Structure

Of

The

Cell

Cell History Robert Hooke is credited with the discovery of the

cell. (1665)

Leeuwenhoek: ( About 1700) He developed microscopes and glasses. He was the first to look at microscopic life. He looked at ditch water and discovered “amimalicules”.

Schleinden: Concluded all plants are made out of cells. (Late 1830’s)

Schwann: Concluded all animals are made out of cells. (Late 1830’s)

This led to the…………………..

The Cell Theory

1. ALL LIVING THINGS ARE MADE OUT OF CELLS.

2. CELLS ARE THE BASIC UNIT OF STRUCTURE AND FUNCTION IN AN ORGANISM.

3. CELLS COME ONLY FROM PRE-EXISTING CELLS.

Francesco RediAt the time, prevailing wisdom was that maggots formed naturally from rotting meat. In the experiment, Redi took three jars and put meat in each. He tightly sealed one, left one open, and covered the top of another with gauze. He waited for serveral days, and saw that maggots appeared on the meat in the open jar, but not in the sealed one, and maggots did not hatch on the gauze covered jar.

What is a Cell?

• The smallest unit that can carry out all the functions necessary to define life.– Storing and releasing energy.– Building and repairing cell parts.– Obtaining nutrients.– Expelling wastes.– Responding to the environment.– Reproducing.

Types of Cells• Prokaryotic Cells: The most ancient life

form on Earth. They have been in existence for at least 3.5 billion years. These cells lack a true nucleus, and contain a single circle of DNA called a plasmid. Bacteria are prokaryotic cells.

• Eukaryotic Cells: A large, complex cell that contains a membrane bound nucleus. This nucleus houses chromosomes, the “blueprints” for life.

PROKARYOTIC CELLS

EUKARYOTIC CELLS

Common Characteristics of Cells

• Both prokaryotic and eukaryotic cells have a cell membrane.

• The interior of both types of cells is mainly composed of a fluid environment called cytoplasm.

• Both types of cells contain ribosomes, which are responsible for building proteins.

Eukaryotic Cell Organelles

• The cytoplasm of eukaryotic cells have various structures suspended within them.

• The CYTOSOL is the aqueous (liquid) space within the cytoplasm.

• Many types of cell ORGANELLES are suspended within the cytoplasm, each with a unique function.

Cell Membrane

• A thin, flexible envelope that surrounds the cell.

• Found in all true cells.• Controls boundaries for the cell, maintains

homeostasis and movement of material in and out of a cell.

• Contains pores.

More About Cell Membranes

• Three Types of membranes.

– Permeable: Everything enters.– Non-permeable: Nothing enters.– Semi-permeable: Selective entrance/exit of

materials.

Cytoplasm

• A constantly moving jelly-like fluid that lies between the cell nucleus and the cell membrane. All the organelles are suspended within this medium.

Nucleus• The “brain” of the cell. Controls all cell

activities.• Contains nucleic acids.

– DNA: Stores information needed to make proteins for cell growth and repair and the genetic blueprints for reproduction.

– RNA: “Reads” DNA codes and guides the protein making process. RNA is able to leave the nucleus.

Nuclear Membrane

• The structure/border that separates the nucleus from the cytoplasm and other organelles suspended within the cytoplasm.

Chromosomes

• A cell organelle composed of tightly coiled DNA wound around a protein core.

• Chromosomes are threadlike in shape.• They carry the genetic blueprints within the

nucleus.

Nucleolus

• Called the “Little Nucleus” housed within the nucleus.

• The nucleolus contains and makes the RNA that functions as the cell messengers of protein construction.

Endoplasmic Reticulum• Tubular passages that lead out from the

nuclear membrane.• Studded with ribosomes.• Transports proteins to various parts of the

cell.• May also connect to the cell membrane.

Ribosomes

• Active in protein synthesis.• Made up of “special” RNA.

– rRNA– tRNA– mRNA

• Generally found attached to the Endoplasmic Reticulum, but some are found floating within the cytoplasm.

Golgi Bodies

• Assists in further processing proteins.• Packs proteins into vesicles.• Makes the lysosomes.

Lysosome

• Contains digestive enzymes.• Breaks down large food particles into

useable portions for the mitochondria.• Much more prominent in animal cells than

plant cells.

Mitochondria

• Rod-shaped structures called the “powerhouse” for the cell.

• Breaks down sugar (glucose) to release energy for life functions.

• The more active a cell is, the more mitochondria they have.

Vacuoles

• Large, spherical, water filled sacs that store food and wastes.

• Small and few in animal cells.• Large and prominent in plant cells.

Centrioles

• Present during cell reproduction.• Duplicates during cell reproduction.• Helps to “pull” the cell apart during cell

division.

Microtubules

• The cell “skeleton”.• Provides a support system for the cell.• Composed of tubes of protein.

Cell Wall

• Found only in plant cells.• A rigid wall of cellulose and protein that

surrounds the cell membrane.• Strengthens and supports plant cells.• Gives cells and more box-like shape.

Chloroplasts

• Found within plant cells.• Contains the green pigment chlorophyll.• Sites of photosynthetic activity.

Cilia or Flagella

• Hair-like projections.• Aids in cell movement.

– Undulating– Whip-like– Oar fashion.