Unit 3: Cellular Energetics
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What is bioenergetics?
the study of how living organisms acquire, transform, and utilize energy through various cellular processes
What is the First Law of Thermodynamics?
cells cannot take energy out of thin air; it must be harvested from some place
What is the Second Law of Thermodynamics?
energy transfer leads to less organization, meaning the universe ends toward disorder; in order to power cellular processes, energy input must exceed energy loss to maintain order
What are exergonic/exothermic reactions?
those in which the products have less energy than the reactants
What are endergonic/endothermic reactions?
those in which the products have more energy than the reactants and thus require an input of energy
What is a catalyst?
something that speeds a reaction up
What are enzymes?
biological catalysts that speed up reactions by lowering the activation energy and helping the transition state to form
What is enzyme specificity?
the trait in which each enzyme catalyzes only one kind of reaction
What are enzymes usually named after?
the molecules they target
What are substrates?
the targeted molecules in enzymatic reactions
What is the active site?
a special region on the enzyme that allows it to perform its job
What is the enzyme-substrate complex?
a structure formed when the enzyme temporarily binds one or more of the substrates to its active site
When does induced-fit occur?
when enzymes have to change their shape slightly to accommodate the shape of the substrates
Why do enzymes operate only under a strict set of biological conditions?
because the fit between the enzyme and the substrate must be perfect
What are cofactors?
factors that help enzymes in catalyzing reactions
What are enzymatic reactions influenced by?
temperature
pH
relative concentration of substrates and products
How does temperature affect enzymatic reactions?
the rate of a reaction increases with increasing temperature because it increases the frequency of collisions among the molecules
What happens if the enzyme is exposed to too much heat?
the enzyme can be damaged and denatured
When is enzyme denaturation reversible?
if the optimal environmental conditions of the enzyme are restored
How does pH affect enzymatic reactions?
enzymes function best a particular pH
How does the relative concentration of substrates and products affect enzymatic reactions?
an increase in substrate concentration will initially speed up the reaction, but once all the enzyme in the solution is bound by substrate, the reaction can no longer speed up
What is saturation point?
the concentration of substance where all of the enzyme in a reaction is bound by substrate
How can a cell control enzymatic activity?
by regulating the conditions that influence the shape of the enzyme
How can enzymes be turned on or off?
by things that bind to them
What is competitive inhibition?
when the substance has a shape that fits the active site of an enzyme so it can compete with the substrate over getting into the active site
How can you identify a competitive inhibitor?
based on what happens when you flood the system with lots of substrate
What is noncompetitive inhibition?
when the inhibitor binds to an allosteric site
What does a noncompetitive inhibitor do?
it generally distorts the enzyme shape so that it cannot function; the substrate can still bind to the active site, but the enzyme will not be able to catalyze the reaction
Where does the cell get its energy through?
adenosine triphosphate (ATP)
What does ATP consist of?
a molecule of adenosine bonded to three phosphates, with an enormous amount of energy packed into those phosphate bonds
What does the cell do when it needs energy?
it takes one of the potential-packed molecules of ATP and splits off the third phosphate, forming adenosine diphosphate (ADP) and one loose phosphate (Pi), while releasing energy in the process
What is the equation for the conversion of ATP to ADP?
ATP → ADP + Pi + energy
What is cellular respiration?
the process of breaking down sugar and making ATP
What is photosynthesis?
the process by which light energy is converted to chemical energy
What is the equation for photosynthesis?
6CO2 + 6H2O -> C6H12O6 + 6O2
What are the raw materials in photosynthesis?
carbon dioxide and water
What are the 2 stages of photosynthesis?
the light reactions and the dark reactions
When does the process of photosynthesis begin?
when photons of sunlight strike a leaf, activating chlorophyll and exciting electrons
What happens in photosynthesis once the chlorophyll is activated?
the activated chlorophyll passes the excited electrons down to a series of electron carriers, ultimately producing ATP and NADPH
What happens to the ATP and NADPH produced in photosynthesis?
they are both used in the dark reactions to make carbohydrates
What are chloroplasts?
the primary sites of photosynthesis that are located in the leaves of plants
What is the stroma?
the fluid-filled region found in the membranes of chloroplasts
What are grana?
the structures stacked liked coins within the stroma
What are thylakoids?
the many disk-like structures that make up grana
What is chlorophyll?
a light-absorbing pigment that drives photosynthesis
What is the thylakoid lumen?
the very inside of a thylakoid
What are antenna complexes?
the units that the light-absorbing pigments that participate in photosynthesis are clustered in
What are antenna pigments?
the pigments that gather light and bounce energy to the reaction center
What are the 2 types of reaction centers?
photosystem I (PS I) and photosystem II (PS II)
What is the principal difference between the reaction centers?
each has its own specific type of chlorophyll a that absorbs a particular wavelength of light
How do autotrophs produce ATP?
by using light, ADP, and phosphates
What does an absorption spectrum do?
show how well a certain pigment absorbs electromagnetic spectrum
What happens when a leaf captures sunlight?
the energy is sent to P680, the reaction center for photosystem II
What happens once energy is sent to P860?
the activated electrons are passed by P680 and passed to a molecule called the primary acceptor, and then they are passed to carriers in the electron transport chain
What is photolysis?
the process by which water is split into oxygen, hydrogen ions, and electrons to replenish the electrons in the thylakoid lumen, establishing a protein gradient, and as the hydrogen ions move back into the stroma through ATP synthase, ATP is produced
What happens when the electrons leave photosystem II?
they go to photosystem I, and the electrons are passed through a second electron transport chain until they reach the final electron acceptor NADP+ to make ADP
How do dark reactions make sugar?
by using the products of the light reactions (ATP and NADPH)
Where is carbon sourced from in dark reactions?
CO2
What is carbon fixation?
the process that converts CO2 from the air to carbohydrates, which occurs in the stroma of the leaf
What is the equation for cellular respiration?
C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP
What is aerobic respiration?
cellular respiration in which oxygen is present
What is anaerobic respiration?
cellular respiration in which oxygen is absent
What are the 4 stages of aerobic respiration?
glycolysis
formation of acetyl-CoA
the Krebs cycle
oxidative phosphorylation
What is glycolysis?
the splitting of glucose
Where does glycolysis occur?
in the cytoplasm
What does glycolysis result in?
2 pyruvic acids, 2 NADH, 2 ATP per glucose molecule (4 total)
What are pyruvic acids?
the 3-carbon molecules that glucose is broken down into during glycolysis
What is the equation for glycolysis?
glucose + ATP + 2 NAD → 2 Pyruvic acid + 4 ATP + 2 NADH
What happens during the formation of acetyl-CoA?
pyruvic acid is transported to the mitochondrion
each pyruvic acid is converted to acetyl coenzyme
acetyl-CoA and CO2 is released
What is the equation for the formation of acetyl-CoA?
2 pyruvic acid + 2 coenzyme A + 2 NAD → 2 Acetyl-CoA + 2CO2 + 2NADH
What is the pyruvate dehydrogenase complex (PDC)?
the enzyme complex that catalyzes the formation of acetyl-CoA
Where does the Krebs cycle occur?
in the mitochondrial matrix
What does the Krebs cycle begin with?
each molecule of acetyl-CoA (produced from the 2nd stage of aerobic respiration) combining with oxaloacetate to form a 6-carbon molecule, citric acid or citrate
What eventually happens to citrate in the Krebs cycle?
it gets turned back into oxaloacetate by joining with the next acetyl-CoA
What is produced with each turn of the Krebs cycle?
1 ATP, 3 NADH, and 1 FADH2
What happens as electrons are removed from a molecule of glucose?
they carry much energy that was originally stored in their chemical bonds, and the electrons are transferred to readied hydrogen carrier molecules
What 12 electron carriers are produced by the first 3 stages of aerobic respiration?
2 NADH from glycolysis
2 NADH from formation of acetyl-CoA
6 NADH from the Krebs cycle
2 FADH2 from the Krebs cycle
What do the 12 electron carriers do?
they “shuttle” electrons to the electron transport chain so the resulting NAD+ and FADH can be recycled to be used as carriers again
What is the proton gradient created by?
the pumping of hydrogen ions into the inter-membrane space
What is chemiosmosis?
the pumping and diffusion of ions to create ATP
What is oxidative phosphorylation?
the process of ATP formation when electrons are transferred by electron carriers from NADH or FADH2 to oxygen
How are photosynthesis and cellular respiration similar?
in both cases, ATP production is driven by a proton gradient, and the proton gradient is created by an electron transport chain
How do photosynthesis and cellular respiration differ?
in respiration, protons are pumped from the stroma into the thylakoids compartment, and they return to the matrix through an ATP synthase
in photosynthesis, protons are pumped form the stroma into the thylakoids compartment, and they return to the stroma through an ATP synthase down their concentration gradient