Transcript Plasma Membrane

Biology Chapter 7
Cells
Section 7.2:
Plasma Membrane
Plasma Membrane
• Survival of a cell depends on its ability to
maintain the proper condition within itself
• Function of plasma membrane– Allow needed supplies into the cell
• ie. Sugar, lipids, amino acids etc
– If too much is let in, it must also be able to
remove it
• This is called “Homeostasis”
– Maintaining the cells internal environment
Homeostasis continued
• Selective permeability– One way cells maintain homeostasis
– Plasma membrane allows some molecules in but
keeps other molecules out
• Think of your screens on your windows at home…
Structure of plasma membrane
• Recall that lipids are “fats” and are insoluble in
water (don’t dissolve)
• Plasma membrane is made of a phospholipid
bilayer (two layers)
– Phospholipids are fats with phosphate groups
attached to them
– Made of fatty acid tails (water insoluble) and
phosphate groups heads (water soluble)
Phospholipid bilayer
Phospholipid bilayer
• The polar (water soluble) heads face out
• The non-polar (water insoluble) tails face in
• This allows water soluble materials to move
through membrane but molecules that are not
soluble don’t pass through
• This model of the plasma membrane if called
the “Fluid Mosaic” model
Fluid Mosaic Model
• The phospholipids flow like water (fluid)
• The proteins move throughout the
phospholipids like boats.
– They make up the “Mosaic”
Other components of membrane
• cholesterol- stabilizes the phospholipids
• Transport proteins- allow larger substances to
move through the membrane
• Other proteins help cells identify one another
– This is important in disease control
7.3 Eukaryotic Cell Structure
• Eukaryotic cells have many small structures
inside them that each play a vital role in the
survival of the cell. They are called organelles.
• Cell wall- Rigid structure located outside the
plasma membrane.
– Provides support
– Found in plant cells but not animal cells
Organelles
• Nucleus- control center of the cell
– Contains DNA which makes up chromosomes
• Is the blueprint of the cell
– Chromatin- strands of DNA that make up
chromosomes
– Nucleolus- makes ribosomes
• Ribosomes- site of protein synthesis
• Cytoplasm- clear liquid that fills up the cell
Organelles
• Endoplasmic reticulum (ER)- site of chemical
and cellular reactions.
– Has many folds giving it much surface area for
reactions to take place
– Ribosomes attached to ER make it “rough” ER
– Without ribosomes attached, it is “smooth” ER
Organelles
• Golgi apparatus- flat tubular membrane used
to package and store proteins
– Acts like the shipping dept. of a business
• Vacuoles- used for temporary storage
– Often store food, enzymes or waste products
• Plant cells have very large water vacuoles
compared to animal cells
Organelles
• Lysosomes- have digestive enzymes in them.
– They eliminate worn out organelles or bacteria
that need to be removed from the cell
• The membrane around the lysosome protects
the cell from the digestive enzymes inside
• Chloroplasts- found in plant cells
– Site of photosynthesis
– Contain chlorophyll
• Traps light energy so plant can make food
Organelles
• Mitochondria- powerhouse of the cell
– Site of cellular respiration
– Produce ATP
– Has many folds to increase surface area for
chemical reaction
• ie sugar + Oxygen = carbon dioxide + water + ATP
• Cytoskeleton- made of rods and filaments that
give structural support to the cell
Other structures
• Microtubules- thin, hollow tubes made of
protein
• Microfilaments- thin solid protein fibers
• Make up cytoskeleton and also found in
flagella and cillia
• Flagella- long hair-like projections used for
locomotion in some cells
• Cilia- shorter hairs used for locomotion
Animal cell