Cell Notes

• What is a cell?
• Cell- the smallest unit of life that can carry out all the functions of a living thing.
• All animals are multi-cellular (many cells)
• Their shape and characteristics depend on their function.

 

Cell Theory

• 3 principals
• cells are the basic units of all life
• all organisms are made of one or more cells
• all cells arise from existing cells

• Basic Cell Structures
• Cell membrane- thin layer of lipid and protein that surrounds all cells
• Controls what enters and leaves the cell.

•   Cytoplasm- fluid made of water and organic

compounds with structures throughout called

organelles

• Cytoskeleton- strands of protein fibers that branch through the cytoplasm

• Nucleus- “control center”, contains most of the genetic material.
• chromosomes- structures that contain the genetic information (nucleic acids- DNA)
• Nucleolus- help with making proteins

• Two kinds of cells

  Prokaryotictic & Eukaryo tic Cells.

1. The kingdom Monera, the bacteria, is characterized by prokaryotic cells, which are cells with no -nucleus.

a. The DNA of prokaryotic cells is concentrated in a region called the nucleoid.

b. Eukaryotic cells, which are much more structurally complex, are found in the other four kingdoms of life: protists, plants, fungi, & animals.

c. They have a true nucleus enclosed in a nuclear membrane & numerous organelles suspended in a semifluid medium called cytosol.

d. The cytoplasm is the entire region between the nucleus & the membrane enclosing the cell.

• Cell Organelles (found in cytoplasm)
• Ribosomes- make proteins that the cell needs
• Endoplasmic reticulum (ER) bundle of membranes
• rough ER- has ribosomes that make proteins
• smooth ER- makes lipids and processes carbohydrates.
• Golgi apparatus- sacs that contain stored molecules, they deliver them to the cell membrane when needed.
• Mitochondria- where energy is made or generated.
• turns it into ATP- the form of energy needed
• Lysosomes- stores enzymes

• Cell Diversity
• Plant vs. Animal Cells
• Plants contain cell walls and chloroplasts- animals do not have these.
• Multicellular organisms depend on the fact that the different cells interact with one another.
• Their cells must be specialized

a. reproduction, digestion, movement, etc.

A TOUR OF THE CELL

I Microscopes provide windows to the world of the cell

1. The growth of scientific knowledge & the development of new instruments & methods usually go hand in hand.

a. The invention of the microscope in the 17TH century led to the initial discovery & study of cells.

2. The glass lenses of light microscopes (LMS) refract (bend) visible light passing through a specimen such that the projected image is magnified.

a. Resolving power is a measure of the clarity of an image - determined by the minimum distance two points must be separated to be distinguished.

b. The resolving power of the light microscope is limited by the wavelength of visible light, so that details finer than 0.2 urn (micrometers) cannot be resolved.

c. Staining of specimens & using techniques such as darkfield & phase ­contrast microscopy improve visibility by increasing contrast between structures that are large enough to be resolved.

3. Most subcellular structures, or organelles, are too small to be resolved by the light microscope.

b. The electron microscope focuses a beam of electrons through the specimen.

4. In a transmission electron microscope (TEM) a beam of electrons is passed through a thin section of a specimen, & electromagnets, acting as lenses, focus & magnify the image.

a. Contrast is increased by staining preserved cells with atoms of heavy metals.

• In a scanning electron microscope (SEM) the electron bean scans the surface of a specimen coated with a thin gold film, exciting electrons from the specimen & collecting & focusing them onto a screen.

a. The resulting image appears three-dimensional.

II. Cell biologists can isolate organelles to study their functions

• Cell fractionation is a technique that separates major organelles of a cell so that their functions can be studied.
• Cells are homogenized by ultrasound or grinding, & the resulting cellular soup is separated into component fractions by differential centrifugation.
• The homogenate is first spun slowly, & nuclei & large

particles settle to form a pellet.

• The remaining supernatant is centrifuged at increasing speeds, each time isolating smaller & smaller cellular components in the pellet.
• Ultracentrifuges can spin at speeds up to 80,000 rpm.
• Each cellular fraction contains a large quantity of the same cellular components, thus permitting the isolated study of their metabolic functions.