This document provides an overview of cell structure and function. It begins by outlining the key topics to be covered, including the differences between prokaryotic and eukaryotic cells. It then defines the cell and describes the basic components of eukaryotic cells, including the cell membrane, cytoplasm, organelles, and nucleus. Specific organelles like the endoplasmic reticulum, Golgi body, lysosomes, mitochondria, and vacuoles are explained. The structure and functions of the cell membrane, its lipids and proteins, are also detailed.

1. UNIT I: STRUCTURE AND
FUNCTION OF THE CELL
Mw. Muki (Msc NMH,BSc N,DHPEd, RN)
Assistant Lecturer
1

2. THEMES TO BE COVERED
1.
2.
3.
4.
5.
6.
Eukaryotic and Prokaryotic cells
Parts of the cell (Mosaic Model)
Plasma membrane structure and
permeability
Membrane proteins and their function
Cytoplasm, organelles and their
function
The nucleus, structure and function
2

3. Definition of cell




Cell is the basic unit of structure and
reproduction for all organism.
There two types of cells that are
Prokaryotic cells
Eukaryotic cells
3

4. TOPIC I: EUKARYOTIC &
PROKARYOTIC CELLS


Cells over millions of years, have developed
two basic structures
Prokaryotic cells are cells that have no
nucleus ( also called Prokaryotes)
 These include unicellular organisms such as
Bacteria
 They are generally very small cells
 They are the earliest forms of life and still the
most abundant which evolved about 4 billion
years ago.
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 Some species are highly evolved pathogens

5. 

Eukaryotic cells are cells having a nucleus
( also spelled Eucaryotes)
– Eukaryotic cells are seen in animals, Plants,
Fungi and Protists
– Some of the Eucaryotes are unicellular while
the majority are multi-cellular
– Eucaryotes evolved later about 1 billion years
ago.
– The sizes of Eucaryotes vary from the tiny
size of yeast to the size of an elephant and
dinosaurs.
We are concerned with the study of eukaryotic
cells which make up the human body
5

6. EUKARYOTIC CELL
STRUCTURES
 Eukaryotic
cells are organized into
different compartments.
 All compartments are bounded by
membranes.
 For simplicity, we divide the cell into
three main compartments: 1. cell
membrane, 2. cytoplasm and the 3.
nucleus.
6

7.  Cytoplasm
is a central metabolic
compartment, bounded by the cell
membrane.
 Other compartments inside cytoplasm are
called organelles
 Compartmentation allows specialized
functions to be carried out in different
locations of the cell.
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8. 8

9. 9

10. 10

11. 11

12. 12

13. 13

14. 14

15. 15

16. 16

17. 1. THE CYTOPLASM
 Generally,
the cytoplasm:
is the site of protein synthesis and many
metabolic processes.
Contains many ribosomes, particles on
which proteins are synthesized
Contains many enzymes for metabolism
in general
Is a compartment in which foodstuffs
enter and from which wastes leave cell
17

18. Cytoplasm contains fiber of the cytoskeletal
system, which organize cytoplasmic structure
Contains many different organelles
18

19.  The
Endomembrane system is involved in
moving materials into different
compartments. It is a set of interconnected
compartments made of the endoplasmic
reticulum (ER), Golgi body, Lysosomes,
cell membrane. The cell membrane is
treated separately in this lecture.
19

20. ENDOPLASMIC RETICULUM
Rough ER : synthesizes proteins for export
or movement to different cell compartments
(but not to cytoplasm).
20

21. Signal hypothesis
Certain mRNAs encode proteins
designated for export. These carry a
peptide signal at growing end, causes
growing protein to move to ER
("docking"), insert peptide into
membrane, and translocate growing
polypeptide chain across ER membrane.
When protein synthesis is complete,
polypeptide folds up inside ER, not in
cytoplasm.
21

22. 
Smooth ER (sER): synthesizes lipids,
detoxifies drugs and poisons should
be in bigger amounts in the liver).
22

23. GOLGI BODY
Functions as intracellular "post office"
for sorting new proteins made on rER.
Vesicles containing protein pinch off from
ER, fuse with cis face of Golgi. Inside
Golgi, oligosaccharide chains on proteins
are modified. Vesicles pinch off from
trans face of Golgi, carry proteins to
several possible destinations: export (out
of cell), Lysosomes, Peroxisomes, Cell
membrane, etc.
23

24. LYSOSOMES
Compartments where old proteins,
foreign materials, many wastes are
broken
Contain ~40 hydrolytic enzymes: lipases,
proteases, nucleases, etc. Break down
organic polymers of all types.
"Suicide bags" if opened up on cell itself
= apoptosis .
Lysosomes are used in Phagocytosis, a
process in which foreign materials are
brought into the cell and "chewed up".
24

25. VACUOLES
Large membrane compartments
Plant cells have especially large vacuole
called the central vacuole , can occupy
most of the volume of a plant cell.
Storage site of pigments, wastes, water,
poisons, and more
25

26. 2. THE NUCLEUS



Location for DNA & RNA synthesis and
protein assembly
Contains chromatin s which are DNAprotein complexes . Chromatin can
condense into chromosomes during cell
division
Site of RNA synthesis . 80% of RNA are
ribosomal RNA. Remaining 20% leaves
nucleus as t-RNA & m-RNA, which direct
protein synthesis
26

27. 
Contains nucleolus, an assembly plant for
ribosomes. Ribosomal proteins are made
in cytoplasm, must be transported back
into nucleus. Ribosomal RNA is made in
nucleus. These two elements are
integrated inside nucleolus to create
ribosomal subunits. These are then
exported out of nucleus through nuclear
pores.
27

28. 
Bounded by nuclear membrane. The
nuclear membrane is a double layered
structure. It Contains many nuclear pores,
which allow material to move in and out of
nucleus
28

29. 
Nuclear Pores have octagonal "doors"
made of protein; open and close on either
side depending on specific signals. Pore
has diameter of about 10 nanometers (10
x 10-9 m), smaller than diameter of a
complete ribosome. Pore can open up to
as much as 26 nm in response to certain
signals. Some signals allow motion in but
not out, other signals control reverse
transport.
29

30. 

Mitochondria are organelles involved in
energy transformations and are separate
from the endomembrane system
"Energy organelles" have unique
properties:
30

31. 




are enclosed by double membrane system
contain DNA and ribosomes (70S, not 80S
like cytoplasmic ribosomes)
make some of their own proteins
from their own genes
divide by binary fission (but not
autonomous, cannot grow or sustain life
outside of cell)
31

32. 


Mitochondria = centers for respiratory
catabolism. Oxygen combined with chemicals to
break down foods, generate cell energy. Contain
outer and inner compartments, with many
membranous cristae that "criss-cross" the
internal space.
Found in virtually every eukaryotic cell.
Are small structures similar to bacteria in some
size.
32

33. 3. The cell membrane
 Structure

Function
33

34. 



The cells have a flexible outer surface
called cell membrane.
Separates the cell’s internal environment
from the external environment
Regulates the flow of material in and out
of the cell maintaining the appropriate
environment for normal cellular activity.
Communication among and between cells
and the external environment.
34

35. 3.1 Structure
[A] Membrane lipids
[B] Membrane proteins
35

36. 3.1.1 Membrane lipids



75 % are phospholipids
5 % are glycolipids
20 % are cholesterol
36

37. 3.1.2 Phospholipids

Description


Are amphipathic
Have a
hydrophilic polar
head and two
hydrophobic
tails.
37

38. 3.1.3 Glycolipids

Description



Are about 5% of
membrane lipids.
Appear only on
surface of the
membrane
facing the
exrtacellular
fluid.
Are target of
attack by
bacteria38
and
certain toxins

39. Glycolipids continued

Descriptio n




Found in large
quantities in brain
tissue
Contain sugar,
sphingosine, and a
fatty acid
No phosphoric acid
present
Bound to cell
poisons e.g
cholera, tetanus
toxins. 39

40. 3.1.4 Cholesterol

Description



Make about 20%
of membrane
lipids
Located among
phospholipids
On both sides of
the bilayer
40

41. Cholesterol continued

Function




Provides
membrane
rigidity
Prevents
crystallization
Decreases
solubility to
water soluble
molecules.
Modulates fluid
state of 41
the
membrane

42. 3.2 MEMBRANE PROTEINS


Peripheral proteins
Integral proteins
42

43. 3.2.1 Membrane protein functions
1.
1.
Receptors

Carriers


1.
Channel
proteins
Docking sites for
specific substances
For specific solutes
across membranes
Have pores, act as
pumps and gates to
selectively move
specific substances
through the cell
membrane.
43

44. Membrane protein functions
1.
Enzymes
1.
Anchoring
1.
recognition



Energy
transforming
enzymes
Bound to
cytoskeleton
E.g. many
glycoproteins.
44

45. Reference
Tortora G.J & Derrickson B. (2006)
Principles of Anatomy and
Physiology (11th ed.) John Wiley &
Sons Inc. NY. Chap 3.
Apps D.K et all (1992) Biochemistry
(5th ed),Bailliere Tindall, Londan
45