Discovery of cells Cells 1st discovered
in 1665 by Robert Hooke
Viewed dead cork cells with simple light microscope
Cell Theory About 150 years
after 1st observations, scientists developed cell theory
Three parts of the theory:
1) All living things are composed of one or more cells
2) Cells are the basic units of structure and function in an organism
3) Cells come only from the reproduction of existing cells
Cell Diversity Size
Lots of variation in size; from bacteria to eggs. Some giraffe nerve cells can be 6.5 feet long!
However, most are microscopic
Cell Diversity Although there is
variation, most cells are microscopic
Cells are limited by their surface area to volume ratio
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Internal Organization Internal structures of
cells are called organelles
Organelles perform specific functions of the cells
Two types of cells Prokaryotes
(bacteria) lack membrane bound organelles
Eukaryotes have membrane bound organelles
We will only study eukaryotes in this course(ZOO ONLY)
Organelles
Cell membrane Membrane must
regulate what wastes and nutrients leave or enter the cell
Because of this the membrane is said to be selectively permeable
Organelles Structure
Made of a bilayer of lipids and proteins
Proteins and lipids move, creating a fluid mosaic
Composition of membrane varies according to cell function
Organelles Cytoplasm
Located between cell membrane and nucleus
Jelly-like substance in which other organelles are located
Organelles Mitochondria
Have double membrane
Have own DNA Has lead scientists to
believe that mitochondria evolved as symbionts with another cell
Organelles Ribosomes
Most numerous organelle in the cytoplasm
No membrane. They consist of proteins and RNA.
Important in production of proteins in the cell.
Organelles
Ribosomes 2 kinds
Those in cytoplasm produce proteins used in the cytoplasm. They are “free floating” in the cytoplasm
Those attached to the endoplasmic reticulum produce proteins for the membrane and those to be exported from the cell
Organelles Endoplasmic
Reticulum (ER) Made up of
membranous tubules and sacs.
Cellular highway for molecules to move from one area of the cell to another
Organelles Endoplasmic
reticulum Rough ER--dotted
with ribosomes. Lot of rough ER in cells that produce proteins to be exported from the cell or inserted into the membrane
Organelles Endoplasmic reticulum
Smooth ER--not covered with ribsomes
Responsible for synthesis of steriods in glands, regulation of calcium in muscles, and breaking down of toxins in liver
Organelles Golgi apparatus--
Processing, packaging, secreting organelle of the cell. Like ER, is a network of membranes
Organelles Lysosomes--
Small spherical organelles that enclose certain enzymes within membranes (digestive and breaking down types)
Organelles Cytoskeleton
Network of long protein strands in the cell.
Provide the cell with support and structure
Move organelles around the cell
Organelles Cilia
Hair like organelles that extend from cell surface
Assist in cellular movement
Ex: moving unicellular organisms through water
Lining respiratory tract to move particles to throat for swallowing
Organelles Flagella
Similar to cilia, though fewer in number
Propel cells though solution
Made of microtubules similar to those of the cytoskeleton
Organelles Nucleus
Nuclear matrix--similar to cytoskeleton
Double membrane--called nuclear envelope
Chromatin--fine strands of DNA and protein
Organelles Nucleus
Chromosomes--chromatin that coils and packs densely prior to reproduction
Site where DNA is copied into RNA. RNA is exported from nucleus and made into proteins
Organelles Nucleus
Has at least one spherical area called nucleolus. This area synthesizes and partially assembles ribosomes.
Multicellular Organization--tissues In most multicellular
organisms, cells combine to form tissues
Tissue-group of cells that carries out a specific function
Tissue Examples Epithelial tissue--
closely packed cells that cover the surface of things such as skin or lining of the nose
Tissue examples Connective tissue--
loosely scattered arrangement of cells that serves to support and link together other tissues.
Multicellular organization--organs Organs--several types
of tissues that interact to perform a specific function
Example-stomach. Made up of
epithelial tissue(lining) Muscle tissue
(movement) Connective tissue (holds
it all together) All work toward one
function; digestion
Multicellular organization: organ systems Organ systems-
groups of organs that carry out a set of related tasks Example: stomach is
part of the digestive systems which also includes the mouth, esophagus, small and large intestines, and other organs.
Evolution of multicellularity Fossil evidence suggests
that the first life on Earth was unicellular, prokaryotic organisms similar to bacteria
Eukaryotes though to have evolved through symbiosis with prokaryotes (mitochondria have their own DNA and membranes--they could have originally been symbionts inside another cell!)
Evolution of Multicellularity Eventually some
unicellular organisms started to live together in colonies. Over time, certain cells began to specialize in certain functions. Eventually, this lead to the development of tissues