3.1 The Cellular Level of Organization

3.1 The Cellular Level of Organization

• The cell is the structural and functional unit of an organism, the smallest structure capable of performing all the functions necessary for life.

3.1 The Cellular Level of Organization

• Prokaryotic cells lack membrane enclosed structures.

• Eukaryotic cells possess membrane enclosed structures.

The Cell Theory

• All organisms are composed of one or more cells.

• Cells are the basic living unit of structure and function in organisms.

• All cells come only from other cells.

Sizes of Living Things

Surface Area / Volume Ratio

• The amount of surface area affects the ability to get materials in and out of a cell.

• A cells increase in volume, the proportionate amount of surface area decreases.

Surface Area / Volume Ratio

Plasma Membrane and Cytoplasm

• All cells are surrounded by a plasma membrane.

• The material inside of a cell is the cytoplasm.

• The plasma membrane regulates what enters and exits a cell.

3.2 Prokaryotic Cells

3.2 Prokaryotic Cells

• Cell Wall

• Capsule

• Flagellum

• Nucleoid

• Ribosomes

Prokaryotes are:

• Structurally simple

• Metabolically diverse

• Adapted to most types of environments

3.2 Prokaryotic Cells

3.3 Eukaryotic Cells

• Eukaryotic cells:

– Are structurally complex

– Have a nucleus

– Possess membrane-bound organelles

– May have a cell wall

3.3 Eukaryotic Cells

3.3 Eukaryotic Cells

The Nucleus

• Stores DNA

The Nucleus

• Stores DNA• Nucleolus - rRNA• Nuclear Envelope

– Nuclear pores

Ribosomes

• Site of protein synthesis

• Two subunits (large and small)– Subunits consist of rRNA and protein molecules

• Polyribosomes– Several ribosomes with a single mRNA molecule

Endoplasmic Reticulum

• Consists of membranous channels and saccules

Endoplasmic Reticulum

• Rough ER– Processing and

modification of proteins

• Smooth ER– Synthesizes

phospholipids– Various other

functions

Golgi Apparatus

• The Golgi apparatus collects, sorts, packages, and distributes materials such as proteins and lipids.

Lysosomes

• Lysosomes contain digestive enzymes that break down unwanted, foreign substances or worn- out parts of cells

Vacuoles

• Vacuoles are membranous sacs that store substances.– For example:

Water

Pigments

Toxins

Peroxisomes

• Membrane bound vesicles containing enzymes.

– The enzymes break down molecules and as a result produce hydrogen peroxide.

Energy-Related Organelles

• Chloroplasts

• Mitochondria

Energy-Related Organelles

Photosynthesis Cellular Respiration

Chloroplasts

• Site of photosynthesis

• Structure:– Double-membrane– Stroma– Grana

• Thylakoids

• Chloroplasts contain:– Their own DNA– Ribosomes– Enzymes

Mitochondria

• Found in all eukaryotic cells

• Site or cellular respiration

• Structure:– Double-membrane– Matrix– Crista

The Cytoskeleton

• Maintains cell shape

• Assists in movement of cell and organelles

• Assemble and disassemble as needed

• Three types of macromolecular fibers

– Actin Filaments

– Intermediate Filaments

– Microtubules

Actin Filaments

• Anchored to the plasma membrane• Allows intestinal microvilli to expand and contract• Found in pseudopods allowing amoeboid movement• Play a role in animal cell division

Actin Filaments

• Actin interacts with motor molecules such as myosin.• In the presence of ATP, myosin pulls actin along• Example: muscle cells

Intermediate Filaments

• Intermediate in size between actin filaments and microtubules

• Functions:– Support nuclear envelope

– Cell-cell junctions, such as those holding skin cells tightly together

Microtubules

• Hollow cylinders made of two globular proteins• Assembly:

– Under control of Microtubule Organizing Center (MTOC)– Most important MTOC is centrosome

• Interacts with specific proteins to cause movement of organelles

Microtubule Operation

Centrioles

• Short cylinders with a 9 + 0 pattern of microtubule triplets

Centrioles

• Help organize microtubules during animal cell division• May be involved with microtubule formation and in the

organization of cilia and flagella

Cilia and Flagella

• Hairlike projections that aid in cell movement

• In eukaryotic cells, cilia are much shorter than flagella

• They are membrane-bound cylinders enclosing a matrix area– The matrix consists of microtubules in a 9 + 2 pattern

Cilia and Flagella

3.4 Evolution of the Eukaryotic Cell