Cytology – The Study of Cells

Discovery of The Cell Robert Hooke (mid 1600s) – looked at thin slice of cork (plant material) Saw that cork was made of thousands of tiny, empty chambers Reminded him of the monastery’s tiny rooms called cells Rila Monastery in Bulgaria

Many Observations Later 1838 German botanist, Matthias Schleiden, concluded all plants were made of cells 1855 German physician, Rudolf Virchow, concluded that news cells could be produced by existing cells THE CELL THEORY Left: Matthias S. Right:

The Cell Theory States: 1.) All living things are composed of cells 2.) Cells are the basic unit of structure and function in living things 3.) New cells are produced by preexisting cells

2 Types of Cells Two main types of cells: Prokaryotes Eukaryotes

Prokaryotes 1. Cells that do not contain a nucleus (control center of the cell) 2. Smaller and simpler 3. No membrane-bound organelles (small structures within the cell) 3. Genetic material is NOT contained in the nucleus Example: bacteria

Eukaryotes 1.) Contains a nucleus (control center) 2.) Larger / More Complex 3.) Contain dozens of tiny membrane bound structures called organelles 4.) Many structures are highly specialized 5.) Genetic material IS contained in a nucleus

Eukaryotes Continued: Some eukaryotes are single-celled organisms Some are multicellular (many cells) – plants, animals, fungi, and protists Green algea protist

Differences and Similarities Prokaryotes Similarities Eukaryotes No nucleus Contain DNA as genetic material ( may be in different forms) Nucleus No membrane-bound organelles ( mitochondria, ER, etc.) Cell membrane Contains many membrane bound organelles Unicellular organisms – bacteria and archaea Both contain ribosomes Multicellular organisms – plants, animals, fungi, protists 1-10 um Both very diverse 10-100 um DNA floats freely DNA contained in nucleus

The Wacky History of Cells

Eukaryotic Cell Structure Think of a Factory: Mechanisms buzz and clatter, people are moving quickly, in different directions ---- Cells are like Factories Many structures in eukaryotic cells act like specialized organs so they were given the name “organelles”

Eukaryotic Cell Parts Two major parts 1.) Nucleus 2.) Cytoplasm

The Cytoplasm - portion of the cell outside the nucleus The cytoplasm and the nucleus wok together in the business of life

The Nucleus The same way a main office controls the factory, the nucleus is the control center of the cell. Contains nearly all of the cell’s DNA Coded instructions for making proteins

The Nucleus The nucleus is surrounded by the nuclear envelope -Contains thousands of tiny pores – allows materials to move in and out of cell -like messages moving in and out of an office, there is a steady stream of information ( proteins, RNA, and other molecules moving into and out the nucleus)

The Nucleus The granular material you can see in the nucleus is called chromatin Chromatin is DNA bound to protein. Chromatin is spread throughout the nucleus When a cell divides, chromatin condenses to form chromosomes

Ribosomes One of the most important jobs in a cellular “factory” is making proteins Proteins are assembled on ribosomes Ribosomes are small particles of RNA and protein found throughout cytoplasm

Ribosome Ribosomes produce polypeptide chains which are then folded into proteins by following the coded instructions given to them by the nucleus (the boss)

Endoplasmic Reticulum Known as the internal membrane system Nickname is the “ER” Found close to the nucleus Where lipid components of the cell membrane are assembled along with proteins

Endoplasmic Reticulum Two types: Rough ER – involved with the synthesis of proteins (contains ribosomes along surface – why it looks “rough” Smooth ER – contains enzymes that perform special tasks ( synthesis of lipids ); NO RIBOSOMES Liver cells – detoxifying drugs, often contain lots of smooth ER

Golgi Apparatus The “mailroom” of the cell Proteins produced in the rough ER move here Appears as a stack of pancakes Modifies, sorts, and packages proteins from the ER for storage in the cell or secretion outside of the cell From the Golgi Apparatus, proteins are “shipped” to their final destinations

Lysosomes Cleanup crew of a factory Small organelles filled with enzymes Function is to digest ( breakdown) lipids, carbohydrates, and proteins into smaller molecules for the rest of the cell to use Serious human diseases like Tay-Sachs disease, can be traced to lysosomes that fail to function properly Rare inherited disorder that progressively destroys nerve cells in the brain and spinal cord Appears in infancy

Vacuoles Storage room of the cell Store materials such as water, salts, proteins, and carbohydrates In plant cells, there is a single, large central vacuole filled with liquid (the pressure of this vacuole allows the plant to support heavy structures like leaves and flowers)

Vacuoles Continued Paramecium ( single-celled organism) contains a contractile vacuole By contracting, it is able to pump excess water out of the cell. This allows the paramecium to maintain homeostasis – a controlled internal environment

Mitochondria All living things require an energy source. Factories are hooked up to a power company but what about cells? Nearly all eukaryotic cells (including plants) contain mitochondria Mitochondria convert chemical energy stored in food into compounds more convenient for the cell to use

Mitochondria Enclosed by two membranes: an outer membrane and an inner membrane The inner membrane is folded up inside the organelle

Mitochondria – Interesting Facts All, or nearly all, of our mitochondria comes from the cytoplasm of the ovum, or egg cell This means that all of the mitochondria you possess in your body came from your mom!

Chloroplasts Also considered the energy source within cells – the Solar Power Plant Found in plants and some other organisms Capture energy from sunlight and convert it into chemical energy in a process called photosynthesis

Chloroplasts Like mitochondria, surrounded by two membranes Inside the organelle are large stacks of other membranes, which contain the green pigment chlorophyll

Organelle DNA Chloroplasts and mitochondria are the ONLY organelles that contain their own DNA besides the nucleus Lynn Margulis, an American biologist, suggested that mitochondria and chloroplasts are actually descendents of ancient prokaryotes Suggests that the prokaryotic ancestors of the organelles developed a symbiotic relationship with early eukaryotes taking up residence within them.

Cytoskeleton A factory building is supported by steel or cement beams and by columns that support its walls and roof A network of protein filaments that helps the cell maintain its shape It is also involved in movement

Cell Membrane A factory has a fence surrounded the premises to keep unauthorized personal out of the area Just like a factory, the cell has a thin, flexible barrier surrounding it known as the cell membrane.

Cell Membrane Continued Regulates what enters and leaves the cell Also provides protection and support The cell membrane is double layered and is made up of phospholipids : phospholipid bilayer

Cell Membrane Continued In addition, the phospholipid bilayer also contains proteins and other molecules “Mosaic of Different Molecules”

Cell Wall Present in many organisms like plants, algae, fungi, and many prokaryotes Animal cells DO NOT contain a cell wall, however, both plant and animal cells have cell membranes Provides support and protection for the cell