Download Plasma Membrane

Cell Structure and Function
Definition of a cell:
 basic structural and functional unit of life
 the smallest units that display the
characteristics of life, i.e. reproduction,
metabolism, response to stimuli
General Subdivisions of a Cell
• Plasma Membrane = selectively permeable
boundary between the cell and the
environment
• Nucleus = regulatory center of the cell
• Cytoplasm = everything between the plasma
membrane and the nucleus (fluid +
organelles)
Plasma Membrane
Structure
• phospholipd bilayer
• proteins embedded in, and attached to, the
inner (intracellular) and outer
(extracellular) surfaces
• phospholipids are liquid at body
temperature, so proteins float around in the
membrane
Plasma Membrane
Function
• Main responsibility: ensure the
composition of extracellular fluid is
not the same as the composition of
the intracellular fluid
• Selectively permeable barrier controls
what enters and leaves the cell
Plasma Membrane
Function
• Water-soluble substances (salts, nutrients) cross
membrane with aid of protein channels, which
are selective about what can pass through
• Lipids can pass directly through bilayer by
diffusion (movement from area of high pressure
to area of low pressure)
• Attachment site of cytoskeleton, the internal
support of the cell
Plasma Membrane
Nucleus
Nuclear Envelope (membrane)
• Phospholipid bilayer with nuclear pores
• Controls what enters/leaves the nucleus
– things only go in or out by passing
through Protein channels, which are
selective
• Encloses all the chromosomes
Nucleus
Chromatin
•
All the chromosomes, which are long strands
of the molecule DNA
•
DNA regulates all cell activities, yet never
leaves the nucleus;
•
produces RNA, short messenger molecules
that exit through nuclear pores
•
RNA carries instructions out into the
cytoplasm
Nucleus
Nucleolus
•
Site of ribosome synthesis
•
Compartment in the nucleus where ribsomes
are assembled
•
Ribosomes are then moved out into cytoplasm
through nuclear pores
•
Ribosomes and RNA work together outside the
nucleus, to build all the proteins in the cell
Nuclear
Compartment
Ribosomes
Ribosomes = site of protein synthesis
--assembled in the nucleolus
--exported into the cytoplasm
Free – unbound in the fluid cytoplasm, produce
proteins for use in the cell
Bound – attached to the endoplasmic reticulum
(ER), produce proteins for export, or for the
plasma membrane
Cytoplasm
Fluid portion = “cytoplasm”
• Water with dissolved salts, nutrients
and enzymes (= proteins that do a
particular job)
• Site of many metabolic reactions
Cytoskeleton
• Network of protein fibers extending
throughout the fluid cytoplasm
• Support and structure for the cell
• Very dynamic, always remodeling itself
• Critical for cells to divide and copy
themselves
Cell Structure
Organelles
•
Separate compartments within the cytoplasm
formed by membranes
Mitochondrion – “thread granule”
•
major source of cell’s energy
•
energy is taken from sugar, stored in molecule
called ATP (adenosine triphosphate)
•
requires oxygen to make this exchange (aerobic
metabolism)
•
contained within double membrane
Mitochondrion
Organelles
Cytomembrane System
• system of tubes and chambers formed by
membranes
• extensively distributed throughout the
fluid cytoplasm
• involved in synthesis, modification,
processing & packaging of cellular lipids
and proteins
Cytomembrane System
Endoplasmic Reticulum (ER) = “within the
cytoplasm network”
•
system of tubes and sacs formed by
membranes (an enclosed space)
Cytomembrane System
• Two Types
• Rough = with bound ribosomes
– modifies proteins produced by the
ribosomes
• Smooth = without bound ribosomes
– doesn’t modify proteins
– functions in lipid synthesis, drug
detoxification, carbohydrate metabolism
Cytomembrane System
Golgi Apparatus
•
series of flattened sacs formed by
membranes,
•
functions in final protein processing prior
to use by the cell
•
proteins get shuttled from the ER to one
end of the Golgi
Cytomembrane System
Golgi Apparatus
• in each sac, different modifications are
made (proteins get individually
tailored)
• proteins get sorted and shipped off to
their destination (like the post office of
the cell)
Cytomembrane System
Vesicles
•
small membrane-bound structures that transport
proteins and lipids around the cell
•
little transporters that shuttle their contents from
one organelle to another
•
when they contact the appropriate organelle,
they fuse with its outer membrane and dump
their contents inside
•
same for plasma membrane, allowing the export
of materials from the cell (exocytosis)
Vesicles move from ER to Golgi
Cytomembrane System
Lysosome
•
membrane-bound vesicle that contains
digestive enzymes or toxic chemicals
•
merges with vesicles containing food
particles, invading bacteria
•
harsh chemicals and enzymes degrade the
food or bacteria, without harming rest of
cell