Cell Structure and Function

• It wasn’t until the 1600s that scientists were able to use microscopes to observe living things.

Cells• In 1665, Robert Hooke observed cork cells under the microscope. He named them cells.

• This is a drawing he made of the cork cells.

• Here is what cork cells look like with a modern microscope with special lighting.

Leeuwenhoek’s Microscope

• Anton Van Leeuwenhoek used a single-lens microscope to view pond water and other things.

• Here is his microscope.

Cell Theory

• It wasn’t long before scientists realized that all living things were made up of cells.

• This discovery brought about the formulation of the cell theory.

The Cell Theory States

1. All organisms are made of cells.

2. Cells are the basic unit of life.

3. New cells are produced from existing cells.

Types of Cells • Cells are classified as prokaryotic or eukaryotic.

• Prokaryotic cells have genetic material that is not inside a nucleus.

• The DNA is located in a region called the nucleoid.

• Eukaryotic cells have genetic material in a “true” nucleus.

• The nucleus has a membrane around it.

A Comparison of Prokaryotic and Eukaryotic Cells

Prokaryotic

• DNA in nucleoid region instead of nucleus.

• Single chromosome• Cytoplasm• Ribosomes• Cell walls• Some have flagella

(locomotion)• May have pili – used for

genetic transfer (conjugation) or attachment.

• Plasmid – other DNA, circular instead of linear

Eukaryotic

• DNA in nucleus• Pairs of chromosomes• Cytoplasm• Ribosomes• Other membrane-

bound organelles (see eukaryotic organelles in this PPT)

• Some have flagella • Some have cell walls

Cell Structures

• Cells contain small structures called organelles.

• Each organelle has a specific task it performs in the cell.

• The cytoskeleton is a network of protein filaments that helps the cell maintain its shape.

• It is also involved in movement.• These protein filaments are

microtubules, intermediate filaments, and microfilaments in eukaryotic cells.

• While eukaryotic and prokaryotic cells both have a cytoskeleton, some of the protein elements are different.

Cytoplasm and Cytosol • The cytoplasm is the

fluid and organelles that are outside the nucleus (all the contents for prokaryotes).

• The liquid portion of the cytoplasm is called cytosol.

• The cytosol is where many chemical reactions occur within the cell.

The Nucleus – Eukaryotic

Cells

• Eukaryotic cells have a nucleus. This is a membrane-bound structure that contains the DNA.

• DNA is the genetic material that is the code for making proteins.

• The nucleolus, also in the nucleus, makes ribosome sub-units.

The Nucleoid – Prokaryotic

Cells • Prokaryotic cells have a nucleoid region. This is the region where the DNA is located, but there is no membrane around the DNA.

• Ribosomes are protein assembly organelles.

• The amino acids are bonded together inside the ribosome.

• Ribosomes can be “free” in the cytoplasm or on the endoplasmic reticulum.

• Both prokaryotes and eukaryotes have ribosomes.

• The endoplasmic reticulum is continuous with the nucleus.

• It is the site where lipids of the eukaryotic cell membrane are assembled, along with proteins and other materials.

• Rough ER has embedded ribosomes.

• Smooth ER does not have ribosomes.

• The golgi apparatus modifies, sorts, and packages proteins and other materials from the ER in eukaryotic cells.

• These materials are then stored or secreted.

Vesicles

•Vesicles are small membrane-bound sacs that serve as “packaging” for some materials in eukaryotic cells.•Some vesicles are made by the ER.

Mitochondria

• The mitochondria is the eukaryotic organelle that converts chemical energy from food into ATP to power cell processes.

• It contains DNA.

Vacuoles

• Vacuoles are storage organelles in eukaryotes.

• They store water, salts, proteins, etc.

• Plants have a large central vacuole that has many storage functions.

Lysosomes • Lysosomes are small eukaryotic organelles that contain enzymes.

• These enzymes catalyze the breakdown of lipids, carbohydrates, and proteins into small molecules that can be used by the cell.

• Lysosomes also remove “junk and clutter” in the cell.

Centrosome and Centrioles

•The centrosome is a small region of cytoplasm that produces microtubules in animal cells. •The centriole is a small structure on the centrosome. There are two of these on each centrosome.•Before an animal cell divides, the centrosome, including the centrioles, doubles and the two new centrosomes move to opposite ends of the cell. •Microtubules grow from each centrosome to form the spindle fibers that are used in animal cell division.

Cell Walls

•Plants, algae, fungi, and most bacteria have a cell wall around the cell membrane. •This rigid layer gives protection, support, and shape to the cell.

• Chloroplasts are organelles that capture sunlight energy and convert it into chemical energy in a process known as photosynthesis.

• Chloroplasts are found in organisms that photosynthesize (plants, algae (protists), and some bacteria). Has its own DNA.

Cell Membrane• The cell or plasma

membrane surrounds the cell and regulates what enters and exits the cell.

• Cell membranes are made of phospholipids and proteins.

• Prokaryotic cells may have more than one cell membrane.

The Phospholipid Bilayer

The Cell Membrane -Phospholipid Molecules

• The phospholipid head is hydrophilic and the fatty acid tail is hydrophobic.

Other Cell Membrane Components

• In addition to phospholipids, there are carbohydrates, cholesterol molecules, and proteins that are in or on the cell membrane.

Cell Membrane Proteins

• Receptors – detects signal molecules and performs an action response.

• Intracellular receptor – receptor inside the cell.

• Membrane receptor – receptor on the membrane.

Cilia and Flagella• Cilia and flagella are used

for movement or to move materials around the cell.

• Cilia are usually shorter and more numerous than flagella. (Eukaryotes)

• Flagella are usually longer than cilia and there is usually just one or two flagella. Eukaryotes and Prokaryotes)

Cilia and Flagella