Introduction to Cells

Cell Structure and Function

Cell biology is the study of the structure, function and diversity of cells.

How do cells grow, divide, specialize and differentiate, communicate and interact?

Agenda

What do you need to know about cells?

Cell Stories Project

Cells are the fundamental units of life.

Evolutionary PerspectiveTypes of Cells--Prokaryotes

and EukaryotesCell Structure and

Organization

What do you need to know about cells?

The Tree of Life

The First Cell

Archaea Bacteria

Eukarya

Precursor to the first eukaryotic cell

Prokaryotes

Eukaryotes

(bacteria, mitochondria, and chloroplasts)

(Methanogens, Halophiles,

Sulfolobus, and relatives)

(Protists, Plants,

Fungi, Animals)

10-15 billion years ago:4.5 billion years ago: Origin of the Solar System3.5 to 4 billion years ago: Oldest bacterial fossils2.7 billion years ago: First protists-the earliest

eukaryotic cells.1 billion years ago: First animals (earliest

multicellular organisms) The blastula is the definitive characteristic of animal species.

0.5 billion years ago: First plants and fungi

Archaea

Dr. Carl Woese

Archaea “The archaea are unique organisms. While prokaryotes in the cytological sense, they are actually more closely related to eukaryotes than to the bacteria. They are of particular interest for this reason alone-they are simple organisms whose study should provide insights into the nature and evolution of the eukaryotic cell.”

Our view of life's place of origin may soon shift from that long-favored "warm little pond" to undersea hydrothermal vents.

extremeophiles

BacteriaE. coli is the most common bacterium in the human gut.

Eukarya

Plants

AnimalsFungi

Protists

2.7 billion years ago

Eukaryotes

Protists

Tetrahymena

SEM thanks to Stanley L. Erlandsen, and Dennis E. Feely, authors of "Trophozoite Motility and the Mechanism of Attachment," in Giardia and Giardiasis, Plenum Press, 1984

Giardia

Giardia lacks mitochondia, but contains two nuclei.

Amoeba

Fungi(yeasts, molds

and mushrooms)morels

The Michigan fungus is estimated to be 1500 years old. It covers about 38 acres and weighs about 11,000 kg.

Number of fungal species: about 65,000.

How Cells Work

Plasma Membrane

Cell Structure and Organization

The Nucleus-Composed of two concentric membranes that form the nuclear envelope.

-Contains a nucleolus

-How did the nucleus evolve?

Nuclear pores are sites where the inner and outer membranes of the nuclear envelope are joined.

The nuclear envelope has pores and is continuous with the ER

Ribosomes are produced in the nucleolus. This is where ribosomal RNA is transcribed.

Nuclear Pores

Nuclear pores allow RNA and protein to move in and out of the nucleus.

How does the cell know which proteins are transported into the nucleus?

Nuclear Transport

Proteins targeted for the nucleus have a signal sequence called the nuclear localization signal

Nuclear import receptors bind to the signal sequence and direct it to the pore

Energy from the hydrolysis of GTP is needed to transport proteins into the nucleus

Endoplasmic Reticulum (ER)

Cell membrane components and materials to be exported from the cell are made here.

Transports proteins to be compartmentalized within the cell or exported out of the cell

Ribosomes attached to the ER can recognize a signal sequence on a protein and transport that protein to the ER

Endoplasmic Reticulum (ER)

Figure (modified) from A Textbook of Histology by D Fawcett. Chapman and Hall, N.Y. 1994

Material is transported between the ER and the Golgiin transport vesicles.

George Palade

The Golgi Apparatus

Synthesis and modification of molecules to be secreted from the cell

Directs proteins made in the ER to the correct cellular compartment or to the plasma membrane for secretion

Mitochondria are the energy factories of the cell

Two membranes Maternally

inherited Contain their own

DNA and replicate Related to bacteria How did they

evolve?

Lysosomes are vesicles that degrade cell debris.

Figure (modified) taken from Molecular Biology of the Cell by Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith Roberts, and James D. Watson, Garland Publishing, NY 1994

Chloroplasts

Chloroplasts Composed of internal membranes with

distinct functions Using energy from sunlight, convert

carbon dioxide and water to sugar (photosynthesis)

Contain their own DNA and replicate by dividing

Like bacteria in composition How did they evolve?

Cellular Architecture The cytoskeleton is a fibrous network

within the cytoplasm that maintains cell shape, allows movement of materials within cells and assists in cell motility.

Only eukaryotic cells have a cytoskeleton.

The cytoskeleton consists of three component filaments: microfilaments, microtubules and intermediate filaments.

The Cytoskeleton

Actin filaments are part of the machinery that generates contractile forces (large numbers in muscle cells)

Microtubules help pull duplicated chromosomes apart

Intermediate filaments give the cell mechanical strength and controls shape

Actin Microtubules Intermediate

Cell Structure and

Organization

Cilia and flagella are projections from the cell, made of microtubules.

The Extracellular Matrix

The extracellular matrix is connective tissue that holds the cells of a tissue together. It can be solid, gelatinous or liquid.

Prokaryotes No nucleus (defining characteristic) No organelles No cytoskeleton Single cell organisms Smaller and simpler than eukaryotic

cells

Eucaryotes

Evolution of Mitochondria

Chloroplast Evolution