4 1 Cells Under the Microscope Our bodies are comprised of several hundred different types of cells with billions of each cell type present 4 1 Cells Under the Microscope cont Light microscopes can be used to view cells but not in much detail Electron microscopes allow the structure of cells to be viewed in greater detail Each type of cell is specialized in its particular function Cells are so small that a microscope is needed to see them 4 1 Cells Under the Microscope cont 4 2 The Two Main Types of Cells There are two components to the cell theory All organisms are composed of cells Cells come only from preexisting cells All cells have an outer membrane called the plasma membrane The plasma membrane encloses a semifluid substance called the cytoplasm and the cell s genetic material 4 2 The Two Main Types of Cells cont Cells are divided into two types according to the way their genetic material is organized Prokaryotic Cells Prokaryotic cells are simpler and much smaller than eukaryotic cells Prokaryotic cells were among the first organisms on the earth Prokaryotic cells which lack a membrane bound nucleus have their genetic material located in a region called the nucleoid Prokaryotic cells live in a wide variety of environments and can be found in water soil and the air Eukaryotic cells have a membrane bound nucleus which stores the DNA 1 Prokaryotic Cells cont Prokaryotic Cells cont Bacteria are a type of a prokaryotic cell Some bacteria cause harmful diseases Some bacteria are beneficial Bacteria decompose dead remains Bacteria can be used to manufacture chemicals for human use e g industrial chemicals medicines Bacteria are an important component of some human foods e g yogurt Bacterial Structure Bacterial cytoplasm is surrounded by a cell membrane a cell wall and a capsule The cell membrane is similar to that of eukaryotic cells The cell wall maintains the shape of the cell The capsule is a protective layer of polysaccharides around the cell wall Bacterial Structure cont The DNA of a bacterium is a single coiled chromosome that resides in the nucleoid The cytoplasm of a bacterium has thousands of tiny particles called ribosomes that synthesize all the proteins needed by the cell Bacterial Structure cont Bacterial Structure cont Bacteria can have appendages with specific functions Flagella can be used to help bacteria move in water Fimbriae are small bristlelike fibers that allow bacteria to attach themselves to surfaces Sex pili are used to transfer DNA from one bacteria to another 2 4 3 The Plasma Membrane cont 4 3 The Plasma Membrane The plasma membrane is the boundary that separates the inside of the cell from the outside environment The plasma membrane is a phospholipid bilayer The polar heads face toward the inside and outside of the cell The nonpolar tails face inward toward each other Cholesterol if present adds structural support Functions of Membrane Proteins Functions of Membrane Proteins cont Channel proteins are simple protein pores that allow substances to move across the membrane Receptor proteins have a shape that can only bind specific signal molecules Transport proteins combine with substances to assist their movement across membranes Enzymatic proteins are membrane proteins that carry out chemical reactions Cell recognition proteins are glycoproteins that have several functions such as recognition of pathogens Junction proteins connect cells to each other and allow them to communicate Functions of Membrane Proteins cont 4 4 Eukaryotic Cells Eukaryotic cells have a membrane bound nucleus that houses their DNA Eukaryotic cells are larger than prokaryotic cells with a lower surface area to volume ratio Eukaryotic cells have a number of membrane bound inner compartments called organelles 3 4 4 Eukaryotic Cells cont The organelles can be divided into four categories The nucleus and ribosomes Organelles of the endomembrane system The energy related organelles The cytoskeleton 4 4 Eukaryotic Cells cont The nucleus communicates with the ribosomes to control protein synthesis Each organelle of the endomembrane system has its own enzymes and produces specific products The products of the endomembrane system are shuttled in the cells as transport vesicles 4 4 Eukaryotic Cells cont The two types of energy related organelles have their own genetic material and ribosomes Mitochondria are found in all eukaryotic cells Chloroplasts are found in the cells of photosynthetic eukaryotes 4 4 Eukaryotic Cells cont The organelles can be divided into four categories The nucleus and ribosomes Organelles of the endomembrane system The energy related organelles The cytoskeleton The cytoskeleton is a protein lattice that maintains cell shape and assists in the movement of organelles 4 4 Eukaryotic Cells cont The organelles can be divided into four categories The nucleus and ribosomes Organelles of the endomembrane system The energy related organelles The cytoskeleton I Nucleus and Ribosomes The nucleus of the eukaryotic cell contains chromatin within a semifluid nucleoplasm Chromatin which is composed of DNA protein and some RNA is usually a network of fine strands The strands condense during cell division to form visible chromosomes 4 Nucleus and Ribosomes cont Nucleus and Ribosomes cont RNA a nucleic acid is produced in the nucleus Messenger RNA mRNA acts as an intermediary to DNA and carries the information for the amino acid sequence of a protein Ribosomal RNA rRNA combines with specific proteins to form the subunits of ribosomes Nucleus and Ribosomes cont The contents of the nucleus are separated from the cytoplasm by the nuclear membrane The nuclear membrane has nuclear pores that permit the passage of ribosomal subunits and mRNA out of the nucleus and proteins into the nucleus Ribosome subunits one large and one small are assembled in the cytoplasm and used to make proteins Ribosomes cont Ribosomes Ribosomes are found in both prokaryotes and eukaryotes In eukaryotic cells ribosomes can be found in different locations and forms Single ribosomes in the cytoplasm Grouped into polyribosomes Attached to the endoplasmic reticulum ER Ribosomes cont The proteins made by these different ribosomes are used in different parts of the cell Proteins from free ribosomes are used in the cytoplasm Proteins from ribosomes attached to the ER are deposited in the ER 5 II Endomembrane System The endomembrane system has four components The nuclear membrane The endoplasmic reticulum ER The Golgi