Transcript L4 Prokaryotes eukaryotes and onion cheek preps

Lesson 4 – Prokaryotic cells
and cell preparations
• Today we will carry out slide preps of
onion and cheek cells
• Complete some calculation of
magnification
• Learn about some differences between
prokaryotes and eukaryotes
Learning aims:
• To understand the similarities and differences
between Eukaryotes and Prokaryotes.
• To be able to prepare, describe and draw a cheek cell
slide preparation, onion cell slide preparation and
plant material slides
Cell types.
Eukaryotic cells:
These include plant and animal cells. They contain a
nucleus that contains the cell’s DNA and they a
collection of complex organelles that have specific
functions.
( Animal, plant, fungi and protoctista are all eukaryotes)
Prokaryotic cells:
Bacteria are prokaryotes. (Evolved long before
eukaryotes). The major difference is, they contain
nucleic acids, but they are not confined inside a
definite nucleus with a nuclear membrane. Instead
there are strands of DNA in the centre of the cell
that are collectively known as the nucleoid.
• Prokaryotes are all bacteria:
• Escherichia coli: Human gut, harmless feeds on food
and breakdown products of digestion.
• 65 billion in your body!
• Makes up 0.1% of bacteria that live in your body!
EXCEPTIONS!
• Epulopiscium fishelsoni : discovered 1980’s, lives in
intestine of Red Sea sturgeon, visible by the naked
eye.
• Thiomargarita namibiensis: lives in marine sediments
off the coast of Afica, 180 micometres in diameter(
just visible without a microscope)But can reach 750
micometres, size of a pinhead.
Prokaryotic cells.
Much smaller than eukaryotic cells,0.5-3.0 micrometres.
Parts and their function:
Much simpler in structure, lack membrane bound organelles
(mitochondria, chloroplasts). Lack complex structures such as
Golgi bodies, cytoskeleton and lysosomes.
• Nucleotide (or Nuclear Zone). The region of the cytoplasm that
contains DNA. It is not surrounded by a nuclear membrane.
• DNA. Always circular, and not associated with any proteins to
form chromatin.( bacterial chromosome)
•
Plasmid. Small circles of DNA, used to exchange DNA between
bacterial cells, and very useful for genetic engineering.
• Cell Wall. Made of murein (not cellulose), which is a glycoprotein
(i.e. a protein/carbohydrate complex, also called peptidoglycan).
Protects the shape of cell,prevents it from bursting.
• Some have a slime capsule, helps cells to stick
together and for protection ( phagocytes)
• Flagellum. A rigid rotating helical-shaped tail used
for propulsion. Each consist of a single rod of
proteins,rather than 9+2 hollow structure in
Eukaryotes.
• Cytoplasm. Contains all the enzymes needed for all
metabolic reactions, since there are no organelles.
Contains glycogen (CHO storage) and lipid droplets.
• Ribosomes. The smaller (70 S) type, scattered in the
cytoplasm.
• There are no membrane bound organelles, but
bacteria often have infolds of the plasma membrane:
• Mesosome. A tightly-folded region of the cell
membrane containing all the membrane-bound
proteins required for respiration and photosynthesis.
• Thylakoids. Present in photosynthetic bacteria,
where bcterial chlorophyll and enzymes of
photosynthesis are located.
Differences between Prokaryotes and
Eukaryotes: