Cell Structure & Function

Chapter 7

The Discovery of the Cell

• Without a tool to make them visible cells were until the invention of the microscope

• 1665 - Robert Hooke used an early microscope to look at cork cells.

• About the same time Anton van Leeuwenhoek observed tiny organisms in pond water. http://www.youtube.com/watch?v=wzI2RrBYZ5U

Early Discoveries

• 1838 - Matthias Schleiden a German botanist concluded that all plants are made of cells.

• 1839 - Theodor Schwann a German biologist stated that all animals are made of cells.

• 1855 - Rudolf Virchow a German physician concluded that new cells can only be produced by division of existing cells

Cell Theory

• All living things are made up of cells.

• Cells are the basic units of structure and function in all living things.

• New cells are produced from existing cells through cell division.

How do microscopes work?

• Most use lenses to magnify the image of an object by focusing light or electrons.

• Types of microscopes:– Light microscopes – images 1 millionth of m– Electron microscopes – images 1billionth of m

• TEM – transmission – thin samples, can see cell structures & molecules

• SEM – scanning – 3-D surface images

Light Microscope image

SEM Images

TEM Images

Examples of Cells

Amoeba Proteus

Plant Stem

Red Blood Cell

Nerve Cell

Bacteria

As you can see cells come in many sizes and shapes

All cells have some similarities:

• At some point they contain DNA

• All cells are surrounded by a thin flexible barrier called a cell membrane or plasma membrane.

But they also have differences and so are seperated into 2 broad groups:

Eukaryotes and Prokaryotes

Prokaryotic

• Do not have structures surrounded by membranes

• Do not separate DNA within a nucleus

• One-celled organisms, Bacteria

Eukaryotic• Contain organelles, specialized structures that perform specific

functions; surrounded by membranes• Nucleus separates DNA from the rest of the cell• Most living organisms, great variety

Plant Animal

http://library.thinkquest.org/C004535/eukaryotic_cells.html

What do these cells haveIn common?

“Typical” Animal Cell

http://web.jjay.cuny.edu/~acarpi/NSC/images/cell.gif

http://waynesword.palomar.edu/images/plant3.gif

“Typical” Plant Cell

Cell Parts

Organelles

Inside the CellTwo major parts

Cytoplasm

• Gel-like mixture also called cytosol

• Portion outside the nucleus

• Surrounded by cell membrane

• Contains organelles of eukaryotes – specialized structures that perform specific tasks

Nucleus • Directs cell activities

• Separated from cytoplasm by nuclear membrane

• Contains genetic material – DNA – which contains coded information to make proteins

• Prokaryote cells lack a nucleus but they do contain DNA

Nuclear Membrane

• Surrounds nucleus• Made of two layers• Openings called

nuclear pores allow material to enter and leave nucleus

• Also called the nuclear envelope

http://library.thinkquest.org/12413/structures.html

Chromosomes

• In nucleus• Made of DNA• Contain instructions

for traits & characteristics

• Usually in the form of long thin threads called chromatin

http://library.thinkquest.org/12413/structures.html

Nucleolus

• Small dense region inside nucleus

• Involved in the assembly of organelles called ribosomes

http://library.thinkquest.org/12413/structures.html

Vacuoles

• Membrane-bound sacs for storage of water, salts, proteins, and carbohydrates

• Plants usually have a large vacuole that helps maintain shape

• Paramecium – contractile vacuole

http://library.thinkquest.org/12413/structures.html

Lysosome• Small organelles filled

with enzymes to digest waste

• Transports digested material to cell membrane for removal

• Also breaks down old organelles no longer needed

http://library.thinkquest.org/12413/structures.html

Cytoskeleton

• Helps maintain cell shape and also in movement.

• Internal network of protein fibers:• Microfilaments • Microtubules

Ribosomes

• Each cell contains thousands

• Make proteins using instructions from DNA

http://library.thinkquest.org/12413/structures.html

Endoplasmic Reticulum• Internal membrane

system where compounds are assembled and transported

• Smooth ER: lacks ribosomes; makes lipids

• Rough ER(pictured): ribosomes embedded in surface; modify proteins made by ribosomes

Golgi Apparatus

• Modifies, sorts, and packages proteins and other materials from the ER for storage in the cell or released outside the cell.

• Bundles proteins in tiny vesicles.

http://library.thinkquest.org/12413/structures.html

Mitochondria

• Convert chemical energy stored in food (glucose) into compounds that are able to be used by cells –ATP

• In humans most all of our mitochondria come from the cytoplasm of the egg cell – so you got yours from your mother.

• They also contain their own DNA!

http://library.thinkquest.org/12413/structures.html

Chloroplast

• Capture energy from sunlight and convert it into food – sugars – that contain chemical energy in a process called photosynthesis.

• Surrounded by two membranes

• Contain pigment called chlorophyll

http://library.thinkquest.org/12413/structures.html

Surrounding the Cell

Cell Membrane

• Outer membrane of cell that controls movement in and out of the cell

• Double layer • Also known as the

plasma membrane

http://library.thinkquest.org/12413/structures.html

Cell Wall

• Most commonly found in plant cells & bacteria

• Supports & protects cells

http://library.thinkquest.org/12413/structures.html