Topic 3: Cells Ch. 6 -All life is composed of cells and all cells have a plasma membrane, cytoplasm, and DNA. pp.105-107 - The development of the microscope was the key to understanding that all living things are made of cells. - Early microscopes were basically magnifying glasses. - Today we have several much more powerful types of microscopes: - 1. Compound Light Microscope Can magnify up to about 1000x. - These microscopes pass light through thin slices of specimens. - 2. Stereomicroscope (Dissecting microscope) Can magnify up to about 100x. - These also use light to see 3D images of larger objects. - 3. Transmission Electron Microscope (TEM) Can magnify up to about 50000x. - These microscopes pass electrons through very thin slices of specimens. - These microscopes can be used to see organelles. - 4. Scanning Electron Microscope (SEM) Can magnify up to about 5000x. - These also use electrons to see 3D images or the outside of small objects. Fig. 4.1 1
Basic Cell Components pp. 108-128 -All life is composed of cells and all cells have a plasma membrane, cytoplasm, and DNA. - DNA is a long molecule that contains sections called genes which are the instructions for making proteins. -Genome All the genes an organism contains along with non-coding sections of DNA. -Proteome All the proteins an organism makes. Basic Cell Components There are two types of cells: 1. Prokaryotic which have no membrane bound organelles. E.g. Bacteria and Archaea 2. Eukaryotic which have membrane bound organelles. E.g. Plants and animals. Fig. 6.5 The Prokaryote Cell pp.108-110 - Includes the Bacteria and Archaea. - Parts of the prokayortic cell: 1. Nucleoid - Where the chromosome is found. 2. Ribosomes Make proteins. They do not have a membrane, so they are often not considered organelles. 3. Flagella (flagellum singular) Tail-like structure that is used for movement. 4. Pili - Enable bacteria to adhere to surfaces and to each other. Fig. 27.6 The Prokaryote Cell -Bacteria can be divided into two groups based on the structure of their cell wall: 1. Gram positive Have a cell wall with a lot of peptidoglycan. They stain purple 2. Gram negative Have a cell wall with less peptidoglycan. They stain pink. 2
Fig. 27.3 The Eukaryotic Cell pp.110-133 Include animal, plant, and fungal cells. They are much larger and more complex than prokaryotic cells. Eukaryotic cells have many organelles. Including: a nucleus, mitochondria, chloroplasts and an endomembrane system. Fig. 6.3 The Nucleus p.110-113 Nucleus Organelle that houses genetic material (DNA). Nuclear envelope The membrane that surrounds the nucleus and separates it from the cytoplasm. Fig. 6.9 Mitochondria p.120-121 The site of cellular (or aerobic) respiration. Cellular respiration - Energy from food molecules is reacted with O 2. This is turned into useable energy known as ATP. Have two membranes: 1. Inner membrane (christae), which is highly folded. 2. Outer membrane Mitochondrial matrix Fluid that fills the mitochondria. Mitochondria contain their own DNA and ribosomes. They are found in all eukaryotic cell types. Fig. 6.17 Chloroplasts pp.120-122 They have two membranes. They contain fluid called stroma and stacks of flattened sacs called grana. They are the site of photosynthesis. Photosynthesis A reaction that converts light energy into sugars. Found in plant cells and other photosynthesizing organisms (i.e. green algae). 3
Fig. 6.18 Endomembrane System pp.114-119 This is a system of membranes within the cell that includes organelles and parts of the cell membrane (plasma membrane). Organelles include: 1. Endoplasmic reticulum 2. Golgi apparatus 3. Lysosomes 4. Vesicles 5. Vacuoles 1. Endoplasmic reticulum (ER) pp. 114-116 There are two types: 1. Smooth endoplasmic reticulum Detoxify the cell and make lipids for membranes. 2. Rough endoplasmic reticulum Have ribosomes imbedded in it. It produces and releases secretory proteins. NOTE: there are also ribosomes in the cytoplasm. Fig 6.11 2. Golgi Apparatus pp.116-117 Modifies, stores, sorts and ships products from the ER. Fig. 6.12 3. Lysosomes p. 117 Special vacuoles that contain digestive enzymes which break down macromolecules through the addition of water (hydrolysis). Fig. 6.13 4
4. Vesicle p. 114 - Small membrane bound sacs that transport materials around the cell. 5. Vacuole pp. 117-118 - Large membrane bound sacs used for storage or sometimes pumping water out of the cell. Fig. 6.14 Fig. 6.15 Other Important Eukaryotic Structures pp.122-128 1. Centrosome Areas of the cell that produce microtubules used in cell division. 2. Microtubules Long thin protein tubes used for moving things around the cell, e.g. DNA or vesicles. 3. Cytoskeleton - Cellular skeleton that move things within a cell, maintain cell shape and can help the cell move. Composed of three filaments: actin filaments, intermediate filaments and microtubules. Other Important Eukaryotic Structures 4. Cilia and flagella are movement producing structures in cells. Consist of a core of microtubules covered by the plasma membrane. Cells tend to possess 1 or 2 flagella at one region whereas cilia are found in high numbers all over the cell. 5
Fig. 6.23 Direction of swimming (a) Motion of flagella Direction of organism s movement Power stroke Recovery stroke (b) Motion of cilia 5 µm 15 µm Plant vs. Animal Cells pp.128-130 - Pant and animal cells are similar but there are some significant differences: 1. Shape Animal cells are more round while plant cells are more box-like and angular. 2. Specific organelles Plant cells contain chloroplasts, animal cells don t. Animal cells contain lysosomes, plant cells don t. Plants cells usually have a large central vacuole for water storage, while animal cells have much smaller vacuoles. Plant vs. Animal Cells 2. Other cell components - Plant cells lack centrioles which aid in cell division, while they are present in animal cells. Plant cells store energy as starch and animal cells store it as fat. 3. Cell wall The shape of a plant cell is maintained by a cell wall made of cellulose. Animal cells lack a cell wall but have an extracellular matrix which helps maintain shape, and aids in attachment and cell to cell communication. Fig 6.28 Prokaryotes vs. Eukaryotes pp.108-109 Characteristic Prokaryote Eukaryote Cell Wall Yes Sometimes DNA Yes Yes Nucleus No Yes Ribosomes Yes Yes Cytoplasm Yes Yes Cell Membrane Yes Yes Size Small Large Division of Labor The cell membrane allows cells to divide their inside form the outside. This makes it easier to perform specific tasks inside the cell. Some cells are capable of performing all the tasks required to live with just one cell (unicelluar organisms). Fig. 28.7 6
Division of labor Eukaryotic cells are further subdivided by membrane bound organelles. This allows for more specialization and greater complexity than found in prokaryotic cells. Furthermore, multicellular can have cells, tissues, or organs that perform a specialized function, allowing for even greater specialization and complexity. Surface Area to Volume Ratio p.109 All cells need to take in materials (nutrients), and eliminate wastes to survive. These materials must travel through the cell membrane. Therefore a cell needs the largest surface area possible so items and enter and leave quickly. Surface Area to Volume Ratio Also, cells with large volumes needs more nutrients and makes more wastes than smaller cells. To keep these amounts low, a cell needs to keep its volume small. These two issues are considered together in the surface area to volume ratio (SA/V). This explains why large organisms are multicelluar and not just composed of huge large cell. Fig. 6.7 7