Transcript Cellular Structure & Function Part 1: Organization of the Human Body

Cellular Structure &
Function
Part 1: Organization of the
Human Body
The Cell
Building block of the all organisms, from
single-celled to human.
 200 Types of cells in the human body,
categorized by cell shape.
 Cell size limited by the volume and surface
area ratio.

 If
the cell is too big, it cannot support itself or
absorb nutrients/excrete wastes effeciently.
Classes of Cell Shapes

Squamous: Thin & flat cells covering surfaces or lining
“tubes”


Cuboidal: Square or cube shaped; approximately as
wide as they are tall.



Example: Lining of the intestines
Spheroid: Egg cells and fat cells; round or oval.
Fusiform: Thick in the middle and tapered towards the
ends.


Example: Liver cells
Columnar: Much taller than they are wide.


Example: Skin, lining of the esophagus
Example: Smooth muscle cells
Stellate: Star-shaped cells.

Example: Some nerve cells
Cell Theory


Based on Robert Hook, Theordore Schwann, &
Louis Pasteur
Modern Cell Theories’ Generalizations:
 All
organisms are composed of cells and cell
products.
 The cell is the simplest structural and functional unit
of life.
 All functions and structures are ultimately due to the
activities of cells.
 Cells come only from pre-existing cells.
 The cells of all species have many fundamental
similarities.
General Cell Structure

Cells have the following general
structures:
 Cell
Membrane
 Cytoplasm
 Nucleus
 Intracellular Organelles
Cell Membrane
All cells are surrounded by a plasma
membrane made up of proteins and lipids
 Composition and function differ from one
area of the body to the other.
 Bilayer of lipids with diverse proteins
embedded in it
 98% of membrane molecules are lipids

 75%
of these are phospholipids
Cell Membrane

Phospholipid Bilayer:
 Two
phospholipid layers thick
 Hydrophilic heads facing the water on each
side of the cell membrane.
 Hydrophobic tails directed toward the center
of the membrane (avoiding the water)
 Membrane is dynamic and “fluid”
Cell Membrane
Cell Membrane is the target site of many
pharmaceutical agents
 Proteins only make up 2% of the
molecules in a plasma membrane, but are
larger then lipids and make up around
50% of the membrane weight.

Cell Membranes

Integral or Transmembrane Proteins: Pass
across the plasma membrane and are
responsible for many functions. Integral proteins
function as…
 Receptors: Specific for one messenger
 Second-messenger Systems: Triggered
by
messengers that bind with surface receptors
 Enzymes: Produce second messengers and help with
digestion in the small intestine
 Channel Proteins: These molecules have “pores” &
allow passage of water & other solutes through the
membrane
 Carriers: Also called “PUMPS” they actively transport
molecules into the cell utilizing ATP in the process
Glycocalyx
The “fuzzy” coat external to the plasma
membrane on all animal cells, including
humans
 Acts as an “identification” tag that enables
the body to distinguish its own healthy
cells from transplanted tissue, invading
organism, and diseased cells.

Surface Extensions
Surface extensions aid in absorption,
movement, and sensory processes.
 Microvilli: Extensions of the plasma
membrane; serve primarily to increase a
cell’s surface area; best developed in cells
that specialized in absorption (e.g. the
cells lining the small intestine)

Surface Extensions

Cilia: Multiple hair-like processes that
project from the surface of the cell
 Nonmotile
Primary Cilium: Nearly every
human cell has a single nonmotile primary
cilium.

Play a role in balance in the inner ear.
 Motile
Cilia: Less widespread but occur
widely in respiratory tract and fallopian tubes;
“wave” to help move materials through
internal tubes
Surface Extensions

Flagella: A single whip-like structure much
longer than cilia.
 The
only functional flagellum in humans is the
tail of the sperm cell.
Cytoplasm

Cytoplasm: The fluid that is contained
inside the plasma membrane.
 Crowded
with fibers, tubules, passageways,
and compartments.
 Contains cytoskeleton (supportive
framework) and intracellular organelles
embedded in the cytosol or Intracellular
fluid (ICF).

Extracellular fluid (ECF) is the fluid
outside the cell.
Nucleus
Nucleus: The structure at the center of
the cell containing the genetic information
for the organism.
 Nucleic Acid: DNA or RNA.

 DNA
is the principle type of nucleic acid
contained in the cell nucleus.

DNA contains the genetic code for organisms and
is involved in protein synthesis, cell division
(mitosis), and reproduction of the organism.
Plasma Membrane
Plasma Membrane: Acts as a barrier and
gateway between the cytoplasm and the
extracellular fluid.
 Selectively Semi-Permeable: The
plasma membrane lets some things
through and blocks other things; this is
tremendously important in clinical practice!

Plasma Membrane
Methods of Transporting Substances:
Passive and Active transport.
 Passive Transport includes…

 Filtration
 Diffusion
 Osmosis

Active Transport requires ATP and
includes…
 Active
transport
 Vesicular transport
Filtration

Filtration: The process by which particles are
driven through a filter, or selectively permeable
membrane, via hydrostatic pressure exerted
on a membrane by water.
 Example:


Coffee Filter
Weight of water forces water through the grounds and coffee
filter.
Filter holds back the larger particles (coffee grounds)
 Most
important filtration in the human body occurs in
the capillary wall – transfer of water, salts, nutrients,
etc. from blood stream to tissue and extracellular fluid
& wastes to kidneys
Simple Diffusion

Simple Diffusion: The net movement of particles from
an area of higher concentration to an area of lower
concentration.



The result of constant, spontaneous movement of molecules
known as Brownian Movement.
Concentration Gradient: When the concentration of a
substance differs from one point to another.
Movement occurring down or with the concentration
gradient is movement from the higher concentration area
to the lower.
Simple Diffusion
IF the membrane is semi-permeable and
permeable to that substance, than
diffusion will occur.
 IF the membrane is not permeable to the
substance, it will not diffuse across the
membrane.

Diffusion Rates


Diffusion Rates: Important to cell survival because they
determine how quickly a cell can acquire nutrients or rid
itself of wastes.
Factors affecting diffusion rate:







Temperature: The higher the temp, the faster the diffusion rate.
Molecular Weight: Heavy molecules diffuse more slowly.
Membrane Surface Area: The more surface area the faster the
diffusion rate.
“Steepness” Of Concentration Gradient: The greater the
concentration difference, the faster the diffusion.
Membrane Permeability: The permeability of the membrane.
Diffusion Distance: Distance diffusion occurs across.
Facilitated Diffusion: Whether a solute binds to a specific
transporter (changes the shape and releases the solute on the
other side of the membrane).
Osmosis

Osmosis: The diffusion of water through a
selectively permeable membrane from the
area of higher water concentration to the
area of lower water concentration.
 The
higher solvent (water) concentration area
has a low solute concentration.
 The higher solute concentration has a low
solvent concentration.
Tonicity

Tonicity: The ability of a solution to affect
the fluid volume and the pressure in a cell.
 If
a solute cannot pass through a plasma
membrane, but remains more concentrated
on one side of the membrane than on the
other, it triggers osmosis.
Tonicity

Hypotonic Solution: Area surrounding a cell
has a lower concentration of nonpermeating
solutes than the intracellular fluid.
 Cells

Hypertonic Solution: Area surrounding cell has
a higher concentration of nonpermeating solutes
than the intracellular fluid.
 Cells

absorb water, swell, and lyse (burst).
will lose water and crenate (shrivel).
Isotonic Solution: The area surrounding the
cell has the same total concentration of
nonpermeating solutes as the intracellular fluid.
 Cells
will neither loose nor gain water molecules & do
not change size or shape.
Active Transport

Active Transport: The carrier-mediated
transport of a solute through a plasma
membrane but against a concentration
gradient.
 Utilizes ATP
and energy to move against the
normal concentration gradient from an area of
low concentration to high concentration.

Example: The sodium-potassium pump.
Sodium-Potassium Pump


Used to regulate the balance of sodium and
potassium within the cell.
1 ATP molecule exchanges 3 sodium atoms
(Na+) for 2 potassium (K+) atoms.
 Keeps
the potassium higher and sodium lower within
the cell.
 Plasma membrane continuously leaks Na+ and K+,
so the pump keeps the balance corrected.
 Na+ and K+ play a critical part in nerve impulses and
cardiac function.
Vesicular Transport


Vesicular transport moves large particles and
droplets of fluid or numerous molecules through
the plasma membrane all at once.
Endocytosis: Vesicular processes that bring
matter into the cell. Two types:
“Cell eating” where foreign particles
are engulfed (e.g. monocytes)
 Pinocytosis: “Cell drinking” where droplets of
extracellular fluid containing molecules used by cells
are taken in.
 Phagocytosis:

Exocytosis: Vesicular processes that release
matter from the cell.
Organelles

Organelles: The internal structures within a cell
that carry out specific functions.
 Some
are surrounded by one or two layers of a unit
membrane and are therefore referred to as
“membranous organelles.”


Membranous Organelles: Nucleus,
mitochondria, lysosomes, endoplasmic
reticulum, golgi complex.
Non-Membranous Organelles: Ribosomes,
centrosome, centrioles, basal bodies.
Membranous Organelles: Nucleus

Nucleus: The largest organelle, spheroid in
shape.
 Most cells have a single nucleus
 Skeletal muscle cells have multiple nuclei
 Mature red blood cells are anuclear – have no nucleus.
 Liver cells are multinuclear
 Nucleus surrounded by nuclear envelope or
membrane

Nucleoplasm: The material contained within the
nucleus.
 Includes…
 Chromatin (DNA and protein)
 Nucleoli (produces ribosomes)
Membranous Organelles:
Endoplasmic Reticulum (ER)


Endoplasmic Reticulum: “Little network within
the cytoplasm”
A system of interconnected channels that extend
through the cytoplasm and reach the nuclear
membrane.
 Channels

called Cisternae
Two Types:
 Rough
Endoplasmic Reticulum: Channels are
covered with ribosomes (synthesize proteins).
 Smooth Endoplasmic Reticulum: Extends from the
Rough ER to form membranous tubules network.
Membranous Organelles:
Endoplasmic Reticulum (ER)
Smooth ER synthesizes steroids & lipids
 Rough ER is responsible for detoxifying
alcohol and other drugs
 Rough ER most abundant in cells that
produce large amounts of proteins – such
as those in the digestive glands
 Skeletal and cardiac muscle contain
extensive networks of smooth ER that
store and release calcium to trigger
muscle contraction.

Membranous Organelles: Golgi
Complex

Golgi Complex: The small system of
cisternae which synthesize carbohydrates
and put the finishing touches on protein
and glycoprotein synthesis.
 Primary
function is to package protein into
membrane-bound golgi vesicles
 Some become secretory vesicles and store
cell products such as breast milk & digestive
enzymes

Some of these can become lysosomes
Membranous Organelles:
Lysosomes

Lysosomes: A package of enzymes which are
bounded by a single unit membrane – usually
produced by the Golgi complex
 Primary
function is to hydrolyze or digest proteins,
nucleic acids, complex carbohydrates, and
phospholipids
 Autophagy: The digestion of surplus cells by their
own lysosomal enzymes (as in the liver).
Membranous Organelles:
Peroxisomes

Peroxisomes: Resemble lysosomes but
are smaller and contain different enzymes
(oxidase) and are not produced by the
Golgi Complex\
Membranous Organelles:
Mitochondria

Mitochondria: Organelles specialized for
synthesizing ATP
 Power-house
 Bean
of cells
shaped
 Outer and inner membranes
 Generate most of the cell’s ATP
 Cristae contain enzymes for aerobic respiration
 Matrix enclosed in the inner membrane; site of
oxidation of organic molecules; contains DNA and
ribosomes.
Non-Membranous Organelles:
Ribosomes

Ribosomes: Small granules of protein
and ribosomal RNA found in several
places in the cytoplasm:
 On
Rough ER
 In the Nuclear Envelope
 Floating freely in cytoplasm
Responsible for assembling amino acids
based on messenger RNA codes.
 Primary function is protein synthesis.

Non-Membranous Organelles:
Centrioles

Centrioles: A short cylindrical assembly of
microtubules.
2
centrioles lie at right angles to each other
within a small clear area of cytoplasm called
the centrosome

Play a role in cell division – Mitosis
Cytoskeleton

Cytoskeleton: A collection of protein
filaments and cylinders that determine the
shape of a cell.
 Lend
structural support
 Organize cellular contents
 Help move stuff through the cell
 Contribute to movements of the cell
 Connected to integral proteins of the plasma
membrane
 Made up of microfilaments and microtubules
Inclusions

Inclusions: 2 Kinds
 Stored
cellular products such as glycogen
granules or fat droplets OR foreign bodies
such as dust particles
 NO unit membrane
 Not essential to cell survival
 Not organelles
 Temporary structures; not permanent
Mitosis

Mitosis: The process by which cells divide to
grow or to repair damage. 4 Stages:
 Prophase:
Condensing of chromatin fibers into
chromatid pairs
 Metaphase: The chromatid pairs line up along the
metaphase plate
 Anaphase: The centromeres joining the chromatids
split, identical sets move to opposite sides of the cell
 Telophase: Nucleoli reappear around two new sets of
chromosomes and cell begins to split for cytokinesis –
the division of the cell material.