7–1 Life Is Cellular Vocabulary: cell - basic unit of all forms of life cell theory - idea that: 1. all living things are composed of cells, 2. cells are the basic units of structure and function in living things, 3. new cells are produced from existing cells

nucleus - in cells, structure that contains the cell's genetic material (DNA) and controls the cell's activities eukaryote - organism whose cells contain nuclei prokaryote - single-celled organism lacking a nucleus

The Discovery of the Cell Early Microscopes Mid 1600’s – discovery of cells 1665, Englishman Robert Hooke used an early compound microscope (two lenses) to look at a thin slice of cork, a plant material. Under the microscope, cork seemed to be made of thousands of tiny, empty chambers. Hooke called these chambers “cells” because they reminded him of a monastery's tiny rooms, which were called cells.

In Holland around the same time, Anton van Leeuwenhoek used a single-lens microscope to observe living cells. He called them “animalcules”.

The Cell Theory 1838, German botanist Matthias Schleiden concluded that all plants were made of cells. 1839, German biologist Theodor Schwann stated that all animals were made of cells. In 1855, the German physician Rudolf Virchow concluded that new cells could be produced only from the division of existing cells.

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  Fluorescent labels are used with light microscopy to follow molecules moving through the cell.  Confocal light microscopy uses a laser to construct 3-dimensional images of cell structures.  High-resolution video technology makes it easy to produce movies of cells as they grow, divide, and develop.

Electron microscopes  Electron microscopes show details as much as 1000 times smaller than those visible in light microscopes. Specimens must be dehydrated, preserved, put in a vacuum to be viewed. o Transmission electron microscopes (TEMs) show cell structures and large protein molecules (shows the inside of the cell) o Scanning electron microscopes (SEMs) show 3-dimensional images of the outsides of cells.

Prokaryotes and Eukaryotes pro – before eu – true karyon – nucleus (or literally, “walnut” or “kernel”)

Prokaryotes and Eukaryotes (cont.) There are two basic types of cells, prokaryotes and eukaryotes. Prokaryotes do not have a nucleus (prokaryote – “before nucleus”), and eukaryotes do have a nucleus (eukaryote – “true nucleus”).

Prokaryotes and Eukaryotes (cont.) The nucleus contains the genetic material (DNA). In prokaryotes, the DNA is not separated from the rest of the cell. Numerous other differences will be pointed out after the next section.

Prokaryotes and Eukaryotes (cont.) Examples of prokaryotes are bacteria. Examples of eukaryotes are protists, fungi, plants, and animals.

7–2 Eukaryotic Cell Structure Vocabulary: Organelle - specialized structure that performs important cellular functions within a eukaryotic cell Cytoplasm - material inside the cell membrane—not including the nucleus Nuclear envelope - layer of two membranes that surrounds the nucleus of a cell

Chromatin - granular material visible within the nucleus; consists of DNA tightly coiled around proteins Chromosome - threadlike structure within the nucleus containing the genetic information that is passed from one generation of cells to the next

Nucleolus - small, dense region within most nuclei in which the assembly of ribosomes begins

Ribosome - small particle in the cell on which proteins are assembled; made of RNA and protein Endoplasmic reticulum - internal membrane system in cells in which lipid components of the cell membrane are assembled and some proteins are assembled

Golgi apparatus - stack of membranes in the cell that modifies, sorts, and packages proteins from the endoplasmic reticulum Lysosome - cell organelle filled with enzymes needed to break down certain materials in the cell

Vacuole - cell organelle that stores materials such as water, salts, proteins, and carbohydrates

Mitochondrion - cell organelle that converts the chemical energy stored in food into compounds that are more convenient for the cell to use Chloroplast - organelle found in cells of plants and some other organisms that captures the energy from sunlight and converts it into chemical energy

Cytoskeleton - network of protein filaments within some cells that helps the cell maintain its shape and is involved in many forms of cell movement Centriole - one of two tiny structures located in the cytoplasm of animal cells near the nuclear envelope

Comparing the Cell to a Factory The eukaryotic cell is divided into 3 major parts:  The cell membrane  The cytoplasm  The nucleus

The Nucleus The nucleus contains nearly all the cell's DNA and with it the coded instructions for making proteins and other important molecules. It acts as the control center for the cell.

The nucleus is enclosed by 2 layers of membranes, called the nuclear envelope. The nuclear envelope has thousands of holes called nuclear pores, to allow materials in and out.

DNA in the nucleus contains the genetic code. It is normally spread out, in a form called chromatin. When the cell divides, chromatin forms thread-like structures called chromosomes, which will be discussed in detail in the chapter on cell division.

Within the nucleus, a dense area called the nucleolus produces the cell organelles called ribosomes.

Cytoplasm The cytoplasm is the area of the cell between the nucleus and the cell membrane. It contains the organelles (specialized structures), and the liquid part of the cell, the cytosol. The cytosol is mostly water, with essential molecules dissolved or suspended in it.

Organelles Ribosomes – Ribosomes are the smallest organelles, really large molecules made of protein and RNA. Ribosomes assemble proteins from amino acids, using the instructions encoded in DNA.

Endoplasmic Reticulum – The ER is a network of membranes connected to the nuclear pores of the nuclear envelope. It is divided structurally and functionally into two portions:  Rough ER – Close to the nucleus, this portion is called “rough” because most of the cell’s ribosomes are attached to it. Because of the ribosomes, the rough ER is the site where most proteins are assembled. Smooth ER – The lack of ribosomes makes this area “smooth”. The smooth ER used enzymes to construct lipids and carbohydrates needed for the cell.

Golgi Apparatus – The function of the Golgi apparatus is to modify, sort, and package proteins and other materials from the endoplasmic reticulum for storage in the cell or secretion outside the cell

Mitochondria and Chlorplasts Chlorplasts (in plant and algae cells only) capture light energy from the sun, and store the energy by making carbohydrate molecules. Mitochondria (in all eukaryotic cells) release the energy stored in carbohydrates and other molecules, making it available for cellular work.

Origins of mitochondria and chloroplasts – Both organelles seem to have originated from prokaryotic organisms that began living inside larger cells. This idea, called endosymbiosis, was first proposed by scientist Lynn Margolis in the 1970’s.

Evidence in favor of this hypothesis is: Both organelles are very similar in size, shape and function, to prokaryotic organisms still in existence today.  both are surrounded by a double layer of membrane, the outer membrane similar to the cell membrane, whereas the inner membrane resembles the cell membrane of a prokaryotic cell both organelles contain their own DNA, in the form of a circular chromosome (the same as in prokaryotic cells) and prokaryotic ribosomes.

Lysosomes – Lysosomes are membrane bags, filled with enzymes that break down all 4 classes of macromolecules (carbohydrates, lipids, proteins, and nucleic acids). They break down food particles taken in by the cell, and old molecules and organelles of the cell itself, so the monomers can be recycled.

Vacuoles – Storage bags. Plant cells contain large central vacuoles to store water. Some single-celled organisms living in fresh water tend to accumulate too much water. To fix this, they contain contractile vacuoles that fill with excess water, then contract and expel the water from the cell.

Cytoskeleton - The cytoskeleton is a network of protein filaments and microtubules that helps the cell to maintain its shape. The cytoskeleton is also involved in movement. Microtubules also help to build projections from the cell surface, which are known as cilia (singular: cilium) and flagella (singular: flagellum), that enable cells to swim rapidly through liquids.