Cell Theory

CELLS All living organisms are composed of one or more cells. The cell is the basic unit of structure and organization in organisms. Cells arise from pre- existing cells.

Studying Cells Throughout History Robert Hooke: In 1665, he first described ‘cells’ as box-like structures when he viewed cork through a microscope to look at cork slices – observed cell walls of the individual cells

Robert Brown and Antonie van Leeuwanhoek: observed and named the nucleus of the cell Spherical “control center” of the cell Surrounded by a nuclear membrane with pores Contains cell’s DNA, its genetic material The nucleus and ribosomes work together in the cell to synthesize the production of proteins

Felix Dujardin: observed and identified cytoplasm Cytoplasm: The gel-like substance found throughout the interior of the cell It holds all of the organelles in place Molecules like sugar, water, oxygen can move through it

Components of Cells All cells share four common components: a plasma membrane: an outer covering that separates the cell’s interior from its surrounding environment, controls the passage of organic molecules, ions, water, and oxygen into and out of the cell, wastes also leave the cell by passing through the membrane. cytoplasm: a gel-like matrix within the cell in which other cellular components are found DNA: the genetic material of the cell ribosomes: where protein synthesis occurs

Prokaryotic Cells Prokaryotes organisms are divided into two domains: Archaea and Bacteria Pro = before Karyon = kernel; referring to the nucleus Prokaryotic Cells lack a nucleus and, instead, possess a “nucleoid region” where a single chromosome is found (a coiled loop of DNA)

Prokaryotic Cells Cell Wall: composed of peptidoglycan, the cell wall acts as an extra layer of protection from the often harsh environment that they live in, helps to maintain the shape of the cell, and prevents dehydration by holding in water Capsule: the polysaccharide capsule allows the cell to attach to surfaces in its environment Flagella: a whip-like tail used in locomotion Fimbriae: fine, hair-like extensions which are used for attachment to surfaces Pili: extensions that are used in the transfer or exchange of DNA during a process called conjugation (mixture of DNA between two prokaryotes to create new, unique individuals)

Eukaryotic Cells A third domain, Eukarya, contains all organisms that are composed of eukaryotic cells Eu = true Karyon = kernal (true nucleus) Eukaryotes possess a true nucleus which houses and protects the cell’s DNA which form chromosomes Nucleus is also the control center of the cell as it controls the cell’s activities through gene expression

Eukaryotic Cells Mitochondria: they are responsible for making adenosine triphosphate (ATP), an energy-carrying molecule through cellular respiration Endoplasmic Reticulum: modifies proteins and synthesizes lipids Golgi Body: where the sorting, tagging, packaging, and distribution of lipids and proteins takes place Vesicles and Vacuoles: membrane-bound sacs that function in storage and transport

Plant Cells Mathias Schleiden – determined that all plants are made of plant cells

Animal Cells Theodore Schwann – determined that all animals are made of animal cells

Plant Cells cell walls: a rigid outer covering composed of cellulose for protection and shape Chloroplasts: carry out photosynthesis Central Vacuole: regulates the cell’s water concentration and is responsible for digestive processes Animal Cells lysosomes: responsible for the cell’s digestive process (i.e. garbage disposal) centrioles: aid in mitosis by pulling the duplicated chromosomes to opposite ends of the dividing cell