Download 1 Tripoli University Faculty of Science / Zoology Department Lecture

Tripoli University
Faculty of Science / Zoology Department
Lecture notes in General Zoology course Zo 105
Part one: cytology
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Textbook: Kenneth Saladin. Anatomy and Physiology: the unity of form and function. 1st ed. 1998.
McGraw Hill.
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Syllabus
Cytology = Cell Biology
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Definition
Cell discovery and cell theory (p. 107 Table 4.1)
Prokaryotic and eukaryotic cells
Cell sizes and cell shapes (p. 111 Table 4.2)
Structure of a typical animal cell (p. 110 Fig. 4.4)
Cell organelles: structure and function of the following (p. 124 Table 4.4)
o Nucleus
o Endoplasmic reticulum
o Golgi apparatus
o Lysosomes
o Peroxisomes
o Mitochondria
o Centrosome
o Centerioles
o Ribosomes
o Cytoskeleton
Plasma membrane: Structure and function
o Fluid mosaic model (p. 112 Fig. 4.6)
o glycocalyx
Plasma membrane extensions
o Cilia (p. 115 Fig. 4.9)
o Flagella
o Microvilli
Plasma membrane junctions
Plasma membrane transport (p. 134 Table 4.5)
o Passive transport
o Active transport
o Bulk transport
Nucleic acids (p. 145 Table 5.1)
o Nucleotide (p.142 Fig 5.3)
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Nitrogen bases
DNA (p. 142 Fig 5.2, 5.4)
• Structure
• function
• Replication (p. 152 Fig 5.12)
o RNA
Structure
Types of RNA
Functions
Gene structure in eukaryotes
Gene expression
o Transcription
o Translation
Protein synthesis (p. 149 Fig 5.8)
o Genetic code
o Initiation codon
o Termination codons
Cell cycle (p.154 Fig 5.14)
Mitosis (p. 155 Fig 5.15)
Meiosis (p. 977 Fig 27.14)
Gametogenesis
o Spermatogenesis (p. 979 Fig 27.16)
o Oogenesis (p. 1003 Fig 28.11)
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Cellular respiration
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Glycolysis (p.942)
Kreb cycle (p. 944)
Electron transport chain (p.946)
Overview of ATP production (p. 947)
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Lecture notes
Cytology is a branch of biology, which deals with the study of cells in terms of structure, function and
chemistry.
Cell Discovery
In 1591 the Dutch merchant Anton van Leewenhoek invented single lense microscope. He was the first
man to witness live microscopic organisms, named them animalcules “little animals”.
The invention of the microscope led to the discovery of cells. In 1665 the English scientist Robert Hooke
introduced the term “cell” while examining very thin slices of cork using a compound microscope. He
observed a multitude of pores that looked like the wall compartments of a honey comb, he called them
cells.
Three German scientists developed the concept of cell theory. The botanist Matthias Schleiden (in 1838)
was the first to clearly state that all plants are made of cells. The zoologist Theodor Schwann (in 1839)
was the first to clearly state that all animals are made of cells. The pathologist Rudolf Virchow (in 1855)
was the first to identify that the nucleus controls the cell activities and cell come from pre existing cells.
Modern Cell Theory
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All living things are made of cells
The cell is the smallest fundamental unit of life
All cells arise from pre existing cells through cell division
Cells contain genetic material, which they pass to daughter cells during cell division
All cells have a similar chemical composition (proteins, nucleic acids, carbohydrates, lipids)
The metabolic processes associated with life occur within cells.
Cell Definition
The cell is the fundamental structural and functional unit of all living organisms
Classification of cells
There are two major categories or types of cells: prokaryotic and eukaryotic.
The main difference between these two cell types is that Prokaryotic cells do not have a nuclear
membrane. The nuclear material consists of a single chromosome and lies in the cytoplasm. The nuclear
region in the cytoplasm is called nucleoid. Membrane-bound organelles are absent. Prokaryotic cells are
found in bacteria and cynobacteria (blue-green algae). Eukaryotic cells include: all other cells, such as
protista, fungal, plant and animal cells. The nucleus in a eukaryotic cell is bound by a nuclear envelope
and contains nucleoplasm. The cytoplasm, found between the plasma membrane and the nucleus,
consists of fluid and the organelles.
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Structural and functional differences between Prokaryotes and Eukaryotes:
Prokaryotic
Eukaryotic
Features
Plant
Animal
Size(diameter)
0.5 - 5 µm
40 µm
15 µm
Cell wall
Yes (contains peptidoglycan)
Yes (contains cellulose)
No
Genetic
Material
DNA linear, associated with histones
DNA is naked. A single circular molecule (proteins), in a nucleus, surrounded by a
nuclear envelope.
Ribosomes
70S ribosomes (smaller)
80S ribosomes (larger)
ER, Golgi
apparatus
No
Yes
Mitochondria
No(respiration occurs on an infolding of
the cell membrane called the
Yes
mesosome.)
Chloroplasts
No
Yes
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No
Cell sizes and shapes
Cells can be remarkably different in size, shape and function. Cells come in many different sizes. Some
cells are visible to the naked eye (such as eggs of birds), however, most cells are microscopic and cannot
be seen by the naked eye. Microscopes were developed to visualize cells. The size of the cell is
measured in micrometers (µm) in diameter. For example bacterial cells range 0.2 to 0.3 µm, liver cell 20
µm, plant cell 30 to 40 µm.
Cells also come in many different shapes (e.g. spindle, aster, and oval, spherical, cylindrical). Some cells
change their shape (e.g. amoebae, macrophage) others have typical shape (e.g. spermatozoa, epithelial
cells). The shapes of cells have evolved to help them carry out their specific function in the body.
Cell Structure
Despite the fact that there are many different cell types, sizes, and shapes, for descriptive purposes, the
concept of a "generalized animal cell" is introduced. It includes features from all cell types. A cell
consists of three parts:
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The cell membrane: a selective barrier which encloses a cell
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The nucleus: contain genetic material (a fine network of treads called chromatin which is DNA
(deoxyribonucleic acid) associated with particular proteins. At the time of cell division,
chromatin becomes condensed to form rod-like bodies known as chromosomes)
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The cytoplasm: all the cellular contents between the plasma membrane and the nucleus. It
includes: the cytosol (a jelly-like fluid ), all the organelles other than the nucleus, and the
cytoskeleton
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Cell membrane = plasma membrane = plasmalemma
Every cell is enclosed by a cell membrane. The cell membrane separates the material outside the cell
(extracellular) from the material inside the cell (intracellular). It defines cell boundaries. It maintains the
integrity of a cell. It regulates the exchange of materials between cytoplasm and extra cellular fluid due
to its selective permeability. It is also important in intercellular communication and cell identity.
STRUCTURE OF THE CELL MEMBRANE
The cell membrane is a “phospholipid bilayer” made of membrane lipids (phospholipids, glycolipids,
cholesterol) and membrane proteins (integral, peripheral).
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The membrane lipids
Phospholipids are the most abundant lipids in the membrane (75%), they form the lipid bilayer.
Phospholipids are amphipathic molecules with polar heads (glycerol attached to phosphate) and
nonpolar tails (two long fatty acid hydrocarbon chains). The phosphate heads are polar molecules and so
are water-soluble (hydrophilic = water loving). They are oriented toward the extracellular space or
cytoplasm (intracellular).The lipid tails are non-polar and therefore are not water-soluble (hydrophobic
= water hating). They are oriented toward the interior of the membrane.
Cholesterol (steroid lipid soluable) is also present in the membrane. Found in both leaflets of lipid
bilayer in between the phospholipd tail molecules. It constitutes 20% of membrane lipids. It maintains
the fluidity and increases the stability of the membrane.
Glycolipids are phospholipids with short oligosaccharide chains. Always found on extra cellular side of
cell membrane. Least common of the membrane lipids (2 to 5 %)
Membrane proteins
Much of the membrane is made up of a 'sea' of phospholipids with protein molecules 'floating' in
between the phospholipids. Some of these proteins span the whole width of the cell membrane. They
are called transmembrane or integral proteins. Peripheral proteins which do not protroude into the
phospholipid layer, they always adhere to the intracellular face of the membrane. There are also short
polysaccharide chains that are attached to the outer surface of the membrane. Most of these
carbohydrates are attached to proteins and are called Glycoproteins. Proteins in the cell membrane
provide structural support, form channels for passage of materials, act as receptor sites, function as
carrier molecules, and provide cell identify markers (glycocalyx).
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The plasma membrane structure is called the Fluid Mosaic Model, because the membrane is fluid
(phospholipids and proteins are not fixed in one place = they float) and because of the mosaic (patterns)
arrangement of the protein molecules created on the membrane’s surface.
Mehods of Membrane Transport
Plasma membrane has selective permeability so some substances pass quickly, some with difficulty, and
some not at all.
It is important that the cell is supplied with all the substances it needs (e.g. oxygen) and that waste
substances (e.g. carbon dioxide), or substances for export, leave the cell. There are various ways by
which substances can be moved or transported through the cell membrane. There are three methods of
membrane transport: Passive transport, Carrier mediated transport, and Bulk transport.
Passive transport
Movement of substances across a cell membrane without any direct energy expenditure by the cell. It
includes diffusion and osmosis.
Diffusion
Diffusion is a movement of particles from an area of high concentration to an area of lower
concentration of the particles or molecules, thus tending to equalize the concentration throughout.
This is the process that is used in oxygen entering a cell, and carbon dioxide leaving (respiratory gases)
and any lipid soluble molecule (e.g. alcohol, steroids).
Osmosis
The movement of water molecules through a semi-permeable membrane in response to a concentration
and or pressure gradient.
Carrier mediated transport
When substances are allowed to cross the cell membrane with the help of integral proteins (carrier or
channel proteins). Two types: facilitated transport and active transport.
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Facilitated transport
Facilitated transport: diffusion of molecules from high concentration to low concentration. Substances
are moving down the concentration gradient so no energy is required. Example glucose molecules.
Active transport
Movement of individual ions and molecules across cell membrane, against. (up) concentration gradient
(from low to high) by ATP expenditure. Example Na – K pump.
Bulk transport
Movement of particles or fluid through cell membrane by means of vesicles needs ATP. Two types:
endocytosis and exocytosis.
Endocytosis
The ingestion of solid or fluid material by cells, materials entering the cell can do so when the plasma
membrane invaginates to surround the material. The membrane seals off to form a vesicle, which can
then move into the cell. Two types: phagocytosis and pinocytosis.
Phagocytosis = “cell eating”
The material is relatively large or solid, and is digested by enzymes after fusion of the vesicle with a
lysosome. This occurs in white blood cells that ingest bacteria and other foreign bodies.
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Pinocytosis = “cell drinking”
The material is fluid, minute vesicles are formed.
Exocytosis
The material to be transported out of the cell is surrounded by membrane. The vesicle will fuse with the
cell surface membrane and the contents leave.
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