CELLULAR METABOLISM
I. Metabolism- the sum of all chemical activities inside the cell
examples- respiration, protein, lipid & carbohydrate synthesis, cell movement, cell division, etc.
A. Metabolic pathways- the individual steps in a chemical reaction which occurs in the cell
1. Anabolic- reaction(s) which utilizes energy from cell to build bonds. Building large molecules
from smaller ones
examples- protein synthesis from amino acids & photosynthesis
2. Catabolic- reaction which gives off energy by breaking bonds. Breaking large
molecules into smaller ones
examples- digestion & cellular respiration
II. Enzymes and Enzymatic reactions
Enzyme- protein that acts as a catalyst in metabolic reactions
-substrate binds to the active site and enzymes perform necessary chemical steps
-named for the substrate and name ending change to (-ase)
Most metabolic pathways require several enzymes working together to produces the needed
products- enzymatic reaction
A. Factors that affect enzymatic reactions
Denaturation- change in shape of an enzyme which renders it inactive; loss of active site
1. Inhibitors- molecules that attach to the enzyme
- competitive inhibitors- attach to the active site
- noncompetitive inhibitors - attach to adjacent side but changes shape of active site
2. Temperature- at low temps molecules don't move around as found and therefore
reaction rates are slow
-as temps increase reaction rates increase
optimal temperature- temp at which reaction rates are highest
critical temperature- temp at which an enzyme denatures
Hydrogen bonds are disrupted and therefore changes secondary structure of enzyme
3. pH- affects the ionization of the side chains therefore changing the tertiary structuring
optimal pH- pH at which reaction rate is highest
critical pH- pH at which enzyme denatures
B. Coenzyme- protein that binds with the enzyme and assists in chemical reactions
-usually carries needed molecules, atoms, or electrons
-most vitamins are coenzymes
C. Dehydrogenase- enzymes which removes hydrogen atoms
-oxidation reaction- reaction where hydrogen atoms are removed (electrons)
-reduction reaction- reaction where hydrogen atoms are added (electrons)
1. NAD- nicotinamide adenine dinucleotide
- a large coenzyme that contains the vitamin niacin
- acts as an oxidizing agent by accepting Hydrogen atoms and electrons
2. FAD- flavin adenine dinucleotide
-works the same as NAD
III. Energy related reactions
-Energy within the body is stored in the chemical bonds within all molecules
1. ATP- Adenosine triphosphate
- molecule which acts as an energy storage molecules
- used in macromolecule synthesis, active transport, muscle contraction, etc.
ATP Cycle-continuous regeneration cycle of ATP from ADP
ATP is oxidized to become ADP
ADP is reduced to become ATP
IV. Aerobic Respiration- Cellular respiration
aerobic- requires oxygen
Cellular respiration is a catabolic pathway with 3 smaller subpathways:
1. Glycolysis
2. Krebs cycle (Citric Acid Cycle)
3. Electron transport chain
* a sub reaction between glycolysis and Krebs occurs - Transition reaction
A. Site for Respiration-- Mitochondria
- 2 membraned organelle responsible for carrying out respiration spaces
- intermembrane space- area between outer and inner membranes; contains a high
H+ concentration- (acidic)
-matrix- area inside the inner membrane; low concentration of H+ (less acidic)
-cristae- folds in the inner membrane - allows for greater surface area
B. Glycolysis- The breakdown of glucose into 2 molecules of pyruvate (pyruvic acid) and
2 net molecules of ATP
The pathway consists of 10 enzymatic rxns.
Some rxns. restructure and some break molecules
Glycolysis overall rxn.
C6H12O6 + 2 ADP + 2 NAD + 2 ATP ---> 2 C3H3O3 + 4 ATP + 2 NADH + 2H2O
(Glucose) (pyruvate)
* A net of 2 ATP is produced from glycolysis
Image: Pathway
C. Gluconeogenesis is the production of glucose from noncarbohydrate precursors (lactate, pyruvate, glycerol, amino acids).
-the brain and red blood cells are completely independent upon glucose as a source of metabolic energy,
which is obtained from glycogen which is stored in the liver. The liver is only able to store enough energy, in fasting states,
to supply the brain with glucose for 12 hours.
-this occurs primarily in the liver and to a smaller extent the kidneys
-all precursors are first converted to oxaloacetate (the first reactant in the Kreb's cycle)
1. three enzymatic steps in glycolysis release large amounts of free energy which makes it thermodynamically
impossible to reverse these steps (hexokinase, phosphofructokinase, and pyruvate kinase) so they are different in
gluconeogenesis. energy profile -- energy comparison -- geography of gluconeogenesis
a. pyruvate carboxylase/ PEP carboxykinase (PEPCK)- these convert pyruvate and HCO3- to oxaloacetate and then
oxaloacetate to phophoenolpyruvate (PEP). Both of these are endergonic so they are coupled with ATP/GTP oxidation.
b. fructose bisphosphatase (FBPase) & glucose-6-phosphatase are both hydrolases that releas inorganic phosphates.
Resource: Regulation of Glycolysis & Gluconeogenesis. --Regulation pathway -- Energy regulation
D. Glycogenesis/Glycogenolysis: Glucose storage in most animals occurs as glycogen, a complex polymer of glucose (containing
glc a1-4 glc and glc a1-6 glc linkages). The high degree of branching promotes in rapid degradation of glucose units.
The rapid mobilization and utilization of glycogen is important because lipid metabolism is slower than carbohydrate metabolism,
fatty acids cannot be metabolized anaerobically, and animals cannot convert fatty acids to glucose.
E. Pentose phosphate pathway is a metabolic pathway that produces ribose-5-phosphate (a precursor for nucleotide biosynthesis)
and NADPH.
-NADPH is not interchangeable with NADH. It is involved in other endergonic reductive reactions, such as lipid and
nucleotide biosynthesis.
F. Transition Reaction (Pyruvate dehydrogenase--oxidative decarboxylation process)
-Between Glycolysis and the Krebs Cycle is an intermediate reaction which prepares
pyruvate for the Kreb's cycle. Pyruvate is transported into the mitochondria by a pryuvate-H+ symport.
-Transition Rxn. pyruvate is converted to Acetyl Coenzyme A (Active acetate) and CO2
is released. The hydrolysis of the thioester bond has a DGo of -31.5 kJ/mol (-30.5 kJ/mol for ATP)
-Five sequential reaction steps for this reaction has the following overall stoichiometry:
pyruvate + CoA + NAD+ --> acetyl-CoA + CO2 + NADH
Question: How important is pyruvate in an organism?
F. Krebs Cycle (Citric Acid Cycle)
-Eight step enzymatic reaction which oxidizes Acetyl CoA to CO2
Overall chemical reaction:
Acetyl CoA +3 NAD+ + FAD + ADP ---> 2 CO2 + 3 NADH + FADH + ATP + CoA-SH
**The Krebs cycle will happen twice per molecule of glucose
Resource: Regulation of Krebs
Resource: Kreb's Cycle and the enzymes
G. Electron Transport Chain. Site of Oxidative Phosphorylation
1.A reaction which uses proteins embedded in the inner membrane of mitochondria
to produce ATP.
2. The reaction is fueled by a proton gradient across the inner membrane
3. Oxygen gas serves as the final electron acceptor in the reaction
4. Each step of the reaction reduces the potential energy of electrons by building potential energy
in the proton gradient. (Pumping H+ ions from low to high concentration)
5. The energy stored in the proton gradient is utilized to convert ADP to ATP
ATP Synthase- carrier protein which passes hydrogen from inter-membrane space to the matrix
and assists in production of ATP
-Each NADH from Krebs makes 3 ATP molecules whereas the NADH from glycolysis makes only 2 ATP
-Each FADH2 from Krebs makes 2 ATP molecules
-So. (8NADH x 3ATP) + (2FADH2 x 2ATP) + (2NADH x 2ATP) + (4 ATP) = 36 ATP per glucose
V. Cellular respiration of macromolecules
metabolite- molecule other than glucose that undergoes cellular respiration
1. Proteins- polymers of amino acids
-The protein must first be broken into individual amino acid monomers
-As the amino acid enters the chain, the alpha amino is stripped off and released
as ammonia(NH3)- exits the body as urea in the urine
-The amino acid will then enter the reaction depending upon the number of
carbon atoms in the side chain
Resource: Protein Metabolism
2. Fats- contain glycerol and 3 fatty acid chains
-cleavage breaks at the ester linkage
-glycerol will transform to PGAL and enter glycolysis there
-the fatty acid chains will be broken into 2 carbon molecules where they will react to form
acetyl CoA and enter the Krebs cycle
Resource:Fat Metabolism
VI. Anaerobic Respiration
-Respiration in the absence of oxygen
-Anaerob- bacteria or yeast that carry out anaerobic respiration
A. Fermentation- anaerobic catabolism of organic molecules
Because there is an absence of oxygen the Krebs cycle and Electron transport chains
are not needed
1.Alcohol fermentation- the final product is ethyl alcohol (ethanol)
Glucose --> 2 ethanol + 2 ATP + 2 CO2
NAD is recycled within the reaction itself
2. Lactic Acid fermentation. Definition
Glucose --> 2 lactic acid + 2 ATP
-human body can produce lactic acid in low levels of oxygen
produced when heavy exercise increases glucose catabolism beyond oxygen
consumption of the muscle --- muscle fatigue
PHOTOSYNTHESIS
I. Light
A. The major source of energy for all life is the sun
Energy comes the from nuclear fusion of hydrogen to helium
Energy emitted from sun is called electromagnetic energy or radiation.
- this energy travels in the the form of waves
1. wavelength - the distance from crest of a wave to the crest of the adjacent wave
2. Electromagnetic spectrum- the entire collection of different wavelengths that are emitted from the sun
3. Photon - bundle of light energy- shorter the wavelength the more energy the wave has
4. Visible light can be reflected or absorbed.
-reflected- the light waves bounce off the surface
-absorbed- the light wave (photon) is taken into the surface.
-White - 100 % of all visible light is reflected
-Black - 100 % of all light is absorbed.
-The color of the object is the wavelength(s) of light reflected, all other light is absorbed
II. Plant Anatomy (for photosynthesis)
A. Chloroplast
1. chloroplast- double membraned organelle in plants which is responsible for photosynthesis
2. stroma- large central space inside inner membrane -contains many enzymes which assist in photosynthesis
3. thylakoid- flattened sacs used to capture light energy
4. thylakoid space- the space inside the thylakoids- high H+ concentration
5. grana- stacks of thylakoids
6. stroma lamellae- connective membranes between grana
7. chlorophyll- green pigment found within the chloroplasts
B. Reactions
1. Light Reaction. Light is absorbed by pigments in the thylakoid membrane where energy-rich electrons stimulate
the production of NADPH and ATP.
a. The thylakoid membrane houses two different photosystems that absorb light which then emit high energy electrons
b. The electrons are replaced from water. This produces H+ ions and O2
c. The high energy electrons move down an electron transport chain which pump H+ ions from the stroma into the
thylakoid interior.
d. The H then fall back through an ATPsynthase which produces ATP
e. The final electron acceptor is NADP+, which forms NADPH
2. Calvin Cycle (Dark Reaction). Carbon dioxide fixation. The NADPH and ATP from the light reaction provide the
the energy for producing glucose from carbon dioxide. This takes place in the stroma of the chloroplast.
a. 6 molecules of CO2 enter the cycle. Rubisco, an enzyme, is responsible for fixing CO2 to an existing molecule.
b. 6 molecules of Ribulose phosphate (5-C each) affix 6 CO2 to make 12 phosphoglycerates (PGA) (3-C each)
c. ATP and NADPH are used to convert these to 12 phosphoglyceraldehydes (PGAL) (3-C each)
d. 2 PGAL are removed to make glucose, while 10 return to remake 5 Ribulose phosphates (5-C each).
