A Cell

CELL

Is the smallest living structural and functional unit of life It is the smallest unit of an organism that is classified as living, and is often called building block of life All cells come from pre-existing cells Most cells are microscopic and can replicate independently Some organisms are unicellular (consist of a single cell) e.g. some bacteria.

Other organisms are multicellular(consist of many cells) e.g. humans

Vital functions of an organism occur within cells, and all cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells Cells of the body perform specific functions, and therefore their structures vary greatly

There are two types of cells:

• 1.Eukaryotic
• 2.Prokaryotic

Eukaryotic Cells

Cells in higher animals (mammals) are eukaryotic, that is they have membrane bound nucleus, which is well protected, inside the cell Eukaryotic cells are often found in multicellular organisms Eukaryote is an organism whose cells contain complex structures inside the membranes

Most eukaryotic cells also contain other membrane-bound organelles such a mitochondria, and the Golgi apparatus

• Eukaryotes do have "true" nuclei containing DNA

Eukaryotic organisms may be unicellular, as in amoebae, or multicellular, as in humans Cell division in eukaryotes is different from that in organisms without a nucleus (prokaryotes)

Prokaryotic Cells

Do not contain membrane bound organelles and genetic material is scattered in the cytoplasm The simple forms of life like bacteria are made up entirely of single cell are prokaryotic, the nucleus is not membrane bound it is scattered in the protoplasm and is vulnerable Prokaryotic cells are usually independent Prokaryotes generally lack membrane-bound cell compartments: such as mitochondria and chloroplasts.

Instead processes such as oxidative phosphorylation and photosynthesis take place across the prokaryotic plasma membrane.

However, prokaryotes do possess some internal structures, such as cytoskeletons.

Prokaryotes also differ from eukaryotes in that they contain only a single loop of stable chromosomal DNA stored in an area named the nucleoid, while eukaryote DNA is found on tightly bound and organized chromosomes

Structure of a generalized animal cell

The cell is divided into three main parts namely: plasma membrane, cytoplasm and nucleus The plasma membrane: Forms the cell’s outer surface separating the cell’s internal environment from the external environment. It regulates the flow of material into and out of the cell The cytoplasm: It is the fluid-filled cell interior. It has two components: cytosol and organelles.

The cytosol is the liquid portion containing water and dissolved solutes.

The organelles are small structures with highly specialized functions, many of which are contained within a membrane.

They include nucleus, mitochondria, ribosomes, endoplasmic reticulum (ER), Golgi apparatus, cell membrane, microfilaments and microtubules.

Characteristics of the Cell

Metabolism-are the sum of all chemical processes that occur in the body including anabolism and catabolism.

Responsiveness- ability to detect and respond to changes like temperature, pressure, sound etc.

Movement- includes motion of the whole cell and tiny structures inside the cell.

Growth- is the increase in the size and number of the existing cells.

Differentiation- the development of a cell from unspecialized to specialized state Reproduction- the formation of new cells for tissue growth, repair and replacement or to the production of a new individual

. Functions of the Human Cell

The functions of animal cell are all carried out by the different cell organelles These cell organelles function as a unit and regulate the activities of the cell on the whole.

• Cell nucleus

The nucleus is referred to as the heart of the cell The nucleus houses the genetic material of the organism which is the DNA. DNA replication and RNA synthesis occurs in the nucleus.

Mitochondria

• The mitochondria is also referred to as the power house of the cell

It is a double membrane organelle that helps in energy production for the cell.

The energy is generated in the form of ATP from the glucose. This occurs in the process called cellular respiration

Vacuole

The vacuole is a large empty storage organelle.

They store excess water or food. It is present in many numbers within the cell floating in the cytoplasm

Endoplasmic Reticulum

The endoplasmic reticulum is a network for transportation of certain critical substances in and out of the nucleus.

• There are two kinds of ER namely ;
• 1.Rough ER
• Smooth ER.
• Rough ER has ribosome molecules attached to its surface

Smooth ER does not have ribosome molecules attached to its surface

Golgi apparatus

Is involved with processing and packaging of the molecules synthesized by the cell mainly the proteins ready for secretion The ER transports the proteins in their crude form to the golgi apparatus

Ribosomes

• Is involved in protein synthesis. It consists of two sub units

Protein synthesis primarily occurs in the ribosomes The ribosomes may be found freely floating in the cytoplasm or may be found attached to the ER

Lysosomes

Are referred to as suicide bags of the cell,they are involved in clearing the unwanted and waste materials from the cell The lysosomes contain hydrolytic enzymes that are destructive that they kill the toxic materials of the cell time to time.

They engulf materials like damaged organelles, virus, bacteria and food particles

Assignment

Explain functions of cell organelles