Introduction To Bio-Chemistry

Study The Cell

Assignment Content

#S.NO. TOPIC #PAGE NO.

1) Introduction To Cell 02

2) Classification Of Cell 02

Prokaryotic Cell 02

Eukaryotic Cell 02

3) Structure Of Prokaryotic Cell 03

Cell Membrane 04

Cytoplasm 04

Ribosomes 04

Genetic Material 05

Plasmids 05

Cell Wall 06

Cell capsule or, Envelope 06

Flagella 06

Pili or, Fimbriae 06

1) Introduction To Cell :-1 Submitted To : Prof. Abdullah Jan Sir (Gold-Medalist)

Introduction To Bio-Chemistry

Study The Cell

Meaning: The word cell comes from a Latin word called “cella” meaning a “small room”.Definition No.1: Cell is the basic structural, functional and biological unit of all known living organism.Definition No.2: Cell is the unit of life which has the power to replicate independently and is called the building block of life.

Cell may consist of a semitransparent or, translucent matter called protoplasm enclosed within membrane.

The number of cell in plants & animals varies from species to species human contain about 100 trillion (1014) cell.

The human and plants cell are visible only under microscope having dimension between 1 - and 100 µm.

All the organisms have been classified as:

UNICELLULAR: An organism consists of only one piece cell is called unicellular. e.g. Bacteria, Archaea

MULTICELLULAR: An organism consist of more than one cell is called multicellular. e.g. Plants, Animals

2) Classification Of Cell :-A cell can be generally classified on the basis of unicellular or, multicellular organism.

Prokaryotic Cell: (include unicellular organism such as bacteria, Archaea) the simplest form of the cell having no membrane bound organelles.

Eukaryotic Cell: (include multicellular organism such as Plants & Animals) the most complex form of the cell having membrane bound organelles.

Prokaryotic Cell:

Prokaryotic cells were the first form of life on this planet (shown in figure a). They are smaller and simpler than eukaryotic cells. Prokaryotic cells lack a well-defined nucleus and membrane-bound organelles such as

the mitochondria. The DNA of a prokaryotic cell consists of a single chromosome which is in direct contact

with the cytoplasm. There are 20 – times more prokaryotic cell on earth than eukaryotic cell, this is only

minimum estimate about trillion of trillion are associated with eukaryotic cell and archaea are also prokaryotes but there number is not sure.

For example, bacteria and archaea.

2 Submitted To : Prof. Abdullah Jan Sir (Gold-Medalist)

Introduction To Bio-Chemistry

Study The Cell

Simple structure of prokaryotic cell (figure a)

3) Structure Of Prokaryotic Cell :- (Typically Study Bacteria )A prokaryotic cell structure have the following component:

Cell Membrane Cytoplasm Ribosomes Cytoplasm Genetic Material Plasmids Cell Wall Cell capsule or, Envelope Flagella Pili or, Fimbriae

ORGANALLES: (Little organ)

Organelles are parts of the cell which are specialized for carrying out one or more vital functions.

3 Submitted To : Prof. Abdullah Jan Sir (Gold-Medalist)

Introduction To Bio-Chemistry

Study The Cell

Both eukaryotic and prokaryotic cells have organelles, but prokaryotic organelles are generally simpler and are not membrane-bound.

There are several types of organelles in a cell. , such as mitochondria, chloroplasts, peroxisomes and lysosomes (hundreds to thousands).

The cell is filled with a gelatinous fluid which surrounds the organelles. This fluid is known as cytosol.

PLASMA MEMBRANEProkaryotic cells can have multiple plasma membranes (shown in figure b).Plasma membrane in prokaryotic cells is responsible for exchange of materials between the cell and its surrounding environment.Plasma membranes also aids in sending and receiving chemical signals from other bacteria and interacting with the cells of eukaryotic organisms during the process of infection.Prokaryotes known as "gram-negative bacteria,"For example, often have two plasma membranes with a space between them known as the periplasm.

CYTOPLASMThe cytoplasm of the prokaryotic cells is a translucent or gel-like fluid substance in which all of the other cellular components are suspended (shown in figure b).It is very similar to the eukaryotic cytoplasm, except that it does not contain organelles.Recently, biologists have discovered that prokaryotic cells have a complex and functional cytoskeleton similar to that seen in eukaryotic cells.The cytoskeleton helps prokaryotic cells maintaining its shape.

RIBOSOMES

Prokaryotic ribosomes are smaller and have a slightly different shape and composition than those found in eukaryotic cells (shown in figure b).Bacterial ribosomes, are about half of the amount of ribosomal RNA (rRNA) and one third fewer ribosomal proteins (53 vs. ~ 83) than eukaryotic ribosomes.Along these differences, the function of the prokaryotic ribosome is totally same to that of eukaryotic cell. Just like in eukaryotic cells, prokaryotic ribosome is involved in the synthesis of proteins by translating messages sent from DNA in the shape of messenger RNA.

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Introduction To Bio-Chemistry

Study The Cell

Figure b

GENETIC MATERIAL

All prokaryotic cells contain large quantities of genetic material in the form of DNA and RNA.As prokaryotic cells do not have a well-defined nucleus, the single large circular strand of DNA which contains most of the genes is found in the cytoplasm (shown in figure c).These genes are required for the growth, survival, and reproduction of the cell.The DNA looks like a mesh of string in the middle of the cell.Generally, the DNA is spread throughout the entire cell, and is readily accessible for the transcription into messenger RNA (mRNA) which is immediately translated by ribosomes into protein.Sometimes, when biologist prepares prokaryotic cells for viewing under a microscope, the DNA will condense in one part of the cell producing a darkened area known as nucleoid (shown in figure c).

PLASMIDS

Just eukaryotic cells, the prokaryotic chromosome is associated with special proteins involved in maintaining the chromosomal structure and regulating gene expression (shown in fig c). In addition to a single large piece of chromosomal DNA, many prokaryotic cells also contain small

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Introduction To Bio-Chemistry

Study The Cell

pieces of DNA called plasmids.These circular rings of DNA are replicated independently of the chromosome and can be transferred from one prokaryotic cell to another through pili, which are small projections of the cell membrane that can form physical channels with the pili of adjacent cells.The transfer of plasmids between one cell and another is often referred to as "bacterial sex."Plasmids encode additional genes, such as antibiotic resistance genes.The genes for antibiotic resistance, or the gradual ineffectiveness of antibiotics in populations, are often carried on plasmids (shown in fig c).If these plasmids get transferred from resistant cells to nonresistant cells, bacterial infection in populations can become much harder to control.

For example, it was recently learned that the multidrug-resistant Staphylococcus aureus , received some of its drug-resistance genes on plasmids.

Transmission Electro Micrograph Image Of Plasmid (Small DNA) Fig – C

CELL WALL

The prokaryotic cells have a cell wall present outside the plasma membrane, with a few exceptions such as Mycoplasma (bacteria) and Thermoplasma (archaea).The cell wall consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior

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Introduction To Bio-Chemistry

Study The Cell

forces.It also prevents the cell from expanding and bursting (cytolysis) from osmotic pressure due to a hypotonic environment.

CELL ENVELOPE or CAPSULE

Some of the bacterial cells have an additional layer around the cell wall called a cell envelop or cell capsule.The envelope gives rigidity to the cell and separates the interior of the cell from its environment, serving as a protective filter.Inside the cell is the cytoplasmic region that contains the genome (DNA), ribosomes and various sorts of inclusions.The prokaryotic chromosome is usually a circular molecule (an exception is that of the bacterium Borrelia burgdorferi).Though not forming a nucleus, the DNA is condensed in a nucleoid.Prokaryotes can carry extra chromosomal DNA elements called plasmids, which are usually circular.

FLAGELLA

The bacterial flagella are long and thick thread or whip-like structures, protein in nature which stretches from cytoplasm through the cell membrane(s) and extrudes through the cell wall.They are most commonly found in bacteria cells but are found in animal cells as well.They are involved in the movements.

FIMBRIAE (PILI)

They are short and thin hair-like filaments, made up of protein called pilin (antigenic).They are responsible for attachment of bacteria to specific receptors of human cell (adherence).There are special types of pili called (sex pili) involved in conjunction.

Simple Structure Of Prokaryotic CellTHE END!!!

7 Submitted To : Prof. Abdullah Jan Sir (Gold-Medalist)