The Cell
• The cell is the basic structural and functional unit of life.
– The cells structural anatomy will determine its overall
function.
• All cells contains organelles which are the equivalent to organs
of an organism.
– They provide a specific function within the cell.
• produces different types of proteins (enzymes)
– That carry out overall cell activity.
• There are many different types of cells that contain different
proportions on organelles and enzymes.
– This will dictate the cells overall specific function.
• It is necessary to understand how the individual cell functions if
you want to understand:
– Function of the whole organism
– Disease: start at a cellular level.
• i.e. cancer
Structure of a Generalized Cell
Variations in cells types
Cell Membrane
• Separates the intracellular fluid (ICF) aka(cytosol )
from the extracellular fluid (ECF)which surrounds the
outside of a cell
• Physical barrier
– Isolates each cell from all of the others
• Membrane protein receptors communicate between
the cell and its external environment
• Plays a dynamic role in cellular activity by controlling
the movement of chemicals into/out of the cell
–
–
–
–
–
ions
monosaccharides
amino acids
nucleotides
water
Fluid Mosaic Model of the Cell Membrane
• Phospholipids bilayer with imbedded and dispersed
proteins.
– Cholesterol provides stability to the membrane.
– Glycolipids: are lipids with bound carbohydrate
– Glycocalyx is a glycoprotein important for cell recognition.
Phospholipids in a Bilayer
• polar heads
• non-polar tails
• The polar heads: of each layer face outward towards the water
molecules both in and out of the cell.
– outer portion is exposed to the ECF
– inside portion is exposed to the ICF
• The non-polar tails face inward toward each other creating a
barrier against the movement of polar substances into or out
of the cell
Integral or Transmembrane Proteins
• Completely pass through the bilayer
Peripheral Proteins
• They associated with integral membrane
proteins.
• They can move and communicated with other
structures inside the cell.
• Mitochondria: Is known as the powerhouse of the cell.
– In the presence of oxygen it can convert organic macromolecules
into energy for the cell. (ATP)
Endoplasmic Reticulum (ER)
Interconnected network tubes within cytoplasm.
Rough ER
Smooth ER
Rough ER
• External surface is studded with ribosomes.
•
Ribosomes are the site for protein synthesis:
– The assembly of amino acids to form proteins .i.e. enzyme,
membrane-bound protein and muscles.
– Free ribosomes in the cytoplasm
– Synthesize proteins that remain inside the cell
•
Membrane-bound ribosomes
– can synthesize proteins such as integral proteins or
proteins that get exported out of the cell.
• Proteins synthesized in the ribosomes are taken inside
(cisterna) the ER where they are modified into functional
proteins
• Roles in the synthesizing both integral proteins, antibodies
and phospholipids.
Ribosome
RER
Chaperones Proteins
• Drags new protein from ribosome into
cisterna of ER where they function to:
– Assist in proper folding of amino acids into
proper 2nd and tertiary molecular structure
• This is a result of the formation of disulfide bridges
and H-bonds
– Remove some amino acids and adding
carbohydrates when necessary.
– Escort protein to Golgi Apparatus
Golgi Apparatus
Golgi Apparatus
• Stacked and flattened membranous sacs that
functions in modifying, concentrating and
packaging proteins.
– Create secretary vesicles contain modified proteins
that leave the Golgi and export them through the cell
membrane
– This functions as the UPS of the cell.
• Produces glycoproteins and proteoglycans
– Lysosomes and peroxiosomes
Organelles of Protein Production and Excretion
Lysosomes
• Vesicles containing digestive enzymes which
hydrolyze macromolecules (intracellular digestion.)
• Lysosomes function to:
– hydrolyze ingested bacteria and viruses and toxins.
– Recycle organic molecules such as amino acids,
monosaccharides, fatty acids and nucleotides to
make new macromolecules
– Degrade nonfunctional organelles
– Breakdown glycogen and release thyroid hormone
– Breakdown bone to release Ca2+
Peroxisomes
• Detoxify harmful or toxic substances such as
alcohol and other drugs.
– Abundant in the liver and kidneys
• Neutralize dangerous free radicals
– Free radicals – highly reactive chemicals with
unpaired electrons (i.e., O2–)
– H2O2
H2O +O2
Catalase:
converts hydrogen peroxide to water and oxygen.
Smooth ER
• Smooth ER
– Storage reserve for calcium (Ca2+) required for the
functioning of the muscular contractions and
transmission of nerve impulses.
– Produce enzymes which:
• Synthesize lipoproteins and metabolize lipids
– Production of steroids based hormones such as
testosterone.
– Detoxify drugs and toxins such as alcohol and
convert them to a less toxic water soluble form
which can be excreted by the kidneys.
• Long term use of drugs increase SER development
resulting in more efficient drug detoxifying and greater
drug tolerance
Cytoskeleton
• The “skeleton” of
the cell
• Dynamic,
elaborate series of
rods running
through the cytosol
• Consists of
microtubules,
microfilaments,
and intermediate
filaments
Nucleus
Nucleus
• Largest organelle: functions as the control
center of the cell.
– Contains (DNA) which provides instructions for the
synthesis of all proteins.
• DNA determines what proteins are synthesized
– The proteins produced determine cellular function.
• Some cells such as the RBC are anuclear
– (no nuclei)
• The liver and muscle cells are multinucleate
– (More than one nucleus)
Nuclear Envelope/ Nucleoli
•
Nuclear Envelope :double membrane (phospholipid
bilayer) structure containing many nuclear pores
(allow passage in and out of the nucleus):
• Raw materials for the production of DNA and RNA
• Enzymes that are made in the cytoplasm but function in
the nucleus.
•
Nucleoli : Dark-staining spherical bodies within the
nucleus contain the RNA that produces rRNA
– code for the production of ribosome subunits.
•
These subunits can leave the nucleus through
nuclear pores and join to form functional ribosomes.
Membrane Transport
• Movement of molecules through a membrane.
• Passive transport: No ATP required!
• Filtration
• Simple diffusion
• Facilitated diffusion
• Osmosis
• Active transport: Requires the break down of ATP!
• Primary
• Secondary
• Exocytosis
• Endocytosis
Passive Transport
• Substances diffuses across the cell membrane from a high
concentration to a low.
• Like a ball rolling down a hill.
– There is no energy expenditure! (ATP)
• Various substances may accomplish this by different
mechanisms:
– nonpolar molecules such as lipids diffuse through the
phospholipid bilayer unimpeded by a process called simple
diffusion.
– Some smaller polar molecules such as electrolytes and use
integral membrane proteins. (channels)
– Larger molecules such as sugar and amino acids require
help (facilitation) of to cross the bilayer in a process called
facilitated diffusion.
Diffusion
• Molecules that are closer to each other collide
and ricochet off each other. This results in a
natural tendency to scatter.
• A substance will always move down its gradient
unless energy is put into the system.
Facilitated Diffusion
Required for larger substances such as glucose, amino
acids, and some ions.
Travel down their concentration gradient binding to a
specific carrier protein. The carrier protein changes
configuration and releases to substance into the cell.
Summery of Diffusion
• Simple diffusion – nonpolar and lipid-soluble substances
– Non polar molecules diffuse directly through the lipid bilayer
• Polar molecules diffuse through channel proteins
Factors Affecting the Rate of Diffusion
1. Concentration (gradient)
• The greater the difference in the concentrations
of a substance, the greater the rate of diffusion.
2. Temperature
• As temperature increases, the rate of diffusion
increases.
3. Size of the substance
• As the size of substances increase, the rate of
diffusion decreases.
Osmosis
• The diffusion of water (solvent) across a selectively
permeable membrane through water channels
(aquaporins)
• Water has a natural tendency to diffuse toward the
area with the greatest amount of solutes
– (dissolved substances in the water)
• Think of making orange juice from concentrate. The concentrated
orange juice is are the solutes. You must add the solvent (water) to it.
• Osmotic pressure
– the greater the difference in concentration of
solutes the greater the osmotic pressure.
– the more water will move toward the area of
higher concentration.
Osmosis
• Diffusion of water through
a semi-permeable
membrane
– from area of more water
to area of less water
– from low to high
concentration of solute.
• Aquaporins = channel
proteins specialized for
osmosis
Osmotic Pressure
• The water shifts to the
left by osmosis.
– Where there is a higher
concentration of solutes.
• Osmosis will stop due to
filtration of water back
across membrane due
to hydrostatic pressure
– The pressure of gravity
on the left side.
Tonicity
• Tonicity - ability of a solution to affect fluid volume
and pressure within a cell.
– depends on concentration and permeability of solute
• Hypotonic solution (dilute outside the cell)
– low concentration of solutes (high water concentration)
– cells absorb water, swell and may burst (lyse)
• Hypertonic solution (concentrated outside cell)
– has high concentration of solutes (low water concentration)
– cells lose water + shrivel (crenate)
• Isotonic solution = (Equal concentrations both in and
out of the cell.)
– Cell will be at an osmotic equilibrium with solution
• Water will always move to where it is more
concentrated with solutes.
Tonicity of Red Blood Cells
Hypotonic
(Swell)
Isotonic
(No change)
Hypertonic
(Crenate/Shrink)
Clinical Application
You are a nurse working in the hospital and your
patient’s doctor orders an IV because their
blood work suggested they were dehydrated.
What would you give the patient.
a. Distilled water
b. Normal saline .9%NACL
c. 2% NACL saline
d. All of the above
e. None of the above
Clinical Application
You are a cyclist finishing a 2 hour ride on a
hot summer day. What would be the
drink of choice to replace your fluid loss.
A. Water
B. Gatorade
C. Protein shake
D. Orange juice
E. Corona
Filtration
• Uses hydrostatic pressure
(fire hose) Pressure
gradient pushes solutecontaining fluid from a
higher-pressure area to a
lower-pressure area.
• The movement of water,
nutrients and gases
through capillary walls to
supply the cells with
nutrients. The pressure
also allows the kidneys to
filter the blood. (filtrate)
Types of Active Transport
• Primary active transport – hydrolysis of ATP
provides the energy to move solutes against their
concentration gradient.
• Secondary active transport – use of an exchange
pump (such as the Na+-K+ pump) indirectly to drive
the transport of other solutes
• Exocytosis-Transport of substances out of the cell
enclosed with in a membranous vesicle. The
secretion of neurotransmitters, hormones, mucus
and cellular waste.
• Endocytosis - Substances are moved into the cell by
engulfing them in a vesicle
Primary Active Transport
• Process that hydrolyzes the high energy bond in a
molecule of ATP (releasing energy)
• Breaking the high energy bonds converts chemical
energy within the bond to mechanical energy.
• A substance can be forced from a region of
lesser to greater concentration :
– High Energy Bonds / lower energy bonds
Examples of Primary Active Transport
•
Na+,K+ Pump
– located in the plasma membrane
– actively pumps:
– 3 Na+ from the ICF →ECF
– 2 K+ from the ECF →ICF
– maintains a Na+,K+ gradient across the cell membrane
Sodium-Potassium Pump
6 K+ is released and Na+ sites
are ready to bind Na+
again; the cycle repeats.
Extracellular
fluid
1 Binding of cytoplasmic Na+ to
the pump protein stimulates
phosphorylation by ATP.
Cytoplasm
2 Phosphorylation causes the
protein to change its shape.
Concentration gradients
of K+ and Na+
3 The shape change expels
5 Loss of phosphate
restores the original
conformation of the
pump protein.
Na+ to the outside, and
extracellular K+ binds.
4 K+ binding triggers
release of the
phosphate group.
Fig
Na+, Glucose Cotransporter
Example of Secondary Active Transport
• Na+, glucose cotransporter
– cotransports: Moves in the same direction as Na+
• Na+ moves down its concentration gradient into
the cell as a result of the gradient created by the
Na+,K+-ATPase located at the basal (bottom)
surface of cells.
• SGLT(Na+ glucose transport protein): At the
apical surface glucose is taken into the cell with
Na+ down their concentration gradient by
facilitated diffusion.
– SGLT are important for reabsorbing glucose in kidney
Exocytosis
Types of Endocytosis
• Phagocytosis (cell eating)
– endocytosis of few very large substances (bacteria,
viruses, cell fragments)
– vesicles containing cells fuse with lysosomes which
digest the cells
• Pinocytosis (cell drinking)
– endocytosis of extracellular fluid
Phagocytosis