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Chapter 1
The Cell: A Microcosm of Life
2009 Cengage-Wadsworth
Cells--the essence of life
• Basic units of the body
• Eukaryotic cells
– Have a defined nucleus
– Evolved from prokaryotic cells (which
don’t)
• Specialization
2009 Cengage-Wadsworth
Components of Typical Cells
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Plasma membrane
Cytoplasmic matrix
Mitochondrion
Nucleus
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Peroxisomes
2009 Cengage-Wadsworth
Plasma Membrane
• Sheetlike structures made of
phospholipids & proteins
• Have hydrophobic & hydrophylic
moiety
• Phospholipids = phosphoglycerides
& phosphingolipids
• Proteins give them their functions
2009 Cengage-Wadsworth
Plasma Membrane
• Asymmetrical
• Fluid structures
• Distinct from other membranes:
– Greater CHO content
– Greater cholesterol content
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Plasma Membrane
• Lipid bilayer concept
• Glycocalyx
• Glycoproteins
• Membrane proteins
– Integral
– Peripheral
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Cytoplasmic Matrix
• Microtrabecular lattice or
cytoskeleton
– Microtubules
– Microfilaments
• Fluid
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Cytoplasmic Matrix
• Structural arrangement influences
metabolic pathways:
– Glycolysis
– Hexose monophosphate shunt
– Glycogenesis & glycogenolysis
– Fatty acid synthesis
• Communication
2009 Cengage-Wadsworth
Mitochondrion
• Energy production & oxygen use site
• Matrix surrounded by double membrane
• Mitochondrial membrane
– Outer membrane - porous
– Inner membrane - selectively permeable;
site of electron transport chain
2009 Cengage-Wadsworth
Mitochondrion
• Mitochondrial matrix
– Site of TCA cycle & fatty acid
oxidation
– Contains DNA so organelle can divide
• In all cells except erythrocytes
2009 Cengage-Wadsworth
Nucleus
• Contains DNA (genome)
• Surrounded by nuclear envelope
• Nucleoli - condensed chromatin
• DNA replication
• Protein synthesis = transcription,
translation & elongation
2009 Cengage-Wadsworth
Nucleus
• Nucleic acids
– DNA & RNA
– Consist of nucleotides or bases
• Adenine, guanine, cytosine in both
• Uracil in RNA only
• Thymine in DNA only
– Complementary base pairing
2009 Cengage-Wadsworth
Nucleus
• Cell replication
– DNA unravels and nucleotides are added to
each strand to make 2 sets
• Cell transcription
– mRNA created from sequence of 1 DNA
strand (sense strand)
– Genes
– Introns - intervening sequences
– Exons - no posttranslational processing
2009 Cengage-Wadsworth
Nucleus
• Translation
– mRNA codes for amino acid sequence
to form protein
– mRNA is synthesized in nucleus, then
moves to RER in cytoplasmic matrix
– Codons - 3-base sequences that code
for amino acids
– tRNA bring AAs to mRNA on
ribosomes
2009 Cengage-Wadsworth
Nucleus
– After AAs are positioned, peptide
bonds form between them =
elongation
– “Nonsense” codon signals end of
protein
2009 Cengage-Wadsworth
Endoplasmic Reticulum &
Golgi Apparatus
• ER = network of membranous
channels
• Types:
– Rough ER (studded with ribosomes) protein synthesis
– Smooth ER - lipid synthesis
– Sarcoplasmic reticulum (SER in
muscle) - calcium ion pump
2009 Cengage-Wadsworth
Endoplasmic Reticulum &
Golgi Apparatus
• Golgi apparatus
– Protein trafficking & sorting
– 4-8 cisternae
– Tubular networks at either end:
• Cis-Golgi network - entrance
• Trans-Golgi network - exit
– Connected to ER by transport vesicles
2009 Cengage-Wadsworth
Lysosomes & Peroxisomes
• Enzyme-filled organelles
• Lysosomes - cell’s “digestive
system”
• Peroxisomes - site of oxidative
catabolic reactions
2009 Cengage-Wadsworth
Lysosomes & Peroxisomes
• Lysosome functions:
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Phagocytosis
Autolysis
Bone resorption
Hormone secretion & regulation
• Peroxisome functions:
– Oxidize fatty acids to acetyl CoA
– Amino acid catabolism
– Detoxifying reactions
2009 Cengage-Wadsworth
Cellular Proteins
• Types:
– Receptors - modify cell’s response to
environment
– Transport proteins - regulate flow of
materials into & out of cell
– Enzymes - catalysts
2009 Cengage-Wadsworth
Receptors & Intracellular
Signaling
• Ligands - molecular stimuli that
attach to receptors
• Types of receptors:
– Bind to ligand & convert it to internal
signal
– Serve as ion channels
– Internalize stimulus intact
2009 Cengage-Wadsworth
Receptors & Intracellular
Signaling
• Internal chemical signal
– E.g. 3’, 5’-cyclic adenosine
monophosphate (cyclic AMP, cAMP)
• Ion channel
– E.g. receptor for acetylcholine
• Internalization stimulus
– E.g. insulin, triiodothyronine
2009 Cengage-Wadsworth
Transport Proteins
• May act as pumps
• May provide pores through which
molecules diffuse
• Most studied = sodium (Na+)
pump
– Na+/K+ -ATPase
2009 Cengage-Wadsworth
Catalytic Proteins (Enzymes)
• Functionality depends on protein &
prosthetic group or coenzyme
• Specificity
• Maximum velocity (Vmax) - enzyme
velocity at substrate saturation
• Km (Michaelis constant) - concentration
of substrate when reaction is at 1/2 of
maximum velocity
2009 Cengage-Wadsworth
Catalytic Proteins (Enzymes)
• Reversibility
• Regulation
– Covalent modification - usually
addition/removal of phosphate groups
– Allosteric - enzymes with another site
besides catalytic site that can bond
with modulator
– Induction - changes in concentrations
of inducible enzymes
2009 Cengage-Wadsworth
Catalytic Proteins (Enzymes)
• Examples of enzyme types
– Oxidoreductases - reactions in which
1 compound is oxidized, another
reduced
– Transferases - functional group
transferred from 1 substrate to
another
– Hydrolases - hydrolysis of carbon-?
bonds
2009 Cengage-Wadsworth
Catalytic Proteins (Enzymes)
– Lyases - cleavage of C-C, C-S, & C-N
bonds (no hydrolysis/O-R)
– Isomerases - interconversion of
optical or geometric isomers
– Ligases - catalyze formation of C-?
Bonds (O, S, N, others)
2009 Cengage-Wadsworth
Practical Clinical Application
of Cellular Enzymes
• Conditions for diagnostic suitability
– Enzyme’s degree of organ/tissue
specificity
– Steep concentration gradient of
enzyme activity between cell and
surroundings
– Enzyme must function in cytoplasm
– Enzyme must be stable
2009 Cengage-Wadsworth
Practical Clinical Application
of Cellular Enzymes
• Increased production factors
– Malignant disease
• Results in tumor markers
2009 Cengage-Wadsworth
Apoptosis
• Programmed cell death
• Potential mechanisms
– Intracellular stimuli
• Create DNA damage
• Release of cytochrome c
– Extracellular stimuli
• Tumor necrosis factor family of hormones
or agonists
– Oncosis
2009 Cengage-Wadsworth
Biological Energy
• ATP - major storage form in cells
• Energy needed for:
– Exertion
– Anabolism
– Active transport
– Transfer of genetic information
2009 Cengage-Wadsworth
Biological Energy
• Energy release and consumption in
chemical reactions
– Energy comes from macronutrients
– Transferred from one form to another
• Units of energy
• Free energy (G) - potential energy
in bonds of nutrients that is
released
2009 Cengage-Wadsworth
Biological Energy
• Exothermic and endothermic reactions
• Activation energy - energy to raise
reactants to transition state
• Cellular energy
• Reversibility of chemical reactions
• Standard free energy change
– 25°C, 1.0 atm, reactants/products at 1.0
mol/L concentrations
2009 Cengage-Wadsworth
Biological Energy
• Equilibrium constant (Keq) and
standard free energy change
• Standard pH - 7
• Nonstandard physiological
conditions
– In cells: ~37°C, concentrations often
not 1.0 mol/L, etc.
2009 Cengage-Wadsworth
Biological Energy
• The role of high-energy phosphate in
energy storage
• Coupled reactions in the transfer of
energy
– Phosphorylation - adding phosphate
• Reduction potentials
– Standard reduction potential (E0) tendency of compound to donate & receive
electrons
2009 Cengage-Wadsworth
Perspective 1
Nutritional Genomics:
The Foundation for
Personalized Nutrition
2009 Cengage-Wadsworth
Nutritional Genomics
• What is nutritional genomics?
• Pharmacogenomics as a model
• Mechanisms underlying nutritional
genomics
• Nutritional genomics & lipid
metabolism
• Opportunities for nutrition
professionals
2009 Cengage-Wadsworth