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Introduction to Cells (Cytology Part I)
• Text: BJ Chap 3, AP Chap 6
• Reading Assignments
– J Chap 3 pp 69– 94, AP pp167 - 192Text: BJ
Chap 2, AP Chap 5
• Homework Assignment
– Chap 3 Review Questions
BJ 3A – The structure of Cells (p
69)
• Hierarchy of Life
– Atoms -> Molecules -> Cell Structures ->
Organs -> Organ Systems
BJ 3 A- 1. (p 70) Cell Theory
• Cytology: Cytology means "the study of cells".
Cytology is that branch of life science, which
deals with the study of cells in terms of structure,
function and chemistry. Based on usage it can
refer to:
– Cell biology - the study of (normal) cellular anatomy,
function and chemistry.
– Cytopathology - the study of cellular disease and the
use of cellular changes for the diagnosis of disease.
Cell as Basic Unit
• Cell: The cell is the structural and functional unit
of all known living organisms. It is the smallest
unit of an organism that is classified as living,
and is often called the building block of life.
Some organisms, such as most bacteria, are
unicellular (consist of a single cell). Other
organisms, such as humans, are multicellular.
(Humans have an estimated 100 trillion or 1014
cells; a typical cell size is 10 µm; a typical cell
mass is 1 nanogram.) The largest known cell is
an unfertilized ostrich egg cell.
Protoplasm:
• Protoplasm is the living contents of a cell that are surrounded by a plasma
membrane.
– This term is not commonly used in modern cell biology.
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Protoplasm is composed of a mixture of small molecules such as ions,
amino acids, monosaccharides and water, and macromolecules such as
nucleic acids, proteins, lipids and polysaccharides.
• In eukaryotes the protoplasm surrounding the cell nucleus is known as the
cytoplasm and that inside the nucleus as the nucleoplasm. In prokaryotes
the material inside the plasma membrane is the bacterial cytoplasm, while in
gram-negative bacteria the region outside the plasma membrane but inside
the outer membrane is the periplasm.
• Protoplasm is distinct from non-living cell components lumped under
"ergastic substances" or inclusion bodies, although ergastic substances can
occur in the protoplasm. In many plant cells most of the volume of the cell is
not occupied by protoplasm, but by "tonoplast," a large water filled vacuole
enclosed by a membrane. A protoplast is a plant or fungal cell that has had
its cell wall removed.
Cell Theory:
• Cell Theory: refers to the idea that cells are the
basic unit of structure in every living thing.
Development of this theory during the mid 1600s
was made possible by advances in microscopy.
This theory is one of the foundations of biology.
The theory says that new cells are formed from
other existing cells, and that the cell is a
fundamental unit of structure, function and
organization in all living organisms.
Cell as a Functional Unit (AP 167)
•
(Table 3A-1 p 71)
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The cell performs all of the major functions of all living things. Examples:
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Nutrition: Absorption - transport of dissolved substances (nutrients) into the cells
Digestion - Breakdown of nutrient with enzymes.
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Internal Functions: Synthesis, Respiration, Movement, Irritability
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Material Release: Excretion - removal of soluble wastes
– Egestion - Elimination of non soluble wastes
– Secretion - Synthesis and release of substance from a cell
– Continuation of Existence: Homeostasis - keeping steady state in the cell
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Reproduction
– Cell as a Reproductive Unit
– Cells reproduce by dividing.
BJ 3A-2 Levels of Cellular
Organization (BJ 73 – 74)
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Unicell organism: Most microorganisms are single-celled, or unicellular. Some
are so small they are microscopic, but some unicellular protists are large enough
to be visible to the average human. (See cell size table BJ page 72)
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Multicell organisms: composed of more than one cell, typically many cells.
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Colonial organisms: A collection of similar cells living together. Each cell except
for reproductive cells can carry on all process of organism if separated by the
colony.
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Tissue: group of similar cells that work together to perform a specific function.
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Organs: An organ is a fully differentiated structural and functional unit
composed of one or more tissue types in an animal that is specialized for some
particular function or functions.
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Organ system: A group of organs that work together to perform a certain task.
See BJ Table 3A-2 page 77.
• 3A-3 Cellular Anatomy
• Three broad categories of cell anatomy:
– Boundary the encloses the cell
– Cytoplasm containing various kinds of
structures and molecules
– Nucleus that contains DNA and other
materials
Two Types of Cells:
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Eukaryotic: A is an organism whose cells contain complex structures enclosed within
membranes. Most living organisms, including all animals, plants, fungi, and protists, are
eukaryotes. The defining membrane-bound structure that differentiates eukaryotic cells from
prokaryotic cells is the nucleus. The presence of a nucleus gives these organisms their name,
which comes from the Greek ευ (eu, "good", "true") and κάρυον (karyon, "nut"). Many
eukaryotic cells contain other membrane-bound organelles such as mitochondria, chloroplasts
and Golgi bodies.
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Cell division in eukaryotes is different from organisms without a nucleus (prokaryotes). It
involves separating the duplicated chromosomes, through movements directed by
microtubules. There are two types of division processes. In mitosis, one cell divides to produce
two genetically identical cells. In meiosis, which is required in sexual reproduction, one diploid
cell (having two instances of each chromosome, one from each parent) undergoes
recombination of each pair of parental chromosomes, and then two stages of cell division,
resulting in four haploid cells (gametes). Each gamete has just one complement of
chromosomes, each a unique mix of the corresponding pair of parental chromosomes.
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Eukaryotes appear to be monophyletic, and so make up one of the three domains of life. The
two other domains, Bacteria and Archaea, are prokaryotes and have none of the above
features.
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Organelle: a cytoplasmic structure within the cell that performs special functions within the
cells.
• Prokaryotic: The prokaryotes (singular pronounced
/proʊˈkæriət/) are a group of organisms that lack a cell
nucleus (= karyon), or any other membrane-bound
organelles. They differ from the eukaryotes, which have
a cell nucleus. Most are unicellular, but a few
prokaryotes such as myxobacteria have multicellular
stages in their life cycles.[ It is also spelled "procaryote".
• The prokaryotes are divided into two domains: the
bacteria and the archaea. Archaea were recognized as a
domain of life in 1990. These organisms were originally
thought to live only in inhospitable conditions such as
extremes of temperature, pH, and radiation but have
since been found in all types of habitats.
Cell Boundaries (BJ 77)
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Cell boundaries include the plasma membrane which is part of the cell, and the cell walls, capsules and
sheaths which are on the outside of the cell itself.
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Plasma Membrane: The cell membrane (also called the plasma membrane or plasmalemma) is the
biological membrane separating the interior of a cell from the outside environment. It is a semipermeable lipid
bilayer found in all cells. It contains a wide variety of biological molecules, primarily proteins and lipids, which
are involved in a vast array of cellular processes such as cell adhesion, ion channel conductance and cell
signaling. The plasma membrane also serves as the attachment point for both the intracellular cytoskeleton
and, if present, the extracellular cell wall.
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Cell Walls: A cell wall is a tough, flexible and sometimes fairly rigid layer that surrounds some types of cells. It
is located outside the cell membrane and provides these cells with structural support and protection, and also
acts as a filtering mechanism. A major function of the cell wall is to act as a pressure vessel, preventing overexpansion when water enters the cell. They are found in plants, bacteria, fungi, algae, and some archaea.
Animals and protozoa do not have cell walls. The materials in a cell wall vary between species, and in plants
and fungi also differ between cell types and developmental stages. In plants, the strongest component of the
complex cell wall is a carbohydrate called cellulose, which is a polymer of glucose. In bacteria, peptidoglycan
forms the cell wall. Archaean cell walls have various compositions, and may be formed of glycoprotein Slayers, pseudopeptidoglycan, or polysaccharides. Fungi possess cell walls made of the glucosamine polymer
chitin, and algae typically possess walls made of glycoproteins and polysaccharides. Unusually, diatoms have
a cell wall composed of silicic acid. Often, other accessory molecules are found anchored to the cell wall.
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Capsules: The cell capsule or sheath is a very large organelle of some prokaryotic cells, such as bacterial
cells. It is a layer that lies outside the cell wall of bacteria. It is a well organized layer, not easily washed off,
and it can be the cause of various diseases.
Cytoplasm:
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Cytoplasm: The cytoplasm is the part of a cell that is enclosed within the plasma
membrane. In eukaryotic cells, the cytoplasm contains organelles, such as
mitochondria, which are filled with liquid that is kept separate from the rest of the
cytoplasm by biological membranes. The cytoplasm is the site where most cellular
activities occur, such as many metabolic pathways like glycolysis, and processes
such as cell division. The inner, granular mass is called the endoplasm and the outer,
clear and glassy layer is called the cell cortex or the ectoplasm.
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The part of the cytoplasm that is not held within organelles is called the cytosol. The
cytosol (cytoplasm matrix) is a complex mixture of cytoskeleton filaments, dissolved
molecules, and water that fills much of the volume of a cell. The cytosol is a gel, with
a network of fibers dispersed through water. Due to this network of pores and high
concentrations of dissolved macromolecules, such as proteins, an effect called
macromolecular crowding occurs and the cytosol does not act as an ideal solution.
This crowding effect alters how the components of the cytosol interact with each
other.
• Mitochondria (BJ p80): In cell biology, a mitochondrion (plural
mitochondria) is a membrane-enclosed organelle found in most
eukaryotic cells.[1] These organelles range from 0.5–10
micrometers (μm) in diameter. Mitochondria are sometimes
described as "cellular power plants" because they generate most of
the cell's supply of adenosine triphosphate (ATP), used as a source
of chemical energy. In addition to supplying cellular energy,
mitochondria are involved in a range of other processes, such as
signaling, cellular differentiation, cell death, as well as the control of
the cell cycle and cell growth. Mitochondria have been implicated in
several human diseases, including mitochondrial disorders and
cardiac dysfunction, and may play a role in the aging process.
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Ribosomes and Endoplasmic
Reticulum (BJ p80):
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• Ribosomes (from ribonucleic acid and "Greek: soma (meaning
body)") are complexes of RNA and protein that are found in all cells.
Ribosomes from bacteria, archaea and eukaryotes (the three
domains of life on Earth), have significantly different structure and
RNA. The ribosomes in the mitochondria of eukaryotic cells
resemble those in bacteria, reflecting the evolutionary origin of this
organelle.The ribosome functions in the expression of the genetic
code from nucleic acid into protein, in a process called translation.
Ribosomes do this by catalyzing the assembly of individual amino
acids into polypeptide chains; this involves binding a messenger
RNA and then using this as a template to join together the correct
sequence of amino acids. This reaction uses adapters called
transfer RNA molecules, which read the sequence of the messenger
RNA and are attached to the amino acids.
• Endoplasmic Reticulum (ER): is a eukaryotic organelle
that forms an interconnected network of tubules,
vesicles, and cisternae within cells. These structures are
responsible for several specialized functions: protein
translation, folding and transport of proteins to be used in
the cell membrane (e.g. transmembrane receptors and
other integral membrane proteins), or to be secreted
(exocytosed) from the cell (e.g. digestive enzymes);
sequestration of calcium; and production and storage of
glycogen, steroids, and other macromolecules. The
endoplasmic reticulum is part of the endomembrane
system. The basic structure and composition of the ER
membrane is similar to the plasma membrane.
• Golgi Apparatus: The Golgi apparatus (also called the
Golgi body, Golgi complex, dictyosome, or more
colloquially Golgi) is an organelle found in most
eukaryotic cells. It was identified in 1898 by the Italian
physician Camillo Golgi and was named after him. The
primary function of the Golgi apparatus is to process and
package macromolecules, such as proteins and lipids,
after their synthesis and before they make their way to
their destination; it is particularly important in the
processing of proteins for secretion. The Golgi apparatus
forms a part of the cellular endomembrane system.
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Lysosomes: Lysosomes are organelles containing digestive enzymes (acid
hydrolases). They are found in animal cells, while in plant cells the same roles are
performed by the vacuole. They digest excess or worn-out organelles, food particles,
and engulfed viruses or bacteria. The membrane surrounding a lysosome allows the
digestive enzymes to work at the 4.5 pH they require. Lysosomes fuse with vacuoles
and dispense their enzymes into the vacuoles, digesting their contents. They are
created by the addition of hydrolytic enzymes to early endosomes from the Golgi
apparatus. The name lysosome derives from the Greek words lysis, which means
dissolution or destruction, and soma, which means body. They are frequently
nicknamed "suicide-bags" or "suicide-sacs" by cell biologists due to their role in
autolysis. Lysosomes were discovered by the Belgian cytologist Christian de Duve in
1955. The size of lysosomes varies from 0.1–1.2 μm. At pH 4.8, the interior of the
lysosomes is acidic compared to the slightly alkaline cytosol (pH 7.2). The lysosome
maintains this pH differential by pumping protons (H+ ions) from the cytosol across
the membrane via proton pumps and chloride ion channels. The lysosomal
membrane protects the cytosol, and therefore the rest of the cell, from the
degradative enzymes within the lysosome. The cell is additionally protected from any
lysosomal acid hydrolases that leak into the cytosol as these enzymes are pHsensitive and function less well in the alkaline environment of the cytosol.
• Cytoskeleton (BJ p81 also see Facets of Biology
page 82 - 83)): The cytoskeleton (also CSK) is a cellular
"scaffolding" or "skeleton" contained within the
cytoplasm. The cytoskeleton is present in all cells; it was
once thought this structure was unique to eukaryotes,
but recent research has identified the prokaryotic
cytoskeleton. It is a dynamic structure that maintains cell
shape, protects the cell, enables cellular motion (using
structures such as flagella, cilia and lamellipodia), and
plays important roles in both intracellular transport (the
movement of vesicles and organelles, for example) and
cellular division.
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Flagella and Cilla (BJ p 81)
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• Flagella: a long, single or double tail-like projection from
a single celled organism that "whips"around and also
moves its host through space.
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• Cilla: short bristle-like projections on the membrane of a
single-celled organism are for locomotion. They beat
slowly and propel the organism through its environment.
Example: a paramecium
• Basal Body: A basal body (sometimes basal granule or
kinetosome) is an organelle formed from a centriole, a short
cylindrical array of microtubules. It is found at the base of a
eukaryotic undulipodium (cilium or flagellum) and serves as a
nucleation site for the growth of the axoneme microtubules.
Centrioles, from which basal bodies are derived, act as anchoring
sites for proteins that in turn anchor microtubules within
centrosomes, one type of microtubule organizing center (MTOC).
These microtubules provide structure and facilitate movement of
vesicles and organelles within many eukaryotic cells. Basal bodies,
however, are specifically the bases for cilia and flagella that extend
out of the cell.
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Plastids (BJ p84):
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Plastids are major organelles found in plants and algae. Plastids are the site of manufacture and storage of
important chemical compounds used by the cell. Plastids often contain pigments used in photosynthesis, and the
types of pigments present can change or determine the cell's color. Two types:
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Leucoplasts: Colorless structures uses as storehouses
Chromoplast: structure that contain color and usually involved in synthesis process.
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Chloroplast: Green organelle that convert light energy to organic compounds through photosynthesis.
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Thylakoids: A thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria. They are the
site of the light-dependent reactions of photosynthesis. The word "thylakoid" is derived from the Greek thylakos,
meaning "sac". Thylakoids consists of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast
thylakoids frequently form stacks of disks referred to as "grana" (singular: granum). "Grana" is Latin for "stacks of
coins". Grana are connected by intergrana or stroma thylakoids, which join granum stacks together as a single
functional compartment.
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Vacuoles and Vesicles (BJ p 84)
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Vacuole is a membrane organelle which is present in all plant and fungal cells and
some protist, animal and bacterial cells. Vacuoles are essentially enclosed
compartments which are filled with water containing inorganic and organic molecules
including various enzymes in solution, though in certain cases they may contain
solids which have been engulfed. Vacuoles are formed by the fusion of multiple
membrane vesicles and are effectively just larger forms of these. The organelle has
no basic shape or size, its structure varies according to the needs of the cell. The
function and importance of vacuoles varies greatly according to the type of cell in
which they are present, having much greater prominence in the cells of plants, fungi
and certain protists than those of animals and bacteria. In general, the functions of
vacuole include:
* Isolating materials that might be harmful or a threat to the cell
* Containing waste products
* Maintaining internal hydrostatic pressure or turgor within the cell
* Maintaining an acidic internal pH
* Containing small molecules
* Exporting unwanted substances from the cell
• Food Vacuole: A vacuole in which
phagocytized food is digested.
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• Waste Vacuole: stores waste, food, and
water - combines wastes and ejects them
outside of cell though process called
egestion.
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Contractile Vacuole: a small fluid-filled cavity in the cytoplasm of certain
unicellular organisms; it gradually increases in size and then collapses; its
function is thought to be respiratory and excretory. A contractile vacuole is a
sub-cellular structure (organelle) involved in osmoregulation. It pumps
excess water out of a cell and is found prominently in freshwater
protists.They are found in both plant and animal cells. In Paramecium, a
common freshwater protist, the vacuole is surrounded by several canals,
which absorb water by osmosis from the cytoplasm. After the canals fill with
water, the water is pumped into the vacuole. When the vacuole is full, it
expels the water through a pore in the cytoplasm which can be opened and
closed. Other protists, such as Amoeba, have contractile vacuoles that
move to the surface of the cell when full and undergo exocytosis.In amoeba
contractile vacuoles collect excretory waste, such as ammonia, from the
intracellular fluid by both diffusion and active transport. The contractile
vacuole stores extra water. If the cell has a need for water, the contractile
vacuole can release more water into the cell. But if water is in excess, the
contractile vacuole will remove it to maintain homeostasis. If you put fresh
water protists in marine environment ,it's contractile vacuole will disappear.
In protists, it is considered as an organelle for osmoregulation and
excretion.
• Central Vacuole: Many plant cells have a large, single central
vacuole that typically takes up most of the room in the cell (80
percent or more). Vacuoles in animal cells, however, tend to be
much smaller, and are more commonly used to temporarily store
materials or to transport substances.
• Turgor pressure' or turgidity is the main pressure of the cell
contents against the cell wall in plant cells and bacteria cells,
determined by the water content of the vacuole, resulting from
osmotic pressure, i.e. the hydrostatic pressure produced by a
solution in a space divided by a semipermeable membrane due to a
differential in the concentration of solute. Turgid plant cells contain
more water than flaccid cells and exert a greater osmotic pressure
on its cell walls. Turgor is a force exerted outward on a plant cell
wall by the H2O contained in the cell. This force gives the plant
rigidity, and may help to keep it erect. Turgor may also result in the
bursting of a cell.
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Vesicle is a small bubble of liquid within a cell. More technically, a vesicle is
a small, intracellular, membrane-enclosed sac that stores or transports
substances within a cell. Vesicles form naturally because of the properties
of lipid membranes (see micelle). Most vesicles have specialized functions
depending on what materials they contain.Because vesicles tend to look
alike, it is very difficult to tell the difference between different types of
vesicles without sampling their contents.The vesicle is separated from the
cytosol by at least one phospholipid bilayer. If there is only one phospholipid
bilayer, they are called unilamellar vesicles; otherwise they are called
multilamellar. (Lamella means membrane).Vesicles store, transport, or
digest cellular products and waste. The membrane enclosing the vesicle is
similar to that of the plasma membrane, and vesicles can fuse with the
plasma membrane to release their contents outside of the cell. Vesicles can
also fuse with other organelles within the cell.Because it is separated from
the cytosol, the inside of the vesicle can be made to be different from the
cytosolic environment. For this reason, vesicles are a basic tool used by the
cell for organizing cellular substances. Vesicles are involved in metabolism,
transport, buoyancy control, and enzyme storage. They can also act as
chemical reaction chambers.
• Secretion Vesicle: Membrane bounded
vesicle derived from the Golgi apparatus
and containing material that is to be
released from the cell.
• Peroxisome: Peroxisomes are organelles from the
microbody family and are present in almost all eukaryotic
cells. They participate in the metabolism of fatty acids
and many other metabolites. Peroxisomes harbor
enzymes that rid the cell of toxic peroxides. Peroxisomes
are bound by a single membrane that separates their
contents from the cytosol (the internal fluid of the cell)
and contain membrane proteins critical for various
functions, such as importing proteins into the organelles
and aiding in proliferation. Peroxisomes can replicate by
enlarging and then dividing.
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The Nucleus (BJ p 85)
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In cell biology, the nucleus (pl. nuclei; from Latin nucleus or nuculeus, or kernel), also sometimes referred to as the
"control center", is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic
material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as
histones, to form chromosomes. The genes within these chromosomes are the cell's nuclear genome. The
function of the nucleus is to maintain the integrity of these genes and to control the activities of the cell by
regulating gene expression - the nucleus is therefore the control center of the cell.
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The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire
organelle and separates its contents from the cellular cytoplasm, and the nuclear lamina, a meshwork within the
nucleus that adds mechanical support, much like the cytoskeleton supports the cell as a whole. Because the
nuclear membrane is impermeable to most molecules, nuclear pores are required to allow movement of molecules
across the envelope. These pores cross both of the membranes, providing a channel that allows free movement of
small molecules and ions. The movement of larger molecules such as proteins is carefully controlled, and requires
active transport regulated by carrier proteins. Nuclear transport is crucial to cell function, as movement through the
pores is required for both gene expression and chromosomal maintenance.
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Although the interior of the nucleus does not contain any membrane-bound subcompartments, its contents are not
uniform, and a number of subnuclear bodies exist, made up of unique proteins, RNA molecules, and particular
parts of the chromosomes. The best known of these is the nucleolus, which is mainly involved in the assembly of
ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate
mRNA.
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Nuclear Envelope - double membrane that completely surrounds the nucleolus
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Nuclear Pores - openings in the nuclear envelope than can let material into and out
of the nucleolus
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Chromatin Material: Chromatin is the complex combination of DNA, RNA, and
protein that makes up chromosomes. It is found inside the nuclei of eukaryotic cells,
and within the nucleoid in prokaryotic cells. It is divided between heterochromatin
(condensed) and euchromatin (extended) forms. The major components of chromatin
are DNA and histone proteins, although many other chromosomal proteins have
prominent roles too. The functions of chromatin are to package DNA into a smaller
volume to fit in the cell, to strengthen the DNA to allow mitosis and meiosis, and to
serve as a mechanism to control expression and DNA replication. Chromatin contains
genetic material-instructions to direct cell functions. Changes in chromatin structure
are affected by chemical modifications of histone proteins such as methylation (DNA
and proteins) and acetylation (proteins), and by non-histone, DNA-binding proteins.
• Nucleolus: The nucleolus (also called nucleole) is a
non-membrane bound structure[1] composed of protein
and nucleic acids found within the nucleus. The
ribosomal RNA is transcribed within the nucleolus. The
nucleolus ultrastructure can be visualized through an
electron microscope, while the organization and
dynamics can be studied through fluorescent protein
tagging and fluorescent recovery after photobleaching
(FRAP). Malfunction of nucleoli can be the cause for
several human diseases.
BJ 3B Cells and their
Environment (BJ 87)
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BJ 3B-1 Homeostasis (BJ 87)
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Homeostasis is the property of a system, either open or closed, that regulates its
internal environment and tends to maintain a stable, constant condition. Typically
used to refer to a living organism. The current view of Homeostasis is that it involves
multiple dynamic equilibrium adjustment and regulation mechanisms.
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Steady state versus dynamic equilibrium: A system in dynamic equilibrium is a
particular example of a system in a steady state. In a steady state the rate of inputs is
equal to the rate of outputs so that the composition of the system is unchanging in
time. For example, a lake is in a steady state when water flows in at the same rate as
water flows out. The term dynamic equilibrium is used in thermodynamics for systems
involving reversible reactions. It is said that the rate of the forward reaction is equal to
the rate of the backward reaction. Both reactions do in fact occur, but to such a
minuscule extent that changes in composition cannot be observed.
Optimal Point and Range of
Tolerance (BJ p 87- 88)
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Optimal Point: The point at which the condition, degree, or amount of
something is the most favorable. In biology The most favorable condition for
growth and reproduction.
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Optimal Range of Tolerance: Most organisms can optimally growth and
reproduce with a range of conditions. The range of conditions that allow for
optimal growth and reproduction is called the optimal range of tolerance.
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Range of Tolerance: organisms must be able to survive a range of
conditions, called 'range of tolerance'. Outside of the range of tolerance, are
the 'zones of physiological stress', where the survival and reproduction
are possible but not optimal.
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Limits of Tolerance: The points above or below which death occurs.
The Solution Around Cells (p88)
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- All cells surrounded by solution inside the cell membrane,
- Review diffusion, semipermeable membranes and osmosis
- Types of solutions
-- Isotonic - concentrations of solutes same inside and outside of cell
-- Hypotonic- concentrations of solutes higher inside than outside of
cell
• -- Flow of water into cell can cause cell to burst called Cytolysis
• -- Hypertonic- concentrations of solutes lower inside than outside of
cell
• -- Flow of water can cause dehydrations and crenate (wrinkled cells)
(See Table 3B1 - BJ p 89)
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Cells in Hypotonic Solutions
• - Organism that live in fresh water, tend to live in an
hypotonic environment, so the need strategies to prevent
cytolysis
• - Central vacuole expands to help cause an internal cell
pressure to prevent cytolysis
• - Cell membrane flexible so it can stretch and not burst.
• - Contractile vacuole, pumps water out.
• - Cells pump out solutes, lowers osmosis rate.
Cells in Hypertonic Solutions
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- Most cells do not live in hypertonic situation - so not as well equipped to deal with it.
- Plasmolysis (wilting): Plasmolysis is the process in plant cells where the plasma membrane
pulls away from the cell wall due to the loss of water through osmosis.
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- This state does occur in seawater so the cells of sea animals/fish must handle this state as well.
BJ 3B-2 Transportation Across the Membrane (BJ 91)
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Passive Transport: Passive transport means moving biochemicals and atomic or molecular
substances across the cell membrane. Unlike active transport, this process does not involve
chemical energy. The four main kinds of passive transport are diffusion, facilitated diffusion,
filtration and osmosis.
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Passive Mediate Transport: Passive mediated transport, or facilitated diffusion uses a helper
molecule (transport proteins) to speed up the passive transport. Member transport proteins: A
transmembrane protein that helps a certain substance or class of closely related substances to
cross the membrane
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Transport protein can refer to:
• * Membrane transport protein
• * Vesicular transport protein
• * Water-soluble carriers of small molecules
• A membrane transport protein (or simply transporter) is a protein
involved in the movement of ions, small molecules, or
macromolecules, such as another protein across a biological
membrane. Transport proteins are integral membrane proteins; that
is they exist within and span the membrane across which they
transport substances. The proteins may assist in the movement of
substances by facilitated diffusion or active transport.
• The mechanism of action of these proteins is known as carriermediated transport. There are two forms of carrier-mediated
transport, active transport and facilitated diffusion.
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Active Transport Across
Membranes (BJ p92):
• Active transport is the mediated process of
moving particles across a biological membrane
against a concentration gradient. If the process
uses chemical energy, such as from adenosine
triphosphate (ATP), it is termed primary active
transport. Secondary active transport involves
the use of an electrochemical gradient. Active
transport uses energy, unlike passive transport,
which does not use any energy.
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Endocytosis and Exocytosis (BJ
93)
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• Endocytosis: Endocytosis is the process by
which cells absorb material (molecules such as
proteins) from outside the cell by engulfing it with
their cell membrane. It is used by all cells of the
body because most substances important to
them are large polar molecules that cannot pass
through the hydrophobic plasma membrane or
cell membrane. The process opposite to
endocytosis is exocytosis.
• Phagocytosis is the cellular process of phagocytes and
protists of engulfing solid particles by the cell membrane
to form an internal phagosome, which is a food vacuole,
or pteroid. Phagocytosis is a specific form of endocytosis
involving the vesicular internalization of solid particles,
such as bacteria, and is therefore distinct from other
forms of endocytosis such as pinocytosis, the vesicular
internalization of various liquids. Phagocytosis is
involved in the acquisition of nutrients for some cells,
and in the immune system it is a major mechanism used
to remove pathogens and cell debris. Bacteria, dead
tissue cells, and small mineral particles are all examples
of objects that may be phagocytosed.
•
Pinocytosis: In cellular biology, pinocytosis ("cell-drinking", "bulk-phase pinocytosis",
"non-specific, non-adsorptive pinocytosis", "fluid endocytosis") is a form of
endocytosis in which small particles are brought into the cell suspended within small
vesicles which subsequently fuse with lysosomes to hydrolyze, or to break down, the
particles. This process requires energy in the form of adenosine triphosphate (ATP),
the chemical compound used as energy in a majority of cells. Pinocytosis is primarily
used for the absorption of extracellular fluids (ECF), and in contrast to phagocytosis,
generates very small vesicles. Unlike receptor-mediated endocytosis, pinocytosis is
nonspecific in the substances that it transports. The cell takes in surrounding fluids,
including all solutes present. Pinocytosis also works as phagocytosis, the only
difference is that phagocytosis is specific in the substances it transports.
Phagocystosis actually engulfs whole food particles, which are later broken down by
enzymes and absorbed into the cells. Pinocytosis, on the other hand, is when the cell
engulfs already dissolved/broken down food.
•
•
Exocytosis: Exocytosis is the durable process by which a cell directs the contents of
secretory vesicles out of the cell membrane. These membrane-bound vesicles
contain soluble proteins to be secreted to the extracellular environment, as well as
membrane proteins and lipids that are sent to become components of the cell
membrane.