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cell jp4 : Cytomembrane System, Slides of Cell Biology

cell biology course material : 1. Cytomembrane System 2.Endoplasmic Reticulum 3. Golgi Body and Secretion 4.Lysosomes and Peroxisomes 5.Mitochondria, etc

Typology: Slides

Pre 2010

Available from 02/02/2023

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Cytomembrane System
The cytomembrane system is
a group of organelles that has
3 basic functions: to
manufacture new lipids and
membranes, to modify
polypeptides into their final
proteins, and to package
proteins and other molecules
for export.
We will talk about 4 organelles
as part of this system: the
endoplasmic reticulum (ER),
the Golgi bodies, the
lysosomes, and the
peroxisomes.
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Cytomembrane System

  • (^) The cytomembrane system is

a group of organelles that has

3 basic functions: to

manufacture new lipids and

membranes, to modify

polypeptides into their final

proteins, and to package

proteins and other molecules

for export.

  • (^) We will talk about 4 organelles

as part of this system: the

endoplasmic reticulum (ER),

the Golgi bodies, the

lysosomes, and the

peroxisomes.

Endoplasmic Reticulum

  • (^) “Reticulum” means network; the ER is a network of tubules in the cytoplasm, composed of membranes just like the cell membrane. It provides a membrane channel from the nucleus to the cell membrane.
  • (^) Two types, connected together: rough ER and smooth ER
  • (^) Rough ER looks rough because it is studded with ribosomes, the cellular machines that synthesize proteins. Ribosomes on the rough ER make the proteins that go into the membrane. Other ribosomes, not attached to the ER, make other proteins.
  • Smooth ER has no ribosomes. It is used to synthesize the lipids of the membrane. It is also used in liver cells to detoxify harmful chemicals in the blood. Other functions as well.

Lysosomes and Peroxisomes

  • (^) Lysosomes are intracellular stomachs: they are

full of digestive enzymes that operate at low

pH. Vesicles transport materials to the

lysosomes, and the lysosomes digest them. In

the process of “programmed cell death”, cells

scheduled to die are destroyed from within by

their lysosomes. An example is the tail of a

tadpole, which is destroyed to make a tailless

frog.

  • (^) Lysosomal storage diseases are caused by

genetic defects. An example is Gaucher

disease, in which certain lipids accumulate

inside of lysosomes instead of being broken

down. This leads to interference with bone

marrow function: blood and bone problems.

  • (^) Peroxisomes are membrane-bound sacs used

to break down fatty acids and some other

molecules. They generate hydrogen peroxide,

a poisonous molecule, in the process, which is

the source of the name peroxisome.

Mitochondria

  • (^) The mitochondria are the site where most of the cell’s ATP is generated, when organic compounds are broken down to carbon dioxide and water, using oxygen.
  • (^) All eukaryotes have mitochondria. The number in a cell depends on that cell’s energy needs.
  • (^) Mitochondria have their own circular DNA, the same kind found in bacteria. This and other evidence has led to the theory that mitochondria were once free- living bacteria that developed a mutually beneficial relationship with a primitive eukaryotic cell.
  • (^) Mitochondria have 2 membranes, forming 2 compartments inside. To generate energy, hydrogen ions are accumulated between the 2 membranes. Then they flow down the concentration gradient into the inner compartment through a protein that uses the energy of their flow to create ATP.
  • Genetic defects in the mitochondria affect tissues that use a lot of energy: nerves, muscles, liver, kidney. They are unusual because they are inherited strictly from the mother—only the egg’s mitochondria go into the next generation.

Plant Cell Organelles

  • (^) Plants have three special structures not found in animals: the chloroplast, the cell wall, and the central vacuole.
  • (^) The chloroplast is the site of photosynthesis, the process of converting carbon dioxide into sugar and oxygen using sunlight. Most life depends on photosynthesis, directly or indirectly. It uses the green pigment chlorophyll to capture the energy from light.
  • (^) Like the mitochondria, chloroplasts have two membranes and their own circular DNA. Chloroplasts are also thought to have originated from an ancient mutually beneficial relationship between photosynthetic bacteria and a primitive eukaryote.
  • In some plant cells, chloroplasts are modified to store starch (as in potatoes) or to contain other pigments (as in flowers).

More Plant Organelles

  • (^) Each plant cell is surrounded

by a rigid cell wall made of

cellulose and polysaccharides.

The cell wall is outside of the

cell membrane. In woody

plants, the cell walls can

become very thick and rigid.

  • Plant cells contain a central

vacuole, which stores water.

Osmotic pressure from the

central vacuole squeezes the

rest of the cytoplasm against

the cell wall, giving the cell its

strength.