Cells are the basic structural and functional units of all living things. They arise through cell division of existing cells and contain a plasma membrane, cytoplasm, and nucleus. The nucleus contains DNA and controls cellular activities through protein synthesis directed by RNA. Within the cytoplasm are various organelles that perform specialized functions like mitochondria which generate energy. Molecules move into and out of cells through passive transport like diffusion and osmosis or active transport powered by the cell.

1. Chapter2:Cells
2/16/2023 BY.NIGATU.A 1

2. • Cells are the structural units of all living things.
All cells arise from existing cells by the process
of cell division, in which one cell divides into
two identical cells.
• The English scientist Robert Hooke first
observed plant cells with a crude microscope in
the late 1600s. Then, in the 1830s two German
scientists, Matthias Schleiden and Theodor
Schwann, proposed that all living things are
composed of cells.
2/16/2023 BY.NIGATU.A 2

3. 3
Levels of organization of human body
Chemical level (H+, Na+ Ca2+....form molecules)
Nerve cells ,
Muscle cells
Cells 4 types Epithelial cells
Cells in the connective tissues
Muscle tissue
Tissues 4 types Nerve tissue
Epithelial tissue
connective tissues
Organs: are structures that are made of two or more different
types of tissues. They have specific functions and a defined shape.
E Example: Heart, lungs
Organ system: Example: Respiratory system, CVS
Organism: e.g., Human
2/16/2023 BY.NIGATU.A

4. Cell diversity
2/16/2023 BY.NIGATU.A 4

5. PARTS OF A CELL
A human cell has three main parts:
• The plasma membrane: the outer
boundary of the cell.
• The cytoplasm: the intracellular fluid
packed with organelles, small structures
that perform specific cell functions.
• The nucleus: an organelle that controls
cellular activities. The nucleus lies near the
cell’s center.
2/16/2023 BY.NIGATU.A 5

6. cell structure

7. A. Cell membrane/ plasma membrane
A sheet-like structure that surround (enclose) the cell,
separating the cellular contents from the ECF.
They form barriers between different cellular
compartments and define inside from outside
Without this separation, cells would not be able to
function, and as such, proper membrane structure and
function is essential for life.
7
2/16/2023

8. Plasma membrane
Function: enclose cell contents, control
exchange of substances with environment, cell
communication
Made of:
Lipid bilayer
Cholesterol
Glycolipids
Proteins

9. 2/16/2023 BY.NIGATU.A 9

10. B. THE CYTOPLASM
The cellular material between the plasma
membrane and the nucleus, is the site of most
cellular activities. It consists of three elements:
–The cytosol
–Organelles
–Inclusions.
2/16/2023 BY.NIGATU.A 10

11. 1. The cytosol: it is the viscous, semitransparent
fluid in which the other cytoplasmic elements
are suspended.
2. The organelles are the metabolic machinery
of the cell. Each type of organelle carries out a
specific function for the cell.
3. The inclusions are chemical substances that
may or may not be present, depending on cell
type.
2/16/2023 BY.NIGATU.A 11

12. Cytoplasm
Between plasma membrane & nucleus
Three elements:
Cytosol: fluid
Eg. water, proteins, salts, sugars
Organelles: specific functions
Inclusions: chemical substances that vary
depending on cell type
Eg. glycogen (liver), melanin (skin & hair)

13. organelles
“little organs”
Specialized compartments  specific
functions
Membranous = membrane-bound
Mitochondria, peroxisomes, lysosomes,
ER, Golgi apparatus
Nonmembranous = no membrane
cytoskeleton, centrioles, ribosomes

15. Cellular organelles
Embedded within the cytoplasm are organelles or inner
organs of the cell.
These include the ribosomes, endoplasmic reticulum (ER)
golgi apparatus, mitochondria, lysosomes, peroxisomes
15
2/16/2023

16. 16
Ribosome:
They are not membrane bounded
Sites of protein synthesis in the cell
Small particles composed of rRNA and proteins
Found as free ribosomes in the cytosol or bound to rough
endoplasmic reticulum (RER)
Endoplasmic reticulum (ER):
An extensive membranous structure that connects various parts of
the inner cell.
It also connected with the nuclear membrane
There are two types of ER: rough ER and smooth ER.
2/16/2023

17. Mitochondria
Second largest organelle
Usually many per cell; the distribution depends upon the activity of
the cell; the more active the cell, the more mitochondria.
Rod shaped, enveloped by double membrane
containing a number enzymes which aid in the production of
ATP
The mitochondria are literally the “power plants or power house” of
the cell, capable of producing the energy rich compound ATP
17
2/16/2023

18. Lysosomes
Lysosomes are vesicular organelles that form by breaking
off from the Golgi apparatus and then dispersing
throughout the cytoplasm.
Surrounded by a single membrane and spherical in shape
Are called suicide bags
It has protein aggregates of as many as 40 different
hydrolase (digestive) enzymes per lysosome.
Is used to break down old proteins, many wastes, dead
cells and phagocytized foreign materials
18
2/16/2023

19. Peroxisomes
sacs of
oxidase
• Membranous
catalase and
enzymes.
• The enzymes detoxify
a number of toxic
substances. The most
important enzyme,
catalase, breaks down
hydrogen peroxide.
2/16/2023 BY.NIGATU.A 19

20. Lysosomes
• Membranous sacs
containing acid
hydrolases.
• Sites of intracellular
digestion.
2/16/2023 BY.NIGATU.A 20

21. Microtubules
of tubulin
• Cylindrical structures made
proteins.
• Support the cell and give it shape. Involved
in intracellular and cellular movements.
Form centrioles and cilia and flagella, if
present.
2/16/2023 BY.NIGATU.A 21

22. Microfilaments
• Fine filaments composed of the protein
actin. Involved in muscle contraction and
other types of intracellular movement, help
form the cell’s cytoskeleton.
2/16/2023 BY.NIGATU.A 22

23. Cellular Extensions
• The major cellular extensions are
1. Cilia
2. Flagellum
3. Microvilli
2/16/2023 BY.NIGATU.A 23

24. C. NUCLEUS
• The nucleus is a spherical or oval-shaped
structure that usually is the most prominent
feature of a cell.
• Surrounded by the nuclear envelope;
contains fluid nucleoplasm, nucleoli, and
chromatin.
• Control center of the cell; responsible for
transmitting genetic information and
providing the instructions for protein
synthesis.
2/16/2023 BY.NIGATU.A 24

25. 2/16/2023 BY.NIGATU.A 25

26. Nucleus
Control center  contains DNA
Most cells have only 1 nucleus
Multinucleate: many nuclei (muscle, some liver
cells)
Anucleate: no nucleus (mature RBC)
Three main structures:
1. Nuclear envelope
2. Nucleoli
3. Chromatin

27. 27
The nucleus
The control center for the cells.
Contains the genes, which are units of heredity.
Chemically each gene consists of a highly
compressed DNA in the form of chromosomes
Genes control cellular activity by determining the
type of proteins, enzymes, and other substances
that are made by the cell.
The site of RNA synthesis.
2/16/2023

28. DNA
• DNA or deoxyribonucleic acid, contains
the information needed for the creation
of proteins (which include enzymes and
hormones) and is stored in the nucleus,
as already said, in the form of chromatin
or chromosomes.
• The nucleus is the site of DNA
duplication, which is needed for cell
division (mitosis) and organism
reproduction and growth.
2/16/2023 BY.NIGATU.A 28

29. 2/16/2023 BY.NIGATU.A 29

30. RNA
• RNA are made fromthe DNA template:
1. Messenger RNA (mRNA) directs the synthesis
of a protein.
2. Ribosomal RNA (rRNA) joins with ribosomal
proteins to make ribosomes.
3. Transfer RNA (tRNA) binds to an amino acid
and holds it in place on a ribosome until it is
incorporated into a protein during translation
2/16/2023 BY.NIGATU.A 30

31. Proteins and Cell Regulation
• The nucleus oversees cells’ functions and
regulatory mechanisms for keeping the cell
healthy and alive.
• The nucleus controls growth of the cell through
the synthesis of structural proteins, energy and
nutrient metabolism.
• The nucleus regulates the secretion of
ribosomes, which are made in the nucleolus
and are the sites of gene transcription.
2/16/2023 BY.NIGATU.A 31

32. Molecule Movement
• Passive Transport
• Active Transport
• Endocytosis
(phagocytosis & pinocytosis)
• Exocytosis
2/16/2023 BY.NIGATU.A 32

33. Passive Transport
• No energy required
• Move due to gradient
– differences in concentration, pressure, charge
• Move to equalize gradient
– High moves toward low
2/16/2023 BY.NIGATU.A 33

34. Types of Passive Transport
1. Diffusion
2. Osmosis
3. Facilitated diffusion
2/16/2023 BY.NIGATU.A 34

35. Diffusion
• Molecules move to equalize concentration
2/16/2023 BY.NIGATU.A 35

36. Osmosis
• Special form of diffusion
• Often involves movement of water
– Into cell
– Out of cell
2/16/2023 BY.NIGATU.A 36

37. Solution Differences
• Solvent + solute = solution
• Hypotonic
– Solutes in cell more than outside
– Outside solvent will flow into cell
• Isotonic
– Solutes equal inside & out of cell
• Hypertonic
– Solutes greater outside cell
– Fluid will flow out of cell
2/16/2023 BY.NIGATU.A 37

38. Facilitated Diffusion
• Differentially permeable membrane
• Channels (are specific) help
molecule or ions enter or leave the
cell
• Channels usually are transport
proteins
• No energy is used
2/16/2023 BY.NIGATU.A 38

39. Active Transport
• Molecular movement
• Requires energy (against gradient)
• Example is sodium-potassium pump
2/16/2023 BY.NIGATU.A 39

40. Endocytosis
• Movement of large material
– Particles
– Organisms
– Large molecules
• Movement is into cells
2/16/2023 BY.NIGATU.A 40

41. Forms of Endocytosis
• Phagocytosis – cell eating
• Pinocytosis – cell drinking
2/16/2023 BY.NIGATU.A 41

42. Exocytosis
• Reverse of endocytosis
• Cell discharges
material
• Vesicle moves to cell
surface
• Materials expelled
2/16/2023 BY.NIGATU.A 42

43. Thank You
2/16/2023 BY.NIGATU.A 43