Ch 5: Metabolism Flashcards
What is metabolism?
What is its ultimate function?
sum total of all biochemical reactions within a cell; their ultimate function is to reproduce the organism
What is catabolism and anabolism?
How are they made possible?
Catabolism: breakdown of complex organic molecules into simpler ones - energy is released (exergonic)
Anabolism: building complex organic molecules from simpler ones; energy is used (endergonic)
Coupling of these reactions is made possible through ATP - energy retrieved from catabolism is stored in ATP and later released to drive anabolic reactions
Describe redox
Oxidation and Reduction Reactions
Electron transfer from an electron donor to an electron acceptor
Reactions always occur simultaneously
Cells use electron carriers to carry electrons
Three important electron carriers:
Nicotinamide adenine dinucleotide (NAD+)
Nicotinamide adenine dinucleotide phosphate (NADP+)
Flavine adenine dinucleotide (FAD) → FADH2
Redox includes the transfer of what two things? What is this reaction called?
In biological systems, redox often includes the transfer of both the electron and the accompanying proton (electron + proton = hydrogen), so they’re often called dehydrogenation reactions
What is an enzymes role in metabolism?
Enzymes are organic catalysts
Increase likelihood of a reaction
What are the six categories of enzymes based on mode of action?
- Hydrolases break bonds
- Isomerases rearrange molecules
- Ligases or polymerases make bonds
- Lyases break bonds
- Oxidoreductases transfer electrons thru redox
- Transferases transfer organic functional groups
What is an enzyme and what are two characteristics?
Proteins which catalyze reactions in cells by lowering the activation energy (make reactions more efficient)
Enzymes are not altered or destroyed during the reaction (can be used over and over)
Enzymes exhibit specificity (they can drive one reaction but can’t drive a different reaction)
What are substances acted upon by the enzymes called?
Substrates
Maximum number of substrate molecules an enzyme molecule can convert to product each second is called what?
turnover number
What is the typical enzyme turnover rate?
Typically turnover time = 1 – 10,000 reactions per second for each enzyme
Some turnover numbers are as high as 400,000 - 500,000 per second for each enzyme!
Describe the structure of an enzyme
All contain protein - can be entirely protein, some have other components
Protein portion is called the apoenzyme
Non-protein component is the co-factor
Co-factors can be either organic or inorganic (he says inorganic)
If a co-factor is a complex organic molecule, it is called a coenzyme (he says organic)
When fully assembled they form the holoenzyme
Some enzymes are RNA molecules called ribozymes
Describe 5 steps of enzymatic action
- Substrate binds to active site on the surface of enzyme
- Temporary intermediate complex forms - enzyme-substrate complex
- Substrate transformed (other molecule added, molecule rearranged, bond broken, etc.)
- Transformed substrate (product or products) no longer conforms to the active site, is released from enzyme
- Unchanged enzyme is ready to react with more substrate molecules
What are four factors influencing enzyme rates?
Temperature
pH
Substrate Concentration
Inhibition
Describe the effect of temperature on enzymes.
What happens if temperature increases, gets above optimum, or below minimum?
Temperature – as temperature begins to increase, enzymatic activity increases due to an increase in molecular collisions
At some point (unique for each enzyme) optimum temperature will be reached. Enzyme operates at peak efficiency.
Higher temperatures (above optimum) will cause protein portion of enzyme to denature (unravel) destroying the function.
Each enzyme will have a minimum, optimum and maximum operating temperature.
Describe the effect of pH on enzyme activity. What is the effect of extreme pH changes?
As with temperature, enzymes will have a minimum, optimum and a maximum pH.
Alterations away from the optimum may affect protein’s shape & effectiveness
Extreme pH changes can cause the protein portion to denature, destroying the enzyme function
Where does a noncompetitive enzyme inhibitor (allosteric inhibitor) bind?
Allosteric site, located on the bottom of enzyme, changes shape of the active site.
Where does a competitive enzyme inhibitor bind?
Directly on active site so that the active site is altered
In end product inhibition, what switched off the pathway?
Making excess product
Energy is stored through formation of ATP (ADP + P = ATP), what is this process called?
Phosphorylation
What are three types of phosphorylation?
Substrate-Level Phosphorylation: direct transfer of phosphate to ADP from phosphorylated substrate
Oxidative Phosphorylation: electrons transferred from organic compounds to electron carriers (NADH and FADH2); energy is transferred down an electron transport chain, which is then used to generate ATP
Photophosphorylation: light energy is trapped and an electron transport chain is used to generate ATP
What is it called when the enzyme and the substrate are connected?
Enzyme-substrate complex (E-S)
Sometimes called intermediate form
What are the three major phases of carbohydrate catabolism? What is the intermediate phase?
How many ATP are made for each glucose molecule?
Three phases – making a total of 38 ATP for each glucose molecule
1) Glycolysis – splits glucose (6-Carbons) in half making two (3-carbon) pyruvic acid molecules — process releases a small amount of energy and small amount of NADH
“Bridge Step” takes us into mitochondria
2) Krebs Cycle – extracts energy from pyruvic acids (small amount) power is in the reduction of organic molecules like NADH and FADH2
3) Electron Transport Chain – extracts lots of energy by oxidizing those carriers and using it to make ATP
Describe glycolysis
The splitting (oxidizing) of a 6-carbon glucose molecule into two 3-carbon acids (pyruvates) which will be further broken down across the bridge and through Krebs’ Cycle
Preparatory phase – costs cell energy (2 ATP)
Energy conserving phase – produces energy (4 ATP)
Cost = 2 ATP
Gain = 4 ATP through substrate level phosphoylation & 2NAD+ reduced to 2NADH
Produces two pyruvic acids (pyruvates) to send over bridge to Krebs’ Cycle
Glycolysis occurs in the cytoplasm of both prokaryotes and eukaryotes
Describe the bridge
Occurs in cytoplasm
2 pyruvates are oxidized into 2 Acetyl CoA
2NAD+ are reduced to 2NADH
CO2 released (decarboxylate group)
2 Acetyl CoA goes to mitochondria matrix
