cells

• Cellular structures provide the means to drive cellular processes.
• Understanding how cellular structures facilitate specific cellular processes is fundamental to explaining how life works.
• The cell theory states that the cell is the smallest and most basic unit of life and cells grow only from existing cells.
• Understanding the role of cellular organelles (such as nucleus, ribosome, chloroplast and mitochondrion) and cellular structures (for example, the cytoskeleton) is crucial to understanding how organisms and life at large work.
• One key concept often explored in this chapter is "how are the structures of the organelles adapted for their functions?"
• There are significant differences between cells of prokaryotes and eukaryotes.
• Using bacteria as a model, the nucleoid is not enclosed by any membrane.
• Plasmid may be present as extra-chromosomal DNA.
• Membrane-bound organelles, such as mitochondria and endoplasmic reticulum, are absent.
• Prokaryotic ribosomes are different from eukaryotic ribosomes.
• Some bacterial cells have cell walls that consist of peptidoglycan rather than cellulose.
• Examples of eukaryotic organisms are animals, plants, fungi, and protoctists.
• A typical eukaryotic cell consists of a cell surface membrane that defines the boundary of a cell and retains its contents, a nucleus that contains the genetic material that directs cellular activities, and cytoplasm that consists of cytosol, the aqueous solution of ions and organic compounds (e.g., sugars, amino acids, and proteins), and organelles, which include the organic cellular structures, usually enveloped by a membrane, such as the ribosome, endoplasmic reticulum, Golgi body, lysosome, mitochondrion, vacuole, and centriole.
• Eukaryotes are organisms made of cells that have a true, membrane-bound nucleus and possess membrane-bound organelles.
• The Cell Theory arose in the mid-nineteenth century as a result of work by three German biologists, Schleiden, Schwann, and later, Virchow.
• The Cell Theory states that the cell is the smallest, most basic unit of life, all living organisms are composed of cells, and all cells arise from pre-existing cells by cell division.
• Cell Theory states that cells are the smallest unit of life, all cells come from pre-existing cells, and living organisms are composed of cells.
• Polypeptide chain undergoes folding into its 3D shape and may undergo chemical modification/post-translational modification.
• Transport vesicle fuses with the cis face of the Golgi apparatus.
• Polypeptides are then being transported from the cis to the trans face of the Golgi apparatus, through a series of transport vesicles.
• The products of hydrolysis are released into the cytoplasm.
• The enzyme protein is then being packaged into a lysosome, and it buds out from the trans face of the Golgi apparatus.
• The lysosome then fuses with the phagocytic vesicle and the enzymes from the lysosome hydrolyses the contents of the phagocytic vesicle.
• The transport vesicle moves from the RER to the Golgi apparatus.
• The folded polypeptide chain is then packaged into a transport vesicle and it buds out from the RER.
• Within the cisternae of the Golgi apparatus, the polypeptide chain undergoes sorting, packaging and chemical modification/post-translational modification by adding/deleting and/or substituting sugar residues on the polypeptide chain.
• Unlike unicellular organisms which merely undergo cellular division, cells of multicellular organisms undergo both division and differentiation to allow them to carry out their specific functions.
• Both mitochondria and chloroplasts contain their own DNA and ribosomes.
• Mitochondria and chloroplasts divide by binary fission, a process also used by bacteria.
• The DNA of mitochondria and chloroplasts resembles that of prokaryotes, being circular, not wound on proteins and not enclosed by a nuclear envelope.
• The Endosymbiotic Theory suggests that mitochondria and chloroplasts were once prokaryotes.
• Ribosomes of mitochondria and chloroplasts are smaller (70S) and more similar to prokaryotes than ribosomes (80S) of eukaryotes.
• There are significant differences between cells of prokaryotes and eukaryotes, between cells of plants and animals, and between cells of unicellular and multicellular organisms.
• The cytoskeleton consists of a network of microtubules, intermediate filaments and microfilaments made of protein.
• Eukaryotes have centrioles, while prokaryotes do not.
• Animal cells have vacuoles, while plant cells do not.
• Only some cells in animal cells are capable of division, while almost all cells in plant cells are capable of division.
• Animal cells have cilia and flagella, while plant cells often have cilia or flagella.
• Animal cells have lysosomes, while plant cells do not.
• The cell wall of an animal cell is tough, slightly elastic and made of cellulose, while the cell wall of a plant cell is tough, slightly elastic and made of cellulose.