Transcript The Cellular Level of Organization

Cells
Chapter 3
Bio160
Plasma Membrane
• Plasma membrane – flexible yet sturdy
barrier that surrounds and contains the
cytoplasm of a cell.
Fluid mosaic model
Lipid bilayer
Membrane proteins
Plasma Membrane
The plasma membrane is selectively
permeable, which means that only certain
substances can enter or leave the cell
• Cytoplasm – Everything inside the cell
including the fluid (cytosol) and organelles.
Transport Across Membranes
Process
Energy Source
Description
Examples
Passive processes
Simple diffusion
Kinetic energy
Net movement of
Movement of fats,
particles (ions,
oxygen, carbon
molecules, etc.)
dioxide through
from an area of their
the lipid portion
higher concentration
of the
to an area of their
membrane, and
lower concentration,
ions through
that is along their
protein channels
concentration
under certain
gradient
conditions
Osmosis
Kinetic energy
Simple diffusion of
water through a
selectively
permeable
membrane
Movement of water
into and out of
cells via
membrane pores
Transport Across Membranes
Facilitated diffusion Kinetic energy
Same as simple
diffusion, but the
diffusing substance is
attached to a lipidsoluble membrane
carrier protein
Movement of
glucose into cells
Filtration
Movement of water
and solutes through a
semipermeable
membrane from a
region of higher
hydrostatic pressure to
a region of lower
hydrostatic pressure,
that is along a pressure
gradient
Movement of water,
nutrients, and
gasses through a
capillary wall;
formation of kidney
filtrate
Hydrostatic
pressure
Transport Across Membranes
Active processes
Active transport
(solute pumping)
ATP (cellular Movement of a substance
energy)
through a membrane
against a concentration (or
electrochemical gradient;
requires a membrane
carrier protein)
Movement of amino
acids and most ions
across the
membrane
ATP
Secretion of
neurotransmitters,
hormones, mucus,
etc.; ejection of cell
wastes
Bulk transport
Exocytosis
Secretion or ejection of
substances from a cell; the
substance is enclosed in a
membranous vesicle,
which fuses with the
plasma membrane and
ruptures, releasing the
substance to the exterior
Transport Across Membranes
Phagocytosis
(endocytosis)
ATP
“Cell eating”; A large
external particle
(proteins, bacteria, dead
cell debris) is surrounded
by a “seizing foot” and
becomes enclosed in a
plasma membrane
In the human body,
occurs primarily in
protective
phagocytes (some
white blood cells,
macrophages)
Pinocytosis
(endocytosis)
ATP
“Cell drinking”; Plasma
membrane sinks beneath
an external fluid droplet
containing small solutes;
membrane edges fuse,
forming a fluid-filled
vesicle
Occurs in most
cells; important for
taking in solutes by
absorptive cells of
the kidney and
intestine
Transport Across Membranes
Receptor-mediated
endocytosis
ATP
Selective
endocytosis
process; external
substance binds to
membrane
receptors, and
coated pits are
formed
Means of intake of
some hormones,
cholesterol, iron,
and other molecules
Tonicity
• Isotonic – concentrations of solutes are the
same on both sides of the membrane
0.9% NaCl solution (normal physiological saline) is
isotonic for red blood cells (RBC)
• Hypotonic – a solution that has lower
concentration of solutes than the cytosol
Lysis or hemolysis in RBC
• Hypertonic – a solution that has greater
concentration of solutes than the cytosol
Crenation – cell shrinkage
Nucleus
• Nucleus – control center
contains chromosomes - heredity materialcalled chromatin when cell is not dividing
nucleolus - assembly plant for ribosomes
surrounded by nuclear membrane which has
pores in it through which substances enter
and exit
Ribosomes
• Ribosomes - contain both rRNA and
ribosomal proteins
functions as the workbench for protein synthesis
some ribosomes are free ribosomes - no
attachment to organelles - concerned
primarily with synthesizing proteins for use
inside cell
Ribosomes
some ribosomes are attached to the
endoplasmic reticulum (ER), hence rough
ER, involved in the synthesis of proteins for
insertion in the cell membrane or for export
from the cell
Endoplasmic Reticulum
• Endoplasmic reticulum (ER) - system of
membrane-enclosed channels continuous with
nuclear membrane and Golgi complex
rough ER - has attached ribosomes - proteins
synthesized are stored by the ER and sugar
groups may be added to form glycoproteins
- then transported from ER to Golgi
Endoplasmic Reticulum (2)
smooth ER - no ribosomes attached - provides
a surface area for chemical reactions
– site of steroid, fatty acid, phospholipid synthesis
(ex: in testis provides surface for enzymes
involved in testosterone synthesis)
– site of carbohydrate synthesis, detoxification of
alcohol, pesticides, carcinogens (ex: liver
synthesis of glycogen)
– stores Ca++ in muscle (but called sarcoplasmic
reticulum (SR) in muscle)
Golgi Apparatus
• Golgi apparatus - consists of stacks of flattened
sacs (like pancakes) that can form vesicles for
exocytosis, lysosomes, or for storage (vesicles
are membrane bound sacs that are smaller than
vacuoles)
Golgi receives proteins, carbohydrates, lipids
from vesicles made from ER and collects,
sorts, packages as new vesicles, and delivers
vesicles for storage, membrane use, or
exocytosis, lysosomes
Lysosomes
• Lysosome - formed by Golgi and contain
powerful digestive (hydrolytic) enzymes that:
recycle monomers in a cell from polymers
(proteins, carbohydrates, lipids, nucleic acids)
destroy bacteria engulfed by white blood cells
(WBC) when the phagocytic vesicle fuses with
lysosome
Mitochondria
• Mitochondria - powerhouse of cell - double
membraned - found in both animal and plant
cells, but not in bacteria
Major site of chemical reactions that release
energy from certain nutrient molecules and
transfer it to ATP, a chemical form the cell can
use.
Cytoskeleton
• Cytoskeleton - elaborate network of protein
structures = "bones and muscles"
microfilaments - thin strands of actin - aid in
cell movement (ex. amoeboid movement as in
WBC), aid in cytokinesis
– most highly developed in muscles
Cytoskeleton
microtubules - hollow tubes formed of globular
proteins called tubulins
– provide monorail system to move
organelles/vesicles
– also in centrioles, cilia, spindle fibers
Centrosomes and Centrioles
• Centrosomes – a structure near the Golgi and
nucleus that contains two centrioles.
• Centrioles - paired cylindrical bodies, each
composed of microtubules
Organize spindle fibers and asters during
mitosis in animal cells (may not be
necessary for this purpose because plants
produce spindle fibers during mitosis but
they lack centrioles)
Centrosomes and Centrioles
– Having centrioles at each pole in mitosis
provides a vehicle for transmission of
centrioles to all cells
Form the bases of cilia and flagella
Cilia/Flagella
• Cilia/Flagella - Membrane bound sets of
microtubules that move by means of ATP
cannot produce cilia/flagella without centrioles
– Cilia – tiny, hairlike structures that fringe
the surface of some cells
– Flagellum – long, usually single extension,
ex. tail of a sperm