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AS BIOLOGY
The ultrastructure of the cell
LEARNING OBJECTIVES
By the end of this section you should be able to:• Recognise the following organelles from a diagram of the
eukaryotic animal and plant cell (rough and smooth endoplasmic
reticulum, Golgi apparatus, mitochondria, ribosomes, lysosomes,
chloroplasts, plasma (cell surface) membrane, nuclear envelope, centrioles,
nucleus, nucleolus and cilia).
• Outline the functions of the following structures:-rough and
smooth endoplasmic reticulum, Golgi apparatus, mitochondria, ribosomes,
lysosomes, chloroplasts, plasma (cell surface) membrane, nuclear
envelope, centrioles, nucleus, nucleolus and cilia.
The Eukaryotic Cell
The Beginnings
•Robert Hooke was the first person to observe cells in 1665.
•He looked at thin slices of cork under a very simple microscope.
•The cork appeared as little boxes which he called cells.
•In 1883 MathiasSchleiden and Theodor Schwann proposed that all
plants and animals were composed of cells which were the basic
building blocks of life.
•In 1855 Rudolf Virchow stated that new cells arise from the
division of pre-existing cells and that chemical reactions needed for
life occurred inside the cell.
•All this work led to the formation of the cell theory (click to
complete exercise on cell theory)
•For more information click on link below
http://fig.cox.miami.edu/~cmallery/150/unity/cell.text.htm
Eukaryotic Animal Cell
• Eukaryotic means “true nucleus”
• Eukaryotic cells have a nucleus which contains the
DNA.
• Eukaryotic animal cells are surrounded by a cell
membrane.
• Inside is the jelly like substance called cytoplasm.
• Contained in the cytoplasm is the nucleus and other
organelles (copy the glossary file into your area and continue to add words and meanings)
• The other cell organelles include the endoplasmic
reticulum,(rough & smooth) mitochondria, Golgi
apparatus, ribosomes, lysosomes, centrioles, cilia,
nucleolus.
Endoplasmic Reticulum
STRUCTURE
• Complex system of sheet like
double membranes continuous
with the nuclear membrane
• Fluid filled spaces/sacs
between the membranes
called CISTERNAE which
allow materials to be
transported through cell
• Two types of ER –
– smooth – has no ribosomes
attached (RER)
– rough – has ribosomes
attached (SER)
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FUNCTION
Forms an extensive transport
system
Site of protein synthesis
(Rough ER)
Site of lipid, steroid and
carbohydrate synthesis
(smooth ER)
Stores and transports these
materials
SEE DIAGRAM
Mitochondria
STRUCTURE
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Relatively large organelle
Rod/sausage shaped – 1um –
5um
Have a double membrane
– The outer controls the entry &
exit of materials
– Inner has many folds called
cristae
Surface of each crista is covered
with stalked particles where ATP is
made
Mitochondria are filled with a jelly
like matrix
The matrix contains proteins,
lipids, ribosomes and loops of
DNA
Mitochondria can replicate
themselves when the cell divides
FUNCTION
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Site of aerobic respiration (Krebs
cycle & oxidative phosphorylation)
Responsible for the production of
energy rich ATP molecules
The numbers of mitochondria
reflect the metabolic activity of the
cell – so large numbers are found
in muscle and liver cells
SEE DIAGRAM
Golgi apparatus
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STRUCTURE
Formed from small pieces of
rough ER which form small
vesicles which join to make a
Golgi body
Chemicals made in the ER
collect in the Golgi body where
they are modified
Small vesicles can then be
‘pinched’ off the Golgi body
carrying new chemicals away
which are secreted when the
vesicle reaches the cell
membrane
Some of the vesicles become
lysosomes
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FUNCTION
Assembling glycoproteins
(such as mucin) by combining
carbohydrate and protein
Transporting and storing lipids
Formation of lysosomes
Producing digestive enzymes
Secretes carbohydrates which
are used in the formation of
plant cell walls and in insect
cuticles
SEE DIAGRAM
What have you learnt?
Click here to walk the plank
Ribosomes
STRUCTURE
• Small dense structures found
in huge numbers.
• Can be attached to the rough
ER of floating in the cytoplasm.
• Are about 20 – 25 nm in
diameter in eukaryotic cells
and slightly smaller in
prokaryotic cells
• (80s type – prokaryotic)
• (70s type – eukaryotic)
• Made up from two sub units
FUNCTION
• Synthesize proteins
• Synthesize enzymes
• SEE DIAGRAM
Lysosomes
STRUCTURE
• Small vacuoles formed when
small pieces of Golgi body are
pinched off
• Contain hydrolytic enzymes
which digest materials in the
cell
• SEE DIAGRAM
FUNCTION
• Release enzymes which
destroy worn out organelles
• Digest material taken into the
cell (eg white blood cells which
have engulfed a bacterium) –
phagocytosis
• Release enzymes to the
outside of the cell which digest
material around the cell –
exocytosis
• Completely break down cells
after they have died – autolysis
Plasma (cell surface) membrane
STRUCTURE
• This is the boundary between
the cell cytoplasm & the
environment
• Is partially permeable
• Made up 45% protein & 45%
phospholipids with the
remaining 10% cholesterol,
glycoprotein & glyolipids
FUNCTION
• Controls movement of
substances in & out of the cell
• Forms a recognition site so
that the body’s immune system
can recognize its own cells
• Acts as a receptor site for the
attachment of specific
hormones and
neurotransmitters.
• SEE DIAGRAM
STRUCTURE
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Nucleus, Nucleolus &
Nuclear envelope
Largest organelle in the cell (10um
diameter)
Surrounded by a nuclear membrane
/ envelope
Double membrane – outer is
continuous with the ER
Nuclear pores in the membrane
allow the passage of large
molecules in & out (eg
messengerRNA)
Material inside the nucleus is called
nucleoplasm – this contains
chromatin which makes up the DNA
of the cell – in non-dividing cells it is
spread out and during cell division it
condenses to form the
chromosomes
A spherical structure called the
nucleolus is found in the nucleus –
this makes ribosomal RNA and
assembles the ribosomes.
FUNCTION
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Acts as the control centre of the
cell through the production of
mRNA and protein synthesis
Retains the genetic material in the
cell in the form of DNA /
chromosomes
Manufactures ribosomal RNA
(rRNA) & ribosomes
Starts the process of cell division
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SEE DIAGRAM
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What have you learnt?
Click here to complete the
crossword
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Cilia
STRUCTURE
• 3-10 um in length, 0.2um
in diameter
• Made of rings of 9 pairs
of microtubules
• Have basal body
embedded in cytoplasm
• Rest extends from basal
body
• Only a few types of cell
possess cilia
• On cells which have cilia
there are large numbers
FUNCTION
• To move an entire
organism (eg in
paramecium it propels it
through the water)
• To move material within
an organism ( eg cilia in
the lining of the
respiratory tract)
• SEE DIAGRAM
CENTRIOLES
(not found in plant cells)
• Two short bundles of hollow cylinders (microtubules)
positioned at right angles to each other
• Found just outside the nucleus in a clear area of
cytoplasm called the centrosome
• Wall of each centriole is made of 9 triplets of tubes
arranged at an angle
• During cell division they migrate to opposite poles to
produce the spindle – which helps to move the
chromosomes during cell division
• SEE DIAGRAM
Chloroplasts
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Found inside photosynthetic tissues of plants (abundant in palisade
mesophyll cells of leaves)
Flat discs 2-10 um in diameter & 1um thick
Have a double membrane called the chloroplast envelope
Inner membrane folded into a series of lamellae
Membrane controls the entry & exit of substances
Inside the membrane is a fluid – stroma – which contains the enzymes
involved in photostnthesis
Small amounts of DNA and oil are found in the stroma
In stroma is a network of flattened sacs called thylakoids
Grana (granum = sing) are formed when many thylakoids are stacked
together (like a pile of coins) (thylakoids also called lamella)
Chlorophyll molecules are attached to the thylakoids
Large starch grains are also present which act as a tempory store of
charbohydrate made in photosynthesis
SEE DIAGRAM
Click here to label the eukaryotic animal cell
Click here to play cell organelles
catch phrase