Lecture 1
Cell Biology
Overview.
Tools of biochemistry to study the cell.
Comparison of prokaryotic cell and Eukaryotic
cell structure.
Prepared by Mayssa Ghannoum
Cell: the fundamental unit of life
 The
cell is as fundamental to the living systems of biology
as the atom is to chemistry: all organisms are made of cells.
 In
biological organization, the cell is the simplest
collection of matter that can live.
 There
are diverse forms of life existing as single-celled
organisms. More complex organisms, including plants and
animals, are multicellular.
 Cells
are arranged into higher levels of organization, such
as tissues and organs, but still they are an organism’s basic
units of structure and function.
Study of cells: Microscopes and other
tools of biochemistry
 It
can be difficult to understand how a cell, usually too
small to be seen by the unaided eye, can be so complex.
 There
are two methods to study the cell:
Microscopy
II. Cell fractionation
I.
I.
Microscopy
 The
discovery and early study of cells progressed with the
invention of microscopes which are still indispensable for
the study of cells.
 The
major two types of microscopes are:
1. light microscope (LM)
2. electron microscope (EM)
 Two
important parameters in microscopy are:
Magnification: it’s the ratio of an object’s image size to its
real size.
Resolution: it’s a measure of the clarity of the image.
The size range of cells
LM vs EM

Electron microscopes reveal many organelles and
other subcellular structures that are impossible to
resolve with the light microscope.

But the light microscope offers advantages,
especially in studying living cells.

A disadvantage of electron microscopy is that
methods used to prepare the specimen kill the cells.
II. Cell fractionation

It’s a useful technique for studying cell structure and function,
which takes cells apart and separates the major organelles and
other subcellular structures from one another.

The instrument used is the centrifuge, which spins test tubes
holding mixtures of disrupted cells at various speeds.

The resulting forces cause a fraction of the cell components to
settle to the bottom of the tube, forming a pellet.

At lower speeds, the pellet consists of larger components, and
higher speeds produce a pellet with smaller components.
Properties of life
Living organisms:
– are composed of cells
– are complex and ordered
– respond to their environment
– can grow and reproduce
– obtain and use energy
– maintain internal balance
– allow for evolutionary adaptation
Levels of Organization
Cellular Organization :Each level of organization builds
on the level below it but often demonstrates new
features.
4.cells
3.
organelles
2.molecules
1. atoms
The cell is the
basic unit of life.
9
Levels of Organization
 Organismal
level
Organism
Organs systems
Organs
Tissues
Unifying themes in Biology
Cell theory
- All living organisms are made of cells, and all living
cells come from preexisting cells.
Molecular basis of inheritance
- DNA encodes genes which control living organisms
and are passed from one generation to the next.
Comparing Prokaryotic and Eukaryotic cells

The basic structural and functional unit of every
organism is one of two types of cells:
Prokaryotic
Eukaryotic .
OR

Only organisms of the domain Bacteria and
Archaea consist of prokaryotic cells.

Plants, animals, protists and fungi all consist of
eukaryotic cells.
Comparing Prokaryotic and Eukaryotic cells
 All
cells have several basic features in common:
* They are all bounded by a selective barrier: The plasma
membrane (will be discussed in details in lecture 3)
* Enclosed by the membrane is a semifluid, jellylike
substance: cytosol
* All cells contain chromosomes, which carry gene in
form of DNA.
* All cells have ribosomes.
Comparing Prokaryotic and Eukaryotic cells

Differences between prokaryotic and eukaryotic cells
1. The location of their DNA
* In eukaryotic cell, most of the DNA is in an organelle called the
nucleus, which is bounded by a double membrane.
* In prokaryotic cell, there is no true nucleus. the DNA is
concentrated in a region that is not a membrane-enclosed, called the
nucleoid.
2. Membrane-bounded structures
* Within the cytoplasm of a eukaryotic cell, suspended in cytosol, are
a variety of membrane-bounded organelles of specialized structure and
function.
* These membrane-bounded structures are absent in prokaryotic
cells.
3. Size
* Eukaryotic cells are generally much larger than prokaryotic cells.
* Typical prokaryotic cell (bacteria) are 1-5 Micrometer in diameter.
* Eukaryotic cells are typically 10-100 Micrometer in diameter.
* Larger organisms do not generally have larger cells than smaller
organisms—simply more cells.
Fig. 7.4 The prokaryotic cell is much simpler in structure, lacking a nucleus
and the other membrane-enclosed organelles of the eukaryotic cell.
Nutrition of Prokaryotes
 Nutrition
refers to how an organism obtains energy and
a carbon source from the environment to build the
organic molecules of its cells.
 Prokaryotes
are grouped into four categories according to
how they obtain energy and carbon
Nutrition of Prokaryotes

Phototrophs: Organisms that obtain energy from light.

Chemotrophs: Organisms that obtain energy from
chemicals in their environment.

Autotrophs: Organisms that use CO2 as a carbon source.

Heterotrophs: Organisms that use organic nutrients as a
carbon source.
Nutrition of Prokaryotes
 There
1.
are four major modes of nutrition
Photoautotrophs: use light energy as energy source and CO2 as
carbon source to synthesis organic compounds.
2.
Chemoautotrophs: use chemical inorganic substances as energy
source, and CO2 as carbon source.
3.
Photoheterotrophs: use light as energy source and organic
substances as carbon source.
4.
Chemoheterotrophs: use organic substances as a source for both
energy and carbon.
Prokaryotic modes of nutrition
Based on Carbon source and Energy source that can be used
by a prokaryotic organism to synthesis organic compounds.
Prokaryotes
Autotrophs
CO2 as Carbon Source
Photoautotroph
Chemoautotroph
Heterotrophs
Organic compounds as
Carbon Source
PhotoHeterotroph
ChemoHeterotroph
- Light as energy
source
- Chemicals as
energy source
- Light as
energy source
- Chemicals as
energy source
-CO2 as C source
-CO2 as C source
-Organic
compounds as
C source
- Organic
compounds as C
source
A panoramic view of the Eukaryotic cell
 The
two basic types of eukaryotic cells are :
Animal cell and Plant cell
 There
are so many common structures between animal and
plant cell, therefore there are major differences between
them.
Animal cell
Plant cell
In plant cells but not in animal cells are
found the following organelles:

Chloroplasts: Photosynthetic organelle; converts energy of
sunlight to chemical energy stored in sugar molecules.

Cell wall: outer layer that maintains cell’s shape and protects it
from mechanical damage; made of cellulose, and protein.

Central vacuole: prominent organelle in plant cells.
Function in storage, breakdown of waste products, hydrolysis
of macromolecules;
enlargement vacuole is a major mechanism of plant growth.

Plasmodesmata: channels through cell walls that connect the
cytoplasm of adjacent cells.