Nucleus,er, golgi

1. Nucleus

2. The Nucleus
• These are found in all eukaryote cells
except
red blood cells, phloem sieve tubes and
xylem vessels
• Some cells are multinucleate
• The nucleus is about 10-20µm in diameter
• It is surrounded by a double membrane or
an envelope
• The outer layer of the membrane is
continuous with the endoplasmic reticulum

3. Nucleus
It is surrounded by a
double membrane
or an envelope
The outer layer of the
membrane is
continuous with the
endoplasmic
reticulum

4. Nucleus
There are pores in the
envelope, about 80-
100nm in diameter,
which allow
exchange of
materials
The
nucleoplasm is
a gel-like
matrix which
contains

5. Nucleus
Chromosomes are seen as
diffuse chromatin unless the
cell is dividing and they have
been stained
Chromatin is coils of DNA and
histone proteins bound to the
DNA
Heterochromatin is seen under
EM as darker staining
because it is more tightly
coiled
Euchromatin is lighter
staining and less
tightly coiled

6. Nucleus
There is one or more
nucleolus (plural =
nucleoli)
where ribosomal RNA
(rRNA) is
manufactured
It is seen as a dense,
dark staining region

10. Endoplasmic Reticulum
(ER)

11. This is a system of flattened sacs or cisternae
throughout the cytoplasm, continuous with the outer
membrane of the nucleus

12. Rough ER- this is associated with ribosomes
Rough ER is involved in the synthesis of proteins and
then the transport of protein around the cell

13. Smooth ER –has no ribosomes
It is involved in steroid and lipid production

15. In an electron micrograph
ER is seen as a series of
parallel lines
Sometimes it is possible to
see the ribosomes on rough
ER as small dots

16. Ribosomes
these are 20nm in diameter
They are free in the
cytoplasm or bound to ER
Ribosomes are made of RNA
and proteins
The RNA is ribosomal RNA
(rRNA),made in the
nucleolus
Ribosomes are the site of
protein synthesis

17. Ribosomes
They "read" the RNA
code
Free ribosomes make
cell proteins
Ribosomes on the ER
make proteins that
may be secreted from
the cell
Chloroplasts,
mitochondria and
Prokaryotes have 70S
ribosomes (smaller)
Eukaryotes have 80S
(larger ) ribosomes

18. The ribosome is made of two sub-
units:
• A smaller and a lager subunit
• A polysome is several ribosomes
simultaneously reading the same
strand of mRNA to increase the
efficiency of protein synthesis

19. Model of a ribosome – the blue area is the smaller subunit

20. Golgi apparatus
These are found in all cells and are
abundant in metabolically active
secreting cells
They are a system of flattened sacs
called cisternae only visible under EM

21. Golgi apparatus
Note the curved
parallel lines
These are
vesicles
containing
substances being
made by the Golgi
apparatus

23. 1. . Proteins or lipids made in the ER are transported, in vesicles, through
the cytoplasm

24. 2. The proteins/lipids are modified through the Golgi apparatus, often by
having a carbohydrate attached

25. 3. These vesicles fuse with the outer forming face of the Golgi apparatus

26. 4. The modified product buds off in Golgi vesicles from the inner maturing
face

27. 5. The vesicles move to the cell surface membrane and fuse with it to release
the contents outside (e.g. digestive enzymes)
If the product is not to be secreted the vesicle will transfer it to where it is
needed within the cell

29. Lysosomes

30. • about 0.1 – 0.5µm in diameter
• only seen under using EM
• made by rough ER and Golgi
apparatus
• spherical membrane bound
structures containing digestive
enzymes

31. • These enzymes may be
– used to digest other organelles or the
entire cell (autolysis)
– Released form the cell by exocytosis (such
as when sperm digest the ovum barrier)
– Digest foreign matter taken in to the cell by
endocytosis. They fuse with the food
vacuole to form a secondary lysosome
In plant cells the vacuole may act as a lysosome

32. Lysosomes digesting a food
particle in a phagocyte
This is a food particle
This is a simplified
Amoeba
Golgi
apparatus

33. Lysosomes digesting a food
particle in a phagocyte
1. endocytosis – the food particle is taken into
the cell
It is in a food vacuole made from the cell
surface membrane

34. Lysosomes digesting a food
particle in a phagocyte
2. The Golgi apparatus has modified proteins
to form hydrolytic (digestive) enzymes
These are budded off in lysosomes

35. Lysosomes digesting a food
particle in a phagocyte
3. The lysosome and food vacuole fuse to form
a secondary vacuole

36. Lysosomes digesting a food
particle in a phagocyte
4. The hydrolytic enzymes digest the food
particle and the digested nutrients are
absorbed into the cytoplasm

37. Lysosomes digesting a food
particle in a phagocyte
5. Undigested matter is removed by exocytosis
Note – in white blood cells this step does not occur.
The entire cell will be destroyed eventually