Download Recognise structures as seen under the electron microscope, e.g.

Lesson 2
• Recognise structures as seen under the
electron microscope, e.g. nucleus, nucleolus,
nuclear envelope, rough and smooth
endoplasmic reticulum, Golgi apparatus,
ribosomes, mitochondria, lysosomes and
chloroplasts.
• Outline the functions of these structures.
The detail of the inside of cell is called the
cell’s ultrastructure.
• Usually only one nucleus per
cell
• Regulates all cell activity
• Contains the DNA which
carries the information for
protein synthesis
• The DNA is associated with
histone protein to form
chromatin
• Surrounded by a nuclear
envelope (double layer
membrane) which has nuclear
pores
• Nucleus is continuous with
endoplasmic reticulum
Nucleus
• Found inside the
nucleus
• Makes RNA and
ribosomes which pass
into cytoplasm.
• Usually stains darker
than the rest of the
nucleus on EM
Nucleolus
Rough and smooth endoplasmic reticulum
• Rough ER – with ribosomes
– Protein synthesis
• Smooth ER – without ribosomes
– Synthesis of steroids and lipids
• Intracellular
membrane system –
substances are
transported in the
spaces
Golgi Apparatus • Stack of flattened sacs
(cisternae), each
separated from the
cytoplasm by a
membrane
• Modifies and packages
cell products (proteins
from rER)
• Encloses substances in
vesicles to be secreted
• Involved in production
and secretion of many
proteins, carbohydrates
and glycoproteins
• Vesicles containing
digestive enzymes
(hydrolytic enzymes)
to break down
materials
• Surrounded by a
single membrane.
• White blood cell
lysosomes break down
microorganisms.
• Lysosome (acrosome)
in sperm cell helps to
penetrate egg
Lysosomes
• Site of aerobic
respiration – where ATP
(adenosine
triphosphate) is
produced
• 2 membranes separated
by fluid filled space
• Internal membrane
folded into cristae
• Lots of mitochondria
found in active cells –
skeletal muscle
(physically active),
hepatocytes
(metabolically active)
Mitochondria
(2-5 µm long)
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•
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Chloroplasts
Only found in plant cells – site of
photosynthesis.
2 membranes separated by fluid filled
space
Inner membrane – flattened sacs called
thylakoids. A stack of thylakoids is
called a granum.
Inside – stroma which is also involved in
photosynthesis
Chlorophyll molecules found on thylakoid
membranes.
(4-10 µm long)
Ribosomes
• Lots of ribosomes in a cell (50 000 or
more)
• Found on rough ER and also as free
ribosomes in the cytoplasm
• Site of protein synthesis (where
mRNA and tRNA meet so the protein
is assembled).
Centrioles
• Two short cylinders of microtubules
• Pair found next to nucleus in animal cells
• Aid cell division – move to opposite poles
(ends) of the cell as spindle develops