Transcript Airgas template - Morgan Community College

Chapter 1
Cell Structure and Function
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Cell Structure
Mitochondrion
Golgi apparatus
Nucleolus
Nucleus
Ribosomes
Endoplasmic
reticulum
Cell membrane
Lysosome
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Cell Components
• Nucleus and nucleolus
• Cytoplasm and cytoplasmic organelles
– Ribosomes
– Endoplasmic reticulum
– Golgi complex
– Lysosomes, peroxisomes
– Mitochondria
• Cytoskeleton
– Microtubules, microfilaments
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Red Blood Cells Start Out With All the
Organelles
• As they mature, they:
–
Lose their lysosomes
–
Produce hemoglobin
–
Have small Golgi bodies
–
Have enlarged endoplasmic reticulum
• When they are mature, they:
– Lose their endoplasmic reticulum
– Lose their mitochondria
How does this relate to their function?
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Question
By the time a red blood cell (RBC) is mature, it has lost all
but which of the following?
a. Lysosomes
b. Endoplasmic reticulum
c. Hemoglobin
d. Mitochondria
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Answer
c. Hemoglobin
Rationale: Because the function of the RBC is to carry
oxygen, hemoglobin is an essential component of the
cell (each hemoglobin molecule can carry four molecules
of oxygen). Lysosomes, endoplasmic reticulum, and
mitochondria all exert some metabolic function in other
cells. But, if they remained in the RBC, the oxygen on
board would be consumed before reaching its
destination.
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Anaerobic Energy Metabolism—Glycolysis
• In the cytoplasm, molecules are broken into 2-carbon
chunks
– Glycolysis breaks sugar  2 ATP molecules formed
– Other pathways break fatty acids or amino acids
– Breaking molecules involves removing electrons
º Handed to electron carriers like NAD and FAD
º H+ follows the electrons
– Afterwards, they are put back on the 2-carbon
chunks
º Forming lactic acid
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Aerobic Energy Metabolism—Krebs Cycle
• 2-carbon molecules
enter the
mitochondrion
matrix space
– Krebs cycle
breaks them
down  1 ATP
molecule
formed
– Carbon is lost
as CO2
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Krebs Cycle Occurs Within Mitochondria
• Breaking molecules involves removing electrons
– Handed to electron carriers like NAD and FAD
– H+ follows the electrons
– Many of these electron carriers are loaded up
with electrons by the Krebs cycle
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Question
Tell whether the following statement is true or false.
ATP is produced in the mitochondria.
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Answer
True
Rationale: The Krebs cycle occurs in the mitochondria.
Each Krebs cycle produces one molecule of ATP.
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Aerobic Energy Metabolism—Oxidative
Phosphorylation
Inside mitochondrion matrix:
Many electron carriers carry
electrons
Many H+ ions follow them,
attracted to the negative
electrons
In inner
mitochondrial
membrane:
Proteins that can
carry electrons
cross the
membrane
And that can
make ATP when
H+ ions pass
through them
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Aerobic Energy Metabolism—Oxidative
Phosphorylation (cont.)
• Electron carriers
pass electrons to
the membrane
proteins
• H+ ions follow the
electrons across
the membrane,
but the electrons
are passed back
into the
mitochondrion
electrons
H+
H+
H+
H+
H+
H+
electrons
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Aerobic Energy Metabolism—Oxidative
Phosphorylation (cont.)
• H+ ions are attracted electrons
to the electrons
+
H
but can only get
back into the
mitochondrion by
H+
going through the
ATP-producing
+
H
protein
• This is how most
ATP is made
electrons
H+
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H+
H+
H+
Aerobic Energy Metabolism—Oxidative
Phosphorylation (cont.)
• Now the H+
ions are
reunited with
the electrons
inside the
mitochondrion
electrons
• They combine
with oxygen to
form H2O
H+
H+
H+
H+
H+
H+
electrons
oxygen
H+
H+
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Basic Energy Metabolism—What Three Points
Would You Add to This Diagram?
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Diffusion Is Movement of Molecules
• Passive diffusion: molecules move randomly
away from the area where they are most
concentrated
• Facilitated diffusion: molecules diffuse across
a membrane by passing through a protein
• Osmosis: diffusion of water molecules
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Osmosis: Which Way Will Water Move?
Blood:
Few solutes
Lots of water
Cell:
Many
solutes
Less water
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Water Diffuses From the Place With Lots of
Water to the Place With Less Water
Blood:
Few solutes
Lots of water
Cell:
Many
solutes
Less water
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“Water Follows Solutes”
Blood:
Few solutes
Lots of water
Cell:
Many
solutes
Less water
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Na+ Diffuses into a Cell—What Will Water
Do?
Na+
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The Cell’s Na+/K+ ATPase Pumps the Na+
Back Out—What Will Water Do Now?
3 Na+
2 K+
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Question
Your patient has been given an intravenous solution of
water. What will happen to this patient’s red blood cells?
a. They will burst/lyse.
b. They will shrink.
c. They will not be affected by the water solution.
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Answer
a. They will burst/lyse.
Rationale: Osmosis causes movement from “more watery”
to “less watery.” Because water is “more watery” than
the RBC (it’s water, after all), water moves into the cell,
causing it to expand and burst/lyse.
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Cell Communication
• A messenger molecule attaches to receptor
proteins on cell surface
• Receptor proteins cause cell to respond by:
– Opening ion channels to let ions in or out
– Causing a second molecule to be released
inside the cell
– Turning on enzymes inside the cell
– Stimulating the transcription of genes in the
nucleus
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The Basics of Cell Firing
• Cells begin with a
negative charge:
resting membrane
potential
Action
potential
Threshold
potential
• Stimulus causes
some Na+ channels
to open
Resting
membrane
• Na+ diffuses in,
potential
making the cell
more positive
Stimulus
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The Basics of Cell Firing (cont.)
• At threshold
potential, more
Na+ channels open
• Na+ rushes in,
making the cell
very positive:
depolarization
• Action potential:
the cell responds
(e.g., by
contracting)
Action
potential
Threshold
potential
Resting
membrane
potential
Stimulus
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The Basics of Cell Firing (cont.)
Action
potential
• K+ channels open
• K+ diffuses out,
making the cell
negative again:
repolarization
• Na+/K+ ATPase
removes the Na+
from the cell and
pumps the K+
back in
Threshold
potential
Resting
membrane
potential
Stimulus
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Question
Tell whether the following statement is true or false.
An action potential is the result of K+ movement out of the
cell.
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Answer
False
Rationale: An action potential occurs when Na+ moves
into the cell, making it more positive on the inside
(depolarization). When K+ leaves the cell, it becomes less
positive (more negative) until it returns to resting
membrane potential (repolarization).
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Acetylcholine (ACh)
Starts Contraction
• What will happen
if ACh receptors
are destroyed?
• What will happen
if you block
acetylcholinesterase?
acetylcholine
released from
motor neuron
attaches to receptor
on muscle cell
acetylcholinesterase
destroys
acetylcholine and
stops the firing
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opens Na+
gates
Na+ enters cell
and muscle cell
depolarizes
Na+ enters cell
and muscle cell
depolarizes
Ca2+ released
from sarcoplasmic
reticulum into the
sarcoplasm
Ca2+
attaches to
troponin
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Ca2+
attaches to
troponin
troponin and
tropomyosin move
off actin binding site
myosin attaches
to actin binding
site
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Contraction Uses
Energy
• Myosin uses
ATP to pull
actin
• It also needs
ATP to let go
of actin
• Why does a
dead body
become stiff?
myosin attaches
to actin binding
site
myosin uses
energy from ATP
to pull actin
myosin lets go of
actin and reaches
forward
myosin picks up a
new molecule of
ATP
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Question
What happens to the sarcomere when myosin slides across
the actin binding sites?
a. It gets longer.
b. It gets shorter.
c. There is no change in length.
d. It releases acetylcholinesterase.
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Answer
b. It gets shorter.
Rationale: When the myosin binds with exposed actin
sites (myosin “reaches” forward like your hands do
when pulling end-over-end on a rope), the Z lines get
pulled closer together, and the muscle cell
shortens/contracts.
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