CHAPTER 7CELL STRUCTURE AND FUNCTION

7-1Life is Cellular

Cells cannot be seen without a microscope

Early Microscopes • Scientist began to use microscopes to observe

living things in the m id-1600s.• In 1665, Robert Hooke used an early compound

microscope to look at a thin slice of cork. It seemed to be made out of thousands of tine, empty chambers that Hooke called cells.

• Anton van Leeuwenhoek used a microscope to look at pond water and other things and found tiny living organisms, even in our drinking water

The Cell Theory

• Cells – the basic units of life • The cell theory states:• All living things are composed of cells• Cells are the basic units of structure and

function in living things• New cells are produced from existing cells

Exploring the Cell • New technologies make it possible for researchers to study

the structure and movement of living cells in great detail. • Electron microscopes are capable of revealing details as

much as 1000 times smaller than those visible in light microscopes.

• Transmission electron microscopes (TEMs) make it possible to explore cell structures and large protein molecules.

• With scanning electron microscopes (SEMs), a pencillike beam of electron is scanned over the surface of a specimen. Specimens to not have to be cut into thin slices. It produces a 3-D image if cells.

• Scanning probe microscopes, which were perfected in the 1990s make it possible to observe single atoms.

Prokaryotes and Eukaryotes

• All cells have two things in common: They are surrounded by a cell membrane and at some point in their lives, they contain DNA (molecule that contains biological information)

• Cells fall into two categories, depending on whether they contain a nucleus, which is a large membrane-enclosed structure that contains the cell’s genetic material in the form of DNA. It controls the cell’s activities.

• Eukaryotes – cells that contain nuclei • Prokaryotes – cells that do not contain nuclei.

• Prokaryotes

• are smaller and simpler than eukaryotic cells• have genetic material that is not contained in a

nucleus • Eukaryotes

• larger and more complex than prokaryotic cells• contain a nucleus in which their genetic

material is separated from the rest of the cell

7-2 Eukaryotic Cell Structure

Comparing a Cell to a FactoryOrganelles – Structures inside of a cell

• Eukaryotic cells are divided into two major parts: the nucleus and the cytoplasm

Cytoplasm – portion of the cell outside the nucleus

Nucleus • The nucleus contains nearly all the cell’s DNA and with

it the coded instructions for making proteins and other important molecules

• The nucleus is surrounded by a nuclear envelope

with is made up of two membranes. The nuclear envelope is dotted with thousands of nuclear pores, which allow material to move into and out of the nucleus. A steady stream of proteins, RNA, and other molecules move through the nuclear pores to and from the rest of the cell

• Chromatin – granular material you see in the nucleus. Consists of DNA bound to protein

• Chromosomes – distinct, threadlike structures

contain the genetic information that is passed from one generation of cells to the next

• Nucleolus – where the assembly of ribosomes

begins

Ribosomes

• They are small particles of RNA and protein found throughout the cytoplasm. They produce proteins.

Endoplasmic Reticulum

• The site where lipid components of the cell membrane are assembled, along with proteins and other materials that are exported from the cell. There is rough and smooth endoplasmic reticulum.

• Rough ER is abundant in cells that produce large amounts of protein

• Smooth ER have no ribosomes on the surface. Contain a collection of enzymes that perform specialized tasks.

Golgi Apparatus

• Proteins produced in the rough ER move next into the golgi apparatus.

• Golgi apparatus modifies, sorts, and packages proteins and other materials from the endoplasmic reticulum for storage in the cell or secretion outside the cell.

Lysosomes

• Small organelles filled with enzymes. They break down lipids, carbs, and proteins into small molecules that can be used by the rest of the cell.

Vacuoles

• Store materials such as water, salts, proteins, and carbs.

Mitochondria and Chloroplast

Mitochondria – organelles that convert the chemical energy stored in food into compounds that are more convenient for the cell to use. Chloroplasts – Found in plants and other organisms. Organelles that capture the energy from sunlight and convert it inot chemical energy in a process called photosynthesis Organelle DNA – Chloroplasts and mitochondria contain their own genetic information in the form of small DNA molecules.

Cytoskeleton

• Cytoskeleton is a network of protein filaments that helps the cell to maintain its shape. The cytoskeleton is also involved in movement.

• Centrioles – located near the nucleus and help to organize cell division. They are NOT found in plant cells.

7-3 Movement Through the Membrane

Cell Membrane

• The cell membrane regulates what enters and leaves the cell and provides protection and support. The cell takes in food and water and eliminates wastes through the cell membrane.

Diffusion • Every living cell contains a liquid interior and is

surrounded by liquid. • Cytoplasm of a cell is a solution of many different

substances in water. In a solution, molecules move constantly. They collide with one another and spread out randomly through space. As a result, the molecules tend to move from an area where they are more concentrated to an area where they are less concentrated. This is diffusion.

• Diffusion cases many substances to move across a cell membrane but does not require the cell to use energy.

Osmosis • Most biological membranes are selectively permeable,

meaning that some substances can pass across them and others cannot.

• Osmosis – the diffusion of water through a selectively

permeable membrane • Water moves across the membrane until equilibrium is

reached. At that point, the concentrations of water and sugar will be the same on both sides of the membrane. When this happens the two solutions will be isotonic, which means “same strength”.

Active Transport

• when material moves from an area of lower concentration to an area of greater concentration

endocytosis – the process of taking material into the cell by mean of pockets of the cell membrane . The pocket breaks loose from the outer portion of the cell membrane and forms a vacuole within the cytoplasm. Large molecules, clumps of food, and whole cells can be taken up by endocytosis.

Phagocytosis – when large particles are taken into the cell by endocytosis. Extensions of cytoplasm surround and engulf large particles. Exocytosis – the removal of large amounts of material from a cell. The membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell.

7-4 The Diversity of Cellular Life

Unicellular Organisms

• Some organisms are unicellular (made of just one cell)

• Unicellular organisms include both prokaryotes and eukaryotes. Bacteria is an example of a unicellular prokaryote.

• Algae is an example of a unicellular eukaryote

Multicellular Organisms • Multicellular organisms have cell

specialization, or separate roles for each type of cell.

• Cells in multicellular organisms are specialized to perform particular functions within the organism.

Levels of Organization

• Biologists have identified levels of organization that make it easier to classify and describe the cells within an organism.

• The levels of organization in a multicellular organism are individual cells, tissues, organs, and organ systems.

• A tissue is a group of similar cells that perform a particular

function. • An organ is many groups of tissues that work together. • An organ system is a group of organs that work together to

perform a specific function.