Cell biology structure of cell

This is useful to students studying cell biology

1. Cell Biology Because cells are the fundamental units of life, it is to cell biology— the study of the structure, function, and behavior of cells —

2. Cell is defined as a structural and functional unit (performing all the vital activities of life) comprising the protoplasm limited by a membrane and containing one or more nuclei at some time in its life. Living organisms can be classified in to two groups on the basis of cell structure Prokaryotic cell Eukaryotic cell

3.   Prokaryote Eukaryotic Organisms Bacteria, cyanobacteria,mycoplasm Protists, fungi, plants and animals Cell size 1-10 um in linear dimension 10-100 um in linear dimension Metabolism Anaerobic or aerobic Aerobic. Organelles Few or none Many-E.R., Golgi nucleus, mitochondria, chloroplast. DNA Circular DNA in cytoplasm, naked Very long linear, inside the nucleus, combined with proteins, many non-coding regions. RNA and protein Both are synthesized in same compartment RNA synthesized and processed in nucleus. Proteins in the cytoplasm. Cytoplasm No cytoskeleton, cytoplasmic streaming, endocytosis, and exocytosis Cytoskeleton composed of protein filaments. Cytoplasmic streaming endocytosis, exocytosis. Cell division Chromosomes pulled apart by attachments to plasma membrane Chromosomes pulled apart by cytoskeletal spindle apparatus. Cellular organization single Multicellular with differentiation of many cell types. Locomotion Single fibril Cilia and flagella Ribosomes Small -70 S Large- 80S

4. Structure of Animal Cells

5. Ultrastructure of eukaryotic cell Eukaryotic cells are complex. Nucleus exists as a separate compartment surrounded and limited by the nuclear envelope. Another larger compartment is cytoplasm. There is also a plasma membrane. Each of these compartments contains several sub compartments and subcomponents.

6. Plasma membrane The outer boundary of the cell is plasma membrane. It separates cell contents from the external environment. It is a continuous sheet of Phospholipid molecule intercalated with proteins. Some of these proteins serve as pumps and channels for transporting specific molecules into and out of cell. In plant cell plasma membrane is covered and reinforced by the cell wall . In animal cells cell coat is present. The cell coat is made up of glycoprotein , glycolipids and polysaccharides. The cell coat protects the cell, contains enzymes , antigens and is fundamental in the association of cells in tissues.  

7. Nucleus Most conspicuous organelle in the cell. It is separated from the cytoplasm by an envelope consisting of two membranes. The envelope is perforated at intervals by nuclear pores. The entire chromosomal DNA is packaged into chromatin fibers. The shape of the nucleus may be irregular, depends on the shape of the cell. Almost all cells are mononucleate but binucleate , polynucleate cells also exist. The nucleoplasm fills most of the space. The nucleoli are present in the nucleus.  

8. Endoplasmic reticulum It constitutes the bulk of the endomembrane system. These are flattened sheets, sacs and tubes of membrane extend throughout the cytoplasm of eukaryotic cell. The E.R. membrane is structurally continuous with the outer nuclear membrane. It specializes in the synthesis and transport of lipids and membrane proteins. The rough E.R. is studded with ribosome. The smooth E.R. is generally more tubular and lacks studded ribosome. Main function is lipid synthesis

9. Golgi Complex A system of stacked membrane bounded flattened sacs involved in modifying, sorting, and packaging macromolecules for secretion. Around the Golgi apparatus are numerous small membrane bound vesicles. These are thought to carry material between the Golgi and other different components of the cell.  

10. Mitochondria These are cylindrical structures less than 1 um in diameter. They consist of double membrane. Inner membrane is folded to form cristae. The matrix contains various enzymes involved in Kreb’s cycle. Mitochondria bring about oxidation of food material to release energy in the form of ATP, hence they are called power house of the cell.  

11. Chloroplast Present in plant cells. They contain green pigment chlorophyll. It has a double membrane. The inner membrane surrounds a large space called stroma . Stroma contains various enzymes and DNA. The small granules embedded in stroma are granna . In stroma a set of flattened disc like sacs, the thalykoids are present. It forms a specialized membrane system for photosynthesis, electron transport chain and ATP synthesis.

12. Lysosomes Polymorphous organelles, enclosed by a single membrane. They contain a vast array of hydrolytic enzymes. These enzymes are responsible for the digestion of foreign substances. Lysosomes originate from E.R. and Golgi complex. Peroxisomes Bounded by single membrane. They contain enzymes related to production and breakdown of peroxides. Protective in function, B oxidation of fatty acids is another function Present in liver and kidney cells.