant with A

20
Q

O allele

A

Encodes a nonfunctional protein due to a single nucleotide deletion that causes a frameshift
Recessive

21
Q

Two exocytosis pathways

A

Constitutive exocytosis pathway
-default pathway–go to the plasma membrane

Regulated exocytosis pathway (clathrin-coated vesicles)

  • found in specialized secretory cells such as those that secrete large quantities or hormones or digestive enzymes
  • Proteins diverted into secretory vesicles
  • Vesicles will only fuse in response to an extracellular signal
  • Aggregate into the trans golgi network
22
Q

Two types of endocytosis

A

Pinocytosis

  • via small vesicles, classical endocytosis
  • take up fluid and macromolecules
  • clathrin coated pits
  • can be receptor mediated

Phagocytosis

  • Large particles ingested via phagosomes, requires receptor activation at cell surface
  • Macrophages and neutrophils
23
Q

Uptake of cholesterol

A
  • Receptor mediated endocytosis
  • Most blood cholesterol transported as low density lipoprotein (LDL)
  • When cholesterol needed for membrane synthesis cells make LDL receptors and insert them into plasma membrane
  • LDL receptors associate with newly forming clathrin-coated pits and are internalized along with any bound LDL particles in clathrin coated vesicles
  • Vesicles shred clathrin coats and fuse with early endosomes, LDL dissociates from receptor
  • LDL transported to lysosomes and hydrolyzed to free cholesterol which is then released into the cytosol for membrane synthesis
  • LDL receptor us recycled back to plasma membrane from the early endosome
24
Q

Familiar hypercholesterolemia

A

LDL receptors are defective, cholesterol accumulates in the blood and forms plaques

25
Q

Early endosomes

A
  • Located near the plasma membrane
  • Main sorting station in the endocytic pathway
  • Acidic environment (pH 6) allows some receptors to release their ligands, ligands usually degraded in lysosomes
26
Q

Late endosomes

A
  • Located near the nucleus
  • Endocytosed materials arrive here from early endosomes 5-15 min after uptake
  • Materials are ultimately transported to lysosomes via transport vesicles or the gradual conversion of the late endosome into a lysosome by import of lysosomal proteins
27
Q

Transcytosis

A

Return to a different plasma membrane domain in polarized cells

28
Q

Lysosomes

A
  • Principle sites of intracellular digestion found in all eukaryotic cells
  • Contain acid hydrolases (about 40)
  • ATP proton pump maintains pH 5 inside
  • Membrane proteins heavily glycosylated to help protect them from lysosomal proteased
29
Q

Lysosomal hydrolases

A

-Tagged with mannose-6-phosphate (M6P) marker that is recognized by the m6P marker in the trans golgi network. Allows delivery to lysosomes.

30
Q

3 pathways to deliver things to lysosomes

A
  • Endocytosis
  • Phagocytosis
  • Autophagy–double membrane surrounds an organelle and then fuses with a lysosome (mechanism not well understood)
31
Q

Lysosomal storage diseases

A

Genetic defects affecting one or more lysosomal hydrolases

Often fatal

32
Q

Mucopolysaccharidoses

A

Defect in enzyme required for degradation of glycosaminoglycans, causes accumulation, cellular damage, and eventually cell death

patients show progressive decline in physiccal and mental function

33
Q

Oligosaccharidoses

A

Defect in enzyme required for degradation of oligosaccharides

Patients show facial dysmorphism and progressive mental retardation

34
Q

Sphingolipidoses

A

Defect in enzyme required for degradation of sphingolipids

35
Q

Inclusion cell disease

A

Defect in enzyme responsible for generating the M6P marker on lysosomal hydrolases

Basically have empty lysosomes

Usually death by age 8

MCP Unit 1 (14 decks)

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