Chapter 4 The Structure and Function of the Cell

4-1: Introduction to the Cell Everything is made of elements Living things organize elements into structures called cells Cell: smallest unit of matter that can carry on all processes of life

Discovery of Cell Made possible by development of microscope in early 17 th century 1665: Robert Hooke –Looked at thin slice of cork –“a great many little boxes” –Formation: like small rooms monks lived in, cells –Really looked at DEAD plant cells

Anton van Leeuwenhoek First to observe living cells 1673: used simple microscope to observe simple microscopic organisms

Matthias Schleiden Botanist 1838 Concluded all plants are composed of cells

Theodor Schwann Zoologist 1839 Concluded all animals are composed of cells

Rudolf Virchow Physician studying how disease affects living things 1855 Reasoned cells come only from other cells

Cell Theory 150 years after observations of Hooke and Van Leeuwenhoek 1.All living things composed of cells 2.Cells are the basic units of structures and function in an organism 3.Cell come only from reproduction of existing cells

Cell Diversity Not every cell is alike Human body has 200+ different kinds of cells Cells differ in... –Size –Shape –Internal organization

Cell Size Some cells can be seen without microscope Most cells only visible with microscope Limited in size by ratio between surface area and volume Oxygen, nutrients, and other materials enter though surface

Surface Area: Volume SA:V

Cell Shape Form reflect functions Long nerve extensions  transmit impulses Flat skin cell  cover body White blood cell change shape  move throughout body

Internal Organization Organelle- “little organ”; cell component that performs specific functions for the cell Maintain life of cell

Cell membrane Thin membrane that surrounds cell Encase variety of organelles that each have own membrane surrounding them

Nucleus Large organelle near center of cell Contains majority of cell’s genetic information Directs most of cell’s activities

Eukaryote vs. Prokaryote Eukaryote Has membrane bound nucleus and other organelles Prokaryote NO membrane bound nucleus –Genetic information may be concentrated in ONE general area but NOT bound by membrane

4-2 Parts of the Eukaryotic Cell

Components No two eukaryotic cells alike FORM determined by FUNCTION Cell membrane Nucleus Organelles

Cell Membrane All cells must take in nutrients and release waste Anything in/out of cell must pass through cell membrane Selectively permeable: some substance cross membrane easily, others more difficult to pass

Cell membrane structure Structure depends on function Some secrete materials Others recognize harmful invaders Components: –Lipids –Proteins

Membrane lipids PHOSPHOLIPIDS!!!!! Polar “head” = hydroPHILLIC –Orients towards water Nonpolar “tail” – hydroPHOBIC –Orients away from water

BILAYER!!!!! Water is both INSIDE and OUTSIDE of cell Must be TWO layers of phospholipids  PHOSPHOLIPID BILAYER!

Membrane Steroids (also lipid) Steroid molecules fit between tails of phospholipids Major membrane steroid in animals : Cholesterol

Membrane Proteins Types: –Peripheral –Integral

Peripheral Membrane Proteins Located on interior AND exterior surfaces of cell membrane Weak bonds link them to membrane lipids or other proteins embedded in membrane

Integral Membrane Proteins Embedded in cell membrane Extend across entire cell membrane OR partially in/out of membrane

Some have Carbohydrates attached –Hold adjoining cells together –Act as sites where viruses or chemical messengers (hormones) attach

Due to cell selective permeability…MUST have ways to transport things through membrane Membrane proteins do so! Integral proteins can act as channel or pore

Fluid Mosaic Model Scientist used to think cell membrane was fixed in place Advances in technology (SEM)  cell membrane act more like fluid than solid

Fluidity  proteins can move laterally within bilayer THUS! The pattern or “mosaic” or proteins is constantly changing

Cytoplasm Contains various organelles Between cell membrane an nucleus Makes up most of cell

Cytosol What organelles exist in Gelatin-like aqueous fluid Contain dissolved salts, minerals, and organic molecules

4-3 Multicellular Organization

Big Ideas In unicellular organism: All functions of life carried out by the ONE cell In multicellular organism: most cells specialized to carry out specific functions THUS! cells depend on other cells to survive

Organization Cells  Tissues  Organ  Organ system  Organism

Tissues Groups of cells that carry out specific functions Different types of tissues perform different types of tasks Ex: Epithelial: cover body Muscle: Pull against one another

Organs Several types of tissue that interact to perform a specific function Ex: Stomach –Epithelial- absorb nutrients –Muscles- move/contract stomach –Connective- hold stomach together –Nerve- transmits message to/from brain

Organ System Made up of group of organs that work together to perform a set of related tasks Ex: Respiratory system, Digestive system, Nervous system

Different organ system interact to carry out all processes of life Not one of the body’s organ systems can survive without the rest

In Plants... Have tissues in organs arranged differently than in animals Tissues: –Dermal tissue forms outer layer in plant –Vascular tissue system transports water throughout plant Organs: –flowers, roots, stems, leaves

Evolution of Multicellular Organization Fossil evidence  earliest cells were simple prokaryotes Due to limited resources, cells began to compete Adaptations evolved  some eukaryotes

Colonial Organizations Prokaryotes living in groups with other cells of the same kind and carrying out specific functions A collection of genetically identical cells that live together in a closely connected group

Volvox Green alga Hollow Volvox sphere contains 500–60,000 cells Each cell can maintain its own individual existence

Many cells carry out specific functions that benefit entire colony Certain cells: –along outside use flagella to propel sphere though water –specialize in reproduction to produce large offspring colonies

Colonial Organisms and Evolution Colonial organisms lack tissues and organs but have cell specialization Scientists believe that animals plants and fungi evolved from similar colonial organisms As cells became more specialized they became less capable of living independently