Topic 3: Cell
Structure
(part 2)
Chapter 6: Concepts 6.2–6.7
Slide 1
(C) Jennifer Doering 2022
Slide 2
(C) Jennifer Doering 2022
Housekeeping Notes
1. Important Dates
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Wednesday, Sept. 21st: ADD date
2. First quiz is next Monday (Sept. 26th)
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Covers topics 1-3 (Intro to Biology, Chem Review, Biomolecules,
Cell structures)
Available from 6pm-9pm (i.e. window of opportunity)
20 minutes to write, +2 min grace period to ensure your answers
are saved
Can expect a variety of question types (e.g. MC, T/F, matching,
ordering, etc.)
Will need to complete an Academic Integrity Declaration “quiz” to
gain access to the quiz
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Slide 3
Will be released at 5:30pm on the day of the quiz
(C) Jennifer Doering 2022
After today’s lecture, you should be able to:
• Upon successful completion of this topic, you, the student, will be able to:
1. Describe the limitations to cell size based on the surface area to volume ratio.
2. Compare the structure of bacterial and eukaryotic cells.
3. Explain the endomembrane theory and the evolution of eukaryotes.
a. Outline the evidence supporting this theory.
4. List the organelles of the endomembrane system.
a. Describe the structure of these organelles.
b. Outline the function(s) of these organelles.
5. Explain the endosymbiont theory and the evolution of mitochondria and chloroplasts.
a. Outline the evidence supporting this theory.
6. Compare the structure and basic function(s) of the three cytoskeletal elements.
7. Compare the flagellum structure between bacteria and eukaryotes.
8. List the basic functions of bacterial pili.
9. Compare the cell walls of bacteria, fungi, and plants.
10. Describe the four types of cellular junctions.
11. Diagram the linkage between the extracellular matrix and intracellular cytoskeleton.
12. Draw and label a bacterium and the typical cells of a plant and animal.
Slide 4
(C) Jennifer Doering 2022
6.4 The Endomembrane system drives cell processes
ER lumen (space
inside the ER)
Cytosolic
ribosomes make:
RER ribosomes
make:
• EM proteins
• Secreted
proteins
• Cytosolic proteins
• Proteins that go to
the mitochondria
and chloroplast
Slide 5
(C) Jennifer Doering 2022
6.4 The Endomembrane system drives cell processes
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With all of these proteins, how do they know where they are
supposed to go in the cell?
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Built in “postal codes” within their amino acid sequence
Other proteins in the cell recognise these postal codes and direct
these newly made proteins to their final destination
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Hydrophobic amino acids in a specific order -> endomembrane
signalling sequences
Charged amino acids in a specific order -> mitochondrial signal
sequences
No signalling sequence amino acids are destined for the cytosol
The signal sequence gets recognized by another protein, which guides the ribosome to
the rough ER. The protein will then be made through the RER membrane into the ER
lumen.
This figure is from 2nd
year cell bio… don’t
memorize it!
Slide 6
(C) Jennifer Doering 2022
6.4 The Endomembrane system drives cell processes
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The endomembrane
system (EM) is
comprised of:
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Slide 7
Nuclear envelope
(discussed in
Lecture 6)
Endoplasmic
reticulum
Golgi apparatus
Lysosomes
Vesicles and
vacuoles
Plasma membrane
The EM system has many functions:
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Protein synthesis (for both proteins staying in the cell or being
exported)
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Protein transport (into membrane-bound organelles or out of the cell)
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Metabolism
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Movement of lipids
(C) Jennifer Doering 2022
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Detoxifying the cell
6.4 The endoplasmic reticulum (ER) – the factory
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An extensive network of flattened
membrane sacks (called
cisternae)
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ER lumen is the space between
ER membranes
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Slide 8
Endoplasmic = within the
cytoplasm
Reticulum = little net
Space is continuous with the
nuclear lamina
(C) Jennifer Doering 2022
6.4 The endoplasmic reticulum (ER) – the factory
Rough ER
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Studded with ribosomes
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Continuous with nuclear envelope
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Production of glycoproteins
• Proteins with carbs covalently
bonded to them
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Separates and transports proteins out
by transport vesicles
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Production of phospholipids and other
proteins
Smooth ER
Slide 9
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Lacks ribosomes
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Production of lipids (oils, steroids
(sex hormones), and phospholipids)
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Metabolises carbs
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Detoxifies the cell (adds hydroxyl
groups to drugs) -> in liver cells
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Storage of calcium ions -> in muscle
cells to trigger contraction
(C) Jennifer Doering 2022
6.4 The Golgi Apparatus – the sorting facility
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A series of flattened sacs
(cisternae)
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Sugars added to glycoproteins,
production of complex
carbohydrates (ex. Pectin),
refining of phospholipids
Vesicles pinch off of the trans
face and head to their final
destination within or outside of
the cell
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Slide 10
The cis side faces the rough ER
(younger)-> “the receiving end”
The trans side points out
towards the rest of the cell
(older) -> “the shipping end”
Vesicles bring material from the
rough ER to the cis face, fusing
with the Golgi membrane
Materials are modified as they
pass through the Golgi apparatus
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Camillo
Golgi,
1843-1926
Based on those amino acid
“postal codes”
Looks like a stack of
pancakes with
berries
TEMs are snapshots of the cell at a
certain time but cells and organelles
(C) Jennifer Doering 2022
are dynamic
6.4 The Lysosome – the digestor and recycler
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Membranous sac of hydrolytic enzymes
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Can break down all of the macromolecules into monomers
Inside is very acidic (low pH) -> around pH 5
If a lysosome ruptures (lyses), contents aren’t digested because the cytosol
pH is too high for the enzymes (pH 7)
Two kinds of intracellular digestion:
Phagocytosis
Slide 11
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Amoebas and other unicellular eukaryotes
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Food vacuole merges with a lysosome
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Digestive enzymes break down the food
molecules into monomers
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Macrophages (White blood cells) use this
process to kill bacteria and other invaders
(C) Jennifer Doering 2022
6.4 The Lysosome – the digestor and recycler
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Membranous sac of hydrolytic enzymes
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Can break down all of the macromolecules into monomers
Inside is very acidic (low pH) -> around pH 5
If a lysosome ruptures (lyses), contents aren’t digested because the cytosol
pH is too high for the enzymes (pH 7)
Two kinds of intracellular digestion:
Autophagy (“self eating”)
Slide 12
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Damaged organelles get surrounded by
a magic double membrane
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Merges with a lysosome which digests
the materials with hydrolytic enzymes
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Monomers and molecules are recycled
by the cell
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Lacking lysosomal enzymes can result
in rare genetic disorders
• Tay-Sachs disease -> brain
becomes impaired due to too much
lipids in the cells
(C) Jennifer Doering 2022
6.4 The Vacuole – the transporter
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Large vesicles made from the
rough ER and Golgi apparatus
Food and digestive vacuoles
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Contractile vacuoles
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Previous slide
Pump out excess water from
freshwater single-celled
organisms
Plant vacuoles
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Storage for small molecules
Some hydrolysis of molecules
(similar to animal lysosomes)
Large central vacuole contains
inorganic ions (potassium and
chloride) and swells up due to
osmosis
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Slide 13
Pushes on the cell wall, giving
turgor pressure to allow plants
to stand upright against gravity
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Essential for plant growth
Contractile
vacuole of
Paramecium
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(C) Jennifer Doering 2022
6.5 Mitochondria and Chloroplasts – the energy converters
• Mitochondria
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In most eukaryotic cells (red blood cells lack)
Site of cellular respiration (another topic!)
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Slide 14
Extracts energy from C-C bonds by adding O2 to carbohydrates and fats,
etc. (oxidising fuels)
The energy is converted to ATP
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Energy is stored in high energy P-P bonds
(C) Jennifer Doering 2022
6.5 Mitochondria and Chloroplasts – the energy converters
• Chloroplasts
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Only in plants and algae
Absorbs energy from photons (light)
Energy is converted into ATP and NADPH which is then used to make
carbohydrate C-C bonds using CO2
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Slide 15
i.e. Photosynthesis (another topic!)
(C) Jennifer Doering 2022
6.5 Mitochondria and Chloroplasts – the energy converters
Some terminology:
• Heterotrophs = organisms that obtain their energy through consuming other
material
• Autotrophs = organisms that obtain their energy themselves (usually by
photosynthesis)
• Anaerobes = organisms that can’t survive in O2, and that can’t use O2 to
extract energy from molecules by aerobic respiration
• Aerobes = organisms that can survive in O2, and that can use O2 to extract
energy from molecules by aerobic respiration
• Note: using O2 as the final electron acceptor when extracting energy from
food yields the most energy! This is because the oxygen atom is so
electronegative! (this will all make more sense when we go over oxidative
respiration and discuss redox chemistry)
Slide 16
(C) Jennifer Doering 2022
6.5 How did these organelles get here?
• There was no oxygen in the atmosphere
• The first cells to arise were heterotrophs and anaerobes
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Couldn’t use O2 to fully extract energy from food via aerobic respiration
• Then autotrophs arose from prokaryotes
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Couldn’t use O2 to fully extract energy from food via aerobic respiration
Could make their own food via photosynthesis
By-product was oxygen, which “polluted” the air
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Oxygen is toxic to anaerobic organisms
• Then heterotrophic aerobes arose
in prokaryotes
• Could use O2 to fully extract
energy from food
• Couldn’t do photosynthesis
• Then eukaryotes arose
(endomembrane theory)
• Likely from anaerobic and
heterotrophic Archaea prokaryote
Slide 17
(C) Jennifer Doering 2022
6.5 How did these organelles get here?
• Endosymbiont theory
describes how mitochondria
arose
• A eukaryotic cell engulfed an
aerobic heterotrophic
prokaryotic cell that could use
oxygen
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The prokaryote was retained
and became the
mitochondria
Became an endosymbiont =
a cell living inside another
cell in a beneficial
relationship
• Evidence to support this theory
• Mitochondria (and
chloroplasts) are doublemembraned (unlike singlemembraned organelles)
• Contain their own set of DNA
and ribosomes
• Autonomous organelles (able
to grow and reproduce in the
cell)
Slide 18
(C) Jennifer Doering 2022
6.5 How did these organelles get here?
DISCUSSION:
The initial interaction between
the aerobic prokaryote and
the anaerobic eukaryote led
to a mutualistic relationship.
What did the aerobic
prokaryote get in this
interaction?
Hint: think of what the
anaerobic cell couldn’t do at
the time.
What did the anaerobic
eukaryote get in this
interaction?
Slide 19
(C) Jennifer Doering 2022
6.5 How did these organelles get here?
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Endosymbiont theory happened
again in photosynthetic
organisms!
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May have happened several
times, independently amongst
plant lineages
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It’s a debate that is still
ongoing!
• A eukaryotic cell with mitochondria
engulfed an autotrophic
prokaryote which could do
photosynthesis
• Eventually became the
chloroplast
What’s the advantage for
having both chloroplasts
and mitochondria???
Slide 20
(C) Jennifer Doering 2022
6.5 Mitochondria structure and function
• Consists of two membranes
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Intermembrane space in between
Inner membrane folded to make cristae which encloses the mitochondrial
matrix
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Contains the DNA and ribosomes
Catalyses cellular respiration
• Krebs cycle
• Electron transport chain
• Later topic (topic 6)
• Range in size (1-10µm)
• Number per cell varies depending on cell function/metabolic activity
Note:
Mitochondria do
not make
energy, they just
convert chemical
energy into
different forms
Slide 21
(C) Jennifer Doering 2022
6.5 Chloroplast structure and function
• Consists of two membranes
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Intermembrane space in between
Inner membrane folded to make thylakoids which are stacked to form grana
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Contains the DNA and ribosomes in the stroma
Photosynthesis
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Photon capture
Electron transport chain
ATP and NADPH synthesis
Calvin cycle
Later topic (topic 7)
• Range in size (3-6µm)
• Contains chlorophyll (green pigment)
Slide 22
Note: Chloroplasts do not make energy,
they just convert photon energy into
different forms (carbon-carbon bonds)
Stroma: space between the
thylakoid space and inner
membrane
(C) Jennifer Doering 2022