- CELL BIOLOGY – 02
- ENDOPLASMIC RETICULUM (ER)
- FUNCTIONS OF ENDOPLASMIC RETICULUM (ER)
- SUICIDE BAGS’ OF A CELL
CELL BIOLOGY – 02
PROKARYOTIC CELLS VS EUKARYOTIC CELLS
- Organisms whose cells lack a nuclear membrane, are called prokaryotes , Pro means Primitive Or Primary; Karyote means Nucleus).
- Organisms with cells having a nuclear membrane are called eukaryotes.
- Prokaryotic cells also lack most of the other cytoplasmic organelles present in eukaryotic cells.
- Many of the functions of such organelles are also performed by poorly organised parts of the cytoplasm.
- The chlorophyll in photosynthetic prokaryotic bacteria is associated with membranous vesicles (bag like structures) but not with plastids as in eukaryotic cells.
Prokaryotes → defined nuclear region, the membrane-bound cell organelles are absent.
Eukaryotic Cells → have nuclear membrane as well as membrane-enclosed organelles.
|ORGANISMS||Monera: Eubacteria and|
|Protists, Fungi, Plants and Animals|
|MEANING OF NAME|
Pro = before
Karyon = nucleus
Eu = after
Karyon = nucleus
|EVOLUTION||3.5 billion years ago (older type of cell)||1.5 billion years ago|
|Multicellular (more complex)|
|CELL WALL||almost all have cell walls (murein)||fungi and plants (cellulose and chitin): none in animals|
|ORGANELLES||usually none||many different ones with specialized functions|
|METABOLISM||anaerobic and aerobic: diverse||mostly aerobic|
|Single Circular Double Stranded DNA||complex chromosomes usually in pairs; each with a single double stranded DNA molecule and associated proteins contained in a nucleus|
|LOCATION OF GENETIC INFORMATION||Nucleoid region||Nucleus|
|binary fission mostly; budding||mitosis and meiosis using a spindle: followed by cytokinesis|
- In some organisms like bacteria, the nuclear region of the cell may be poorly defined due to the absence of a nuclear membrane. Such an undefined nuclear region containing only nucleic acids is called a Nucleoid.
- Empty structure in the cytoplasm is called vacuole. It could be single and big as in an onion cell (plant cell). Cheek cells (animal cells) have smaller vacuoles.
- Large vacuoles are common in plant cells. Vacuoles in animal cells are much smaller.
- Vacuoles are storage sacs for solid or liquid contents.
- The central vacuole of some plant cells may occupy 50-90% of the cell volume.
- In plant cells vacuoles are full of cell sap and provide turgidity [swollen and distended or congested] and rigidity to the cell.
- Many substances of importance in the life of the plant cell are stored in vacuoles. These include amino acids, sugars, various organic acids and some proteins.
- In single-celled organisms like amoeba, the food vacuole contains the food items that the amoeba has consumed.
- In some unicellular organisms, specialized vacuoles also play important roles in expelling excess water and some wastes from the cell.
ENDOPLASMIC RETICULUM (ER)
- The endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets. It looks like long tubules or round or long bags (vesicles).
- The ER membrane is similar in structure to the plasma membrane.
- There are two types of ER –– rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER).
FUNCTIONS OF ENDOPLASMIC RETICULUM (ER)
- Some of these proteins and lipids help in building the cell membrane. This process is known as membrane biogenesis.
- Some other proteins and lipids function as enzymes and hormones.
- Although the ER varies greatly in appearance in different cells, it always forms a network system.
- Thus, one function of the ER is to serve as channels for the transport of materials (especially proteins) between various regions of the cytoplasm or between the cytoplasm and the nucleus.
- The ER also functions as a cytoplasmic framework providing a surface for some of the biochemical activities of the cell.
- In the liver cells of the group of animals called vertebrates, SER plays a crucial role in detoxifying many poisons and drugs.
Golgi Apparatus or Golgi Complex
- The golgi apparatus consists of a system of membrane-bound vesicles arranged approximately parallel to each other in stacks called cisterns.
- These membranes often have connections with the membranes of ER and therefore constitute another portion of a complex cellular membrane system.
- The material synthesized near the ER is packaged and dispatched to various targets inside and outside the cell through the golgi apparatus.
- Its functions include the storage, modification and packaging of products in vesicles.
- In some cases, complex sugars may be made from simple sugars in the golgi apparatus.
- The golgi apparatus is also involved in the formation of lysosomes.
- Lysosomes are a kind of waste disposal system of the cell.
- Lysosomes help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles.
- Foreign materials entering the cell, such as bacteria or food, as well as old organelles end up in the lysosomes, which break them up into small pieces. Lysosomes are able to do this because they contain powerful digestive enzymes capable of breaking down all organic material.
SUICIDE BAGS’ OF A CELL.
- During the disturbance in cellular metabolism, for example, when the cell gets damaged, lysosomes may burst and the enzymes digest their own cell. Therefore, lysosomes are also known as the ‘suicide bags’ of a cell.
- Structurally, lysosomes are membrane-bound sacs filled with digestive enzymes. These enzymes are made by RER.
- Mitochondria are known as the powerhouse of the cell.
- The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP (Adenosine Triphosphate) molecules.
[If Mitochondria is the Power Plant. ATP is the Electricity].
- ATP is known as the energy currency of the cell.
- The body uses energy stored in ATP for making new chemical compounds and for mechanical work.
- Mitochondria have two membrane coverings instead of just one.
- The outer membrane is very porous while the inner membrane is deeply folded. These folds create a large surface area for ATP-generating chemical reactions.
- Mitochondria are strange organelles in the sense that they have their own DNA and ribosomes. Therefore, mitochondria are able to make some of their own proteins [ribosomes prepare proteins].