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
The Plasma Membrane
Transport Across the Plasma
• 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
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
3% salt solution
??? Water
High to low
No energy needed
5% salt solution
??? Water
Low to high
Energy needed
Concentration Gradients
• Differences between ICF and ECF in solute
3% salt solution
97% Water
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
– 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
• 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
– Lower solute concentration = lower osmotic
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
• Shrinkage of red blood cells referred to as crenation
Short Video Review
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 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
– 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: 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 ”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
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
• 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: 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
• Consists of all the cellular contents between
the plasma membrane and the nucleus and
includes both cytosol and organelles.
• 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
• Extends throughout cytosol
• Network of three different types of protein
– Microfilaments
– Intermediate filaments
– Microtubules
• Contribute to cell strength and shape
• Function:
– Provide mechanical support and help generate movement
– Anchor cytoskeleton to integral proteins
– Provide support for 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 &
• 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
• Functions and identification of the organelles
are your responsibility since this a total
biology review area
– Information found on pages 58-62 of your
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
• Smaller than lysosomes
• Contain enzymes called oxidases that oxide
(remove hydrogen atoms from) various
– 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
• 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
• On your own, this is also a biology review
– 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
• Information found on pages 64-65 of your
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
• 1st step is DNA replication
• Then production of new organelles and
cytoplasmic components fro the new cell
• High metabolic activity
• A lot of cell growth
Mitotic Phase
Mitosis followed by Cytokinesis (splitting of the
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
– Nuclear envelop breaks down
• Metaphase
– Chromatids line up at equator (metaphase plate)
• Anaphase
– Centromeres split chromatids into chromosomes
– Chromosomes dragged towards the poles
• Telophase
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
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
• DNA sequences that code for cell division
break down.
• Free radical control becomes limited.
• Autoimmune responses slow down.

similar documents