The Cell Robert Hooke 1665 l British scientist

The Cell

Robert Hooke (1665) l British scientist l used a microscope to study a thin slice of cork from the bark of an oak tree l named the box-like structures “cells” l saw only dead cells

Hooke’s microscope

Anton van Leeuwenhoek (1600 s) l Dutch businessman; his single-lens microscope magnified objects 200 X and allowed him to see tiny organisms in a drop of water (animalcules)

Robert Brown (1831) l Scottish botanist; used newly developed stains; first to describe the cell nucleus

Matthias Schleiden (1838) l German botanist; concluded that all plants are made up of cells

Theodor Schwann (1839) l German scientist; concluded that all animals are made up of cells

Rudolf Virchow (1855) l German physician; studied cell reproduction l “Where a cell exists, there must have been a preexisting cell…”

Cell Theory l All living things are made up of cells (organisms are either unicellular or multicellular) l Cells are the basic units of structure and function in living things l All cells arise from preexisting cells

2 Main Types of Cells Prokaryotic cells Monera (bacteria) 1/10 th the size of eukaryotic cells no nucleus

Prokaryotic cell

Eukaryotic cells Found in protists, plants, fungi, and animals have a true nucleus containing chromosomes contain several membrane bound organelles cells are 10 -100 um in length

Parts of the Eukaryotic Cell

Cell Organelles l “little organs” l specialized parts of the cell which carry out specific life functions

A. Plasma (Cell) Membrane l separates cell from surrounding environment l controls the movement of molecules into or out of the cell l selectively permeable (semi-permeable) l visible with the compound microscope

Fluid Mosaic Model of Membrane Structure flexible structure with freely moving pieces l composed mainly of lipids and proteins l http: //home. earthlink. net/~shalpine/ani m/Life/memb. htm l

l proteins extend through the membrane or are found on the outer/inner surface (transport proteins) l other proteins act as receptors for hormones or chemicals, are involved in cell-cell communication, or join one cell to another

B. Cytoplasm watery material between the cell membrane and the nucleus l suspends organelles l site of chemical reactions l

C. Nucleus contains DNA on structures called chromosomes l surrounded by a nuclear membrane that has pores (selectively permeable) l visible under the compound light microscope l

Nucleus

D. Nucleolus l site of ribosome synthesis l located within the nucleus

E. Ribosomes l site of protein synthesis l some ribosomes are found in the cytoplasm l other ribosomes are attached to the outside of an organelle called the endoplasmic reticulum (ER)

F. Endoplasmic Reticulum l network of channels for carrying substances from one part of the cell to another

There are two types of endoplasmic reticulum (ER) l Rough ER is dotted with ribosomes

l smooth ER lacks ribosomes

G. Golgi apparatus

l stacks of membranes forming flattened sacs l process, package, store cell products to be secreted (transported out of the cell) http: //www. johnkyrk. com/golgi. Alone. html http: //student. ccbcmd. edu/~gkaiser/biotutori als/eustruct/endomembanim. html

H. Lysosomes l “breakdown body” l sac of digestive enzymes l digest organic molecules, worn-out cell structures, harmful bacteria

I. Vacuoles l variety of functions: 1) food vacuoles 2) contractile vacuoles in freshwater protists pump out excess water 3) plant cells have a large central vacuole for water and nutrient storage

J. Mitochondria (Mitochondrion) “powerhouse of the cell” l site of cellular respiration: glucose + oxygen is converted to energy in the form of ATP l each cell contains between 300 -800 mitochondria depending on activity level l

l although most of a cell's DNA is contained in the cell nucleus, mitochondria have their own DNA

Endosymbiotic Theory l mitochondria are descended from independent prokaryotes that were engulfed by other cells but not digested l the mitochondria gave the cell that engulfed it a selective advantage over other cells

K. Chloroplasts l found in plants, algae l contain chlorophyll, a green pigment that absorbs light to start photosynthesis

Chloroplasts

Chloroplasts l contain their own DNA l chloroplasts are also part of the endosymbiotic theory

L. Centrioles l found in pairs near cell nucleus l involved in cell division l found in animal cells but not plant cells

M. Cell Wall l found in plant cells only l made of cellulose l provides protection & structure for the cell; prevents expansion

l http: //www. cellsalive. com/cells/cell_mod el. htm