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

1
THEMES TO BE COVERED
1.
2.
3.
4.
5.
6.

Eukaryotic and Prokaryotic cells
Parts of the cell (Mosaic Model)
Plasma membrane ...
Definition of cell






Cell is the basic unit of structure and
reproduction for all organism.
There two types of cel...
TOPIC I: EUKARYOTIC &
PROKARYOTIC CELLS




Cells over millions of years, have developed
two basic structures
Prokaryoti...




Eukaryotic cells are cells having a nucleus
( also spelled Eucaryotes)
– Eukaryotic cells are seen in animals, Plant...
EUKARYOTIC CELL
STRUCTURES
 Eukaryotic

cells are organized into
different compartments.
 All compartments are bounded b...
 Cytoplasm

is a central metabolic
compartment, bounded by the cell
membrane.
 Other compartments inside cytoplasm are
c...
8
9
10
11
12
13
14
15
16
1. THE CYTOPLASM
 Generally,

the cytoplasm:

is the site of protein synthesis and many
metabolic processes.
Contains m...
Cytoplasm contains fiber of the cytoskeletal
system, which organize cytoplasmic structure
Contains many different organe...
 The

Endomembrane system is involved in
moving materials into different
compartments. It is a set of interconnected
comp...
ENDOPLASMIC RETICULUM

Rough ER : synthesizes proteins for export
or movement to different cell compartments
(but not to ...
Signal hypothesis
Certain mRNAs encode proteins
designated for export. These carry a
peptide signal at growing end, causes...


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

22
GOLGI BODY
Functions as intracellular "post office"
for sorting new proteins made on rER.
Vesicles containing protein pi...
LYSOSOMES
Compartments where old proteins,
foreign materials, many wastes are
broken
Contain ~40 hydrolytic enzymes: lip...
VACUOLES
Large membrane compartments
Plant cells have especially large vacuole
called the central vacuole , can occupy
m...
2. THE NUCLEUS






Location for DNA & RNA synthesis and
protein assembly
Contains chromatin s which are DNAprotein co...


Contains nucleolus, an assembly plant for
ribosomes. Ribosomal proteins are made
in cytoplasm, must be transported back...


Bounded by nuclear membrane. The
nuclear membrane is a double layered
structure. It Contains many nuclear pores,
which ...


Nuclear Pores have octagonal "doors"
made of protein; open and close on either
side depending on specific signals. Pore...




Mitochondria are organelles involved in
energy transformations and are separate
from the endomembrane system
"Energy...







are enclosed by double membrane system
contain DNA and ribosomes (70S, not 80S
like cytoplasmic ribosomes)
mak...





Mitochondria = centers for respiratory
catabolism. Oxygen combined with chemicals to
break down foods, generate ce...
3. The cell membrane
 Structure


Function

33






The cells have a flexible outer surface
called cell membrane.
Separates the cell’s internal environment
from the...
3.1 Structure
[A] Membrane lipids
[B] Membrane proteins

35
3.1.1 Membrane lipids




75 % are phospholipids
5 % are glycolipids
20 % are cholesterol

36
3.1.2 Phospholipids


Description




Are amphipathic
Have a
hydrophilic polar
head and two
hydrophobic
tails.

37
3.1.3 Glycolipids


Description






Are about 5% of
membrane lipids.
Appear only on
surface of the
membrane
facing t...
Glycolipids continued


Descriptio n









Found in large
quantities in brain
tissue
Contain sugar,
sphingosine, ...
3.1.4 Cholesterol


Description







Make about 20%
of membrane
lipids
Located among
phospholipids
On both sides of
...
Cholesterol continued


Function








Provides
membrane
rigidity
Prevents
crystallization
Decreases
solubility to...
3.2 MEMBRANE PROTEINS



Peripheral proteins
Integral proteins

42
3.2.1 Membrane protein functions
1.

1.

Receptors



Carriers




1.

Channel
proteins

Docking sites for
specific sub...
Membrane protein functions
1.

Enzymes

1.

Anchoring

1.

recognition







Energy
transforming
enzymes
Bound to
cyt...
Reference
Tortora G.J & Derrickson B. (2006)
Principles of Anatomy and
Physiology (11th ed.) John Wiley &
Sons Inc. NY. Ch...
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Unit i cell structure and function 2008

  1. 1. UNIT I: STRUCTURE AND FUNCTION OF THE CELL Mw. Muki (Msc NMH,BSc N,DHPEd, RN) Assistant Lecturer 1
  2. 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. 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. 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. 4  Some species are highly evolved pathogens
  5. 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. 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. 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. 7
  8. 8. 8
  9. 9. 9
  10. 10. 10
  11. 11. 11
  12. 12. 12
  13. 13. 13
  14. 14. 14
  15. 15. 15
  16. 16. 16
  17. 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. 18. Cytoplasm contains fiber of the cytoskeletal system, which organize cytoplasmic structure Contains many different organelles 18
  19. 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. 20. ENDOPLASMIC RETICULUM Rough ER : synthesizes proteins for export or movement to different cell compartments (but not to cytoplasm). 20
  21. 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. 22.  Smooth ER (sER): synthesizes lipids, detoxifies drugs and poisons should be in bigger amounts in the liver). 22
  23. 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. 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. 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. 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. 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. 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. 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. 30.   Mitochondria are organelles involved in energy transformations and are separate from the endomembrane system "Energy organelles" have unique properties: 30
  31. 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. 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. 33. 3. The cell membrane  Structure  Function 33
  34. 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. 35. 3.1 Structure [A] Membrane lipids [B] Membrane proteins 35
  36. 36. 3.1.1 Membrane lipids    75 % are phospholipids 5 % are glycolipids 20 % are cholesterol 36
  37. 37. 3.1.2 Phospholipids  Description   Are amphipathic Have a hydrophilic polar head and two hydrophobic tails. 37
  38. 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. 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. 40. 3.1.4 Cholesterol  Description    Make about 20% of membrane lipids Located among phospholipids On both sides of the bilayer 40
  41. 41. Cholesterol continued  Function     Provides membrane rigidity Prevents crystallization Decreases solubility to water soluble molecules. Modulates fluid state of 41 the membrane
  42. 42. 3.2 MEMBRANE PROTEINS   Peripheral proteins Integral proteins 42
  43. 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. 44. Membrane protein functions 1. Enzymes 1. Anchoring 1. recognition    Energy transforming enzymes Bound to cytoskeleton E.g. many glycoproteins. 44
  45. 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

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