SCHOOL OF BIO AND CHEMICAL ENGINEERING
DEPARTMENT OF BIOMEDICAL ENGINEERING
UNIT – I -Cell Biology & Genetics – SBMA1101
1
,CELL STRUCTURE
Cells are the building blocks of life. A cell is chemical system that is able to maintain its structure
and reproduce. Cells are the fundamental unit of life. All living things are cells or composed of
cells. Although different living things may be as unlike as a violet and an octopus, they are all built
in essentially the same way. The most basic similarity is that all living things are composed of one
or more cells. This is known as the Cell Theory.
Our knowledge of cells is built on work done with microscopes. English scientist Robert
Hooke in 1665 first described cells from his observations of cork slices. Hooke first used the word
"cell". Dutch amateur scientist Antonie van Leeuwenhoek discovered microscopic animals in
water. German scientists Schleiden and Schwann in 1830's were first to say that all organisms are
made of one or more cells. German biologist Virchow in 1858 stated that all cells come from the
division of pre-existing cells.
The Cell Theory can be summarized as:
Cells are the fundamental unit of life - nothing less than a cell is alive.
All organisms are constructed of and by cells.
All cells arise from preexisting cells. Cells contain the information necessary for their own
reproduction. No new cells are originating spontaneously on earth today.
Cells are the functional units of life. All biochemical processes are carried out by cells. •
Groups of cells can be organized and function as multicellular organisms
Cells of multicellular organisms can become specialized in form and function to carry out
subprocesses of the multicellular organism.
Cells are common to all living beings, and provide information about all forms of life. Because
all cells come from existing cells, scientists can study cells to learn about growth, reproduction,
and all other functions that living things perform. By learning about cells and how they function,
we can learn about all types of living things.
Classification of cells:
All living organisms (bacteria, blue green algae, plants and animals) have cellular organization
and may contain one or many cells. The organisms with only one cell in their body are called
unicellular organisms (bacteria, blue green algae, some algae, Protozoa, etc.). The organisms
having many cells in their body are called multicellular organisms (fungi, most plants and
animals). Any living organism may contain only one type of cell either
A. Prokaryotic cells; B. Eukaryotic cells.
The terms prokaryotic and eukaryotic were suggested by Hans Ris in the 1960’s. This
classification is based on their complexity. Further based on the kingdom into which they may fall
i.e the plant or the animal kingdom, plant and animal cells bear many differences. These will be
studied in detail in the upcoming sections
PROKARYOTIC CELLS
Prokaryote comes from the Greek words for pre-nucleus. Prokaryotes:
i. One circular chromosome, not contained in a membrane.
ii. No histones or introns are present in Bacteria; both are found in Eukaryotes and Archaea.
iii. No membrane-bound organelles. (Only contain non membrane-bound organelles).
iv. Bacteria contain peptidoglycan in cell walls; Eukaryotes and Archaea do not.
v. Binary fission.
2
, Size, Shape, and Arrangement of Bacterial Cells.
i. Average size of prokaryotic cells: 0.2 -2.0 µm in diameter 1-10 µm (0.001 – 0.01 mm) [book
says 2 – 8 µm] in length.
1. Typical eukaryote 10-500 µm in length (0.01 – 0.5 mm).
2. Typical virus 20-1000 nm in length (0.00000002 – 0.000001 m).
3. Thiomargarita is the largest bacterium known. It is about the size of a typed period (0.75
mm).
4. Nanoarchaeum is the smallest cell known. It is at the lower theoretical limit for cell size
(0.4 µm).
ii. Basic bacterial shapes:
1. Coccus (sphere/round).
2. Bacillus (staff/rod-shaped).
3. Spirilla (rigid with a spiral/corkscrew shape).
a. Flagella propel these bacteria.
4. Vibrio (curved rod).
5. Spirochetes (flexible with a spiral shape).
Axial filaments (endoflagella) propel these bacteria.
iii. Descriptive prefixes:
1. Diplo (two cells).
2. Tetra (four cells).
3. Sarcinae (cube of 8 cells).
4. Staphylo (clusters of cells).
5. Strepto (chains of cells).
iv. Unusual bacterial shapes:
1. Star-shaped Stella.
2. Square/rectangular Haloarcula.
v. Arrangements:
1. Pairs: diplococci, diplobacilli
2. Clusters: staphylococci
3. Chains: streptococci, streptobacilli.
vi. Most bacteria are monomorphic. They do not change shape unless environmental conditions
change.
vii. A few are pleomorphic. These species have individuals that can come in a variety of shapes
ULTRA STRUCTURE OF PROKARYOTIC CELLS:
Fig 1.1 Structure of Prokaryotic cell
3
, Structures External to the Prokaryotic Cell Wall.
a. Glycocalyx (sugar coat).
i. Usually very sticky.
ii. Found external to cell wall.
iii. Composed of polysaccharide and/or polypeptide.
iv. It can be broken down and used as an energy source when resources are scarce.
v. It can protect against dehydration.
vi. It helps keep nutrients from moving out of the cell.
1. A capsule is a glycocalyx that is neatly organized and is firmly attached to the
cell wall. a. Capsules prevent phagocytosis by the host’s immune system.
2. A slime layer is a glycocalyx that is unorganized and is loosely attached to the
cell wall.
b. Extracellular polysaccharide (extracellular polymeric substance) is a
glycocalyx made of sugars and allows bacterial cells to attach to various surfaces.Prokaryotic
Flagella.
i. Long, semi-rigid, helical, cellular appendage used for locomotion.
ii. Made of chains of the protein flagellin.
1. Attached to a protein hook. iii. Anchored to the cell wall and cell membrane by
the basal body.
iv. Motile Cells.
1. Rotate flagella to run and tumble.
2. Move toward or away from stimuli (taxis).
a. Chemotaxis. b. Phototaxis.
c. Axial Filaments (Endoflagella).
i. In spirochetes:
1. Anchored at one end of a cell.
2. Covered by an outer sheath.
3. Rotation causes cell to move like a corkscrew through a cork.
d. Fimbriae.
i. Shorter, straighter, thinner than flagella.
ii. Not used for locomotion.
iii. Allow for the attachment of bacteria to surfaces.
iv. Can be found at the poles of the cell, or covering the cell’s entire surface.
v. There may be few or many fimbriae on a single bacterium.
e. Pili (sex pili).
i. Longer than fimbriae.
ii. Only one or two per cell.
iii. Are used to transfer DNA from one bacterial cell to another, and in twitching & gliding
motility.
IV. The Prokaryotic Cell Wall.
a. Chemically and structurally complex, semi-rigid, gives structure to and protects the cell.
b. Surrounds the underlying plasma membrane.
4
DEPARTMENT OF BIOMEDICAL ENGINEERING
UNIT – I -Cell Biology & Genetics – SBMA1101
1
,CELL STRUCTURE
Cells are the building blocks of life. A cell is chemical system that is able to maintain its structure
and reproduce. Cells are the fundamental unit of life. All living things are cells or composed of
cells. Although different living things may be as unlike as a violet and an octopus, they are all built
in essentially the same way. The most basic similarity is that all living things are composed of one
or more cells. This is known as the Cell Theory.
Our knowledge of cells is built on work done with microscopes. English scientist Robert
Hooke in 1665 first described cells from his observations of cork slices. Hooke first used the word
"cell". Dutch amateur scientist Antonie van Leeuwenhoek discovered microscopic animals in
water. German scientists Schleiden and Schwann in 1830's were first to say that all organisms are
made of one or more cells. German biologist Virchow in 1858 stated that all cells come from the
division of pre-existing cells.
The Cell Theory can be summarized as:
Cells are the fundamental unit of life - nothing less than a cell is alive.
All organisms are constructed of and by cells.
All cells arise from preexisting cells. Cells contain the information necessary for their own
reproduction. No new cells are originating spontaneously on earth today.
Cells are the functional units of life. All biochemical processes are carried out by cells. •
Groups of cells can be organized and function as multicellular organisms
Cells of multicellular organisms can become specialized in form and function to carry out
subprocesses of the multicellular organism.
Cells are common to all living beings, and provide information about all forms of life. Because
all cells come from existing cells, scientists can study cells to learn about growth, reproduction,
and all other functions that living things perform. By learning about cells and how they function,
we can learn about all types of living things.
Classification of cells:
All living organisms (bacteria, blue green algae, plants and animals) have cellular organization
and may contain one or many cells. The organisms with only one cell in their body are called
unicellular organisms (bacteria, blue green algae, some algae, Protozoa, etc.). The organisms
having many cells in their body are called multicellular organisms (fungi, most plants and
animals). Any living organism may contain only one type of cell either
A. Prokaryotic cells; B. Eukaryotic cells.
The terms prokaryotic and eukaryotic were suggested by Hans Ris in the 1960’s. This
classification is based on their complexity. Further based on the kingdom into which they may fall
i.e the plant or the animal kingdom, plant and animal cells bear many differences. These will be
studied in detail in the upcoming sections
PROKARYOTIC CELLS
Prokaryote comes from the Greek words for pre-nucleus. Prokaryotes:
i. One circular chromosome, not contained in a membrane.
ii. No histones or introns are present in Bacteria; both are found in Eukaryotes and Archaea.
iii. No membrane-bound organelles. (Only contain non membrane-bound organelles).
iv. Bacteria contain peptidoglycan in cell walls; Eukaryotes and Archaea do not.
v. Binary fission.
2
, Size, Shape, and Arrangement of Bacterial Cells.
i. Average size of prokaryotic cells: 0.2 -2.0 µm in diameter 1-10 µm (0.001 – 0.01 mm) [book
says 2 – 8 µm] in length.
1. Typical eukaryote 10-500 µm in length (0.01 – 0.5 mm).
2. Typical virus 20-1000 nm in length (0.00000002 – 0.000001 m).
3. Thiomargarita is the largest bacterium known. It is about the size of a typed period (0.75
mm).
4. Nanoarchaeum is the smallest cell known. It is at the lower theoretical limit for cell size
(0.4 µm).
ii. Basic bacterial shapes:
1. Coccus (sphere/round).
2. Bacillus (staff/rod-shaped).
3. Spirilla (rigid with a spiral/corkscrew shape).
a. Flagella propel these bacteria.
4. Vibrio (curved rod).
5. Spirochetes (flexible with a spiral shape).
Axial filaments (endoflagella) propel these bacteria.
iii. Descriptive prefixes:
1. Diplo (two cells).
2. Tetra (four cells).
3. Sarcinae (cube of 8 cells).
4. Staphylo (clusters of cells).
5. Strepto (chains of cells).
iv. Unusual bacterial shapes:
1. Star-shaped Stella.
2. Square/rectangular Haloarcula.
v. Arrangements:
1. Pairs: diplococci, diplobacilli
2. Clusters: staphylococci
3. Chains: streptococci, streptobacilli.
vi. Most bacteria are monomorphic. They do not change shape unless environmental conditions
change.
vii. A few are pleomorphic. These species have individuals that can come in a variety of shapes
ULTRA STRUCTURE OF PROKARYOTIC CELLS:
Fig 1.1 Structure of Prokaryotic cell
3
, Structures External to the Prokaryotic Cell Wall.
a. Glycocalyx (sugar coat).
i. Usually very sticky.
ii. Found external to cell wall.
iii. Composed of polysaccharide and/or polypeptide.
iv. It can be broken down and used as an energy source when resources are scarce.
v. It can protect against dehydration.
vi. It helps keep nutrients from moving out of the cell.
1. A capsule is a glycocalyx that is neatly organized and is firmly attached to the
cell wall. a. Capsules prevent phagocytosis by the host’s immune system.
2. A slime layer is a glycocalyx that is unorganized and is loosely attached to the
cell wall.
b. Extracellular polysaccharide (extracellular polymeric substance) is a
glycocalyx made of sugars and allows bacterial cells to attach to various surfaces.Prokaryotic
Flagella.
i. Long, semi-rigid, helical, cellular appendage used for locomotion.
ii. Made of chains of the protein flagellin.
1. Attached to a protein hook. iii. Anchored to the cell wall and cell membrane by
the basal body.
iv. Motile Cells.
1. Rotate flagella to run and tumble.
2. Move toward or away from stimuli (taxis).
a. Chemotaxis. b. Phototaxis.
c. Axial Filaments (Endoflagella).
i. In spirochetes:
1. Anchored at one end of a cell.
2. Covered by an outer sheath.
3. Rotation causes cell to move like a corkscrew through a cork.
d. Fimbriae.
i. Shorter, straighter, thinner than flagella.
ii. Not used for locomotion.
iii. Allow for the attachment of bacteria to surfaces.
iv. Can be found at the poles of the cell, or covering the cell’s entire surface.
v. There may be few or many fimbriae on a single bacterium.
e. Pili (sex pili).
i. Longer than fimbriae.
ii. Only one or two per cell.
iii. Are used to transfer DNA from one bacterial cell to another, and in twitching & gliding
motility.
IV. The Prokaryotic Cell Wall.
a. Chemically and structurally complex, semi-rigid, gives structure to and protects the cell.
b. Surrounds the underlying plasma membrane.
4
