Cells
Chapter 3
Generalized View of the Cell
• There are three main parts to a cell and each
part has a very specific function.
• Read pages 49-50 to discover them on your
own….
The Plasma Membrane
Cytoplasm
• Cytoplasm consists of fluid inside plasma
membrane and membrane-bound organelles except
the nucleus
• Cytosol consists of fluid inside plasma membrane
but excludes nucleus and membrane-bound
organelles
Transport Across the Plasma
Membrane
• Fluids in average body = ~60%
• ICF -- inside the cell (cytosol)
• ECF – outside the cell
–
–
–
–
Interstitial fluid (between cells of tissues)
Plasma (blood vessels)
Lymph (lymphatic vessels)
Cerebrospinal fluid (within and around brain/spinal
cord)
Materials dissolve into these body fluids; direction of
movement dependent upon concentration (amount of
solute in solution) 
Concentration Gradients
• Differences between ICF and ECF in solute
concentration
3% salt solution
??? Water
Passive
High to low
No energy needed
5% salt solution
??? Water
Active
Low to high
Energy needed
Concentration Gradients
• Differences between ICF and ECF in solute
concentration
3% salt solution
97% Water
Passive
High to low until dynamic equilibrium reached
Down concentration gradient
No energy needed
5% salt solution
95% Water
Passive Processes
• Does not require the use of energy
• Diffusion defined:
– Substance moves due to kinetic energy
– Movement from high concentration to low
concentration
– Movement of more molecules in one direction is
called net diffusion
– Movement ‘down the concentration gradient’
– Continues until equilibrium is reached
Two types of diffusion
• Simple diffusion: lipid-soluble substances,
simple cross membrane down the gradient
• Facilitated diffusion: ions, through pores of ion
channels of integral proteins
Osmosis
• Net movement of water down the gradient;
lower solute concentration to higher solute
concentration through
– Lipid bilayer
– Integral proteins
20% sucrose
80% water
Osmotic Pressure
• Pressure exerted on plasma membrane due to
a solution containing solute particles that
cannot pass through membrane
– Higher solute concentration = higher osmotic
pressure
– Lower solute concentration = lower osmotic
pressure
Osmotic Solutions
• Isotonic solution: cells maintain normal shape and volume;
concentration of solutes equal on both sides of membrane
• Hypotonic solution: higher concentration of water outside;
higher concentration of solutes than cytosol inside cell
– Water molecules will enter cell faster than they leave it = cell will
swell, eventually burst
• Bursting of red blood cells referred to as hemolysis
• Hypertonic solution: higher concentration of water inside;
lower concentration of solutes than cytosol inside cell
– Water molecules will leave cell faster than they enter it = cell will
shrink
• Shrinkage of red blood cells referred to as crenation
Cell Tonicity
• Tonicity is a measure of the effective osmotic
pressure gradient (as defined by the water potential
of the two solutions) of two solutions separated by
a semi-permeable membrane.
– relative concentration of the solutions determines the
direction and extent of diffusion
• Unlike osmotic pressure, tonicity is influenced only
by solutes that cannot cross the membrane.
– solutes able to freely cross the membrane do not affect
tonicity because they will always be in equal
concentrations on both sides of the membrane
• There are three classifications of tonicity
– Hypertonic (hypertonicity)
– Hypotonic (hypotonicity)
– Isotonic (isotonicity)
Short Video Review
http://highered.mheducation.com/sites/00724958
55/student_view0/chapter2/animation__how_osm
osis_works.html
https://www.youtube.com/watch?v=l33rQYic5ro
Passive or Active?
• Have I been talking about passive, active, or
passive and active transport?
Active Transport
• From low to high concentration; ‘up the
concentration gradient’
• Requires the use of energy
– Comes from splitting of ATP molecule
– Changes shape of transporter protein, called a pump
– Transports ions: Na+, K+, H+, Ca+2, I-, Cl• Example: sodium-potassium pump
– 40% of a cell’s ATP expended on active transport
• Drugs like cyanide can turn off ATP production-FATAL
Cyanide
• Cyanide can be a colorless gas, such as hydrogen cyanide (HCN) or
cyanogen chloride (CNCl), or a crystal form such as sodium cyanide
(NaCN) or potassium cyanide (KCN).
• Cyanide sometimes is described as having a “bitter almond” smell,
but it does not always give off an odor, and not everyone can detect
this odor.
• You could be exposed to cyanide by breathing air, drinking water,
eating food, or touching soil that contains cyanide.
• Cyanide enters water, soil, or air as a result of both natural processes
and industrial activities. When present in air, it is usually in the form
of gaseous hydrogen cyanide.
• Smoking cigarettes is probably one of the major sources of cyanide
exposure for people who do not work in cyanide-related industries.
Transport in Vesicles
• Vesicles small sacs formed by budding off of
membranes
– Transport substances within the cell from one
structure to another
• Energy source again is ATP
– Take in substances from ECF and transport
substances out to ECF
• Endocytosis: materials moved into cell
– Phagocytosis  ‘to eat’ - solids
– Bulk-phase endocytosis(pinocytosis)  liquids
• Exocytosis: materials moved out of cell
Endocytosis
• Endocytosis: capturing substance or particle from outside the cell by
engulfing it within membrane folds from the cell membrane and
releasing it into cytosol.
• There are two main kinds of endocytosis:
– Phagocytosis
– Bulk-phase endocytosis (pinocytosis)
Phagocytosis
– Phagocytosis ”cellular eating”
• Particles bind to plasma membrane receptors
• Projections called pseudopods extend surround particles and portions of the
membrane fuse to form a vesicle
– Extensions of the plasma membrane and cytoplasm
– Pseudopods vesicle formed called a phagosome
• Phagosome enters the cell, fuses with lysosomes
• Lysosome enzymes break down phagosome’s contents
– Any undigested content remains in the phagosome, now called a residual body
Occurs only in phagocytes
(certain white blood cells
and macrophages), cells
specialized to engulf and
destroy bacteria, viruses,
aged dying cells, and foreign
matters protecting body from
disease
Bulk-phase endocytosis (pinocytosis)
– Bulk-phase endocytosis (pinocytosis) ”cellular drinking”
• Plasma membrane folds inward, forming a vesicle allowing tiny
droplets of extracellular fluid that contain dissolved substances to be
surrounded
• Vesicle detaches or “pinches off” of the plasma membrane and enters
the cytosol
– Liquid is encircled within a pinocytic vesicle
• Vesicle fuses with a lysosome, enzymes degrade engulfed solutes
• Degraded solutes; like amino acids and fatty acids leave the lysosome
to be used elsewhere in the cell
Exocytosis
• Exocytosis: process of vesicles fusing with the
plasma membrane and secretes their contents to
the outside of the cell.
– All cells do exocytosis process, but most important in:
• Secretory cells
– Release digestive enzymes, hormones, mucus, and other secretions
• Nerve cells
– Release neurotransmitters
Cytoplasm
• Consists of all the cellular contents between
the plasma membrane and the nucleus and
includes both cytosol and organelles.
Cytosol
• Cytosol is the liquid portion of the cytoplasm
that surrounds the organelles and makes up
about 55% of the cell’s volume.
– 75%-90% of cytosol is water, the rest is composed
of dissolved solutes and suspended particles.
• Examples: ions, glucose, amino acids, fatty acids,
proteins, lipids, ATP, and waste.
• Site of many chemical reactions
– Maintain cell structure and enable cell growth
Cytoskeleton
• Extends throughout cytosol
• Network of three different types of protein
filaments:
– Microfilaments
– Intermediate filaments
– Microtubules
Microfilaments
• Contribute to cell strength and shape
• Function:
– Provide mechanical support and help generate movement
– Anchor cytoskeleton to integral proteins
– Provide support for microvilli
Microvilli
• Fingerlike projections of the plasma membrane
• Increase cell surface area
– Found mostly in areas with great absorption needs like the small intestines
• Help cells attach to one another or extracellular materials
• Involved in muscle contractions, cell division, and cell locomotion
– Migration of embryonic cells
– Invasion of tissues by white blood cells (WBCs) to fight disease
– Migration of skin cells in wound healing
Intermediate Filaments &
Microtubules
• Intermediate Filaments
– Found in parts of cells subjected to tension (stretching)
– Hold organelles in place
– Attach cells to one another
• Microtubules
– Long, hollow tubes
– Help determine cell shape
– Function as transport system for
• Organelle movement
• Secretory vesicles
• Migration of chromosomes
– Create movement of cilia and flagella
Organelles
• Functions and identification of the organelles
are your responsibility since this a total
biology review area
– Information found on pages 58-62 of your
textbook
Lysosomes
•
•
•
•
Membrane-enclosed vesicles
May contain up to 60 different digestive enzymes
Fuse with other vesicles during endocytosis
Recycle the cell’s own structures (worn-out
organelles)  autophagy
• May destroy own cell  autolysis
– This cause tissue deterioration after death
– Faulty lysosomes can contribute to certain diseases,
i.e. Tay-Sachs disease
Peroxisomes
• Smaller than lysosomes
• Contain enzymes called oxidases that oxide
(remove hydrogen atoms from) various
substances
– Creating a by-product of hydrogen peroxide H2O2
– Potentially toxic compound associated with free
radical superoxides
– BUT peroxisomes also contain catalase which breaks
down H2O2
• Oxidize toxic substances
• Abundant in liver
Proteasomes
• Tiny, barrel-like structure
• Destroys unneeded, damaged, or faulty
proteins from the cytosol
– Contain enzyme called protease
• Cuts proteins into small peptides
• So other enzymes can break them down to amino acids
from which new proteins can be built
Nucleus
• On your own, this is also a biology review
topic
– Label the diagram on page 14 of your packet
– List the functions of the nucleus also
– Information found on page 62 of your textbook
Gene Action: Protein Synthesis
• On your own, this is also a biology review
topic
• Information found on pages 64-65 of your
textbook.
Protein Synthesis
Somatic Cell Division
Damaged, diseased, or worn out cells are replaced
• Two types of cell division:
– Reproductive cell division-meiosis
• Will be discussed in later chapters
– Somatic cell division-mitosis
• Division into two identical cells
Division occurs through a sequence of changes
called the cell cycle
• Two major parts to cell cycle
– Interphase: when cell is not dividing
– Mitotic phase: when cell is dividing
Interphase
• 1st step is DNA replication
• Then production of new organelles and
cytoplasmic components for the new cell
• High metabolic activity
• A lot of cell growth
Mitotic Phase
Mitosis followed by Cytokinesis (splitting of the
cytoplasm)
Chromosomes are visible during this phase
under a microscope
Nuclear Division: Mitosis
Four stages:
• Prophase
– Chromatin condenses into visible chromosomes
– Centrioles migrate to opposite poles
– Mitotic spindles form attach to centromeres of
chromatids
– Nuclear envelop breaks down
• Metaphase
– Chromatids line up at equator (metaphase plate)
• Anaphase
– Centromeres split chromatids into chromosomes
– Chromosomes dragged towards the poles
• Telophase
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–
–
–
Chromosomes uncoil into chromatin
Nuclear envelops reforms
Nucleolus reappear
Mitotic spindles break down
Cytoplasmic Division: Cytokinesis
• Division of cytoplasm and organelles between
two new cells
• Begins with formation of a cleavage furrow in
plasma membrane that pinches inward
• Cells return to Interphase
Complete Process of Somatic Cell
Division
Cellular Diversity
• Average humans has about 100 trillion cells of
varying sizes
– Cell size is measured in micrometers (µm)
• 1 micrometer = 1 one-millionth of a meter
• Largest cell in human body is an oocyte with a
diameter of 140 µm
– Average hair strands is ~100 µm in diameter
• Cells can be round, oval, flat, cube-shaped,
column-shaped, elongated, star-shaped,
cylindrical, or disc-shaped
– Shape is related to function
Round: oocyte
Oval: Liver
Flat: Squamous
Cube-shaped: Cubiodal Column-shaped: Collumnar
Elongated: Collagen
Cylindrical: Skeletal
Star-shaped: Natural Killer Cells
Disc-shaped: RBCs
Aging and Cells
• As we age our cells ability to divide is
diminished.
• DNA sequences that code for cell division
break down.
• Free radical control becomes limited.
• Autoimmune responses slow down.