The document discusses cells and their structures. It begins by defining cells as the basic functional units of living organisms. It then describes the main components of eukaryotic and prokaryotic cells. Eukaryotic cells have a nucleus surrounded by a nuclear membrane, while prokaryotic cells like bacteria do not. The document also discusses the structures within cells called organelles and their specific functions. It explains the cell membrane, cytoplasm, cytoskeleton, and different types of cellular junctions. Finally, it covers the cell cycle, mitosis, meiosis and the role of the cytoskeleton in providing structure and facilitating movement within cells.

1. CELLS
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By: Tefera B.
Haramaya university, health
and medical science
college

2. CELLS
The cell is the functional unit of all living organisms
The simplest organisms such as bacteria and algae
consist of a single cell
The cells of multicellular organisms, such as humans
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3. TYPES OF CELLS
The term eukaryote refers to the group of organisms
whose cells have a defined nucleus surrounded by a
nuclear membrane
This group includes most living organisms other than
bacteria
Prokaryotes (mainly bacteria) have some major
structural differences
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Eukaryoyic cells Prokaryotic cells

4. Human (and all other eukaryotic) cells consist of a
nucleus and cytoplasm
Cytoplasm contains a number of organelles each with a
defined function.
Nucleus may be considered the largest organelle
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5. COMPARING EUKARYOTIC AND PROKARYOTIC CELLS
Eukaryotic cells Prokaryotic cells
Complex and more evolved
In size bigger than prokaryotes
Membrane bound organelles
All organism posses this except
bacteria.
Simple and less evolved
Smaller compare to
eukaryotes
Lack membrane bound
organelles
Bacteria posses this
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6. THE CELL STRUCTURE
Structural and functional unit of life
Mainly made up of a Nucleus bounded by a nuclear
membrane and a cytoplasm
The cytoplasmic organelles are suspended in a fluid
called cytosol in which many metabolic reactions take
place
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7. Within the cytosol, there is a network of minute tubules
and filaments, collectively known as the cytoskeleton,
which provides structural support for the cell and its
organelles, as well as providing a mechanism for transfer
of materials within the cell and movement of the cell
itself.
The outermost component of the cell, separating the
cytoplasm from its extracellular environment, is the plasma
membrane (plasmalemma).
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8. ORGANELLES
Triggers production of new cells
Determines all of the cell’s activities
Stores DNA
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Nucleus

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Nucleolus
Highly active in protein synthesis
Sites of ribosomal RNA synthesis and ribosome assembly
Ribosomal RNA and proteins, synthesized in the
cytoplasm and imported back into the nucleus, are
assembled into subunits.
Nucleolus

10. RIBOSOME
Two types
1. Free / nonmembranous ribosome
2. Bound ribosome (on rough
endoplasmic reticulum)
• Translates RNA into proteins /
assemble proteins
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2

11. ENDOPLASMIC RETICULUM
Two types
1. Rough ER has bound ribosomes for
protein synthesis
2. Smooth ER does not have bound
ribosomes, contains enzymes for
lipid synthesis
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1
2

12. Golgi Apparatus
Series of flattened sacs where newly made lipids and proteins
from the ER are “repackaged” and shipped to the plasma
membrane
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13. MITOCHONDRION
Produces the energy in the
form of ATP for the cell Also
known as the “powerhouse of
the cell”
Has a highly folded inner
membrane known as cristae,
Provides high surface area for
energy production
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Mitochondrion

14. Lysosomes and Vacuoles
Lysosomes Contains a digestive
enzyme
Can fuse with vacuoles to digest food
or can digest worn cell parts
Sometimes referred to as the “trash
can” of the cell
Vacuole is a sac of fluid surrounded by
a membrane used to store food, fluid,
or waste products
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Lysosomes
Vacuole
What would happen to a cell if it didn’t contain any lysosomes (or if its
lysosomes weren’t functioning)? Would the cell be able to survive?

15. Cell membrane
Composed of phospholipid bilayer
Holds the cell together and separates it from its surroundings
Allows materials to pass in and out of the cell
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Cell Membrane

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Non - Membranous organelles
Ribosomes
Microtubules
Centrioles
Filaments
Cilia & flagella

18. Cell – Cell And Cell Matrix Interactions
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Cell – Cell And Cell Matrix Interactions
Plasma membrane specializations, called cell junctions,
mediate between neighboring cells and between cells and
the basal lamina.
Cell junctions are particularly abundant in epithelia
Cell junctions form barriers that inhibit the movement of
water and solutes

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Classes and divisions of the CAMs
Cell Adhesion Molecules can be grouped or divided into four
broad families;
Intergrins; they are heterodimers that bind to various
receptors
Adhesion molecules of the IgG super family of
immunoglobulins
Cadherins, Calcium dependent molecules that mediate cell to
cells adhesion by homophilic reactions
Selectins, which have lectin like domains that bind
carbohydrates

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Intercellular Connections
Two types of junctions form between the cells that make up tissues:
Junctions that fasten the cells to one another and to surrounding
tissues
Junctions that permit transfer of ions and other molecules from
one cell to another
Types of junctions that tie cells together and endow tissues with
strength and stability include the tight junction, which is also known
as the zonula occludens.
Desmosome and zonula adherens hold cells together, and the
hemidesmosome and focal adhesion attach cells to their basal
laminas
junction by which molecules are transferred is the gap junction

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Tight Junctions
Integral proteins of adjacent
cells fuse together
Completely encircle the cell
and form an adhesion belt.
Form an impermeable
junction. Prevent passage of
water and water soluble
substances
Common near apical region

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Anchoring Junction
Two kinds of anchoring junctions, zonula
adherens and macula adherens (desmosome)
Hold cells together
They usually occur between lateral borders of adjacent
epithelial cells

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Anchoring Junction; Zonula Adherens
Intracellular attachment actin flaments
In most epithelia, a zonula adherens usually encircles
the apical part of the whole cell just below the tight
junction

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Anchoring Junctions; Desmosome
Two disc-like plaques connected across intercellular space
Plaques of adjoining cells are joined by proteins called
cadherins
Proteins interdigitate into extracellular space
Intermediate filaments insert into plaques from cytoplasmic
side
Common in tissue that are subject to severe stress such as skin
and cardiac muscles
Depending on location, may have different types of
intermediate flaments, such as keratins, associated with
epithelial cells, and desmin, in cardiac muscle cells

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Hemidesmosomes
Similar to desmosomes but totally different molecular
structure
It is cell - matrix adhesion
Attach cells to basal lamina

29. Cell Cycle
Cell cycle is a sequence of cell growth and division
Cell cycle is the period from the beginning of one division
to the beginning of the next
Time it takes to complete one cell cycle is the generation
time.
Cells divide when they reach a certain size
NO (nerve, skeletal muscle and red blood cells)
Cell division involves mitosis and cytokinesis
Mitosis involves division of the chromosomes
Cytokinesis involves division of the cytoplasm
Mitosis without cytokinesis results in multinucleate cells
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30. THE CELL CYCLE
In the fully developed organism, the terminally
differentiated cells of some tissues, such as the
neurones of the nervous system, lose the ability to
undergo mitosis.
In contrast, the cells of certain other tissues, e.g. the
stem cells of gut and skin, undergo continuous cycles
of mitotic division throughout the lifespan of the
organism replacing cells lost during normal wear and
tear
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31. THE CELL CYCLE
Between these extremes are cells such as liver cells
that do not normally divide but retain the capacity to
undergo mitosis should the need arise (facultative
dividers).
Cell division and differentiation are balanced by cell
death both during the development and growth of the
immature organism and in the mature adult.
In these circumstances, cell death occurs by a
mechanism known as apoptosis
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32. CELL CYCLE
Composed of two phases:
Dividing or mitotic (M) phase
Non dividing phase (Interphase)
Interphase contains a discrete period called the
synthesis (S) phase thru which DNA is replicated
Between the M and S phases is the first gap (G1) phase
in which cells grow and perform their specialized
functions
After S phase is second gap phase (G2) which is
relatively short and is a period in which cells prepare
for mitotic division
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34. Terminally differentiated cells enter the Go phase and
remain there
Facultative dividers enter the Go phase but retain the
capacity to enter the cell cycle when stimulated
In general the S, G2 and M phase are relatively
constant while the G1 phase is highly variable
Go Phase may last for the entire lifespan of the
organism
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35. Why do cells divide?
• Reproduction
• Growth
• Repair
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36. MITOTIC PHASE OF CELL CYCLE
Include four stages or phases as well
Prophase ( chromosomes condensed, shortened and become
visible, mitotic spindles also forms and nuclear envelope
disappear marking end of prophase)
Metaphase ( duplicated chromosomes becomes attached to
the mitotic spindle at the kinetochore, chromosomes become
align at the equator)
Anaphase (splitting of the centromere, creating two identical
daughter cells)
Telophase( uncoiling of chromosomes to regain interphase
conformation, reassembly of nuclear envelop and nucleoli
becomes visible)
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39. kinetochore is a DNA and protein structure on each
duplicated chromosome, located at the centromere, the
structure which binds the duplicated chromosomes
(chromatids) together
Kinetochore also controls entry of the cell into anaphase
so that the process of mitosis does not progress until all
chromatid pairs are aligned at the cell equator.
This is sometimes called the metaphase checkpoint and
prevents the formation of daughter cells with unequal
numbers of chromosomes
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41. OUTCOME OF MITOSIS
Two daughter cells
Genetic conservation as genetic material similar in parent and
daughter cells
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42. 1. Observation shows that most cells are suspended in
interphase for most of their lives. Identify the parts of
interphase, and describe an event that occurs during each
part.
2. List the stages of mitosis in order of occurrence.
Describe a unique activity associated with each stage.
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WHAT DID YOU LEARN?

43. Occurs in gametes
Results into four haploid daughter cells
Genetic material halved
Essential for reproduction
Exchange of genetic material occurs
Occurs in two phases:1 and 2
The process of sexual reproduction involves the
production by meiosis of specialized male and female
cells called gametes.
Meiotic cell division is thus also called gametogenesis
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Meiosis

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Meiosis 1 (Reductional division)
Similar to mitosis but result is two daughter cells with half
the number of chromosomes
Prophase 1; chromosomes that have been replicated,
condense and pair with homologous to form tetrads
Metaphase 1: tetrads are held together by Chiasmata, and
chromosomes arranged themselves at equator
Anaphase 1:homologous chromosomes separate and
migrate to opposite poles of the cell
Telophase 1; the chromosomes at the poles have form two
groups, the cell begins to constrict across the equator and
separate into two daughter cells with haploid number of
chromosome

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Formation of actual number of variants is very much greater
because of a second cell division, division- II of meiosis,
without further DNA replication.
It is called equational division (similar to mitosis).
Prophase II; chromosomes of the two daughter cells condense
in preparations for second meiotic division
Metaphase II; chromosomes migrate to equator
Anaphase II; chromosomes separate and move to opposite
poles
Telophase II;cell constrict along equator to form four daughter
cells with haploid number of chromosomes
Meiosis II (Equatorial Division)

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Comparison of Mitosis And Meiosis
The key differences between the two forms of cell division
are as follows
Meiosis involves one reduplication of the chromosomes
followed by two sequential cell divisions. Thus a diploid cell
produces four haploid germ cells (gametes).
Crossing over occurs only in meiosis, to rearrange alleles such
that every gamete is genetically different.
In contrast, the products of mitosis are genetically identical

49. Cytoskeleton
Cytoskeleton is a network of protein fibers that dominate
the cell .
Function Provides structural support, organelle and cellular
motility, transport of materials, and chromosomal
movement and cell division.
There are three main types of Protein fibers in the
cytoskeleton
Microtubules
Microfilament
Intermediate filament
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50. Microtubules(24-25nm)
Largest of the three and rigid, hollow tubes made of a
protein called tubulin.
The two types of tubulin α and β,combine to create helical
structure .
Have + and – ends attaches to microtubule organizing
center.
Involved in transport material within the cell, in the
separation of chromosomes during cell division and also in
the formation of specialized structure called cilia and
flagella (eukaryotic cell)
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51. MICROFILAMENTS (6-7nm)
The thinnest of the three types of fibers
Composed of a linear protein called actin.
One important use of microfilament is in muscle
contraction.
During muscle contraction , a protein called myosin binds to
actin and is said to “walk” along it and thus creates the
contractile motion
Microfilament contain a – and + end. they use(-) end to
bond to some cell structure and grow from the positive end.
As they grow, push against the cell to create tension. giving
the cell stability, shape and structure, phagocytosis.
Also involved in movement associated with furrow
formation in cell division
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53. Intermediate (8-12nm)
These fibers can be a composed of several types of protein
and are slightly thick than microfilament, just the
microfilaments, intermediate filament give the cell tensile
strength and provide structure stability
Intermediate filament compose the nuclear lamina, are
found in the cytoplasm as well as outside the cell
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Thank you