Cell Structure PDF

Lecture No. 2 The Cell, Cell Theory; Structure and Diversity of Cells  Objectives By the end of this presentation you should be able to 1. Describe the basic structure and organization of protoplasm 2. Compare the structures of eukaryotic cells with prokaryotic cel...

Lecture No. 2 The Cell, Cell Theory; Structure and Diversity of Cells  Objectives By the end of this presentation you should be able to 1. Describe the basic structure and organization of protoplasm 2. Compare the structures of eukaryotic cells with prokaryotic cells 3. Point out the structural & functional differences between animal & plant cells 4. Describe, in general, how major organelles of the cell do their work 2 Levels of Biological Organization  Several cells of one kind that interconnect with each other and perform a shared function form tissues. several tissues combine to form an organ (your stomach, heart, or brain). several organs make up an organ system (such as the digestive system, circulatory system, or nervous system). Several systems that function together form an organism (like a human being).  The Cell A cell is the smallest unit of a living thing. All parts that make up a cell are called protoplasm. A living thing, whether made of one cell (like bacteria) or many cells (like a human), is called an organism. Cells are the basic building blocks of all organisms.  The general composition of the cell The three major components of a cell are: An inner-most NUCLEUS Enclosed within the Nuclear membrane Surrounded by a gelatinous substance called: CYTOPLASM Which is enclosed inside a thin CELL MEMBRANE 7  The Cell: Size & Architecture Most cells vary in size from 1-100 µ (micrometer). They can only be seen using a microscope. The smaller parts of a cell are called organelles. The structure of most organelles can only be seen with an electron Microscope. 8 The Structure of the Cell 1.The Cytoplasm: It is the gel-like fluid inside the cell (not located in the nucleus). The organelles located in the cytoplasm. 2.The Nucleus: It is a compartment that contains the chromosomes, on which are the genes consisting of the DNA that codes for proteins, the main ingredients of living things. The nucleus is surrounded by a nuclear membrane (nuclear envelope). It is the center of control. Responsible for reproduction and coordination of other cellular activities.  The Nuclear Membrane Separates nuclear mass from the rest of the cell. Has pores (notice the arrows). Materials can enter and leave the nucleus: e.g. mRNA from nucleus to cytoplasm. C&M 111 - Semester (1) - Muhammad 11/11/2014 11 Sidahmed,PhD 3.Nucleolus: located inside the nucleus and is involved in making ribosomes. Ribosomes are made of RNA. The nucleolus contains a lot of rRNA (ribosomal RNA). 4.Ribosomes: are minute granules that float free in the cytoplasm or attached to the endoplasmic reticulum. They play important role in protein synthesis. Endoplasmic Reticulum 14 5. The Rough Endoplasmic Reticulum (RER): is a mesh of interconnected membranes. It is so named because the ribosomes attached to it giving it a studded appearance. Ribosomes transfer their newly synthesized proteins into the lumen of the RER where they undergo structural modifications. These modified proteins could be (proteins, enzymes or hormones) The RER is abundant in cells that secrete proteins, for example the liver cells. Rough ER connects to the nuclear envelope through which the messenger RNA (mRNA) that is the blueprint for proteins is transported to the ribosomes. 6. The Smooth Endoplasmic Reticulum (SER): It is ribosomes free. And responsible for synthesis of carbohydrates, lipids, and steroid hormones; detoxification of medications and poisons; and storage of calcium ions. 7.Mitochondria: The powerhouses of the cell, it produces energy by converting glucose to ATP (Adenosine Triphosphate). ATP provides the eukaryotic cell with the needed energy. This is where aerobic cellular respiration occurs. Muscle and liver cells have many mitochondria. It has double membranes, folding increases surface area. One molecule of glucose produces 38 ATP molecules, 36 out of them are made inside mitochondria. 8.Golgi apparatus (Golgi body): is a series of flattened membranes where sorting, tagging, packaging, and distribution of lipids and proteins takes place. 19 9.Lysosome:inaddition to diggesting the food matrials lysosomes also use their hydrolytic enzymes to destroy pathogens (disease-causing organisms) that might enter the cell. 10.Plasma Membrane: It is a membrane made of phospholipid bi-layer plus protein. It surrounds and protects the content of the cell (the protoplasm). 10.Plasma Membrane (Cell membrane)  Cytoskeleton A three-dimensional network of microtubules and filaments that provide internal support for the cells, anchor internal cell structures, and function in cell movement and cell division. 22 Cytoskeleton 23 The Types of the Cells  Types of cells Prokaryotic Eukaryotic Bacteria Animal Plant  Prokaryotic Cell Eukaryotic Cell  It has NO true nucleus ,the genetic  It has true nucleus ,the genetic material (DNA) is NOT surrounded material (DNA) is surrounded by a by a nuclear membrane. nuclear membrane).  It has NO membrane-bound  It has membrane-bound organelles. organelles.. E.g: protista, plants, fungi, E.g: bacteria. animals.  Prokaryote vs. Eukaryote The DNA in eukaryotic cells is separated from the cytoplasm by the nuclear membrane. Membrane- bound organelles such as nuclei, mitochondria and chloroplasts are only present in eukaryotic cells. The Protista, Fungi, Plants and Animals are eukaryotic organisms. 27  Eukaryotic Cells Animal cell Plant cell Animal or Plant Cell 30  Comparison of plant & animal cells Plant cells Animal cells Possess rigid cell walls No cell walls Have green chloroplasts No chloroplasts Contain chlorophyll Do not contain chlorophyll Thin lining of cytoplasm Most of cell is cytoplasm Vacuoles filled with cell sap Small (if any) vacuoles 32  The Diversity of the Cells The lack of a rigid cell wall allows animals to develop a greater diversity of cell types, tissues, and organs. Unicellular organisms are made of only one cell. Multicellular organisms may originate from a special single cell (zygote) but develop a large number of cells.  Free-living Protozoa: Different habitats, different cell structure Euglina sp.: Paramecium sp.: Ameba sp.: autotrophic heterotrophic heterotrophic Notice the similar basic structure: membrane, cytoplasm, nucleus. 34 35  The Cell Theory The unified Cell Theory states that: All living things are composed of one or more Cells. The cell is the basic unit of life. New cells only arise from existing cells.  Exceptions to the Cell Theory 1.Viruses: According to the Cell Theory a virus is not a cell. Viruses are made of two chemicals, protein & nucleic acid. They have no membranes, nucleus, or proper protoplasm. They appear to be alive only when they reproduce after infecting a host cell. 2. Mitochondria & chloroplasts: These cell organelles (small structures inside the cell) have their own different genetic material & reproduce independently from the rest of the cell. Mitochondrial DNA in humans is inherited only from the mother. 37