D’YOUVILLE COLLEGE
BIOLOGY 102 - INTRODUCTORY BIOLOGY II
LECTURE # 7
CELL STRUCTURE I
1.
Methods of Studying Cells: microscopy (light, electron, scanning electron, etc.),
cell fractionation (figs. 6 – 3, 6 – 4 & ppts. 1 – 4)
• microscopy: light microscopes form real images of cells and can resolve detail
down to 0.2 m.; most material needs to be chemically ‘fixed’ and stained to introduce
contrast into the features of the cell; some types of light microscope can achieve optical
staining effects permitting study of living cells (fig. 6 – 3 & ppts. 1 & 2)
- electron microscopes extended the study of cell structure to a much finer
level of resolution, revealing structure of many organelles, previously undiscovered;
two types of electron microscopes: transmission EM & scanning EM, each reveal
different aspects of cellular & subcellular structure (fig. 6 – 3 & ppt. 3)
• cell fractionation: functional properties of organelles may be revealed by
grinding up tissue and segregating different organelles from one another by
differential centrifugation (fig. 6 – 4 & ppt. 4); biochemical studies can then be
performed upon these ‘fractions’ to determine their function
2.
Prokaryotic vs. Eukaryotic Cells:
• prokaryotic cells are exemplified by bacteria; prokaryotes are distinguished by
absence of membranes & nucleus; genetic material is found within a special region of
cytoplasm (‘nucleoid’) that is not separated by a membranous envelope from the rest of
the cytoplasm (fig. 6 – 5 & ppt. 5)
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• eukaryotic cells (most living things) possess a ‘true nucleus’ separated from
cytoplasm by double membrane boundary; cytoplasm of eukaryotic cells has several
membranous organelles not present in prokaryotes
3.
Animal & Plant Cells (fig. 6 – 8 & ppts 7 & 8):
• membrane systems –largely absent from prokaryotic cells (except plasma
membrane), eukaryotic cell membranes include the outer limiting membrane (plasma
membrane)(fig. 6 – 6 & ppt. 6), internal membranes - endoplasmic reticulum (ER),
Golgi apparatus, lysosomes (animal cells), peroxisomes & vacuoles (plant cells only);
these establish compartments within the cytoplasm
- other membranous organelles are the mitochondria (both animal & plant
cells) & chloroplasts (plant cells only)
- nuclear envelope, a double membrane enclosing the nucleus, is continuous
with ER (fig. 6 – 9 & ppt. 9)
4.
Nucleus: (Fig. 6 – 9 & ppt. 9)
• control center – guides cellular processes & serves as repository of genetic
information
• nuclear envelope: double layered membrane separating nuclear contents from
rest of cytoplasm; frequent pores permit traffic between nucleus and cytoplasm; traffic
through pores is regulated by proteins that bound the pores; inner face of nuclear
envelope is supported by a network of proteins, the nuclear lamina; outer layer of
nuclear envelope is continuous with ER
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• chromosomes (chromatin): nucleoprotein threadlike structures constituting
genetic material (“genetic library”)
- dispersed state (chromatin); condensed state (chromosomes)
• nucleolus: site for synthesis of rRNA and ribosomes
- ribosomes: rRNA & protein complexes serving as sites for protein synthesis
(fig. 6 – 10 & ppt. 10)
5.
Endomembrane System: (fig. 6 – 15, ppt. 14 & ppt. movies 15 & 16)
• endoplasmic reticulum (ER) (fig. 6 – 11 & ppt. 11): extensively folded
membranous network found throughout the cytoplasm; serves to organize and
compartmentalize cellular reactions (cytosol separate from cisternae)
- two main types: rough (granular) ER (possesses ribosomes): for protein
synthesis; sheet-like organization
- smooth (agranular) ER (lacks ribosomes): for lipid synthesis, carbohydrate
metabolism, drug detoxification (liver), storage of calcium ion (muscle); mainly tubular
- transport vesicles: synthesized materials passed into cisterna of ER are
exported by budding off from the ER in membrane-enclosed packets
• Golgi Apparatus (fig. 6 – 12 & ppt. 12): arrays of stacked membranes with cis trans polarity; serve as “packaging centers” or distribution centers; final steps in
modifying materials for secretion; buds off vesicles to produce lysosomes, new plasma
membrane
• lysosomes (fig. 6 – 13 & ppt. 13): organelle of cellular digestion; consists of bag
of enzymes, bactericidal, antiviral agents; important in phagocytosis; endocytic vesicles
formed from phagocytosis, fuse with lysosomes to facilitate digestion of contents of the
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endocytic vesicle; damaged cellular structures may also be enclosed in vesicles and the
contents digested by fusion with lysosome