Inside the cell works a traffic policeman, and next to him sits a suicide bag. One guides vesicles all the way to the plasma membrane. The other, when food runs out badly, lets its enzymes loose and destroys the cell's other organelles. This note teaches you to tell the two apart.
1. What the Golgi body is
Near the nucleus, in the cytoplasm, lies an organelle made of small tubules, vesicles, tanks or lamellae, all bound by a double membrane. It is the Golgi body, also called the Golgi apparatus.
The Italian neurologist Camillo Golgi (1843-1926) first saw it in 1898, in the nerve cells of owl and cat.
It has other names too: dictyosome, idiosome and lipochondria. Nearly every animal cell has one.
The Golgi body is called the “traffic police of the cell”, because it carries membrane-bound vesicles from the centre of the cell out to the plasma membrane.
2. Structure: cisternae, cis and trans
The flat sacs of the Golgi are cisternae (singular cisterna). The irregular tubules and vesicles are the trans-Golgi network (TGN). Each stack of cisternae is a Golgi body, or dictyosome.
The end of the stack near the plasma membrane is the trans-face. The end toward the cell centre is the cis-face. The cisternae in between are the medial cisternae.
In an animal cell the Golgi apparatus usually lies together in one place. In a plant cell more than a hundred separate Golgi bodies are scattered through the cytoplasm.
Figure 1.8 has eight points. Tap each one, and keep track of which way cis lies and which way trans lies.
Figure 1.8tap a point
Layers of the Golgi
Rough ER. It makes protein.
Smooth ER. The probable source of the Golgi.
Transition vesicle. It carries ER products.
Cis cisterna. The end toward the cell centre. ER products enter here first.
Medial cisterna. The middle layer.
Trans cisterna. The end toward the plasma membrane.
Secretory vesicle. It carries secreted material.
Plasma membrane. The destination.
All eight seen. Remember: cis faces the cell centre, trans faces the plasma membrane.
Drawn by hand after the book's figure, not to scale.
3. The path, the makeup and the jobs
In plant cells the Golgi body mainly adds side chains to the oligosaccharides of glycoproteins, and makes and secretes complex polysaccharides. That is why it is the carbohydrate factory. It also builds the cell wall.
Before you put the steps in order, watch the trip once. Follow one product from the ER through the Golgi to the plasma membrane.
the triprun it, or step
From the ER to the membrane
A product made in the ER is wrapped in a transition vesicle and enters the cis-cisterna. It passes through the medial cisternae and reaches the trans-cisterna. From there it goes elsewhere in the cell or to the plasma membrane. Put the six steps in order.
in orderput the steps in order
The journey of a product
Where is the product made in the first place?
Yes. Then?
Not yet. Remember, cis faces the cell centre and trans faces the plasma membrane.
Right order. Cis first, trans last.
The Golgi envelope holds 60% protein and 40% lipid. It also contains vitamin K and carotenoids, and enzymes such as ATPase, ADPase and transferase.
The Golgi body has a long list of jobs. It makes lysosomes, synthesises non-protein substances and builds some enzymes. It forms the cell plate in cell division. It makes protein, hemicellulose and microfibrils. It removes water from the cell. It wraps ER products in membrane. It makes and carries polysaccharides.
4. The lysosome, the suicide bag
The cytoplasmic organelle that stores hydrolytic enzymes is the lysosome (Gk. Lyso = digesting, soma = body). It too is bound by a double membrane.
Christian de Duve gave it the name lysosome in 1955.
Lysosomes arise from the ER and are packaged by the Golgi body. White blood cells carry many of them; red blood cells carry none.
Plant cells have a structure much like the lysosome: the spherosome, or oleosome. It is small, bound by a single membrane, and encloses oily substances.
Lysosomes are usually round, 0.2-0.8 millimicron across. The envelope is lipo-protein. Inside are about 60 kinds of enzyme, such as DNAase, RNAase, acid lipase, esterase, saccharase and lysozyme.
Why do such strong enzymes not digest the cell? They work in an acidic medium, not at the neutral pH of the cytoplasm. When needed, the lysosome brings in H⁺ from the cytoplasm and makes its own inside acidic.
A lysosome does four jobs. It destroys germs by phagocytosis. It protects the other organelles by keeping its digestive enzymes shut in. It helps intracellular digestion. And in cell division it helps break the cell and nuclear envelopes.
In severe starvation the lysosome wall bursts, and the enzymes that escape destroy the cell's other organelles. This is autophagy, self-eating. When the whole cell is digested, it is autolysis.
Now put a lysosome to work. Make its inside acidic, send in a germ, and then see what starvation does.
the suicide bagpick a button
When a lysosome digests
Because it destroys useless cells by autolysis, the lysosome is called the suicidal bag (or suicide squad). Now drop the four terms into their meanings.
match themmeaning, then term
The language of the lysosome
Pick up a meaning, then drop it in the term it fits.
Right. Next one.
Not yet. Ask: is the damage to one organelle or the whole cell? To germs, or to the cell's own parts?
All in place. Autophagy takes the other organelles, autolysis takes the whole cell. The lysosome is the suicidal bag because it finishes off useless cells.
5. Where the Golgi comes from, and its side sacs
The Golgi body probably arises from the smooth endoplasmic reticulum.
At the sides of the cisternae sit large rounded, sac-like structures called vacuoles. All the parts are held together by intercisternal material.
Now both organelles together. Eight chips, two boxes.
sort themtap a chip, then pick a box
Which organelle?
Pick up a chip, then drop it in a box. Ask: is this about moving and making, or about digesting?
Right. Next one.
Not yet. Recall the names, years and nicknames separately: 1898 belongs to the Golgi, 1955 to the lysosome.
All in place. Golgi: moves vesicles, a stack of cisternae (dictyosome), makes polysaccharides, packages lysosomes, seen by Golgi in 1898. Lysosome: autolysis, the enzyme store, named by de Duve in 1955.
6. Check yourself
Three questions in the exam's style. Start with the first.
check yourselfpick one answer
Question 1
Functions of the Golgi body are:
i. Forming lysosomes ii. Synthesis of non-protein substances iii. Protein synthesis
Right. The Golgi body forms lysosomes and synthesises non-protein substances; protein synthesis is the ribosome’s job.
i and iii: iii is wrong.
ii and iii: iii is wrong.
Not all three, because iii is wrong.
In the second, do not mix up the nicknames and titles.
check yourselfpick one answer
Question 2
Which one throws out the secreted substances of the cell to the outside?
Mitochondria produce energy and do not secrete.
The nucleus controls the cell.
Right. The Golgi body loads secreted material into vesicles and carries it to the plasma membrane for release.
The cytoplasm holds the small organelles.
Think the last one through before you answer.
check yourselfpick one answer
Question 3
In the light of the stimulus: [Figure: a long flattened sac with a swollen end (marked B), and below it a small round budding sac (marked A).] What is the name of the part marked ‘A’ in the stimulus?
Right. The small round sac budding from the end of a Golgi cisterna is the vesicle.
Cisternae are the flat sacs; A is a small round sac, so it is not a cisterna.
A vacuole is a cell cavity, not a small budding sac.
The thylakoid is a chloroplast sac, not part of the Golgi body.
The whole note on seven cards.
cut from the notetap to turn over
Seven cards
QuestionWhy is the Golgi body called the "traffic police of the cell"?
AnswerBecause it carries membrane-bound vesicles from the cell centre to the plasma membrane.
QuestionWhere are the trans-face and the cis-face?
AnswerTrans-face near the plasma membrane; cis-face toward the cell centre.
QuestionWhy is the Golgi body of plant cells called the carbohydrate factory?
AnswerBecause it adds side chains to glycoprotein oligosaccharides and makes and secretes complex polysaccharides.
QuestionThrough which parts of the Golgi does an ER product pass?