Cells
All living organisms are made of cells and share some common features. Organisms can be prokaryotes or eukaryotes:
• Prokaryotic organisms are prokaryotic cells (i.e. they are unicellular organisms).
• Eukaryotic organisms are made up of eukaryotic cells.
Eukaryotic cells are complex and include all animal and plant cells. Prokaryotic cells are smaller and simpler.
Eukaryotic Cell Structure
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, Eukaryotic Cell Structure
Organelles in Plant Cells and Animal Cells
Nucleus
• Double Nuclear Envelope – contains nuclear
pores to allow substances to pass through;
encloses and protects DNA.
• Nuclear Pores – allow substances to enter and
exit the nucleus; control what passes through.
• Nucleoplasm – contains chromatin granules of
DNA and proteins that condense during mitosis;
contains nucleoli.
• Nucleolus – dense body; produces ribosomes.
• Outer membrane continuous with rough
endoplasmic reticulum membranes –
perinuclear space continuous with lumen of
endoplasmic reticulum, allowing easy transport
of substances.
Ribosomes
• A small organelle that is not membrane-bound.
• Either floats free in the cytoplasm or attached to the rough endoplasmic reticulum.
• Produced in the nucleolus and made up of proteins and ribosomal RNA (rRNA).
• Composed of two subunits – a smaller subunit (where the mRNA codon binds to the tRNA anticodon) and the
larger subunit (where peptide bond formation occurs).
Golgi
• A group of fluid-filled, membrane-bound, flattened sacs.
• It processes new lipids and proteins and packages them in vesicles.
Rough Endoplasmic Reticulum (RER)
• A system of membranous tubules and flattened sacs enclosing a fluid-filled space.
• The surface is covered with ribosomes.
• Folds and processes proteins that have been made at the ribosome.
Smooth Endoplasmic Reticulum (SER)
• A system of membranous tubules and flattened sacs enclosing a fluid-filled space.
• The difference between the SER and the RER is that the SER has no ribosomes.
• Site of lipid and steroid metabolism, i.e. it synthesises triglycerides, cholesterol and phospholipids which
become part of the cell surface membrane.
Mitochondria
• Double Membrane – separates matrix from
cytoplasm; such high compartmentalisation allows
high concentrations of enzymes and substrates to be
maintained, which increases the rate of respiratory
reactions.
• Inner Membrane folds to from Cristae – greatly
increases the surface area for the attachment of
enzymes and co-enzymes involved in respiration.
• Matrix contains enzymes for respiration and DNA /
70S ribosomes for the transcription and translation of
proteins.
• The site of aerobic respiration where ATP is produced.
(See previous page for details on cell surface membrane, lysosome and centrioles).
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