metabolic processes Flashcards
Processes that yield energy
Cells derive their energy from the chemical bonds of organic molecules. The metabolic processes that break down sugars and other food sources to derive energy consist of two major types:
a. Fermentation: Break down 6C sugars to 3C or 2C compounds to derive some energy. Occurs without oxygen.
b. Respiration: Break down 6C sugars in presence of oxygen to CO2 and H2O; most efficient source of energy. C6H12O6 + 6O2 ----> 6 CO2 + 6H2O + energy (ATP + heat)
Cellular Respiration
Most important is the process of respiration, so we will examine these pathways first, then come back to fermentation. Respiration consists of 4 main phases:
Glycolysis
Pyruvate Oxidation
Krebs cycle
Electron transport/oxidative phosphorylation
Four Stages of Cellular Respiration
Glycolysis
10-step process in the cytoplasm
Pyruvate oxidation
Three-step process in the mitochondrial matrix
Krebs Cycle
Eight-step cyclical process occurring in the mitochondrial matrix
Electron transport chain & chemiosmosis
Multi-step process occurring in the inner mitochondrial membrane
Review of cell parts:
Cells in eukaryotic organisms consist of
cell membrane: lipid bilayer that serves as a boundary
nucleus: contains the genetic material of the cell
cytoplasm: the region surrounding the nucleus, made of cytosol and organelles
organelles, such as the mitochondrion: carry out particular specialized functions in the cell. The mitochondrion carries out many processes related to energy metabolism.
Energy Transfer
1st Law of Thermodynamics
Energy cannot be created or destroyed
Cells must convert chemical potential energy in glucose into another usable form of energy
REDOX reactions
In many chemical reactions, there is a transfer of one or more electrons from one reactant to another. These are called oxidation-reduction or redox reactions.
In an oxidation-reduction reaction, one substance loses electrons; we say it is oxidized. The other substance gains electrons; we say it is reduced.
in the REDOX reaction
In the reaction:
Xe- + Y —-> X + Ye-
X is the electron donor or the reducing agent; Y is the electron acceptor or the oxidizing agent.
The overall process of respiration involves oxidation and reduction:
C6H12O6 + 6O2 —-> 6 CO2 + 6H2O
Glucose is oxidized and oxygen is reduced in the process.
Electron carriers
Many of the individual reactions that comprise the process of respiration are oxidation-reduction reactions.
The following are 2 molecules that are typically involved as electron carriers in redox reactions. When we see these molecules involved, we can be fairly certain that oxidation and reduction reactions are going on.
NAD (nicotinamide adenine dinucleotide)
FAD (Flavin adenine dinucleotide)
two key coenzymes
NAD (nicotinamide adenine dinucleotide)
Aids in cellular respiration by carrying electrons and protons (H+)
FAD (Flavin adenine dinucleotide)
Aids in cellular respiration by carrying electrons and protons (H+)
The previous slide shows NAD+: nicotinamide adenine dinucleotide.
The molecule consists of two nucleotides joined together.
Oxidized NAD+ can carry two electrons and a proton donated from an organic substrate. We describe the reaction as:
NAD+ + 2e- + 2H+ ----> NADH + H+ oxidized reduced
*(LEO says GER)
Lose electron Oxidized ; Gain electron Reduced
REDOX cont.
Chemical energy from reduced NADH is usually released by the processes of electron transport and oxidative phosphorylation.
Essentially what happens is the electrons and protons are passed from reduced NADH through a series of electron carriers and ultimately to oxygen, forming water.
The energy is conserved in these transfers and is used to make ATP.
Glycolysis
Glycolysis is the first of the 4 phases of cellular respiration.
- In glycolysis, glucose is broken down in the cytosol into two molecules of pyruvate.
- The products of glycolysis include some stored energy as ATP, NADH, which can be a source of additional energy and the 3 carbon compound pyruvate, which can be oxidized further by the Krebs cycle.
what is glycosis?
Glycolysis means “splitting of sugar”. Glucose (6C sugar) is split into two 3C sugars and the 3C sugars are further oxidized.
The catabolic pathway consists of ten steps each catalyzed by a specific enzyme. We can divide the steps into two phases:
energy investment phase: requires ATP
energy pay-off phase: makes ATP by “substrate-level phosphorylation” and makes NADH by oxidation/reduction.
