metabolic pathways

metabolism

all of an organisms cellular chemical reaction

metabolic pathways

organization of chemical reactions — begins with specific molecules altered through series of steps to form specific product (specific enzyme catalyzes each step)

catabolic pathways

release energy by breaking down molecules — catabolism

• ex. cellular respiration

  • total amount of free energy in bonds is less than reactants — releases energy

anabolic pathways 

use energy to build molecules 

• ex. photosynthesis 

  • total amount of free energy in products is greater than reactants

  • requires energy to drive reactions

coupling of catabolic & anabolic pathways

energy released from catabolic can be stored & used to drive anabolic processes 

1st law of theromodynamics

energy cannot be created nor destroyed, only transferred

• there are losses of usable energy — always converted to heat

2nd law of thermodynamics

energy transfer/transformation increases the entropy of the universe

• entropy: measure of disorder or randomness

  • there is unstoppable trend toward disorganization

free energy

portion of a cell or organism’s energy that is able to perform work — measure of stability 

• high free energy = low stability

exergonic (exothermic reactions)

process with the new release of free energy — change in energy = negative (less energy in products than reactants)

• spontaneous — without help of enzymes

• ex. cellular respiration

endergonic reactions

absorb free energy from surrounds — change in energy = positive, more energy in products than reactants

• require constant input of energy

• ex. photosynthesis

metabolic equilibrium 

if reached — no change in free energy & cells cannot do work 

• prevented bc metabolic reactions are reversible materials & energy constantly flow in & out 

what are the three main types of work a cell does

• mechanical: contraction of muscle cells

• transport: transfer of substances against concentration gradient

• chemical: driving endergonic reactions

hydrolysis of ATP

breaks of a phosphate group (adp) —- releases energy (change from unstable to more stable)

• energy allows for phosphorlyation — phosphorylated molecule can do work

regenerationn of ATP

endergonic process (required energy) — phosphorylates adp 

enzyme

biological catalyst — speed up metabolic reactions, without being used up

• lowers the activation energy

why does forming bonds release energy & not breaking

energy from exergonic reactions (products have less energy than reactants — release energy) is used to drive endergonic reactions

what is required before a reaction occurs

1. has to be enough energy in system to break bonds

2. has to be enough energy for enough reactant molecules to collide

activation energy

initial amount of energy needed to start a chemical reaction — once reached release of energy from new bonds provides energy to drive reaction

importance of enzymes

aid in breakdown of carbohydrates, proteins & lipids —- good sources of energy

enzyme structure

globular proteins (tertiary structure)

• has active site (only fits substrate): where substrate binds to — enzyme-substrate complex

  • r-group interactions of amino acids give active site its shape

induced-fit moedle of enzyme action 

• when substrate binds the active site changes shape (to function better)

  • substrate held by weak bonds — so converted products could be released 

how do r groups of amino acids in active site lower activation energy

1. orienting substrate correctly: best position for new bonds

2. straining bonds: (within substrate) — weakens bonds that need to be broken

3. favorable microenvironment: more favorable to substrate to start reaction (pH)

factors that affect enzyme activity

• temperature: optimal temp — avoid denaturation

• pH: optimal temp — avoid denaturation

effects of increasing enzyme concentration

increases rate of reaction

effects of increasing substrate concentration (enzyme stays same)

rate of reaction increases then flattens — all enzymes taken up by substrate

types of inhibition of enzyme activity 

competative & non-competative 

competative inhibition

competitor molecules compete for active site —- can over come by increasing substrate concentration

noncompetative inhibition

• allosteric: bonds to allosteric site — changes shape, not able to bind with substrate

• blocks out substrate

allosteric regulation

can inhibit & stimulate enzyme activity 

• can activate or keep enzymes inactive 

• changes shape — easier for substrates to bond 

negative feedback

process when a product in metabolic pathways will inhibit something else, causing another pathway to open up —- prevents metabolic equilibrium