Cells and their structure

the smallest unit of life

• 1) All organisms are composed of cells.  
• 2) The cell is the basic living unit of life.  
• 3) All cells arise from pre existing cells.

• All cells have:  
• 1) cytoplasm - jelly like fluid and subcellular components 
• 2) plasma membrane
• 3) concentrated genetic material

• Prokaryote 
• cells have their genetic material concentrated in a region of the cytoplasm. There is no formal nucleus.

• Eukaryote
• cells that have their genetic material separated from the cytoplasm by a membrane called the nuclear envelope.

Most cells are eukaryotes.

• 3 kinds
• 1. Plasma membrane- surrounds cytoplasm
• 2. Nuclear envelope- surrounds nucleus
• 3. Organelle membranes- surround organelles

Sub cellular structures that perform specific jobs.

• 1) selectively permeable
• - Some substances may pass through the membrane while others cannot.

2) Cell protection

• Membrane consists of:     
• - Two layers of phospholipids called a bilayer.

• Glycerol heads face outward  (hydrophyllic)
• Fatty acid tails face inward  (hydrophobic)

• What can pass through the phospholipid bilayer?
• - Water
• - Oxygen and carbon dioxide
• - Small, neutral molecules

• What cannot pass through?
• - Large molecules or compounds
• - Ions or charged particles

Proteins can be found in the lipid bilayer.

• Jobs of these proteins include:    
• - Transport    
• - Communication    
• - Identity markers    
• - Energy transfer

• 1. Diffusion     
• Movement of particles from a high to a low concentration.
• This movement is caused by particle collision.             

Example - crowded elevator

• 1a. osmosis
• The movement of water from a high concentration to a low concentration across a membrane.    
• - Osmosis is diffusion of water.    
• - Water can move across the membrane.

• Solution - defined as water and solutes  
• Solutes - stuff other than water 
• Solutes may not be able to move across the membrane.

To determine which way water will move, we compare the concentration of solutes on the inside and the outside of the cell.

Solutes can be compared using three terms. We are always comparing the inside of the cell to the outside of the cell.

• Isotonic 
• Solutes are equal.  Solute concentration inside the cell is the same as solute concentration outside of the cell.  Water moves into the cell at the same rate as out of the cell.

• Hypertonic
• Hypertonic means more solutes.Solutes are greater on one side of the membrane than the other.
• A hypertonic solution means it has more solutes than the cell.

• - The imbalance of solutes results in more water inside the cell than outside.      
• - The water will move from a high concentration to a lower concentration. 
• 

• Hypotonic      
• - Hypotonic means less solutes      
• - There are less solutes on one side of the membrane than the other.     
• - A hypotonic solution has less solutes than the inside of the cell. 
• 

• Summary
• 

The movement of particles from a high concentration to a low concentration only through special proteins.

• - Movement of particles from a low concentration to a high   concentration against the concentration gradient.
• - This requires an INPUT OF ENERGY.     

Where does the energy come from?  ATP

• 1. Exocytosis     
• Movement of material from inside the cell to outside the cell.

• 2. Endocytosis    
• Bringing materials into the cell.

Two types

• 2a. Phagocytosis  
• Engulfing of large solid particles to bring into the cell.

• 2b. Pinocytosis 
• Bringing fluid/liquid materials into the cell.

Exocytosis and endocytosis require energy.

•   3 regions of a cell                  
• 1) Cytoplasm                  
• 2) Cytoskeleton                  
• 3) Nucleus

1. Endoplasmic reticulum-ER     

• 2 types 
• - Smooth ER 
• - Rough ER

• 1a. Smooth ER
• Jobs- lipid synthesis and material transport

• 1b. Rough ER      
• - Ribosomes are present on the surface.
• - Job is to transport materials.

• 2. Ribosomes     
• Job- Protein synthesis
• *note, dots on rough ER above represent ribosomes 

• 3. Golgi Body  
• Job is to package materials and/or makes lysosomes

• 4. Lysosomes   
• Vesicle that contains digestive enzymes   
• Enzymes break down "old" cells and recycle their materials

• 5. Mitochondrion
• Called the powerhouse of the cell.  Changes the energy in glucose bonds to usable energy of ATP.

• 1. Plastid
• - Commonly called a chloroplast
• - Photosynthesis occurs here.

• 2. Vacuole  
• large vesicle that houses water, wastes or nutrients.

• 3. Cell wall•     
• - Found only in plant cells      
• - Composed of the carbohydrate cellulose

• 1. Centrosome     
• Job is to separate duplicated chromsomes during cell division.

• Cytoskeletal structures
• Cytoskeletal structures give shape to the cell.

•  Microtubules  
• Hollow cylinders of a protein called tubulin

• Organelles with microtubules
• 1) Flagellum
• - Long whiplike structures1 or 2 per cellHuman sperm have a single flagellum

• 2) cilia
• - Short appendages, many per cell.Nasal passages and trachea have cilia.

Connections between plant or animal cells

• Plasmodesmata
• cell connection between plant cells

• Gap junction  
• one type of cell connection between animal cells

• Nuclear envelope 
• Has openings or nuclear pores for large items to pass through.

• Organelles/structures inside nucleus  
• 1) Nucleolus- Makes ribosomes
• 2) Two terms for our genetic material
• Chromosomes- DNA and protein that is tightly coiled and ready for cell division. Chromosomes are visible with a microscope.
• Chromatin- DNA and protein that is thin and not visible with a microscope.