The Cellular Level of
Organization
Cell Diversity
• Lots of shapes and sizes; we have about 200
different types of specialized cells
Typical Cell
Fig. 3.1
What discipline studies cells?
Cell biology
(Cytology)
http://www.youtube.com/watch?v=tkx14B7WFcM
What is around our cells?
Our cells are surrounded by extracellular fluid
frequently called interstitial fluid
Cell Organization
The cell includes three basic parts:
1. Plasma membrane (outer covering of
cell)
2. Cytoplasm (cytosol & organelles)
3. Nucleus
Plasma Membrane Functions
Outer boundary; functions in:
1. Physical isolation
2. Regulates what comes in and out
3. Anchors cytoskeleton (think of this as
scaffolding)
Cell Membrane Structures
The cell membrane contains:
1. Two layers of phospholipids (isolate the
cell from extracellular fluid)
2. Proteins (may attach cell membrane to
other structures, recognize invaders,
speed up chemical reactions, bind &
transport certain substances)
3. Cholesterol (↑ stability of cell
membrane)
Cell Membrane
Selective Permeability
= not all material can enter the cell
Transport processes found in cells:
• PASSIVE: simple diffusion & facilitated
diffusion
• ACTIVE: active transport & transport in
vesicles
Active = requires E; from low to high concentration
Passive = does not require E; from high to low
concentration
Osmosis
– simple
diffusion
of water
Fig. 3.8
Facilitated diffusion or Active
transport - Fig. 3.10 – 3.11
Vesicular Transport
(endocytosis & exocytosis)
Fig. 3.12 – 3.14
Cytoplasm
2 parts:
1. Cytosol = fluid portion, also called
intracellular fluid; contains dissolved
nutrients, ions, proteins, and waste
products
2. Organelles = cell “organs” or functional
parts
Cytoskeleton
• Gives the cytoplasm strength & flexibility
Microfilaments
Microvilli
• ↑ the surface area for absorption of
material
Centrioles
• Direct the movement of chromosomes
during cell division
Cilia & Flagella
• Cilia beat rhythmically to move fluids
across cell surface
• Flagella move cells
Ribosomes
• Sites of protein synthesis
• Attached to ER or free in the cytosol
Endoplasmic Reticulum (ER)
1. Rough – contains
ribosomes; chemically
modifies newly made
proteins and ships
them to the Golgi
apparatus
2. Smooth – no
ribosomes; synthesis
of lipids, detoxifies
certain drugs
Golgi Apparatus
•Involved in packaging of proteins and
production of lysosomes
Lysosomes, Peroxisomes &
Proteasomes
• Vesicles filled with digestive enzymes
• Lysosomes recycle worn out cell
structures
• Peroxisomes neutralize toxins such as
alcohol and hydrogen peroxide (abundant
in liver)
• Proteasomes destroy unneeded and
damaged proteins
Lysosomes & Peroxisomes
Blue arrows = peroxisomes Red arrow = lysosome
Mitochondria
• Produce adenosine triphosphate (ATP) =
our energy currency
Nucleus
• Control center of cell
• Contains DNA needed for synthesis of
100,000 different proteins
Red blood cells of
humans do not
have a nucleus;
Skeletal muscle
cells have multiple
nuclei