Chapter 3 Cell Structure & Function

Transcription

1 History of the cell Chapter 3 Cell Structure & Function Antonie van Leeuwenhoek (1673) constructed a crude microscope to analyze animalcules in pond water & other tiny things Robert Hooke (1665) coined the word cellulae (small roon) to describe the boxlike cavities he saw when viewing cork slices under a microscope Both of these individuals observations were discarded for nearly 200 years, due to social standing Development of the CELL THEORY Matthias Schleiden (1838) using a microscope proposed that all plants are composed of cells Theodor Schwann (1839) using a microscope proposed that all animals are composed of cells Together they stated: 1. Cells are the elementary particle of all living organisms 2. All cells are alive independent to the organisms to which they belong

2 Development of the CELL THEORY Rudolf Virchow (1858) stated 1. Cells never arise from noncellular material 2. Diseases result from changes in specific kinds of cells CELL THEORY 1. All organisms are composed of one or more cells 2. Cells are the basic living unit of organization of all organisms capable of independent existence 3. All cells come from other cells

3 Cell size Chapter 3 Cell Structure & Function

4 Why are cells so small? Surface area / Volume ratio Chapter 3 Cell Structure & Function Nutrients & wastes enter & exit a cell via its surface (plasma membrane) Do you think a larger cell needs more nutrients & produces more wastes than a smaller cell? The only problem here is that as a cell gets larger, the proportionate amount of surface area actually decreases That is the amount of surface area as a ratio to the volume decreases, meaning that a larger cell cannot bring in enough nutrients or expel enough wastes even though its overall surface area is quite large EXAMPLE 1 mm cube has a surface area of 6 mm2 and a volume of 1 mm3 = 6:1 SA to V ratio 2 mm cube has a surface area of 24 mm2, but a volume of 8 mm3 = 3:1 SA to V ratio A cell needs a surface area that can adequately exchange materials with the environment. Surface area to volume considerations require that cells stay small

5 What are cells composed of? Chapter 3 Cell Structure & Function All cells are composed of a boundary, a cell body, & a set of genes The plasma membrane is a boundary that separates the contents of the cell from the surrounding environment It is composed of a phospholipid bilayer in which protein molecules are embedded It serves to regulate the passage of materials into & out of the cell, thus maintaining a homeostatic environment for the cell life processes

6 Cells also contain a set of genes, which are composed of DNA Genes contain all of the necessary information for the growth, development, & maintenance of an organism throughout its life cycle In our cells, along with those of plants, fungi (mushrooms), & protists (amoeba), the genes are contained within a membrane bound structure called a nucleus. The presence of this nucleus defines a category of cells called eukaryotic cells Prokaryotic cells (bacteria) do not possess a gene containing nucleus. Its genes occupy a region called the nucleoid. It is not protected by a membrane barrier. The cell body is defined as the area between the nucleus & the plasma membrane It is filled with a semi-fluid substance called cytoplasm Cytoplasm is 90% water & contains dissolved molecules as well as the organelles of the cell

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8 What kind of functions does a cell have to accomplish in order to survive? Organelles & their functions Nucleus Stores genetic information for the cell. It is surrounded by a double membrane called the nuclear envelope. The nuclear envelope contains nuclear pores to allow the passage of materials between the nucleus & the cytoplasm The nucleus also contains nucleoli which synthesize ribosomes necessary for protein synthesis

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10 The endomembrane system is composed of the nuclear envelope, endoplasmic reticulum, golgi apparatus, & vesicles Endoplasmic reticulum (ER) a series of flattened stacks of vesicles (saccules) which are continuous with the outer membrane of the nuclear envelope ER exists as either Smooth ER (SER) or Rough ER (RER) RER is studded with ribosomes, giving the ER its rough appearance. It is involved in protein synthesis, packaging the newly synthesized proteins for further modification SER does not have attached ribosomes, hence smooth appearance. It is involved in lipid metabolism, hormone production, detoxification, vesicle formation, & other processes

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13 Golgi apparatus a stack of 3 to 20 saccules which are involved in modifying & packaging proteins & lipids delivered to it from the ER Once the molecules have been modified, they exit the Golgi via vesicles which will then migrate to the plasma membrane to secrete the molecule or have them embedded in the plasma membrane Other vesicles will remain in the cytoplasm, becoming organelles like lysosomes & peroxisomes

14 Lysosomes contain digestive enzymes What kind substances do you think lysosomes digest? Autophagy digestion of organelles Autolysis digestion of their host cell Perioxisomes various metabolic tasks dealing with oxidizing organic molecules Vacuoles large membranous sacs for storing substances

15 Energy-Related Organelles Chapter 3 Cell Structure & Function Chloroplasts harness solar energy to synthesize carbohydrates Mitochondria utilizing carbohydrates & other energy rich molecules to form ATP energy currency of the cell

16 Chloroplast structure Chapter 3 Cell Structure & Function It is a double membrane organelle enclosing a fluid-filled space called the stroma. Within the stroma are flattened sacs called thylakoids. Stacks of thylakoids are called grana. The thylakoids are involved in capturing solar energy via pigments like chlorophyll, while carbohydrate synthesis occurs in the stroma

17 Mitochondria structure Chapter 3 Cell Structure & Function It is a double membrane organelle enclosing a fluid-filled space called the matrix. The inner membrane contains the key enzyme ATP synthase which is used to synthesize ATP from the breakdown of energy rich molecules like carbohydrates

18 Cytoskeleton Chapter 3 Cell Structure & Function It is a network of interconnected filaments & tubules that extends from the nucleus to the plasma membrane It determines cellular shape & movement Composed of microtubules, microfilaments, & intermediate filaments 1) Microtubules are composed of the globular protein tubulin. They are important for maintaining asymmetrical cell shape (neurons) & complex cell movements: A) transportation of secretory vesicles within the cell, B) movement of flagella & cilia, & C) distribution of chromosomes during cell division 2) Microfilaments which are composed of the proteins actin (globular) & myosin (golfclub shaped). They are involved in contractile mechanisms (muscle & cytokinesis) contraction & as mechanical stiffeners for several cellular projections (microvilli) 3) Intermediate filaments are highly stable polymers. They primarily support the nuclear envelope & the plasma membrane

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20 Centrioles Form the microtubule organizing centers in cell reproduction / division (mitosis). Involved in assembling & disassembling microtubules necessary for mitosis

21 Cilia & Flagella cell movement or the movement of substances along the cell surface Which of your cells contain cilia or flagella?

22 Evolution of the Eukaryotic Cell Chapter 3 Cell Structure & Function Endosymbiotic hypothesis hypothesis involving the engulfing (endocytosis) of prokaryotic cells by a eukaryotic cell, forming some of the key life sustaining organelles within the eukaryotic cell

23 1. Mitochondria & chloroplasts are similar to bacteria in size & structure 2. Both organelles are bounded by a double membrane, in which the outer membrane may be derived from the engulfing vesicle & the inner one from the prokaryotic cell 3. Mitochondria & chloroplasts have a limited amount of genetic material, which is arranged in a circular loop like bacteria 4. They both possess their own ribosomes, which resemble bacterial types, & produce some proteins 5. The RNA base sequence of their ribosomes suggest a bacterial origin

24 PRACTICE QUESTIONS Chapter 2 The Molecules of Cells 1. Who coined the term cellulae or cell? 2. What does the cell theory state? 3. Why must cells be small? 4. What are all cells composed of? 5. What are the functions of the following structures: plasma membrane, mitochondria, ribosome, peroxisome, Golgi apparatus 6. What are nucleoli, where would you find them, & what is their function? 7. What does the endosymbiotic hypothesis state?