PHYSIOLOGY - Metabolism Flashcards
What is cellular respiration?
Process by which energy is harvested
- complete oxidation of glucose
- food energy is the amount of energy in food that is available through digestion
- use this energy to do work
What is the average amount of energy released by carbohydrates, lipids and proteins
Carbohydrates release 4.18Cal/g
Lipids release 9.46 Cal/g
Proteins release 4.32 Cal/g
Define Metabolism
set of chemical reactions that occur in living organisms in order to maintain life divided into two categories
Define catabolism
Set of metabolic pathways which break down molecules into small units and release energy
Define anabolism
Set of metabolic pathways that construct molecules from smaller units
Define digestion
Process by which the body breaks down food so it can be absorbed by the blood stream
What is ATP?
Adenosine Tri Phosphate -energy currency of cellular metabolism in all organisms A nucleotide consisting of: -Adenine -Ribose sugar -Three phosphate groups
Usually outermost high-energy bond is hydrolysed
ATP -> ADP + Pi (inorganic phosphate)
Pi is often attached to an intermediate molecule (signalling)
Autotrophs and Heterotrophs
Organisms are classified based on how they obtain energy
Autotrophs - able to produce their own organic molecules through photosynthesis
Heterotrophs - live on organic compounds produced by other organisms
All organisms use cellular respiration to extract energy form organic molecules
Cellular Respiration
- -Describes the metabolic reactions and processes that take place in a cell or across a cell membrane to get biochemical energy from fuel molecules.
- Energy can be released by the oxidation of multiple fuel molecules and is stored as high-energy carriers (NAD+ and FADH)
- The reactions involved in respiration are catabolic reactions in metabolism
Glucose catabolism
Glucose + Oxygen->Carbon Dioxide+ Water + ATP (& heat)
C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy
Redox Reactions
Paired reaction in living systems in which electrons are lost from one atom and gained by another
OIL RIG
Redox Reactions - Hydrogen and Oxygen Transfer
Redox - Hydrogen transfer
- Oxidation is the loss of hydrogen
- reduction is the gain of hydrogen
Redox - Oxygen transfer
- oxidation is gain of oxygen
- reduction is the loss of oxygen
Glucose catabolism reaction
-what is oxidised and what is reduced
glucose is oxidised to carbon dioxide
while
oxygen is reduced to water
Glucose catabolism and NAD+
When electrons are stripped from glucose, take with it a proton (H atom)
The H atom is transferred to a co-enzyme called Nicotinamide Adenine Dinucleotide or NAD+
NAD+ is called an electron acceptor
NAD+ accepts 2 electrons and one proton to become NADH
Therefore, NAD+ is reduced to NADH
Substrate level phosphorylation
Transferring a phosphate directly to ADP from another molecule
Oxidative phosphorylation
Use of ATP synthase and energy derived from a proton (H+) gradient to make ATP
glycolysis
- occurs in the cytoplasm of the cell (not the mitochondria as glucose is too big)
- converts glucose (6 carbon molecule) into two 3-carbon molecules called pyruvate (can enter the mitochondria by diffusion)
- conversion occurs over 10 separate reactions/steps
- for each molecule of glucose that is converted into pyruvate –> cell nets 2 ATP molecules by substrate level phosphorylation
Steps in Glycolysis - STEP 1
Preparatory phase or priming reactions
- as soon as a glucose molecule enters the cytosol, a phosphate group is attached to the molecule
- ATP is used
- phosphorylation: glucose 6-phosphate
Steps in Glycolysis - STEP 2
Prepatatory phase, rearrangement of carbon molecules
- a second phosphate group is attached. Together, steps 1 and 2 cost the cell 2 ATP
- rate limiting step
- ATP i used - phosphorylation
- Fructose 6-phosphate becomes Fructose 1,6 -bisphate
Steps in Glycolysis - STEP 3
Preparatory phase or cleavage
- the six carbon chain is split into two three-carbon molecules, each of which then follows the rest of this pathway
- results in the production of 2x glyceraldehyde-3-phosphate (G-3-P)
Steps in Glycolysis - STEP 4
Payoff phase
-another phosphate group os attached to each molecule, and NADH is generated from NAD
-phosphorylation of G-3-P -> high energy bond
-oxidation of G-3-P
PRODUCE 1 NADH per G-3-P (reduction of 2 NAD+ to 2NADH)
Steps in Glycolysis - STEP 5
Payoff phase
- one ATP molecule if formed for each molecule processed
- removal of high energy phosphate bond by ADP produces ATP
Steps in Glycolysis - STEP 6
Payoff phase
- the atoms in each molecule are rearranged, releasing a molecule of water
- removal of water yields PEP molecule; PEP has high-energy phosphate bond
Steps in Glycolysis - STEP 7
Payoff phase
- a second ATP molecule is formed for each molecule processed. This step produces 2 ATP molecules
- removal of high-energy phosphate bond by ADP produces ATP; Pyruvate Generated
What happens to pyruvate?
Fate ofpyruvate depends on whether oxygen is present in the system
- aerobic respiration (oxygen present)
- anaerobic respiration (without oxygen)
Consider the pathway when oxygen is present
-pyruvate is oxidised in a decarboxylation reaction
-pyruvate (3C) -> Acetyl CoA (2C) + CO2
-NAD+ is reduced to NADH
-reaction involves a coenzyme - coenzyme A
(small organic non-protein molecules that carry chemical groups between enzymes)
Mitochondria and pyruvate
Outer membrane -contains large diameter pores -permeable to ions and small organic molecules (pyruvic acid) Inner membrane -contains carrier protein -moves pyretic acid into mitochondrial matrix Intermembrane space -separates outer and inner membranes
The citric acid cycle
CAC = tricarboxylic acid cycle (TCA) = krebs cycle
- occurs in the matrix of the mitochondria
- series (8) of enzyme-catalysed reactions
- oxidation of oranic molecules derived from pyruvate
- Acetyl CoA enters the cycle
- carbon from Acetyl CoA exits the cycle as CO2
- generate NADH and FADH2
Aim of citric acid cycle
Overall aim of this cycle is to remove electrons, in the form of NADH and FADH2, from the organic molecules that enter the cycle
Very little ATP is made during CAC
Electron transport chain: steps
- a coenzyme strips two hydrogen atoms from a substrate molecule
- NADH and FADH2 deliver hydrogen atoms to coenzymes embedded in the inner membrane of a mitochondrion
- coenzyme Q releases hydrogen ions and passes electrons to cytochrome b
- electrons are passes along the electron transport system, losing energy in a series of small steps
- oxygen accepts the low energy electrons, and with hydrogen ions, forms water
Electron transport chain: FMN or Flavin Mononucleotide
prosthetic group of Complex l or NAD dehydrogenase
Electron transport chain: FAD or flavin adenine dinucleotide
Complex ll or Succinate Dehydrogenase
Electron transport chain: Q or ubiquione
not a protein, small mobile hydrophobic molecule
Electron transport chain: cytochrome C
a small mobile protein
Electron transport chain: other two proteins/molecules
b or Complex lll, cytochrome bc1 complex
a & a3 or complex lV cytochrome c oxidase
Chemiosmosis
ATP synthase (aka F0-F1 ATPase)
- F0 is the proton channel
- when H+ moves through the channel -> conformation change (ions aren’t lipid soluble)
- conformation change transmitted to F1 (change allows it to move across the membrane)
Catalyses the phosphorylation of ADP -> ATP in the mitochondrial matrix
1 ATP made for every 3 H+ that moves into the matrix
Alternate Electron Acceptors
Allows for the oxidation of NADH and FADH2 in the absence of oxygen
- produce less energy than during aerobic respiration
- oxygen is NOT the terminal electron acceptor
- processes require another electron acceptor to replace oxygen
- CO2 (eg. archae)
- sulfates (eg. prokaryotes)
- fermentation of organic molecules (e.g. eukaryotes)
Fermentation of organic molecules
Anaerobic respiration (occurs in cytosol)
- anaerobic respiration is often used interchangeably with fermentation
- lactic acid fermentation
- alcohol fermentation
Alcohol fermentation
- Allows the cell to oxidise NADH back to NAD+ in the absence of oxygen **why it is a reverse reaction
- NAD+ can be reused during glycolysis to generate ATP
Lactic acid fermentation
- allows the cell to oxidise NADH back to NAD+ in the absence of oxygen
- NAD+ can be reused during glycolysis to generate ATP
How does the body know when ATP is needed?
-cells regulate the entry of substrates into the series of reactions depending on the needs of the cell (dynamic)
Excess substrates can be stored:
Glucose –> glycogen or fat
Regulation of cellular respiration: Step 3 glycolysis - Phosphofructokinase
- allosteric enzyme: multiple binding sites
- what would happen if ADP binds to it?
- what would happen if citrate or ATP bound to it?
