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Bio 160
Unit 2 – 1
Week Two- Lecture One
Cellular Functions
• Thermodynamics and energy
–
is the capacity to do work
• Kinetic
- actual work
• Potential
- stored work
• Heat
- given off from the movement of
molecules
• Chemical
stored for cells
– Thermodynamic laws- energy transformations
• 1st law- energy can neither be created nor
destroyed, but it may change form
• 2nd law- law of entropy- energy transformation
results in chaos of randomness. (entropy)
– Implication for the 1st law
• Energy that comes to us from the sun can be
transferred into many different forms through
different systems
– Implications for the 2nd law
• As one environment becomes more organized, all
around it becomes disorganized
• Disorganized energy is heat
– A cell creates an ordered space, increasing the entropy
around it, so it can not be transfer or transform energy
100% efficiently, therefore energy can not be transferred
100% through a system. Most is given off as heat
• Chemical reactions store or release
energy
– Endergonic reactions require energy to be put
into the system, then stores energy in the
chemical products. (ex. Photosynthesis)
– Exergonic reactions release energy out of the
system from energy rich bonds being broken
in the reactants. (ex. Cellular respiration)
• Cellular Metabolism- all of the endergonic
and exergonic reactions of a cell
– ATP- adenosine triphosphate powers nearly
all forms of cellular work
• Obtained from food molecules
• Energy coupling reactions for cellular metabolisms
are run by ATP
– ATP is a little unstable, so it can be broken down to ADP
through hydrolysis
» A phosphate is removed, releasing energy
(dephosphorylation)
» Exergonic reaction
» Phosphorylation- ADP receives a phosphate
converting it to ATP, energizing it to perform work
» Dephosphorylated ATP is converted to ADP:
adenosine diphosphate by the removal of a
phosphate, releasing energy for the cell to do work.
– During cell respiration ADP is phosphorylated through
dehydration synthesis and converted back to ATP.
Therefore it is renewable source.
– Enzymes control the rate of chemical
reactions without being consumed or changed
in any way. (Biological catalyst protein)
• Works by lowering the energy barrier or the energy
of activation energy needed to start a reaction
• The enzyme has no effect on the amount of energy
content of reactants or products, just on the rate of
the reaction.
• Enzymes are very specific in where they work
– Use a “lock and key” mechanism. The active site on the
enzyme must have the appropriate “fit” with receptor site
on the protein substrate
• Enzymes require a specific environment to function
optimally. (Temp, pH, salinity, etc.)
– Some enzymes also require a non-protein cofactor or
coenzyme (organic molecule) to function properly.
• Enzymes may be blocked from their substrates by
inhibitor chemicals
– Competitive inhibitor- competes with the enzymes normal
substrate, tying up the enzyme
– Non Competitive inhibitor- binds to the enzyme outside of
the active site, changing the shape of the enzyme,
preventing the enzyme from fitting with its own substrate
– Inhibitors regulate cell reaction rates by slowing it down
» Negative feedback regulation of metabolism
Cellular Membranes
• Cellular Membranes control cellular
metabolic functioning
– Phospholipid bilayer made of a mosaic of
different small fragments that can move
laterally in the membrane
• Membranes are selectively permeable, allowing
certain substances in and out, but not others.
– Types of movement across cell membranes
• Passive Mechanisms allow movement without the
use of energy
• Diffusion- molecules moving from areas of [] to
[] through random molecular motion
• Passive Transport- diffusion of a substance across
a membrane along a [ ] gradient until equilibrium
is reached
• Osmosis- diffusion of water molecules across a
selectively permeable membrane
– When water molecules can move across a membrane
but the solute cannot, different concentrations of solutes
may result
» Hypertonic- a solution with a higher [ ] of solutes in it
that the surrounding solution is considered to by
hypertonic it its solution
» Hypotonic- A solution with a lower [ ] of solutes in it
than the surrounding solution is said to be hypotonic
to its solution
» Isotonic- the [ ] of solute is the same on both sides of
the membrane
» In all of the solutions, water will cross the s.p.
membrane to reach equal concentrations. The
direction of osmosis is determined only by the
difference in total solute [ ].
» Water balance is controlled by osmoregulation
• Facilitated diffusion- a special protein embedded in
the cell membrane called a transport protein
regulates the diffusion of larger molecules down
their [ ] gradients, thereby facilitating the diffusion
– Active transport mechanisms require cell energy to move
substances across the membrane. Uses ATP
phosphorylation to activate transport protein
» Exocytosis- cellular expulsion of molecules using
cellular energy
» Endocytosis- cellular intake of macromolecules using
cellular energy
─ pinocytosis-cellular intake of fluid droplets
─ phagocytosis- engulfing of large particles
from outside the cellular membrane
─ receptor- mediated endocytosis- engulfing of
specific molecules through the use of
receptor proteins
Cellular Respiration
• The process of creating ATP the organism
needs by using the materials the body
takes in
– Overall process
– Cells only use 40% of energy released from
glucose. Other 60% lost as heat
– During the chemical conversion process of
the reaction, e- are released from one set of
molecules and are attached to others, giving
off energy in the process
• Accomplished by H atoms moving places (fig. 6.4)
– H carried by NAD+ (nicotinamide adenine dinucleotide)
through an oxidation-reduction (redox) reaction
» 2 hydrogens and 2 e-’s are first peeled off of a
glucose molecule in an oxidation reaction (loss of e-)
» The H and 2 e- are shuttled through the oxidation by
NAD+ coenzymes and dehydrogenase enzyme
» NAD+ becomes reduced, picking up H+ and 2 ebecoming NADH. The other H+ goes into the fluid
surrounding the cell
− the NADH stores the energy for the cell
» The energy from the redox reaction is released when
NADH releases its e- carriers to become NAD+
again
− The e- carriers “fall” down a series of energy level
carriers like a stair step
−Called electron transport chain (e- “dance”)
−The e- carrier proteins (levels) are
imbedded in mitochondrial membranes of
the cristae
• 2 mechanisms to generate ATP
– Chemiosmosis- uses concentration gradients
and ATP synthatase proteins found in
membranes to generate most of their ATP
– Substrate level phosporylation- without a
membrane, transfers a phosphate group from
an organic molecule to ADP, happens in the
conversion of glucose to CO2 in the Kreb’s
cycle
• 3 stages of Cell Respiration (fig. 6.8)
– Glycolysis- splitting of sugar anaerobically
• Occurs in cytoplasm without oxygen needed\
• Oxidizes glucose into pyruvic acid through 9 chemical steps
• 2 separate stages of glycolysis
– First stages are preparatory and consume energy
» ATP is used to split one glucose into 2 smaller sugars that are
primed to release energy
•
Since the prep phase uses 2 ATP, only 2 ATP are the
end product generated by glycolysis
– Produced through substrate- level phosphorylation
– 2 molecules of NAD+ are reduced to NADH
• 2 ATP are available for immediate use by the cell
• NADH must enter electron transport system for E to be released
– Must have O2 to release E
– Second stages release energy
» Happens in tandem
» NADH is produced when a sugar molecule is
oxidized and 4 ATP are generated
• Total end products of glysolysis:
2 ATP + Heat + 2 pyruvic acid
– Kreb’s Cycle- aerobic respiration
• Pyruvic acid must be groomed to enter the Kreb’s
Cycle
– It is oxidized while a molecule of NAD+ is reduced to
NADH
– A C atom is removed and released in CO2
– Coenzyme A joins with what is remaining of the pyruvic
acid to form AcetylCoenzyme A
– The acetyl part then enters the kreb’s cycle, the
coenzyme A splits off and is recycled
• Kreb’s cycle happens in the cristae of the
mitochondria
– Acetyl fragment combines with the oxaloacetic acid
already in the mitochondria
– This forms citric acid. A molecule of CO2 is released and
NAD+ is reduced to NADH, which releases an e- to the
electron transport system
– Citric acid is converted to alpha- ketoglutaric acid,
phosphorylated to produce ATP and NAD+ is reduced to
NADH, again releasing an e- to the electron dance. Fourcarbon succinic acid results.
– At succinic acid, enzymes rearrange chemical bonds
FAD, a related hydrogen carrier similar to NAD, is
reduced to FADH, releasing more e- to the electron
dance. Malic acid is formed (FAD= flavin adenine
dinucleotide)
– At malic acid NAD+ is reduced to NADH and a H+ ion,
adding more e- to the dance. Malic acid is converted to
oxaloacetic acid, which is ready to accept a new acetyl
group for another turn at the cycle
• End products of Kreb’s: 36 ATP + CO2 + HEAT
– 2 ATP are from substrate- level phophorylation
– Approx 34 ATP are formed by chemiosmotic phosphorylation
» The electron transport chains are built into the convoluted
cristae of the mitochondria, there are many sites for the
electron dance to occur
• Electron transport system is third stage of cellular respiration
• Pathways for dietary carbohydrates, lipids and
proteins
– Carbohydrates break down into sugars that eventually
break down into glucose and then goes into glycolysis
• Quick access energy
– Lipids are broken down through hydrolysis into fatty
acids and glycerol
• Fatty acids may be stored as fat, be converted into ketone
bodies (acetone) and further broken down to enter the Kreb’s
or eliminated, or undergo beta- oxidation and be converted
straight into Acetyl Co A
• Glycerol may be converted into Acetyl Co A and enter the
Kreb’s or be converted to glucose and undergo glycolysis
• Yields high energy when used but likes to be stored rather
than used
• 2x as much ATP as in the same amount of starch
– Proteins undergo hydrolysis to break into amino acids
that are then broken into deaminated portions which
can go to fat, glucose, and acetyl Co A to enter
glycolysis/Krebs cycles. The other portion of the
amino acid is the NH2 (Ammonia) group, which is
excreted through urea
• Long term energy- takes long time to digest
• Food Molecules are used for other stuff besides
Kreb’s Cycle
– Used for biosynthesis (uses ATP to do so)
• Produces proteins, lipids, and polysaccharides
• Used for growth and repair