The Cell: An Overview
Ch. 5; 5.3-5.5
Eukaryotes: The Nucleus
• Nucleus is membrane
bound nuclear
envelope (2x layer)
• How do things move
through the envelope?
– Just like the plasma
membrane, proteins
(nucleoporins) channels
allow entrance (nuclear
pore complexes)
• How do they know what
goes in?
– Short AA sequence
(nuclear localization
signal) acts like a zip code
for the nucleus
Eukaryotes: The Nucleus
• What do you find inside
the nucleus?
1) nucleoplasm
cytoplasm in nucleus
2) Chromatin
DNA/Protein complex
3) Chromosomes
condensed DNA
4) Nucleolus mixture
of gene regions and
RNA complexes
Eukaryotes: Ribosomes
• Why do we have free
floating and membrane
bound ribosomes?
– Different products for
different environments
1) Free ribosomes
produce proteins to be
used in the cytosol
2) Attached ribosomes
produce proteins to be
embedded in membranes
or secreted
• Both have complex
organelle path after
completion
Eukaryotes: Endoplasmic Reticulum
• Smooth ER makes
lipids and digestive
enzymes for drugs and
toxins
• Rough ER makes
secreted proteins and
digestive enzymes
• What cells in the body
would have the largest
smooth and rough ER?
– Liver cells (smooth)
– Digestive tract (rough)
Eukaryotes: Golgi Complex
• Rows of flatten sacs
(cisternae) receive vesicles
from areas of the cell (at
cis face), modify the
contents, and send them
to their next location (at
trans face)
• Most proteins are
embedded or secreted
(exocytosis)
• Some molecules drawn
into the cell (endocytosis)
and destroyed by fusion
with lysosomes
Eukaryotes: Lysosomes
• Digestive sacs in animals
cells (over 300) that act like
recycling centers
• Acidic (pH ~5)
• Why is it important they
only work in a high pH?
– Lowers risk of activity
outside of lysosome; wont
work in basic cytosol
• Enzymes made in rough ER
and then vesicle formed
from Golgi complex
• Roles:
– Autophagy digest useless
organelles
– Phagocytosis digest
bacteria pulled into the cell
Eukaryotes: Mitochondria
• Site of cellular
respiration
• Double layered
membrane with
reactions between the
cristae and the matrix
• What about
mitochondria suggest
that they used to be
independent
organisms?
– The have their own
DNA and ribosomes
Eukaryotes: Microbodies
• Large vesicles that do
various tasks:
– Phospholipid synthesis
– Breakdown fats and
proteins to make ATP
– Breakdown toxins
• Peroxisomes vesicles
of catalase
• What do they do?
– Breakdown hydrogen
peroxide
Eukaryotes: Cytoskeleton
• Reinforce cell shape
and allow movement
around the cell
• Like your organs, a cells
organelles must be
held in place
• 3 groups:
1) Microtubules
2) Intermediate
Filaments
3) Microfilaments
Eukaryotes: Microtubules
• Long, wide tubes (25nm)
made of α and β tubulin
• Charge ends, with more
activity on the + end
• Why do they need charged
ends?
– Can use ionic forces to hold
them in place in the cell
• Network radiates from the
cell center (centrosome) and
have two perpendicular
barrels (centrioles)
• Hold organelles in place and
are tracks for vesicle
movement
– Motor proteins (kinesins and
dyneins)
Eukaryotes: Microtubules
• Main part of flagella and
cilia
• 9 + 2 complex  9 double
tube units around 2 single
tube units
• Wave and oar-like
movements push cell
through mediums
• Flagella are found in all 3
domains, but their genes
are different. What does
this tell us about flagella
evolution?
– It was independent even
though they have the same
structure and function
Eukaryotes: Intermediate Filaments
• Medium sized (8-12nm)
fibers that connect
microtubules/
microfilaments
together; adds stability
• Not found in single-cell
organisms
• Tissue specific have
different proteins
depending on the what
part of the organism
they are in
Eukaryotes: Microfilaments
• Thin fibers (5-7nm) of
actin units
• Charged ends with more
growth on the + end
• Main part of muscle tissue
– Myosin (motor protein)
moves back and forth
along microfibers causing
contractions
• Cytoplasmic streaming
movement of the
cytoplasm
– Cause amoeboid
movement
– Divided cytoplasm during
division
Eukaryotes: Chloroplasts
• Plastid
– Amyloplasts starch forming
cells (potato)
– Chromoplasts red and yellow
pigments give color to fruits and
autumn leaves
• Double membrane around the
stroma (inner area) which is
filled with a 3rd membrane that
makes the thylakoids/grana
• Thylakoids have chlorophyll
pigments that absorb light
energy
• How are chloroplast and
mitochondria similar?
– Both have their own DNA and
ribosomes
Eukaryotes: Central Vacuole
• Functions are giant
lysosome for the cell; also
a storage unit
• Stores pigments that give
flowers their color
• Tonoplast channels that
allow transportation of
materials
• Turgor pressure pushes
against weight of cell well
– What happens with plants
are low on water?
• The wilt; sag because turgor
pressure drops
Eukaryotes: Cell Wall
• Extracellular Structure
• Primary soft/flexible layer
expands as cell grows
• Secondary harder cellulose
fibers used to strengthen wall
– lignin complex alcohol
structure stronger than concrete
(by weight)
• Polysaccharide layer (middle
lamella) acts like glue to hold
plant cells together
– Pectin used in syrup and jams
• How do cells communicate
through these think walls?
– Channels (plasmodesmata) allow
instant communication between
plant cells
Homework
• Read Ch. 6
• Vocabulary for Ch. 6
• “Test Your Knowledge”
Multiple choice questions
on p. 114 and “Interpret
the Data” on p. 115