Lec 13: Energy from Food Flashcards
How do enzymes maximize the energy harvested from the oxidation of food molecules?
They allow the stepwise oxidation of food molecules, which releases energy in smaller amounts
Which step generates the largest number of ATP molecules?
Electron transport chain
In step 6 of glycolysis, glyceraldehyde 3-phosphate, which has one phosphate group, is converted into 1,2-biphosphoglycerate, which has two. Where does the extra phosphate group come from?
A free phosphate molecule. This is the only substrate-level phosphorylation in glycolysis that creates a high-energy phosphate linkage directly from a free phosphate
In eukaryotic cells, why must metabolism be tightly regulated?
The substrate molecules involved in metabolic reactions can be used by a number of different enzymes.
Ex: pyruvate is a substrate for half a dozen or more different enzymes (it can be converted to acetyl coA or lactate, and can be used to make oxaloacetate or the amino acid alanine
How is energy captured from the breakdown of food molecules?
Food molecules are broken down in successive steps, and the energy is captured in activated carriers such as ATP and NADH
What compartments do the different catabolic reactions occur in?
glycolysis in the cytosol, citric acid cycle in the mitochondrial matrix, and oxidative phosphorylation on the inner mitochondrial membrane
What happens to glucose during glycolysis?
It is a 6-carbon sugar that is split into two 2-carbon sugars called pyruvate, and produces small amounts of ATP and NADH
What is the basic metabolic pathway of pyruvate is the presence of oxygen?
eukaryotic cells convert it to acetyl coA plus CO2 in the mitochondrial matris. The citric acid cycle then converts the acrtyl coA to CO2 and H2), capturing the energy as high-energy electrons in teh activated carries NADH and FADH2.
How are fatty acids metabolized?
They are produced from the digestion of fats, and are imported into the mitochondria and are converted to acetyl coA molecules, which are then further oxidized through the citric acid cycle
What are intermediate products used for from glycolysis and the citric acid cycle?
Many of the intermediate products are starting points for the anabolic pathways that lead to the synthesis of proteins, nucleic acids, and the many other organic molecules of the cell.
How do plant and animal cells store glucose?
Animals store it as glycogen, plants store it as starch.
Both plants and animals store fatty acids as fats
acetyl coA
activated carrier that donates carbon atoms in its readily transferable acetyl group to many metabolic reactions, including the citric acid cycle and fatty acid biosynthesis. It releases a large amount of energy when hydrolyzed
catabolism
set of enzyme-catalyzed reactions by which complex molecules are degraded to simpler ones with release of energy; intermediates in these reactions are sometimes called catabolites
cell respiration
process by which cells harvest the energy stored in food molecules. Usually accompanied by the uptake of O2 and the release of CO2
citric acid cycle
series of reactions that generate large amounts of NADH by oxidizing acetyl groups derived from food molecules to CO2. In eukaryotic cells, this central metabolic pathway takes place in the mitochondrial matrix
electron transport chain
a series of membrane-embedded electron carrier molecules that facilitate the movement of electrons from a higher to a lower energy level, as in oxidative phosphorylation and photosynthesis
fermentation
the breakdown of organic molecules without the involvement of molecular oxygen. This form of oxidation yields less energy than aerobic cell respiration
gluconeogenesis
set of enzyme-catalyzed reactions by which glucose is synthesized from small organic molecules such as pyruvate, lactate, or amino acids. In effect, the revers of glycolysis
shape of glucose
6-carbon sugar
Glycogen
branched polymer composed exclusively of glucose units used to store energy in animal cells. Granules of this material are especially abundant in liver and muscle cells
oxidative phosphorylation
membrane-based process in bacteria an mitochondria in which ATP formation is driven by the transfer of electrons derived from food molecules to molecular oxygen
what pyruvate looks like
3-carbon metabolite that is the end product of the glycolytic breakdown of glucose; provides a crucial link to the citric acid cycle and many biosynthetic pathways.
substrate-level phosphorylation
process by which ATP is formed by the transfer of a phosphate group from a substrate molecule to ADP. Substrates that participate in this forms of ATP synthesis must carry a phosphate group that is linked via a “high energy” covalent bond
What is the overall process for cells converting food to energy?
Food is broken down by catabolic pathways into energy, cellular building blocks, and heat.
Energy and cellular building blocks are turned into macromolecules through anabolic pathways
What is the essence of cellular metabolism?
It is one of the most ancient metabolic pathways
Overview of the breakdown of glucose through glycolysis and the citric acid cycle (“central metabolism”)
What is the energy flow in the entire ecosystem?
3 stages of cellular metabolism from food to waste products
Stage 1: breakdown of large food molecules into simple subunits
Stage 2: breakdown of simple subunits to acetyl coA: limited amounts of ATP and NADH produced
Stage 3: Complete oxidation of the acetyl group in the acetyl coA to H2O and CO@. Large amounts of ATP produced in the inner mitochondrial membrane
Steps of glycolysis
How much CO2 is generated from the breakdown of one glucose molecule in pyruvate during glycolysis?
none
What happens during steps 6 and 7 of glycolysis?
energy is harvested
How do steps 6 and 7 of glycolysis allow the formation of a high-energy phosphate bond?
How is pyruvate oxidized to acetyl coA?
It is oxidized to acetyl coA and CO2 by pyruvate dehydrogenase
Pyruvate has 3 carbons, and acetyl coA has two, so one carbon is lost in this part of the cycle
How do animals derive energy between meals?
most animals derive the energy from fatty acids
How are fatty acids metabolized?
They can have a very long fatty acid tail, and two carbon at a time are systematically broken down to generate acetyl coA
What is the citric acid cycle?
a circular reaction where two carbons at a time (one acetyl coA molecule) is turned into 2 CO2 molecules and energy in the form of NADH
almost every intermediate in central metabolism is used as a building block for something else. There are enough citric acid cycle reactions happening at once (millions?) that losing a few molecules for something else is totally fine
What is generated from pyruvate once glycolysis is done?
the electron transport chain drives the synthesis of most of the ATP in most cells.
O2 is consumed, CO2 and H2O are produced
Fermentation leading to the excretion of lactate
in muscle
Fermentation leading to anaerobic microbial growth
The whole point is to generate NAD so you can use it for glycolysis to generate more ATP. Fermentation actually consumes energy
With oxygen. Without oxygen they don’t get the benefit of the citric acid cycle
Think how much of evolution is a probabilities game. What is the probability of a viable alternative pathway just springing up?
There is no definite answer to this question
Steps of the citric acid cycle
pyruvate and fatty acids that are broken down enter the mitochondrial matrix, where they are converted into acetyl coA
The citric acid cycle oxidized acetyl coA into CO2 molecules (the CO2 is supplied by water, not by molecular O2.)
1) acetyl coA (2 carbons) combines with oxaloacetate (4 carbons) to form citrate (aka citric acid).
2) things are rearranged
3) first of four oxidation steps: creates NADH and loses a CO2, down to five carbons
4) second oxidation step: forms NADH and CO2, down to four carbons
5) forms GTP
6) third oxidation step: forms FADH2
7) adds a water into the molecule
8) fourth and final oxidation step: NADH is formed, but still four carbons: the end result is oxaloacetate, which begins the cycle again.
