D’YOUVILLE COLLEGE
BIOLOGY 689 - INTERMEDIATE PHYSIOLOGY I
CELL BIOLOGY I
Endomembrane system, Energetics
1.
Cells:
• chemicals of cells – water (milieu for metabolic reactions, participant in some
reactions, product of some reactions)
- ions (activators of enzymes, maintenance of osmotic balance, basis for electrical
properties of cell membranes)
- proteins – polymers of amino acids; provide structural components of
cytoskeleton & extracellular fibrous components (e.g. tendons, ligaments), provide
motility, provide membrane transport, provide enzymes & specific receptor molecules
- lipids – include phosphoglycerides & cholesterol (constituents of cell
membranes), include triglycerides (storage of energy)
- carbohydrates – especially glucose and glycogen, provide energy
- nucleic acids – hereditary information & genetic implementation
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• physical attributes (derived from light microscopy (fig. 2 - 1 & ppt. 1),
electron microscopy (fig. 2 – 2 & ppt. 2), cell fractionation (ppt. 3), etc.(ppts. 4 - 6)
2.
Organelles: (fig. 2 – 2 & ppt. 7)
• nucleus (nuclear envelope, chromatin, nucleolus - fig. 2 - 9 & ppt. 8); genetic
storage
• plasma membrane – fluid mosaic model (fig. 2 – 3 & ppt. 9): lipid bilayer
with embedded proteins, some carbohydrates – details in lec. 4; exchange with ECF
• endoplasmic reticulum - rough, smooth; biosynthesis – (fig. 2 – 4 ppt. 10)
• ribosomes - protein synthesis
• vesicles (storage, secretion – fig. 2 – 6 & ppt. 11)
• Golgi apparatus - cis-trans polarity, packaging center (fig. 2 – 5 & ppt. 12)
• lysosomes - hydrolytic enzymes, digestion, cellular autolysis (figs. 2 - 11, 2 12 & ppt. 13 to 15)
• peroxisomes (oxidases, detoxification)
• centrosome (microtubules – fig. 2 – 8); formation of microtubules
• cytoskeleton (structural stability, motility)
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• mitochondria (energy metabolism – fig. 2 – 7 & ppt. 16)
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3.
- p. 4 -
Endomembrane System: (fig. 2 - 13 & ppts. 17 - 19)
• nuclear envelope and ER (sites of biosynthesis – product enters cistern)
• transport vesicles pinch off from ER, migrate to Golgi apparatus
• Golgi apparatus – cis face (nuclear side) accept transport vesicles (fusion);
biosynthesized product modified as it passes through
• secretion vesicles or lysosomes pinch off from trans face (cell membrane
side) of Golgi apparatus
4.
Energy Metabolism – Mitochondria: (figs. 2 – 7, 2 – 14 & ppts. 20 to 22)
• ATP – cell’s energy currency (p. 21, fig. 67 – 2 & ppt. 23); contains energyrich bonds
• uses for ATP (fig. 2 – 24 & ppt. 24) – provides energy for transport, for
contractile functions & for biosyntheses, etc.
• oxidation-reduction – oxidation = loss of electrons from a substrate;
reduction = gain of electrons by a substrate; oxidation & reduction must always occur
together
- stepwise oxidations (dehydrogenations) remove electrons with hydrogens
from a substrate; carriers of these high-energy electrons include NAD (fig. 67 - 7 &
ppt. 25) or FAD
• glycolysis (fig. 67 – 5 & ppt. 26) – initial stepwise oxidation of glucose
(occurs in cytosol)
- two phases: energy investment phase – uses 2 ATP to activate glucose
- energy payoff phase – 6-C sugar split into two 3-C molecules, oxidized (2
reduced NAD formed), 4 ATP formed (net gain of 2), ends with 2 pyruvic acids
- aerobic vs. anaerobic pathways – with oxygen present (aerobic
condition), pyruvic acid is converted to acetyl CoA (in mitochondrion) to enter Krebs
cycle; in absence of oxygen (anaerobic pathway), need to restore NAD (oxidized) is
fulfilled by reduction of pyruvic acid to lactic acid
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• Krebs cycle (fig. 67 – 6 & ppt. 27) – within mitochondrion, 2 acetyl CoAs
(2-C molecule) are formed by oxidation (2 reduced NADs formed) and removal of 2
carbon dioxides from 2 pyruvic acids; acetyl CoA is donor to Krebs cycle
- each acetyl CoA combines with a 4-C acceptor acid to form a 6-C acid
(citric acid); 6-C acid progresses through two dehydrogenations (2 reduced NADs
formed) and two decarboxylations (CO2 removal) to form an energy-rich 4-C acid
(succinyl CoA), which provides energy for ATP synthesis; resulting 4-C acid
progresses through two further dehydrogenations (reduced NAD & reduced FAD
formed) to regenerate 4-C acceptor (ready to combine with another acetyl CoA)
- overall energy yield/glucose (2 acetyl CoAs): 6 reduced NADs, 2 reduced
FADs & 2 ATPs + 2 more reduced NADs (from pyruvic acid oxidation)
• oxidative phosphorylation (fig. 67 – 7 & ppt. 28) – high-energy electrons
(from reduced NAD & from reduced FAD) pass through a chain of enzymes, giving
up their energy to drive ATP synthesis (phosphorylation); final electron acceptor is
oxygen, which combines with hydrogen ions to form water
- each reduced NAD furnishes enough energy to produce 3 ATPs;
- each reduced FAD furnishes enough energy to produce 2 ATPs
- summary of aerobic respiration (ppt. 29)
• other fuels (ppt. 30):
• fatty acid oxidation (fig. 68 – 2 & ppts. 30 & 31) – larger energy yield/gram
than glucose; large quantities of acetyl CoA removed by formation of ketone bodies
(p. 823)
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• oxidative deamination and urea formation – mechanism for oxidation of
amino acids yields reduced NAD & ammonia; ammonia is converted to urea for
excretion (ppt. 32)