Unit 1.3 Flashcards
Lysosomes are:
membrane-enclosed organelles that contain about 50 different degradative enzymes
Lysosomes are membrane-enclosed organelles that contain about 50 different degradative enzymes that can hydrolyze (4):
(1) Nucleic acids (nucleases)
(2) Proteins (proteases)
(3) Lipids (lipases)
(4) Carbohydrates (glycosidases(
All lysosomal enzymes are __, which are active at pH __
all lysomal enzymes are acid hydrolases, which are active at pH 5
The lumen of the lysosome is maintained at acidic pH by:
a H+ (proton) ATPase in the membrane that pumps H+ ions (protons) into the lumen
What shields the lysosome membrane from its degradative enzymes?
integral membrane proteins of the lysosome are HIGHLY GLYCOSYLATED
Primary lysosomes
roughly spherical and do not contain obvious particulate or membrane debris.
Secondary lysosomes
larger and irregularly shaped, result from the fusion of primary lysosomes with membrane-engulfed aged and defective organelles; they contain particles of membranes in the process of being digested (autophagy).
Autophagosomes can contain (3):
(1) Organelles
(2) Cytosolic Proteins
(3) Lipids
Three pathways for delivering materials to lysosomes
(1) endocytosis
(2) phagocytosis
(3)autophagy
endocytosis
digestion of molecules taken up from outside the cell
phagocytosis
The digestion of large particles, including bacteria, cell debris, and aged cells
(taken up from outside the cell
autophagy
The digestion of aged or defective organelles (the cell’s own components)
Lysosomal storage diseases
Mutations in the genes that encode lysosomal acid hydrolases are responsible for more than 30 different human genetic diseases
lysosomal storage diseases are called this because:
undegraded material accumulates within the lysosomes of affected individuals
Gaucher’s disease is
a lysosomal storage disease which results from a mutation in the gene that encodes a lysosomal enzyme required for the hydrolysis of the glycolipid glucocerebroside to glucose and ceramide.Treated using Cerezyme, a modified form of glucocerebrosidase that is taken up by endocytosis and delivered to the lysosome.
Peroxisomes are
the site of synthesis and degradation of hydrogen peroxide (H2O2), which is highly reactive and toxic.
Hydrogen peroxide is produced during
oxidation of several substrates.
Functions of peroxisomes
- Oxidation of very long chain fatty acids
- Decomposition of hydrogen peroxide
- Biosynthesis of plasmalogens
- Conversion of stored fatty acids to carbohydrates in germinating seeds of plants, which is critical to providing energy for growth of the germinating plant (in this case the organelle is called the glyoxosome)
Similarities between peroxisomes and mitochondria (3):
- Both are formed from a pre-existing organelle
- Both import preformed proteins from the cytosol
- Both oxidize fatty acids
differences between peroxisomes and mitochondria (2):
- Peroxisomes have a single phospholipid bilayer but mitochondria have two
- Peroxisomes do not contain DNA or ribosomes but mitochondria do
Peroxisomal disorders (2):
(1) Zellweger syndrome
(2)X-linked adrenoleukodystrophy (X-ALD)
Zellweger syndrome:
patients synthesize peroxisomal enzymes but cannot import them into the organelle. Thus, the peroxisomes appear as “ghosts”. Neuronal phenotype.
X-linked adrenoleukodystrophy (X-ALD):
peroxisomes do not import very long chain fatty acids (VLCFA) which then accumulate in the brain and impair the
myelin. Has been treated successfully by gene therapy (adding back a functional VLCFA transporter).
The cytoskeleton
A network of protein filaments extending throughout the cytoplasm.
Functions of the cytoskeleton (2):
- Provides the structural framework of the cell:
- Responsible for movement
elaborate: cytoskeleton provides the structural framework of the cell (2):
(1) determines cell shape
(2) determines the general organization of the cytoplasm
the cytoskeleton is responsible for the movement of (4):
(1) entire cells
(2) organelles
(3) tranport vesicles
(4) chromosomes during cell division
Three main kinds of cytoskeletal filaments:
(1) microtubules
(2) Actin filaments
(3) intermediate filaments
describe microtubules (1/3 of cytoskeletal filaments):
-25 nm in diameter
- built of polymers of the protein tubulin
-intracellular transport, cell dividion and cell organization
Describe actin filaments (2/3 of cytoskeletal filaments):
- 8nm in diameter
-built of protein actin
-motility, contractility (in muscles)
intermediate filaments (3/3 cytoskeletal filaments):
-10 nm in diameter
- built of a number of different proteins (70) some are tissue specific
-provide structural support and mechanical strength
The different types of filaments can be revealed with different fluorescent compounds:
- Phalloidin – actin
- Fluorescently-labeled subunits (tubulin)
- antibodies
