Cell Structure Text Ref Pg 4-7, 63-81

Transcription

1 Cell Structure Text Ref Pg 4-7, The Cellular Basis of Life Before people had a scientific explanation for where life came from, they believed in the theory of spontaneous generation, where organisms could spontaneously arise from non-living matter such as garbage. By 1858, a German microscopist named Rudolf Virchow had scientific evidence supporting the conclusion that cells don t suddenly appear, but rather that they come from preexisting cells. Today the cell theory states that all organisms are made of cells and those cells come only from pre-existing cells. The trillions of cells in the human body include some 200 different cell types that vary greatly in shape, size, and function. A cell s structure gives us insight as to its function. For example, the flat, tile-like epithelial cells that line the inside of your cheek fit closely together forming a living barrier that protects underlying tissue from bacterial invaders. Regardless of type, all cells are composed of carbon, hydrogen, oxygen, and trace amounts of other elements. All cells have the same basic parts and share some common functions. This is a scanning electron micrograph of blood cells taken with a scanning electron microscope (SEM). In this picture: (left) red blood cell, (center) platelet, (right) white blood cell. Did You Know? Depending on the type, cells vary greatly in length ranging in size from 12 micrometers to over a meter! The longest cells in our bodies are nerve cells. The Cell Theory The cell is the basic unit of structure and function in organisms. All organisms are made of one or more cells (unicellular/multicellular) All cells come from pre-existing cells 1

2 Cells: Building Blocks of Tissues Individualized body cells are specialized, with each type performing specific functions that help maintain homeostasis and benefit the body as a whole. Cells DO NOT operate independently, instead they form tight cell communities that live and work together. Groups of cells similar in structure and that perform common or related functions are called tissues. Cells tissue organ organ system organism E.g. Squamous epithelial cells lung tissue lung respiratory system E.g. Columnar epithelial cells intestine tissue small intestine digestive system Tissues & the Cells they are made of 2

3 Generalized Animal Cell 3

4 Cell Organelles the organs of a cell Introduction_to_Cells.mov Cell Membrane (Plasma Membrane) o o The plasma membrane is typically depicted as a fluid phospholipid bilayer with a mosaic of specialized proteins, lipids and carbohydrates dispersed in it The fluidity of the plasma membrane allows cells to change shape and size as needed o acts as a boundary layer to contain the cytoplasm (fluid in cell) o selectively permeable to select chemicals that pass in and out of cells o interlocking surfaces bind cells together o proteins can act as channels for substances moving in and out of cell The Cytoskeleton The Bones & Muscles of a Cell o A network of interconnected microfilaments and tubules that extend from the nucleus to the plasma membrane (outer membrane) o work to maintain cell shape 4

5 The Cytoplasm o A jelly-like substance that makes up about 70 % of the cell volume and is composed of water, salts and organic molecules o a translucent fluid in which other organelles are suspended Ribosomes protein factory o composed of two subunits: protein and rrna o found in the cytoplasm as free floating or can be attached to the ER o assemble proteins during protein synthesis Rough Endoplasmic Reticulum (Rough ER) o sheets of plasma membrane, studded with ribosomes, continuous with the nuclear envelope, which forms a tubular network throughout the cell o Proteins are synthesized by ribosomes on the surface of rough ER and are then transported to the Golgi body for further modification 5

6 Smooth Endoplasmic Reticulum (Smooth ER) For example: o continuous with rough ER, a sheet of plasma membrane but DOES NOT have any ribosomes attached to its surface (hence the name smooth ER). o Smooth ER synthesizes the phospholipids found in cell membranes and also has many other functions depending on the type of cell Cells in the testes of men have a large amount of smooth ER because they produce the hormone testosterone. In liver cells, smooth ER helps detoxify drugs from the body Golgi Apparatus Editing & Re-Packaging o Once proteins, steroids or other molecules have been synthesized by the rough and smooth ER they are packaged into membrane bound transport vesicles to be delivered to the Golgi apparatus for sorting and repackaging. o a stack of 3-20 saccules = cisternae (resemble a stack of )pancakes o The Golgi apparatus edits for errors, modifies and sorts proteins and other molecules 6

7 Nucleus o a prominent organelle separated from cytoplasm by the nuclear envelope, contains nucleoplasm, DNA and a nucleolus o Often called the control center of the cell because it is where DNA is found Did You Know? Mature red blood cells are called anucleate cells, they are the ONLY cells in our bodies that DON T have a nucleus. Nucleolus o Within a cell s nucleus there is/are dark region(s) called the nucleolus (nucleoli pl.) o The nucleolus is NOT membrane bound like other organelles o Makes ribosomal RNA (rrna) and assembles ribosomal subunits This is an electron micrograph of a cell. Label the following: a) Plasma membrane b) Nucleus c) Nucleolus d) Nuclear membrane 7

8 Nuclear Envelope (Nuclear Membrane) o The nucleus is surrounded by a phospholipid bilayer (double membrane) called the nuclear envelope o There are many small openings in the nuclear envelope called nuclear pores which allow the transport of certain biological molecules to and from the nucleus o The nuclear envelope represents the beginning of the endomembrane system and serves a physical barrier that separates the contents of the nucleus (particularly DNA) from the cytoplasm of the cell Lysosomes o Lysosomes are a special class of membrane-bounded vesicles that are produced by the Golgi apparatus which contain hydrolytic enzymes o They contain powerful hydrolytic digestive enzymes which serve to break down macro molecules down for use in the cell, act as cellular janitors and defend against pathogens 8

9 Homeostatic Imbalance The absence or malfunction of lysosomes within cells can cause a variety of serious illnesses or even death. In Tay Sachs disease, the cells that surround nerve cells cannot break down a particular kind of lipid, and these lipids accumulate within the cells of the brain and spinal cord. Illness develops when the lipids cause crowding of other cell organelles with in the cell and limit their ability to function. This disease is often fatal and on average children who inherit it do not live to be more than 3 years old. This debilitating disease causes an individual to lose vision, hearing, the ability to move, and eventually control over vital internal organs. Vesicles/Vacuoles Storage Tanks o Vesicles membrane bound sac in the cytoplasm o Vacuoles form when multiple transport vesicles fuse inside a cell, plant cells have a large central vacuole for storage of water o Isolate wastes or toxic substances that might be harmful or a threat to a cell o Used to export cell products from the cell Mitochondria Energy Factory of the Cell o A jelly bean shaped organelle that has an inner membrane: Cristae the inner membrane that forms folds inside the mitochondria to greatly increase the surface area for the chemical reactions needed to produce ATP Matrix the inner fluid-filled space that contains ribosomes, DNA and enzymes that break down carbohydrates, proteins and fats to make ATP o The main function of mitochondria is to convert oxygen and the chemical energy in carbohydrates into ATP (adenosine triphosphate), a form of useable energy, using a process called cellular respiration C 6 H 12 O O 2 6 CO H 2 O + ENERGY Glucose oxygen carbon dioxide water ATP 9

10 o The energy stored in ATP can then be used to drive processes requiring energy, including the synthesis or breakdown of various macromolecules and the transportation of molecules across cell membranes. Note: Muscle cells, liver cells and kidney cells all do a lot of work and have a lot of mitochondria to produce the ATP (energy) they need to function 10

11 Cilia and Flagella o Cilia are tiny hair-like projections found on the outer surface of the plasma (cell) membrane o A flagellum is a tail-like projection that functions in locomotion o Cells that have a flagella are capable of movement e.g. sperm cells use their flagella to propel themselves through a female s reproductive tract o Cilia are used to move materials past the cilia e.g. moving a egg through the fallopian tubes or moving mucus out of the trachea 11

12 Biology 12 The Endomembrane System The endomembrane system consists of: 1) Nuclear envelope 2) Rough endoplasmic reticulum 3) Smooth endoplasmic reticulum 4) Golgi apparatus 5) Several classes of transport vesicles including lysosomes Organelles that make up the endomembrane system are physically continuous with the outer membrane of the nuclear envelope or are connected by vesicles. The endomembrane system compartmentalizes the cell so that particular enzymatic reactions are restricted to specific regions. 12

13 Biology 12 Plant Cell Biology Since plant cells need to carry out similar functions as animal cells, they have many of the same organelles. However, plant cells do have some specialized organelles animal cells do not. Cell Wall Unlike animal cells, plant cells have a cell wall that contains cellulose. The cell wall provides extra support and protection for plant cells. Plant cells need the support because they have a large central vacuole which can fill up with large amounts of water and take up most of the cell. The cell membrane alone is not strong enough to resist the internal pressure that results (turgor pressure) and so the cell wall provides extra support. 13

14 Biology 12 Large Central Vacuole A storage tank for water and nutrients and a place for cellular digestion. The turgor pressure that results from a full tank is what helps to keep plants standing upright. Plants wilt because they have lost turgor pressure in their large central vacuole. Chloroplasts The energy factory of plant cells. Since plant cells primarily use chloroplasts to make the energy they need, they DO NOT have very many mitochondria compared to animal cells. Use sunlight, carbon dioxide and nutrients to produce sugars and oxygen in a process called photosynthesis. Photosynthesis takes place in the thylakoids. The sugars are then used to make ATP useable energy. Contain chlorophyll pigments a and b responsible for making plants green. 14