Cytology-Ch.8-Lysosomes

how many membs around a lysosomes?

one

what are lysosomes involved in ?

intracellular digestion & storing of certain substances - cell defense - cell nutrition - renewal of membs and organelles

where are real lysosomes found ?

in animal cells - plant cells have vacuoles that share common properties and functions

what do plant vacuoles do ?

regulate osmotic pressure - intracellular digestion - store many compounds

are lysosomes / vacuoles found in bacteria ?

no - the specialized gas vacuoles in cyanobacteria are totally diff from plant vacuoles -- but there are hydrolases in bacteria

desppite not having lysosomes, bacteria have a variety of hydrolases that are especially located in

the space btwn plasma memb & cell wall (periplasmic space - pericytoplasmic space)

space btwn plasma memb and cell wall is called

periplasmic space - pericytoplasmic space

how many types of enzymes are there in lysosomes ? where?

about 50 in the lumen and memb

lysosomes can digest any macromolecule??

yes

lysoosmal enzymes are generally called ..... ? why?

acid hydrolases bc their hydrolyzing activity is optimal at low acidic pH

how much is intralysosomal pH ? why ?

4.6 to 5 --due to the presence of a proton pump (integral memb protein ) in the lysosomal memb that pumps protons into the lumen

what does the lysosomal proton pump depend on?

ATP

the property of low pH of lysosmoal enzymes provides the cell with what ?

protection in case of leakage of lysosomal enzymes to the cytosol - they will be inactive in cytosolic pH=7

how is the lumenal face of the lysosomal memb protected against being digested by the enclosed enzymes?

by its high glycosylation state

lysosomal enzymes find their substrates in ? digest them into

endosomes & phagosomes --- digest them into low-molecular-weight-molecules that can be transported across the lyso memb

how are digestion products transported out of the lyso?

active or passive transport

what can transport substrates into the lysosome lumen to be digested?

permeases in the lysosomal memb

if digestion is incomplete

wastes are produced and they must be expelled out of the cell by exocytosis

what are endosomes?

for transport of materials from golgi to lysosome/vacuole

what are phagosomes?

vesicle formed around engulfed material in phagocytosis

diff btwn autophagy and heterophagy

autophagy is cell death by self destruction while heterophagy is digestion via phagocytosis / pinocytosis

size of lysosomes + comparable to

comparable to small mitochondria - size: 50nm to 1 micrometer in diameter

are lysosomes heterogeneous?

yes they have many sizes, shapes and forms

what are the types pf lysosomes?

-primary
-secondary
-residual bodies & lipofuscin pigment granules

another name for primary lysosomes

protolysosomes

primary lysosomes are ? derived from? what about their enzymes?

newly formed organelles that have derived from the TGN - contain digestive enzymes that have not taken part in hydrolysis rxns

what produces lysosomal enzymes ?where were they matured?

synthesized by attached ribosomes (at the level of RER ) and matured in RER and Golgi where they are sorted and packed into clathrin-coated vesicles

what address code or signal is present in enzymes destined to form lysosomes and are packed in clathrin-coated vesicles?

mannose-6-phosphate

what forms primary lysosomes?

the clathrin coated vesicles after the removal of their coat

secondary lysosomes result from

the fusion of one or more primary lysosomes with vesicles containing material to be hydrolyzed

what are autophagic vacuoles / autophagosomes?

result from the enveloping of an organelle to be destroyed by an ER fragment

what are the types of secondary lysosomes?

-heterolysosomes / heterophagolysosomes
-autophagolysosomes

what is a common event in cell growth - tissue repair - cell differentiation - cell dedifferentiation - insect larva metamorphosis - reduction of uterus size after delivery

organelle turnover by autodigestion

when is organelle turnover by autophagy occur? (processes)

cell growth - tissue repair - cell differentiation - cell dedifferentiation - insect larva metamorphosis - reduction of uterus size after delivery

when does autophagy increase?

when cells are deprived of nutrients - it increases to supply the cells with the missing components

how does organelle turnover happen?

by autodigestion

as digestion in secondary lysosomes proceeds , its hard to know the original secondary lysosome type so we refer to them as

secondary lysosomes or digestive vacuoles

recycling digestion products needs

active and passive transport of molecules across the cell memb

does the cell recycle digestion products ?

yes partially or totally

compare the residual bodies to primary lysosomes

they are larger than the primary lysosomes and have an irregular shape

residual bodies derive from

secondary lysosomes after the end of digestion

what are residual bodies ?

vesicle that enclose the wastes produced by digestion and hydrolysis which are not complete

is digestion and hydrolysis in secondary lysosomes complete?

no - therefore wastes are produced and residual bodies are found

what happens to residual bodies?

they are expelled out of the cell by exocytosis

what are lipofuscin granules ? composed of

residual bodies that are kept in the cytoplasm indefinitely - they are fine granular yellow-brown pigment granules composed of lipid residues

accumulation of lipofuscin granules leads to

disturbing the cell metabolism and aging of cells and organs

ex of cells that keep residual bodies in them for a long time

long-lived cells such as neurons

how does the TGN recognize the phophorylated mannose residues of lysosomal enzymes ?

by specific receptors (integral proteins) of the TGN

where are clathrin coated buds formed?

in trans Golgi cisternae

how is it ensured that lysosomal enzymes are packed in clathrin-coated vesicles only?

bc the mannose-6-phosphate receptors of TGN have clathrin binding sites at the cytosolic face

as coated vesicle migrate in the cytosol what happens?

the mannose-6-phosphate dissociates from its receptor and so the clathrin coat is released -- mannose-6-phosphate is returned to TGN to be used in another budding and sorting process

why are lysosomes absent in plant cells?

bc endo and phagocytosis are imp due to the rigid cells wall

how is the vacuole formed?

from fusion of small ones

vacuole takes up to .... of the plant cell volume

90%

what bounds the plant vacuole? provided with ?

single memb - tonoplast provided with many active transport systems that actively pump ions into the vacuole lumen

where is ion C higher ? in vacuole or cytosol? why?

vacuole bc of the ion pumps in the tonoplast that actively pump ions to the vacuole lumen

what about the tonicity of vacuole lumen?

hypertonic

what about what movement in vacuole ? what follows?

bc the lumen is hypertonic, water flows into the vacuole by osmosis and turgor pressure is generated bc the vacuole is full of water

the water and turgor pressure in plant do what?

providing mechanical support to soft unwoody tissues of a plant and also helps with stretching of the cell wall during cell growth

what about intravacuolar pH?

low bc of proton pumps in the tonoplast

do plant tissues have good excretion systems ? how do they get rid of undesired molecules?

no they dont - by leaves falling

what might vacuoles store?

normal cell molecules (aa-sugars ...) - toxic compounds for defense against pest - undesired molecule and pollutants

do vacuoles share some acidic hydrolases with lysosomes?

yes

where are vacuole and tonoplast produced + matured?

produced at the level of RER by attached ribosomes and are then exported to Golgi for maturation