D’YOUVILLE COLLEGE
PMD 604 - ANATOMY, PHYSIOLOGY, PATHOLOGY II
CELL BIOLOGY I
Lecture 1: Endomembrane system, Energetics
G & H chapter 2 & parts of chapters 67 - 69
1.
Introduction:
• physicochemical system:
- cells are highly organized, highly improbable, living systems that operate
a 'steady state' relationship with their environment, obeying laws of basic chemistry
and physics (physicochemical systems)
- the high degree of order requires energy to maintain it, since the overall
tendency of the universe is to increase disorder (entropy)
- cellular homeostasis (constant conditions) employs a steady state or flowthrough system that avoids establishment of chemical equilibrium (which is a state of
no change = no work) (ppt. 1)
- cellular metabolism (collective reactions) includes both energy-yielding
(exergonic) reactions (ppt. 2) and energy-requiring (endergonic) reactions; by
coupling reactions (ppts. 3 & 4), cells channel energy from the environment towards
maintenance of an exquisite orderly system
2.
Chemicals of a normal cell
• inorganic – 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)
• organic - 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
3.
Organelles (fig. 2 – 2)(ppt. 5):
• plasma membrane (fig. 2 – 3) (ppt. 6): selective permeability; controls
interaction with cellular environment; consists of phosphoglyceride bilayer fortified
by cholesterol (fluid matrix) and proteins (mosaic) that 'float' in or on the fluid
matrix; fluid-mosaic model accounts for transport of materials across membrane
(permeability), signal reception, cell-cell binding & cell recognition (ppt. 7)
- diffusion (channels or lipid bilayer)
PMD 604 - lec 1
- p. 2 -
- carrier-mediated transport (protein shuttles)
- active transport (carriers energized by ATP)
- endocytosis (phagocytosis & pinocytosis) (fig. 2 – 11 & ppt. 8)
- exocytosis (secretion & excretion)
- receptors: signal transduction, cellular recognition, & specific endocytosis
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- p. 3 -
• mitochondrion (fig. 2 – 7 & ppt. 9): ‘powerhouse of the cell’ (provides energy
– synthesis of ATP)
- enzymes of Krebs cycle & electron transport (figs. 67 – 6, 67 – 7 & ppt. 10)
- enzymes of fatty acid oxidation (fig. 68 – 2)
• endoplasmic reticulum (figs. 2 – 4 & ppt. 11): smooth & rough – site of
biosynthesis reactions
- enzymes of protein synthesis (ribosomes of rough ER)
- enzymes of lipid biosynthesis; enzymes of detoxification reactions
(smooth ER)
• Golgi apparatus (fig. 2 – 5 & ppt. 12): modification & distribution of
synthesized products
- formation of lysosomes
• lysosome (fig. 2 – 12 & ppt. 13): bag of digestive enzymes; role in
endocytosis, role in removal of endocytic damage
• cytoskeleton (ppt. 14): maintenance of cell shape & regulation of movement
in the cell (fig. 2 - 17 & ppt. 15)
• nucleus (ppt. 16): stores genetic material; provides genetic control of cell
activities
3.
Endomembrane System: (pp. 20 – 22, fig. 2 – 13 & ppt. 17)
• nuclear envelope and ER (sites of biosynthesis – product enters cistern)
• transport vesicles pinch off from ER, migrate to Golgi apparatus; movement
of organelles or other materials through cytoplasm is facilitated by microtubules
(ppt. 18)
• Golgi apparatus – cis face (nuclear side) accepts 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
Energy Metabolism – Mitochondria: (figs. 2 – 7, 2 – 14 & 2 – 15 +
selected parts of chapters 67, 68 & 69)
4.
• ATP – cell’s energy currency (p. 21, fig. 67 – 2 & ppt. 19); contains energyrich bonds
• oxidation-reduction – oxidation = loss of electrons from a substrate
(exergonic); reduction = gain of electrons by a substrate (endergonic); oxidation &
reduction must always occur together (ppt. 20)
- energy from oxidations drives ATP synthesis via oxidative
phosphorylation
- stepwise oxidations (dehydrogenations) remove electrons with hydrogens
from a substrate; carriers of these high-energy electrons include NAD (pp. 813 – 814
& ppt. 21) or FAD
- energy from active metabolic intermediates drives ATP synthesis via
substrate level phosphorylation (ppt. 22)
PMD 604 - lec 1
- p. 4 -
- some reactions occur in the cytosol; majority occur within mitochondrion
(ppt. 23)
PMD 604 - lec 1
- p. 5 -
• glycolysis (fig. 67 – 5 & ppt. 24) – 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 (ppt. 25) – 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
• Krebs cycle (fig. 67 – 6 & ppt. 26) – within mitochondrion, 2 acetyl CoAs (2C 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) (ppt. 27)
• oxidative phosphorylation (fig. 67 – 7 & ppts. 28 & 29) – 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 (fig. 67 –
7 & ppt. 29)
- each reduced FAD furnishes enough energy to produce 2 ATPs
• fatty acid oxidation (fig. 68 – 2 & ppt. 30) – larger energy yield/gram than
glucose; large quantities of acetyl CoA removed by formation of ketone bodies (p.
844)
• oxidative deamination and urea formation (ppt. 31) – mechanism for
oxidation of amino acids yields reduced NAD & ammonia; ammonia is converted to
urea for excretion
• uses for ATP (fig. 2 – 15 & ppt. 32) – provides energy for transport, for
motility & for biosyntheses