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Chapter 7: Cellular Structure and Function

Chapter Worksheet

Ch. 7.1 Cell Discovery and Theory

The invention of the microscope led to the discovery of cells.

History of the Cell Theory

1665 Robert Hooke made a simple microscope and looked at a piece of cork. He named the boxlike cells "cellulae" which is Latin for small rooms. Cell- the basic structural and functional unit of all living organism.

Late 1600's Anton Van Leeuwenhoek designed a microscope and observed organisms in pond water, milk, and other substances.

The Cell Theory

1838 Matthias Schleiden studied plants: concluded all plants are composed of cells. 1839 Theodor Schwann concluded that animal tissues are composed of cells. 1855 Rudolph Virchow proposed that all cells are produced from the division of existing cells.

Cell theory-one of the fundamental ideas of modern biology and includes:

  1. All living things are composed of one or more cells
  2. Cells are the basic unit of structure and organization of all living organisms.
  3. Cells arise only from previously existing cells, passing their genetic material on to their daughter cells.

Microscope Technology

Detail increases as magnification and resolution (ability to make individual components visible) increase.

Compound Light Microscopes: Uses light and a series of lenses; dyes can help to see cells better. Properties of light will always limit resolution; limit of magnification is around 1000x

Electron Microscopes: Uses magnets to aim a beam of electrons at cells.

  1. Transmission (TEM) passes electron through specimen to fluorescent screen. Thicker parts absorb more electrons. Can magnify up to 500,000x
  2. Scanning (SEM) directs electrons over the surface of the specimen producing 3D image.
  3. Scanning tunneling (STM) uses a charged tip of a probe extremely close to the specimen so that electrons "tunnel" through the small gap between probe and specimen.
  4. Atomic force microscope (AFM) measures forces between the tip of a probe and the cell surface.

TEM, SEM specimen is dead, sliced thin, stained with heavy metals. STM can be used with live specimen.

Basic Cell Types

All cells have at one physical trait in common: a plasma membrane. Plasma membrane- is a special boundary that helps control what enters or leaves the cell.

Cells have a number of functions in common: Genetic material that serves as instructions for substances, break down molecules to generate energy.

Two types of cells: prokaryotic cells and eukaryotic cells. Eukaryotic cells are 1 to 100x larger than prokaryotic cells. Both have a plasma membrane while one has many organelles. Organelles- specialized structures that carry out specific cell functions.

Eukaryotic cells- contain a nucleus and other membrane-bound organelles. Nucleus- a central organelle that contains the genetic material as DNA.

Organelles allow many cell functions to occur in different parts of the cell at the same time. Most organism are made up of eukaryotic cells and are called eukaryotes. Some are unicellular: yeast, some algae.

Prokaryotic cells- cells without a nucleus or other membrane-bound organelles. Most unicellular organisms are prokaryotes: for example bacteria. Prokaryotes are believed to be similar to the first organisms that lived on Earth.

Origin of Cell Diversity

Endosymbiotic theory: a symbiotic relationship involving one prokaryotic cell living inside of another and both cells benefiting. Cells having organelles allowed specialization, which has led to diversity. This cell diversity has lead to diversity of organisms to different environments.

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Ch. 7.2 The Plasma Membrane

The plasma membrane helps to maintain a cell's homeostasis.

Function of the Plasma Membrane

Plasma membrane is a thin, flexible boundary between a cell and it's environment. It allows nutrients into the cell and allows waste and other products to leave. All prokaryotic and eukaryotic cells have a plasma membrane.

Membranes are selectively permeable- allowing some substance to pass through while keeping others out.

Structure of the Plasma Membrane

Most molecules in the plasma membrane are lipids composed of glycerol and three fatty acids. The plasma membrane is composed of a phospholipid bilayer- two layers of phospholipids are arranged tail to tail.

The Phospholipid Bilayer

Has a polar head that is attracted to water, the two fatty acid tails are non-polar and repelled by water. Forming a double layer with heads facing toward inside of cell and outside of cell, while tails are in center. Creates a barrier that is polar on surfaces so water soluble substance will not move easily through the membrane. The are stopped by non-polar middle.

Other Components of the Plasma Membrane

With the phospholipids are cholesterol, proteins, and carbohydrates. Proteins on outside surface are receptors that transmit signals inside the cell, proteins on inside surface anchor the membrane to give the cell shape, proteins that span the membrane create tunnels allowing certain substance to enter and leave the cell.

Transport proteins- move needed substances or waste materials through the membrane.

Cholesterol helps to prevent the fatty-acid tails from sticking together. carbohydrates attached to proteins stick out from the membrane and help cells identify chemical signals.

Fluid Mosaic Model- components of the plasma membrane are in constant motion, sliding past one another.

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Ch. 7.3 Structures and Organelles

Eukaryotic cells have organelles allowing specialization and separation of functions in the cell.

Cytoplasm and Cytoskeleton

Cytoplasm- a semi-fluid material inside the cell. In prokaryotes, all cell processes occur in cytoplasm while eukaryote cells use organelles. Cytoskeleton- a supporting network of long, thin protein fibers that form a framework for the cell and anchors the organelles. Also helps with cell movement and other activities.

Made of: Microtubules- long, hollow protein cylinders that form a rigid skeleton for the cell and assist in moving substances within the cell, Microfilaments- thin protein threads that help give the cell shape and enable the entire cell or parts of the cell to move.

Are able to assemble and disassemble as well as slide past one another allowing cells/organelles to move.

Cell Structures

Membrane bound organelles make it possible for different chemical processes to take place at the same time in different parts of the cytoplasm.

Nucleus

Directs the cell processes and contains most of the cell's DNA which is used in making proteins. Nuclear envelope: a double membrane surrounding the nucleus. Has pores that allow larger sized substance to move in and out. Chromatin-DNA attached to protein; fills nucleus.

Ribosomes

Site of protein synthesis. Made of RNA and protein, not bound by membrane. Found free floating or attached to the endoplasmic reticulum. Nucleolus-produces ribosomes and is found in nucleus.

Endoplasmic Reticulum (ER)

Site of protein and lipid synthesis. Folded membranes to increase surface area. Rough ER has ribosomes attached. Smooth ER site of lipid and complex carbohydrate production.

Golgi Apparatus

Flattened stack of membranes that modifies, sorts, and packages proteins into vesicles. Vesicles are sacs that can fuse with plasma membrane to release proteins outside the cell.

Vacuoles

Used for temporary storage of materials within the cytoplasm. Stores: waste products, food, enzymes, other materials. If animal cells have them they are small, plants are large.

Lysosomes

Vesicles that contain substances that digest excess or worn-out organelles and food particles. Also digest bacteria and viruses that enter the cell. Membrane of the lysosome protects the cell.

Centrioles

Organelles made of microtubules that function during cell division. Are located in the cytoplasm of animal cell's and most protists near the nucleus.

Mitochondria

Converts food particles (mostly sugars) into usable energy. Has two membrane systems: inner and outer in which bonds are broken in sugar molecules and then stored in bonds of other molecules.

Chloroplasts

Organelles that capture light energy and convert it to chemical energy through photosynthesis. Inside is a membrane system of disk shaped compartments called thylakoids. The pigment chlorophyll within thylakoids traps the energy from sunlight.

Plastids are organelles for storage. Some store starches or lipids, others (chromoplasts) store pigments that trap light energy and give color to plant structures.

Cell Wall

A thick, rigid, mesh of fibers that surrounds the outside of the plasma membrane,protests the cell, and gives it support. Made of cellulose.

Cilia & Flagella

Cilia- short, numerous projections that look like hairs. Movement is similar to oars of a boat. Flagella- long, whip-like projection. Typically a cell will have one or two.

Both made of microtubules in a 9+2 configuration in which nine pairs surround two single tubules.

Comparing Cells

Animals generally don't have vacuoles, if they do they are small. Plants have cell walls, and chlorophyl to capture suns energy.

Organelles at Work

Each organelle has it's job to do , and the cell depends on all of the parts to work together.

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Ch. 7.4 Cellular Transport

Cellular transport is the movement of substance within the cell as well as in/out of the cell.

Diffusion

Particles in gases, liquids, and solids are in random motion. Substances dissolved in water also move constantly and is called Brownian motion. Diffusion- is the net movement of particles from an area where there are many particles of the substance to an area where there are fewer particles .

Concentration is the amount of a substance in a area. So substances diffuse from high concentration to low. Particles continue moving until no overall change occurs: Dynamic equilibrium.

Three factors for rate of diffusion:

  1. Concentration: high concentration increases the rate of diffusion since there are more particles bouncing off each other.
  2. Temperature & Pressure: Temperature increases speed of movement, Pressure changes closeness of particles. Both can change the rate of diffusion.
  3. Size and charge of particles can also influence rates of diffusion.

    Diffusion Across the Plasma Membrane

    Water can diffuse across the plasma membrane but most other substances cannot. Facilitated diffusion- uses transport proteins to move other ions and small molecules across the plasma membrane.

    • Channel protein: opens and closes to allow substance to diffuse through the membrane.
    • Carrier protein: changes shape as diffusion occurs to move particles through membrane.

    Water & these protiens are Passive Transport; requires NO ENERGY.

    Osmosis: Diffusion of Water

    Osmosis- the diffusion of water across a selectively permeable membrane. Regulating movement of water is an important factor in homeostasis.

    How osmosis works

    In a cell, water is a solvent. The concentration of a solution changes due to amount of solvent. Example: Cells have semi-permeable membrane; sugar can't pass through, but water can; if high concentration of sugar is on one side of the membrane then water will move to that side until reaching dynamic equilibrium.

    Cells in an Isotonic Solution: iso means equal. Solution in which solvent and solutes are equal. Water moves equally in & out of cell. Cells maintain their shape.

    Cells in a Hypotonic Solution: hypo means under. Cell in a solution with lower concentration of solute (more water). Water moves into cell, it increases in size.

    Pressure generated as water moves through the membrane is osmotic pressure. Animal cells can burst, plant cells do not because of cell wall.

    Cells in a Hypertonic Solution: hyper means above. Cell in solution with higher concentration of solute (less water). Water moves out of cell. Animal cells shrivel, plant cells shrinks causing wilting.

    Active Transport

    When a substance moves against the the concentration (against diffusion) it requires energy and is called Active transport. Active transport uses carrier proteins, called pumps. Some pumps move one type of substance in one direction. Others move two substances in the same direction or in opposite directions.

    Na+/K+ ATPase Pump

    Found in membrane of animal cells and maintians the levels of Na+ and K+ inside and outside of cell. The pump is an enzyme that uses the energy to transport three Na+ out of the cell while moving two K+ into the cell.

    The sodium then couples with a sugar outside of the cell and uses a channel protien to move sugar into the cell (facilitated diffusion).

    Transport of Large Particles

    When particles are too big to pass through the membrane or a carrier protein the cell uses another process.

    Endocytosis- the process by which a cell surroungs a substance in the outside environment, enclosing the substance in a portion of the plasma membrane. The membrane pinches off resulting in a vacuole that moves into the cell.

    Exocytosis- the secretion of materials at the plasma membrane. It is the reverse of endocytosis and is used to expel wastes and secrete substance produce by the cell.

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