Cell Structure 1

Only available on StudyMode
  • Download(s) : 59
  • Published : December 16, 2014
Open Document
Text Preview
CELL STRUCTURE I:
CHARACTERISTICS OF 
PROKARYOTES AND 
EUKARYOTES

TERMINOLOGY





molecule ­   cluster of atoms held together by chemical bonds organelle  ­   structure within a cell that performs a specific  function
cell  ­   simplest entity that has all the properties of life;   a  membrane­bounded unit containing  DNA and cytoplasm
tissue  ­  a group of similar cells that carry out a particular  function in an organism
organ  ­  structures composed of more than one tissue type



organ system  ­   related organs performing a  common function



organism   ­   an individual, independent, living entity 




ALL  LIVING  THINGS  SHARE  
KEY  CHARACTERISTICS






Cellular organization - all organisms consist of one
or more cells
Sensitivity - organisms respond to various stimuli in
different ways
Growth - organisms interconvert chemical molecules
(metabolism) and energy released is used to grow
Reproduction - organisms reproduce passing on traits
to new generations
Homeostasis - organisms maintain relatively constant
internal conditions eg pH, different from their environment

Are viruses living or non-living?
• Made up of a core of nucleic acid,
surrounded by a protein sheath (and
sometimes a lipid envelope)
• They lack cell membranes, nucleus and
cell organelles
• Cannot reproduce on their own (require
host cell)
• Do not carry out metabolism
• Not considered as organisms, and are not
considered to be alive

THE  CELL  THEORY
Incorporates the following three
principles:

• all organisms are composed of cells
• the cell is the basic building block of life ­    

chemical reactions of life take place 
within cells
• all cells arise by division of a pre­existing cell

SIZE  OF  CELLS
• Most cells are so small they can't be seen with the naked  •



eye 
Use of microscopes;   light vs electron microscope
Why are multicellular organisms usually composed of 
many small cells rather than a few 
     
large ones?      As an object gets larger it’s volume  increases more rapidly than it’s surface area. 
Cells must maintain a large surface area­to­volume ratio  in order to function

ORGANIZATION  OF  CELLS
Survival of cells is dependent on:

• obtaining and processing energy
• converting the genetic information of DNA into 
protein
• allowing biochemical reactions to occur
• to do the above there are structures within cells.    Among all kinds of cells there are 2 distinct 
general arrangements:
          prokaryotes and  eukaryotes

CHARACTERISTICS  OF  
PROKARYOTES  AND  EUKARYOTES
 prokaryotic cells  ­  lack a nucleus   

• DNA is coiled into a nucleoid (nucleus­like) region    • Because no membrane surrounds the nucleoid region,  •

the DNA is in direct  contact with the cytoplasm    Some prokaryotes have more than one nucleoid

 eukaryotic cells  ­   contain a large, membrane­ bounded nucleus, containing DNA   

• Cell is typically separated into many compartments  •

(organelles), having specialized functions   
Organisms made up of eukaryotic cells are called 
eukaryotes  

CLASSIFICATION  OF  
PROKARYOTES  AND  EUKARYOTES

• All plants, animals, fungi and protists are eukaryotes    • Eubacteria and Archaebacteria are prokaryotes
• Eukaryotic cells are generally  much larger than  prokaryotic cells  

 
animal cell
plant cell
prokaryotic cell

      µm diam.
5­30    
35­80
0.2­2

PROKARYOTIC  CELL  FEATURES

• All prokaryotic cells have a plasma membrane,


nucleoid, and cytoplasm containing ribosomes
Although structurally less complex than eukaryotes,
some prokaryotes have specialized features:
- located outside the plasma membrane may be a cell
wall (containing peptidoglycan in bacteria).
- an outer membrane may enclose the cell wall
- enclosing the cell wall and outer membrane may be a
capsule
- some bacteria (cyanobacteria) carry out photosynthesis
- some...
tracking img