The Modern Study of Cells (Cytology) Has Been Made Possible with the Invention of Microscopes

Cell Biology

The Modern study of cells (cytology) has been made possible with the invention of Microscopes.

Transmission Electron Microscope (TEM)

- Electrons are shot through very thin layers of specimen and the image appears 2-dimensional on a television screen.

Scanning Electron Microscope (SEM)

- Specimen is coated with gold and electrons are scanned across the specimen. Image is 3-dimesional.

Scanning Tunneling Microscope (STM)

- Highest magnification down to the molecular level.

- shows 3-dimensional image as a series of bumps and ridges.

THE CELL THEORY

·  All living things are composed of one or more cells

·  The cell is the smallest entity that retains the properties of life

·  New cells arise only from cells that already exist (from preexisting cells)

THERE ARE TWO MAJOR CLASSIFICATIONS OF CELLS:

·  PROKARYOTIC CELLS do not have their chromosomes surrounded by a casing (do not have a membrane-bound nucleus)

Example: Monera (bacteria)

·  EUKARYOTIC CELLS has a membrane surrounding its chromosomes (has a true nucleus)

Example: Plant and Animal Cells

CELL STRUCTURE AND ORGANELLES

All living cells have a protective boundary around them call a cell membrane. All material inside the cell is called the protoplasm. Inside the nucleus is found nucleoplasm and all material outside of the nucleus makes up the cytoplasm.

TYPICAL PLANT and ANIMAL CELLS

TYPES OF ORGANELLES within Eukaryotic cells

NUCLEUS:

·  Most important organelle

·  Contains: - chromatin (chromosomal material) that hold genetic information (made of DNA)

- Nucleolus (dark spot) that makes ribosomes

- nuclear membrane ( nuclear envelope) which controls what goes in and out of the nucleus using small holes called nuclear pores

- proteins in the membrane help organize DNA during mitosis or meiosis

·  Function: - holds genetic information

- controls cell’s activity and division

·  Most cells have a nucleus when they are mature (except red blood cells)

THE ENDOMEMBRANE SYSTEM

-  A group of interacting organelles between the nucleus and the plasma membrane. Its main function is to make lipids, enzymes, and other proteins

-  Includes the endoplasmic reticulum, vesicles, vacuoles, and, golgi bodies

ENDOPLASMIC RETICULUM (ER)

·  Extension of the nuclear envelope that forms a continuous network of double membrane flattened sacs and tubes that transport materials quickly from one part of the cell to another part

·  Also acts as a framework inside the cell

·  Two types: Rough ER (with ribosomes)

Smooth ER (without ribosomes)

VESICLES

·  Membrane-enclosed, saclike organells the may transport, store or digest substances in the cell

·  Plants and animals have Vacules that appear empty but act to isolate and dispose of wastes, debris, and toxins.

·  Central Vacuoles are very large in plants and control water content in the cell (turgor pressure).

·  LYSOSOMES are small, circular sacs found in animals cells that contain digestive chemicals (enzymes) that are used to break down food material, bacteria, and toxins in the cell

- will break open to digest the dead cell (suicide sac)

GOLGI BODIES

·  Also known as [aka] golgi apparatus or golgi complex

·  Stack of flattened double layered disks with small round sacs near the ends

·  Function: - processes proteins and fats for export from the cell

- packages them into vesicles to be carried to the plasma membrane or lysosomes

OTHER ORGANELLES

MITOCHONDRIA (Mitochondrion)

·  Oval shape and surrounded by double membrane with the inner one folded into projections called cristae

·  Contains: - has its own ribosomes and circular chromosomes

- Many enzymes inside and embedded in the cristae involved in cellular respiration

·  Function: - converts sugar (glucose) into usable energy (ATP) during cellular respiration;

Requires OXYGEN (aerobic)

·  Cells that need more energy usually have more mitochondria

CM

RIBOSOMES

·  Very small two piece organelles made of RNA and protein

·  Found free floating or on the rough ER

·  Function: makes proteins using mRNA as guide

PLASTIDS

·  Special sacs found in plants

·  Contain chlorophyll (chloroplasts), starch (amyloplast) or pigment (chromoplast)

·  CHLOROPLASTS --Contains chlorophyll pigment which changes light energy into usable chemical energy

·  Chlorophyll found imbedded in membranes of thylakoids

·  Many thylakoids found in stacks called grana

THE DYNAMIC CYTOSKELETON

Interconnected system of filaments that provide cell structure, helps with cell division, and allows for the cell and inner organelles to move around.

MICROFILAMENTS AND MICROTUBULES

·  Microfilaments are solid wire-like filaments that provide support and movement for the cell. Muscles have many microfilaments

·  Microtubules are hollow tubes that transport materials around the inside of the cell. They are also found in cilia and flagella

·  Intermediate filaments proteins coiled into cables that maintain the shape of the cell; anchors oraganelles; internal support.

CELL MEMBRANE (plasma membrane)

·  Outer layer of the cell made of.

·  Contains: - a double layer (bilayer) of fat molecules called phospholipids

- has protein molecules dispersed through it which perform special functions such as regulating what enters and exits the cell, receptor sites for hormones, identification, and movement.

- Cholesterol molecules between the layers help keep the membrane flexible.

·  Function: - give the cell a defined shape, protects the cell from infection, allows for movement

- Selectively permeable (controls what passes through into and out of the cell)

- sends and receives information through chemicals such as hormones and steroids.

Flagella and Cilia and Pseudopods

·  Flagella (flagellum) are whip-like tails that spin and push cells around. They may be single or multiple.

·  Cilia are shorter hair like structures on the outside of cells. They aid with movement and can create a flow of current across the cell.

· 
Pseudopods are lobes that extend like “false feet” from amoebas and white blood cells. This temporary bulges allow the cell to move in a direct and engulf external objects and prey.

· 

THE CELL SURFACE

PLANT CELL WALLS

·  Composed of carbohydrate called cellulose

·  Function: - protect and support the plant

·  May be thin (petals)

·  May have 1 wall (primary) or 2 much stronger walls (secondary)

EXTRACELLULAR MATRIX (ECM)

·  Non-living, complex mixture of fibrous proteins and polysaccharides secreted by cells and tissues

·  Supports and anchors cells; separates tissues, and functions in cell signaling.

·  cellulose in plants; chitin in fungi; protein and carbohydrates in animals

·  basis of tissue organization and structural support

o  bone is mostly ECM of fibrous protein hardeded by mineral deposits

o  insect exoskeletons and clam shells are ECM

·  cell junctions connect a cell to another cell; send and receive ions, molecules, and signals