Transcript Document

Ch. 2
Cell Physiology
Objectives
• Understand what the Cell Theory states
• Identify organelles and state their function
• Know how Mitochondria produce ATP
The Cell Theory
• All living things are composed of cells
• Cell are the smallest unit of life
• All cells come from pre-existing cells
• The cell is the structural and functional unit of
life
Cells
• Cells vary in size
• Small size of cells makes them efficient
• Focus on eukaryotic cells
Two major kinds of cell
• Eukaryotic cell
– Complex organization
– True nucleus present
• Stores DNA
– Many membrane bound organelles
• Specialized for a particular function
• Not all membrane bound
– Cell wall present in some organisms
– Size: 10 – 100 μm
Eukaryotic Cell Structure
• Nucleus
– Control center of the cell
– Bound by nuclear membrane
– Stores hereditary information
• Nucleolus
– Within nucleus
– Responsible for making rRNA
• Ribosome subunits
• Ribosomes
– Sites of protein synthesis in a cell
• Two subunits
–
Three binding sites where mRNA and tRNA interact
– Free floating or attached to membranes
Eukaryotic Cell Structure
• Endoplasmic reticulum (ER)
– Two types
• Rough ER
– Synthesis of proteins for export and
membrane construction
– Ribosomes present
• Smooth ER
– Synthesis of lipids
– Detoxification of drugs and poisons
– produces vesicles for transport
Eukaryotic Cell Structure
• Golgi Complex
– UPS of the cell
– Receive molecules from the ER
• Modify, sort, and deliver
– Vesicles do the delivering
– Vesicles are specific in the
cargo they carry
Specificity of Vesicles
• Finished proteins contain sorting signals
– Bind to specific recognition sites
• Coatomers bind to vesicle membrane surface
– Cause bulging to occur
– Eventually buds off
• V-SNARE bind to t-SNARE on plasma membrane
– Ensures that content of vesicle is secreted out of the
cell
Eukaryotic Cell Structure
• Lysosomes
– Digestive compartments
• Hydrolysis
• Breakdown old or damaged organic matter
– Autophagy
• Foreign material
– Endocytosis
» Phagocytosis
» Pinocytosis
» Receptor-mediated
– Also function in programmed cell death
– Defects may lead to storage disorders
• Pompe’s disease
• Tay-Sachs disease
Eukaryotic Cell Structure
• Peroxisomes
– Contain oxidative enzymes
– Enzymes remove H from various substrates and
add it to O, producing hydrogen peroxide
• catalase
– Have many functions
• Metabolism of fatty acids
• Detoxification
Mitochondria and ATP Production
• Mitochondria
– The powerhouse of the cell
– Site of cellular respiration and ATP production
• Endosymbiotic theory
– Believed to have been prokaryotes that formed a
symbiotic relationship with precursor eukaryotic cells
• Cellular respiration
–
–
–
–
Glycolysis
Acetyl CoA production
Citric acid cycle
Electron transport chain
Overview of ATP Production
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Key
Glucose
Carbon atoms
ATP
Phosphate
groups
1 Phosphorylation
ADP
Glucose 6-phosphate
Glycogen
Fat
Fructose 6-phosphate
ATP
2 Priming
ADP
Fructose 1,6-diphosphate
3 Cleavage
2 PGAL
2 Pi
2 NAD+
2 NADH + 2 H+
4 Oxidation
2
2 ADP
2 H2O
2 ATP
2
5 Dephosphorylation
2 ADP
2 ATP
2
2 pyruvic acid
2 NADH + 2 H+
2 NAD+
2
2 lactic acid
Anaerobic fermentation
Aerobic respiration
End-products of
glycolysis are:
2 pyruvic acid + 2 NADH
+ 2 ATP + 2 H+
Aerobic Respiration
• Most ATP generated in mitochondria
– Oxygen required as final electron acceptor
• Pyruvate decarboxylated
– Combines with coenzyme A to enter matrix
• Occurs in two principal steps:
– Matrix reactions – controlling enzymes are in the fluid of the
mitochondrial matrix
– Membrane reactions - controlling enzymes are bound to the
membranes of the mitochondrial cristae
Mitochondrial Matrix Reactions
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Pyruvic acid (C3)
6
CO2
NAD+
7
NADH + H+
Acetyl group (C2)
8
Acetyl-Co A
Coenzyme A
H2O
9
Citric acid (C6)
Oxaloacetic acid (C4)
H2O
10
NADH + H+
NAD+
(C6)
Citric
acid
cycle
18
H2O
NAD+
11
NADH + H+
(C4)
12
CO2
17
(C5)
H2O
NAD+
13
Occurs in
mitochondrial
matrix
(C4)
14
16
FADH2
NADH + H+
(C4)
CO2
FAD
(C4)
Pi
15
GTP
ADP
GDP
ATP
Membrane Reactions
• Membrane reactions have two purposes:
– to further oxidize NADH and FADH2 and transfer their energy
to ATP
– to regenerate NAD+ and FAD and make them available again
to earlier reaction steps
• Mitochondrial electron-transport chain – series of
compounds that carry out this series of membrane
reactions
Members of the Transport Chain
• Flavin mononucleotide (FMN) – derivative of riboflavin similar
to FAD
– bound to a membrane protein FMN accepts electrons from NADH
• Iron-sulfur (Fe-S) centers – complexes of iron and sulfur atoms
bound to membrane proteins
• Coenzyme Q (CoQ) – accepts electrons from FADH2
– small mobile molecule that moves about in the membrane
• Copper (Cu) ions – bound to two membrane proteins
• Cytochromes – five enzymes with iron cofactors
– brightly colored in pure form
– in order of participation in the chain, b, c1, c, a, a3
Electron Transport
• hydrogen atoms are spilt apart as they transfer from
coenzymes to the chain
• protons pumped into the intermembrane space
• electrons travel in pairs (2 e-) along the transport chain
• each electron carrier becomes reduced when it receives an
electron pair and oxidized again when it passes the electrons
along to the next carrier
• oxygen is the final electron acceptor
– each oxygen atom accepts two electrons from cytochrome a3 and two
protons from the mitochondrial matrix forming water
• body’s primary source of metabolic water – water synthesized in the body
– this reaction explains the body’s oxygen requirement
– no oxygen, cell produces too little ATP to sustain life
Electron Transport Chain
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50
NADH + H+
Relative free energy (kcal/mole)
40
NAD+
FADH2
Enzyme complex 1
F AD
30
1
20
Enzyme complex 2
10
½ O2 + 2 H+
Enzyme complex 3
0
Reaction progress
H2O
Chemiosmotic Mechanism
• electron transport chain energy fuels respiratory
enzyme complexes
– pump protons from matrix into space between inner and
outer mitochondrial membranes
– creates steep electrochemical gradient for H+ across inner
mitochondrial membrane
• inner membrane is permeable to H+ at channel
proteins called ATP synthase
• chemiosmotic mechanism - H+ current rushing back
through these ATP synthase channels drives ATP
synthesis
Chemiosmotic ATP Synthesis
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Intermembrane
space
Matrix
Cristae
Figure 26.6
Inner membrane
Outer membrane
NADH +
H+
½ O2 + 2 H+
NAD+
6 H+
H2O
Matrix
2e–
Inner
membrane
Enzyme
complex
1
CoQ
2e–
2e–
Enzyme
complex
2
Enzyme
complex
3
Cyt c
Intermembrane
space
Outer
membrane
2 H+
2 H+
2 H+
3 ADP + 3 Pi
3 ATP
ATP
synthase
Overview of ATP Production
• NADH releases an electron pair to electron
transport system and H+ to prime pumps
– enough energy to synthesize 3 ATP
• FADH2 releases its electron pairs further along
electron-transport system
– enough energy to synthesize 2 ATP
• complete aerobic oxidation of glucose to CO2 and
H2O produces 36-38 ATP
– efficiency rating of 40% - 60% is lost as heat
ATP Generated by Oxidation of Glucose
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Glucose
2
Glycolysis
ATP
(net)
2 NADH + 2 H+
Cytosol
2 pyruvate
Mitochondria
2 NADH + 2 H+
CO2
6 NADH + 6 H+
Citric acid
cycle
2 ATP
Figure 26.7
2 FADH2
Electron-transport
chain
O2
H2O
4 ATP
28–30
Total 36–38
ATP
ATP
Vaults and Cytosol
• Vaults
– May function as cellular transporters
– True function unknown
• Cytosol
– Gel-like semiliquid that occupies most of the cell
volume
– involved with
• Intermediary metabolism
• Ribosomal protein synthesis
• Inclusions
The Cytoskeleton
• Structural support of the cell
• Composed of three types of protein fibers
– Microtubules
• Tubulin
• Maintain shape of asymmetrical cells
• Also functions in cellular locomotion and movement
– Microfilaments
• Actin
• Cellular contractile systems
• Mechanical stiffeners
– microvilli
– Intermediate filaments
• Resist mechanical stress
The Cytoskeleton
The Cytoskeleton
• Centrioles
– Assembly of microtubules
– Function in cell divison
• Other functions
– Cellular movement
• Cilia and flagella
– Transport of materials
• Dynein-kinesin motor proteins
The Plasma Membrane
• Surrounds all living cells
• Composed of a phospholipid bilayer
– Polar hydrophilic heads on the outside, nonpolar
hydrophobic tails on the inside
• Fluid mosaic model
– Proteins and cholesterol embedded
Beyond the Plasma Membrane
• Extra Cellular Matrix
– Surrounds plasma membrane of animal cells
• Protection and regulation