Quiz 3: Cells As Units of Life

The difference between a light microscope and a transmission electron microscope is that light microscope uses light to view the specimen while the transmission electron microscope uses electrons to view the specimen. As we see in the diagram above, the only difference is the source. One is a source of light while the other has a source of electrons.

The structure and function of the following cell components are: Plasma membrane: • Structure: Plasma membrane is made of a phospholipid bilayer with integral and peripheral proteins. • Function: the plasma membrane acts as a barrier which prevents entry of unwanted molecules into the cell. It is a selectively permeable membrane. Chromatin: • Structure -composed of long double stranded DNA • Function -contains information that control cell metabolism and heredity. Nucleus: • Structure: it is a round or oval organelle which contains the genetic material of the cell which is either DNA or RNA. It is surrounded by a nuclear membrane. • Function: it is responsible for protecting the genetic material against damage by cell nucleases. Nucleolus: • Structure: it is present inside the nucleus and it is a round or oval organelle. • Function: they are used to synthesize ribosomal RNA.   Rough endoplasmic reticulum or RER: • Structure: it is a membranous system which has ribosomes situated on top of it. • Function: protein synthesis Golgi complex: • Structure: it is composed of a stack of membranous vesicles • Function: storage, modification, packaging of proteins and polypeptides. Lysosomes: • Structure: they are vesicles • Function: they break down old cells or other foreign material. They are the suicide bags of the cell. Mitochondria: • Structure: it has a double membrane with inner folds called cristae present on the inner membrane. It has its own DNA. • Function: synthesis of ATP Microfilaments: • Structure: they are thin, linear structures which are made up of actin. • Functions: they help in the process of contraction. Microtubules: • Structure: these are tubular structures which are made up of tubulin • Function: organization and transport, cell division Intermediate filaments: • Structure: these filaments are larger than microfilaments but smaller than microtubules • Function: act as a framework for the cell Centrioles: • Structure: they are present within centrosomes and made up of microtubules • Function: they help in cell division Basal body (kinetosome): • Structure: it is identical to a single centriole • Function: movement as they are present in cilia and flagella Tight junction: • Structure: they are junctions between two adjacent cells. • Function: they serve to bind the two cells together and prevent any traffic in the gaps between cells. Gap junction: • Structure: they are tiny canals which are present between the cytoplasm of one cell and the cytoplasm of the adjacent cell. • Function: they serve as a means of communication between cells. Desmosome: • Structure: these are small ellipsoid discs at certain spots on the plasma membrane • Function: they increase the strength of the tissue on the whole  Glycoprotein: • Structure: they contain a carbohydrate group attached to a protein molecule • Function: they are usually present as integral membrane proteins and play a role in cell interactions.   Microvilli: • Structure: The microvilli are tiny, hair-like structures on the surface of epithelial cells • Function: they are involved in absorption and secretion. They increase the surface area of absorption tremendously. 

Functions of actin:  • To form microfilaments • To cause the contraction of muscles and other cells with the help of myosin Functions of tubulin: • To form microtubules • To indirectly help in the transport and intracellular architecture