Cellular Classification &
Organelles:
A Look at the Endomembrane System
Biology 111
Holyoke Walsh
Cells
• All cells are classified as either
1. Prokaryote
2. Eukaryote
Prokaryote Cells
• no membrane bound nucleus, chromosomes
grouped together in an area called the
"nucleoid"
• no membrane bound organelles
• smaller than eukaryotes
• have cell wall and cell
membrane, some have
a capsule on the outside
• ribosomes make protein
• consist of bacteria and
archaebacteria
• Appendages
include: fimbriae/pili,
flagella
Figure 4.4a
E. coli
Eukaryotes
•
•
•
•
has a membrane bound nucleus
has membrane bound organelles in cytoplasm
Organelles perform specific functions
much larger than prokaryotes
Organisms within the animal, plant, fungi and
protista kingdoms are all eukaryotes
Endosymbiosis theory:
All organelles seem to share many properties with
bacteria. Lynn Margulis proposed endosymbiont
hypothesis: that organelles derived from ancient
colonization of large bacteria (became the eukaryotic
cell) by smaller bacteria (became the mitochondria,
chloroplast, etc.) Symbiosis = "living together".
IOW..Mito/Chloro were ancient prokaryotes and they became part of
another prokaryote in a mutualistic/symbiotic relationship 
*Mitochondria & Chloroplasts have their own
DNA
Animation at Microbiological Concepts
Commonalities…of all cells!!
•
•
•
•
Plasma Membrane
Cytoplasm
Chromosomes (DNA)
Ribosomes
Key Differences?
• The location of their DNA; membrane
bound organelles
• Prokaryote = nucleoid region
• Eukaryote = nucleus
Prokaryote vs. Eukaryote
Prokaryote or Eukaryote??
Prokaryote or Eukaryote??
Prokaryote or Eukaryote??
Eukaryotes
• In addition to the plasma membrane at its outer
surface, a eukaryotic cell has extensive &
elaborately arranged internal membranes,
which divide the cell into compartments.
• These provide different local environments
that facilitate specific metabolic functions, so
incompatible processes can go on
simultaneously in a single cell
• The plasma and organelle membranes
participate directly in the cell’s metabolism
b/c many enzymes are built right into the
membranes themselves.
Cell Membranes..in general
• Phospholipid bilayer
• Embedded proteins
• Each type of membrane has a unique
composition of lipids and proteins suited
to that membrane’s specific function
Ex: enzymes embedded in the mitochondrial
membrane function in cellular
respiration…which creates the ATP
energy our cells need to function!
Cell Membrane
Eukaryotes…genetic info…
• Two cellular components involved with the
genetic control of the cell are the
NUCLEUS & the RIBOSOMES
NUCLEUS
The Nucleus
The Nucleus
• Nuclear envelope contains nuclear pores for some things to enter
and exit (nucleoplasm within)
• Chromatin is DNA and proteins, when the cell begins to divide,
chromatin condenses and forms chromosomes
• DNA remains in the nucleus, it sends instructions to the cytoplasm
via messenger RNA
• RNA directs the synthesis of proteins on ribosomes in the
cytoplasm
• Nucleolus assembles ribosomes within the nucleus, ribosomes
contain the "tools" to construct proteins
Chromosomes – made of
DNA/Protein!
• DNA: Polymer of millions of nucleotides
Nucleotide = Deoxyribose Sugar
(pentose)
+Phosphate + Nitrogen Base
One Strand of DNA
• The backbone of
the molecule is
alternating
phosphates and
deoxyribose
sugar
• The teeth are
nitrogenous
bases.
phosphate
deoxyribose
bases
24
DNA Double Helix
Bases:
Cytosine
Thymine
Adenine
Guanine
T
G
http://www.youtube.com/watch?v=qy8d
k5iS1f0
C
T
A
G
Ribosomes
• Made of some RNA (genetic info) and
Protein
• each is composed of two subunits, one
large and one small
• Non-membranous organelles
• Vary in size (smaller in prokaryotes)
• Main function is to carry out protein
synthesis.
Ribosomes cont…
• Cells that have high rates of protein synthesis
have particularly high rates of ribosomes
• Located in the cytoplasm/ER (structurally
identical)
• Free ribosomes – function within the cytosol (ie.
enzymes that catalyze reactions)
• Attached ribosomes – generally destined for
insertion into organelles membranes or for
export (cells that secrete enzymes)
• Why does the human pancreas have millions
of ribosomes?
Protein Synthesis Summary
Protein Synthesis
1. The DNA double helix unwinds to expose a sequence of
nitrogenous bases. (A,T,C,G)
2. A copy of one of the strands is made in a process known as
transcription. The copy is made of messenger ribonucleic acid
(mRNA) which, following transcription, travels out of the
nucleus into the main body of the cell, where protein synthesis
occurs.
3. The mRNA couples with the protein synthesis apparatus
(the ribosome). Another type of RNA, known as transfer RNA
(tRNA), brings free amino acids to the ribosome.
4. The anticodon present on the tRNA recognises the codon
present on the mRNA, and the ribosome adds the amino acid
to the growing chain of linked amino acids (polypeptides),
cleaving it away from the tRNA. This process is known as
translation.
5. As the polypeptide chain grows, it folds to form a protein.
http://www.youtube.com/watch?v=983lhh20rGY
ENERGY RELATED ORGANELLES
Mitochondria - The Cell's Chemical Furnaces
• contains its own DNA, support for Endosymbiosis Theory
• singular is "mitochondrion“
• 2 membranes, one smooth outer membrane, and an inner
membrane folded into layers called cristae
• Cristae has two compartments: the matrix and the inter
membrane space
• function to store energy for cell
use. Energy is stored in the form
of ATP - adenosine triphosphate
• (Made by cellular respiration…
which we will learn later!)
Figure 4.17
Chloroplasts - Where Photosynthesis Takes Place
• only found in plant cells
• has its own DNA, like
mitochondrion
• functions to convert light
energy to carbohydrates
• carbohydrates then broken
down in mitochondria to
produce ATP
• consists of grana, closed compartments that are stacked
• thylakoids are the individual disk shaped compartments that make
up the grana (stack of thylakoids)
• stroma is the fluid surrounded the thylakoids
*Chloroplasts are a type of plastid
Chromoplasts – red, yellow and orange pigment
Leucoplasts – colorless (potatoes)
Endomembrane System
• Many of the different membranes of the eukaryotic cell
are part of this system which carry out a variety of tasks
in the cell. i.e. synthesis of proteins, metabolism and
movement of lipids, & detoxification of drugs and
poisons
• The membranes of this system are related either through
physical continuity or by the transfer of membrane
segments as tiny vesicles (sacs made of membrane)
• This system includes: nuclear envelope, the
endoplasmic reticulum, golgi apparatus, lysosomes,
various vacuoles, and the plasma membrane
Endomembrane System
Endoplasmic Reticulum
• Extensive network accounting for more than half
the total membrane in eukaryotic cells
• Consists of a network of membranous tubules
and sacs called cisternae
• The ER membrane separates the internal
compartment of the ER, called the ER lumen
(cavity) or cisternal space, from the cytosol.
• The ER membrane is continuous with the
nuclear membrane
ER cont…
Two types of ER: smooth and rough
1. Smooth ER – lacks ribosomes and
involved in diverse metabolic processes
such as lipid synthesis, metabolism of
carbohydrates, and detoxification of
drugs and poisons
2. Rough ER – has ribosomes and is
involved in protein synthesis
Figure 4.10a
Golgi Apparatus -- Delivery System
• flattened stacks of
membranes
• functions in
collection, packaging
and distribution of
molecules made in
the cell and used
elsewhere
• front end (cis) faces
the ER, and the back
end (trans) faces the
cell membrane
* folded stacks are called cisternae
• unprocessed
proteins enter the
Golgi apparatus from
ER and proteins are
packaged and
exported to the
nearest membrane
Jobs of the Golgi Apparatus
(aka Golgi Complex)
1. separates proteins
according to their destinations
2. modifies proteins (adds
sugar and makes
glycoproteins)
3. packages materials into
vesicles which are exported
outside the cell - secretion
Summary of Endomembrane System
See Handout*
Lysosomes - Intracellular Digestion Centers
• vesicles that are used to digest
• contain high levels of degrading
enzymes – low pH
(to "lyse" means to dissolve)
• recycle old and worn out cell
parts
• "suicide sac" - apoptosis
(BONUS) digest other particles
taken in by phagocytosis
http://www.youtube.com/watch?v=
m6qJ69wcSnc
• found in animal cells
TAY-SACHS disease – missing an
enzyme of the lysosomes that breaks
down a fatty substance. Over time this
fat builds up in the brain and nervous
tissue, smothering the cells. Results in
degeneration and death.
Vacuoles
Types:
1. Food vacuoles – formed by phagocytosis
http://www.youtube.com/watch?v=W6rnhiMxtKU
2. Contractile vaculoes – pump excess water
out of the cell
http://www.youtube.com/watch?v=kkPiRT2ewVA
3. In plants & Fungi – Central vacuole: stores
food, nutrients, water and waste…maintains
turgor pressure (prefer a hypotonic state)
Mini Quiz
1. What part of the cell
produces vesicles for export?
2. What part of the cell makes
proteins?
3. What part of the cell
produces ATP?
4. What part of the cell
transports materials
throughout the cytoplasm?
5. What part of the cell has a
cis and a trans face?
a. ________________
b. ________________
c. _________________
d. _________________
e. _________________
f. __________________
f.
What is this structure?
Figure 4.7b
Figure 4.10a
What is this structure?
What is this
structure?
Figure 4.11
Describe the
processes occurring in
this image.
Figure 4.13
Figure 4.16b
What is this structure?
What is this structure?
What is its function?
Find the:
a. Nucleolus
b. Centriole
c. Vesicle
d. Smooth ER
e. Lysosome
Summary Video Clip
http://www.youtube.com/watch?v=cj8dD
THGJBY&list=PLb3m_5kPlQwPK22qq6t
BsUt_pkt4UQUvQ