chapter 6 - cell metabolism

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59 Terms

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energy

the capacity to do work

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2 types of energy

kinetic and potential

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kinetic energy

energy of motion

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potential energy

stored energy

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how do we get energy?

  1. light energy absorbed by chloroplasts in plant cells

  2. plants photosynthesize glucose

  3. animals/humans consume glucose, breaking it down into water and CO2

  4. energy stored in the bonds between carbon atoms, ATP released when these bonds are broken

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what happens to energy between transitions

some energy is lost as heat

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the laws of thermodynamics

  1. energy cannot be created or destroyed, only converted

  2. energy transformation creates disorder outside of the cell

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entropy

a measure of disorder - heat released that is unavailable to do work

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oxidation-reduction reactions (redox reactions)

transfers energy; often involves hydrogen

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oxidation

atom or molecule loses an electron (gains positive charge)

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reduction

atom or molecule gains an electron (gains negative charge)

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metabolism

all chemical reactions of a cell or organism

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metabolic pathway

series of biochemical reactions that converts one or more substrates (reactants) into a final product

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catabolic reactions

breaks down larger molecules - releases energy

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examples of catabolic reactions

hydrolysis, cellular respiration

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anabolic reactions

synthesizes larger molecules - uses energy

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examples of anabolic reactions

dehydration synthesis, photosynthesis

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free energy

the amount of energy available to do work; also known as G

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Gibb’s free energy (G)

all chemical reactions affect G

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ΔG (delta G)

abbreviation for a change in G after a reaction

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free energy formula

ΔG = ΔH - TΔS

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chemical reactions can be predicted based on…

…changes in free energy

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positive ΔG

  • products have more free energy than reactants

  • nonspontaneous; requires input of energy

  • endergonic

  • anabolic

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negative ΔG

  • products have less free energy than reactants

  • spontaneous

  • exergonic

  • catabolic

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exergonic reaction

  • net release of free energy

  • spontaneous

  • negative ΔG

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if energy is released in a chemical reaction…

…ΔG < 0 - products of these reactions will have less free energy than the reactants

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endergonic reaction

  • absorbs free energy from its surroundings; requires energy

  • nonspontaneous

  • positive ΔG

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if a chemical reaction requires an input of energy…

ΔG G > 0 - products of these reactions will have more free energy than the reactants

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activation energy

the energy required for a reaction to proceed

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“transition state”

reactant(s) become contorted and unstable, which allows the bond(s) to be broken or made

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reaction rate can be increased by:

increasing energy of reacting molecules (heating) or lowering activation energy (catalyst)

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ATP (adenosine triphosphate)

bonds that link the 3 phosphate groups are high-energy bonds - when they are broken, the products have lower free energy than reactants

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ADP

adenosine diphosphate - 2 phosphates

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ATP cycle

energy released from splitting ATP is used during anabolic reactions, ATP is created during anabolic reactions

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ATP is not used for ____

long-term energy storage

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enzymes

protein catalysts that speed up reactions by lowering the required activation energy

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enzymes bind with ___ ___

reactant molecules

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enzyme-substrate specificity

enzymes catalyze a single reaction

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what determines enzyme-substrate specificity?

the 3D shape of the enzyme and reactants (substrates) - substrate molecules interact at the enzyme’s active site

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2 parts of enzyme’s active site

binding and catalytic sites

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binding sites

bind and orient substrate(s)

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catalytic sites

reduce chemical activation energy

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what determines the active site?

the proteins primary sequence and tertiary structure; protein folding brings specific amino acids close to each other to form the active site

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induced fit

a slight change in enzyme chape maximizes catalysis

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changes in pH on enzyme activity

can reduce substrate-enzyme binding

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changes in temp on enzyme activity

can denature the enzyme (loss of shape)

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enzymes lower activity rate by:

helping the substrate reach its transition state

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enzymes help the substrate reach transition state by either:

  1. positioning 2 substrates to they align for the reaction

  2. provide an optimal environment within the active site for the reaction

  3. contort/stress the substrate so it’s less stable and more likely to react

  4. temporarily react with the substrate (chemically change it) making it less stable and more likely to react

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what happens after a catalyzed reaction?

the product is released and the enzyme becomes available to catalyze another reaction

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enzyme activity regulation

helps cells control their environment to meet their specific needs

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enzyme activity can be regulated by:

  • modifications in temp or pH

  • production of molecules that inhibit or promote enzyme function

  • availability of coenzymes or cofactors

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coenzymes

organic molecules - including ATP, NADH+, vitamins

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cofactors

inorganic ions

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how are coenzymes/cofactors provided?

from diet

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2 forms of enzyme inhibition

competitive and allosteric (noncompetitive) inhibitors

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competitive inhibitor

binds to active site to block substrate

  • slows reactions rates

  • does not effect maximal rate

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allosteric (noncompetitive) inhibitor

binds in a separate site to change 3D shape of enzyme and therefore active site, so the substrate cannot fit

  • slows reaction rates

  • reduces maximal rate

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maximal rate

speed of a reaction when substrate is not limited

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feedback inhibition

where the end product of the metabolic pathway inhibits an upstream step; one reaction along pathway can inhibit another reaction