Life of the Cell
“Society” on a micro-scale
Learning Objectives
1. What are the characteristics that distinguish
prokaryotic and eukaryotic cells? Which type of cell
is believed to be older (more primitive)?
2. Describe the four characteristics shared by all cells.
3. Describe the structure and function of the various
eukaryotic cell organelles. What adaptive
advantage(s) is/are associated with having
organelles?
4. Describe the theories that describe the origin of
membranous organelles in eukaryotic cells.
The Cell:
What do we know so far?
• Smallest unit of life
• Can survive on its own or has potential to do so
• Is highly organized for metabolism
• Senses and responds to environment
• Has potential to reproduce
p. 52
Cellular Diversity in the Human Body
• A huge population of 75-100 trillion cells in the adult
body- @ 200 different types of cells
• What does cell shape tell you about its function?
Early Discoveries
p.54
• Mid 1600s - Robert
Hooke observed and
described cells in cork
• Late 1600s - Antony van
Leeuwenhoek observed
sperm, microorganisms
• 1820s - Robert Brown
observed and named
nucleus in plant cells
Visible light has wavelengths of light that are 400-750 nm. How
does this limit our ability to see objects with a light microscope?
An Introduction to Viruses
Why Are Cells So Small?
• Surface-to-volume ratio
• The bigger a cell is, the less surface area there is per
unit volume
• Above a certain size, material cannot be moved in or
out of cell fast enough
p. 53
Structure of Cells
Common structures:
Two types:
– Plasma membrane
– Prokaryotic
– DNA
– Eukaryotic
– Ribosomes
– Cytosol
Is this cell
prokaryotic or
eukaryotic?
Could it be an animal
or a plant cell?
p. 52
Explain.
Cell Membranes:
The Phospholipid Bilayer
p. 56
• Main component of all cell
membranes
• Gives the membrane its
fluid properties
• Two layers of
phospholipids
• The dense arrangement of
phospholipids makes
membranes selectively
permeable
What does this mean?
Fluid Mosaic Model
p. 56
 Membrane is a mosaic of
1. Phospholipids
•
Responsible for what characteristic of membranes?
2. Glycolipids & Glycoproteins
•
What combination of molecules make up glycolipids and
glycoproteins?
3. Cholesterol
•
Found in all cells?
4. Proteins
 Most phospholipids and some proteins are
fluid, and can move within the membrane
Identify the 3 types of lipid molecules found in cell
membranes: glycolipids, cholesterol and phospholipids.
Describe the function(s) of each.
Membrane Proteins
See Figure 4.10
Integral vs. Peripheral Proteins
Overview of Membrane Proteins
Prokaryotic Cells
• Archaea and Eubacteria
• DNA is not enclosed in nucleus
• Generally the smallest, simplest cells
• No organelles
p. 58
Sympathy for the life of bacteria
If you were a bacterium…
– You live in a medium which has the viscosity
similar to asphalt.
– You have a motor for swimming that only runs in
two directions… and you can never stop.
– While you can “learn”, you divide @ every 20
minutes and have to restart your education.
– You can have “sex”. However, since you are going
30mph (relative to your size), it is difficult to find
each other.
Prokaryotic Cell Structure
bacterial flagellum
plasma membrane
Sex pilus
bacterial flagellum
Most prokaryotic cells have a cell
wall outside the plasma membrane,
and many have a thick, jelly-like
capsule around the wall.
Describe the difference(s) between a cell
membrane and a cell wall. Can you explain
why a cell wall is a necessary adaptation for
prokaryotes?
cytosol, with
ribosomes
Circular DNA in
“nucleoid” region
Eukaroytic Cells
What? Where? Who?
• Have a nucleus and
other organelles
• Tend to be larger, but
no more important than
prokaryotes!
• Diverse environments
• Eukaryotic organisms
–
–
–
–
Plants
Animals
Protistans
Fungi
Functions of a Nucleus:
• Keeps DNA molecules
separated from
(potentially damaging)
metabolic machinery of
cytoplasm
• Makes it easier to
organize DNA and to
copy it before parent
cell divides into
daughter cells
p. 60
Nuclear Envelope
p. 61
• Two outer membranes (lipid bilayers)
• Pores span bilayer
Why are there pores in the nuclear envelope?
one of two lipid bilayers
(facing nucleoplasm)
nuclear pore (protein complex
that spans both lipid bilayers)
one of two lipid bilayers
(facing cytoplasm)
NUCLEAR
ENVELOPE
Nucleus
vs.
• Chromatin = cell’s
collection of DNA and
associated proteins w/in
the nucleus
• Chromosome = one DNA
molecule and its
associated proteins
• Appearance of nucleus
changes as cell divides
Nucleolus
• Dense mass (one or
more) inside nucleus
• Cluster of RNA and
proteins
– Materials from which
ribosomes are built
What is the role of
ribosomes?
• Subunits must pass
through nuclear pores to
reach cytoplasm
• Nucleolus disappears
during cell division
Why?
Figure from:
micro.magnet.fsu.edu/cells/nucleus/nucleolus.html
Endomembrane System
• Group of related
organelles in which
membrane materials
are assembled,
modified, and shared
Endoplasmic reticulum
Golgi bodies
Vesicles
• Products are sorted,
labeled, and shipped to
destination
– Export from cell
– Insertion into cell
membranes
p. 62
Rough ER
• Arranged into flattened sacs
• Ribosomes on surface give
it a “rough” appearance
• Some polypeptide chains
enter rough ER and are
modified
• Cells that specialize in
secreting proteins have lots
of rough ER
Where else do you find ribosomes?
Smooth ER
• A series of interconnected
tubules
• No ribosomes on surface
• Lipids assembled inside tubules
• Smooth ER contains enzymes,
and may store some cell
chemicals.
– Smooth ER of liver inactivates
wastes, drugs
– Sarcoplasmic reticulum of muscle
is specialized to store Ca+2
Golgi Bodies
• Put finishing touches on
proteins and lipids that
arrive from ER
• Package finished material
for shipment to final
destinations
• Material arrives and
leaves in vesicles
– Lysosomes
• digestive enzymes
• pumps in H+ ions for acidic
internal pH
– Peroxisomes
• Enzymes breakdown
hydrogen peroxide (H2O2)
Central Vacuole
• Single membrane
organelle
• As cell grows, expansion
of vacuole as a result of
hydrostatic pressure
forces a weakened cell
wall to expand
• In mature cell, central
vacuole takes up 50-90
percent of cell interior
What happens if you don’t water your plants?
• Stores amino acids, sugars, wastes
(including alkaloids: nicotine, cocaine, caffeine, ephedrine,
morphine, heroin codeine, theobromine, & quinine.)
Mitochondria
• Double membrane organelle
– central cavity filled with matrix
– inner membrane folds = cristae
• large surface area for chemical
reactions of cellular respiration
• Function
– efficient generation of ATP
– “powerhouse of cell”
• Mitochondria self-replicate
– increase in # when need for ATP
increases
– circular DNA with 37 genes
– only inherited from mother (in egg)
p. 64
Chloroplasts
Convert sunlight energy to ATP through photosynthesis
• Notice the larger surface area created by thylakoid discs.
What chemicals are found embedded in these membranes?
• The fluid-filled portion of the chloroplast is called stroma.
Origin of Membranous
Organelles?
• No fossil record recording the
origin of eukaryotes, however…
• Both mitochondria and
chloroplasts resemble bacteria:
– Similar in size
– Reproduce by binary fission
– Have own DNA, RNA, and
ribosomes
• All eukaryotes share same
characteristics:
– Cytoskeleton made of microtubules
(tubulin protein) and actin
– DNA in chromosomes
– Membrane-bound organelles
Two Theories for the
Origin of Eukaryotes
Autogenous
p. 294
Endosymbiosis
The Autogenous theory may explain the origin of ____, and the
Endosymbiotic theory may explain the origin of ____.
Mechanisms of Intracellular
Movement
p. 66
• Length of microtubules or
microfilaments can change
• Parallel rows of microtubules or
microfilaments actively slide in a
specific direction
• Microtubules or microfilaments can
shunt organelles to different parts
of cell (see video)
Which human cells change their shape
dramatically with conscious control?
Plant Cell Features
Compare and contrast plant and prokaryotic cell walls.
What other eukaryotic organisms produce a cell wall?
CELL WALL CHLOROPLAST
CENTRAL
VACUOLE
NUCLEUS
CYTOSKELETON
RIBOSOMES
ROUGH ER
MITOCHONDRION
SMOOTH ER
PLASMODESMA
GOLGI BODY
PLASMA
MEMBRANE
LYSOSOMELIKE VESICLE
p. 65
Animal Cell Features
NUCLEUS
CYTOSKELETON
RIBOSOMES
ROUGH ER
MITOCHONDRION
SMOOTH ER
CENTRIOLES
GOLGI BODY
PLASMA
MEMBRANE
LYSOSOME
p. 65