Chapter 5 - Cell Metabolism: Synthesis & Degradation of Biological Molecules

endergonic

energy requiring

• active transport

• anabolism

• cell movements

exergonic

releases energy

• cell respiration

• catabolism

• ATP hydrolysis

oxidation

the loss of one or more electrons (Hydrogen)

reduction

gain of one or more electrons (hydrogen)

• the more reduced a molecule is, the more potential energy

is NAD+ oxidized or reduced?

NAD+ (oxidized form)

• coenzyme NAD+ is a key electron carrier

is NADH oxidized or reduced?

NADH (reduced form)

Reduction of NAD⁺ is highly _______

Oxidation of NADH is highly ________

Reduction of NAD⁺ is highly endergonic:

NAD⁺ + H⁺ + 2e^– ⇌ NADH

Oxidation of NADH is highly exergonic:

NADH + ½ O₂ ⇌ NAD⁺ + H₂O

Cellular respiration is a major ______ pathway.

Photosynthesis is a major _____ pathway. 

Cellular respiration is a major catabolic pathway.

Glucose is oxidized: 

carbohydrate + 6 O₂ ⇌ 6 CO₂ + 6 H₂O + chemical energy

Photosynthesis is a major anabolic pathway. 

Light energy is converted to chemical energy:

6 CO₂ + 6 H₂O + light energy ⇌ 6 O₂ + carbohydrate

oxidation occurs in a series of steps in 3 pathways:

1. glycolysis

2. pyruvate oxidation

3. citric acid cycle

glycolysis

• 10 reactions

• takes place in cytosol

• end products:

  • pyruvate (pyruvic acid)

  • ATP

  • NADH

pyruvate oxidation

• end products:

  • CO2

  • acetate (which is then bound to coenzyme A)

  • NADH

2 types of fermentation and what they do:

• lactic acid fermentation: pyruvate is converted to lactic acid

• alcoholic fermentation: pyruvate is converted to ethanol

citric acid cycle (krebs cycle)

• 8 reactions

1. starts with Acetyl CoA; acetyl group is oxidized to two CO₂

2. oxaloacetate is regenerated in the last step

3. lots of NADH is made throughout

4. the organic molecules are oxidized and NAD+ is reduced

oxidative phosphorylation

transfers energy from NADH to ATP

chemiosmosis

• diffusion of protons across a membrane, which drives the synthesis of ATP

• converts potential energy of a proton gradient (proton motive force) across a membrane into the chemical energy in ATP

O2 is the _____________ in the respiratory chain

O₂ is the final electron (H) acceptor in the respiratory chain

electron transport/ATP synthesis recap

• NADH is re-oxidized to NAD⁺ and O₂ is reduced to H₂O in a series of steps.

• Electron transport chain (aka Respiratory chain) —series of redox carrier proteins embedded in the inner mitochondrial membrane.

• Electron transport—electrons from the oxidation of NADH (and FADH₂) pass from one carrier to the next in the chain, coupling this electron transfer with the transfer of protons across membrane.

• Oxidation reactions are exergonic ; the released energy is used to actively transport H⁺ ions out of the mitochondrial matrix (in eukaryotes), setting up a proton gradient.

• ATP synthase in the membrane uses the H⁺ gradient to synthesize ATP by chemiosmosis.

2 pathways that photosynthesis involves:

• light reactions convert light energy into chemical energy

• carbon-fixation reactions use the ATP and NADPH, along with CO2, to produce carbohydrates (glucose)

primary production

synthesis of organic compounds from atmospheric or aqueous CO2

what are the different ways photons can behave?

• photons can be absorbed by a molecule, adding energy to the molecule-it moves to an excited state (higher energy)

• photons can also be scattered (bouncing off)

• photons can also be transmitted (pass through)

higher energy > ____
_______ > longer wavelength

higher energy > shorter wavelength

lower energy > longer wavelength

accessory pigments

• absorb wavelength between red and blue and transfer some of that energy to the chlorophylls

• in plants, chlorophyll absorbs light energy

photosystem components (Light-harvesting complexes)

• spans the thylakoid membrane in the chloroplast

• consists of:

  • antenna systems

  • reaction center

excitement of an electron

1. When chlorophyll (Chl) absorbs light, it enters an excited state (Chl*), then rapidly returns to ground state, releasing an excited electron.

2. Chl* gives the excited electron to an acceptor and becomes oxidized to Chl⁺.

3. The acceptor molecule is reduced.

4. Chl* + acceptor ⇌ Chl⁺ + acceptor^–

the reaction center has converted light energy into chemical energy

cyclic electron transport

• traps light energy as ATP

  • ATP is needed for carbon-fixation pathways

  • cyclic electron transport uses only photosystem 1 and produces ATP

  • the electron passed from an excited chlorophyll is recycled back to the same chlorophyll

what do plants use all the NADPH for?

• One of the main functions of photosynthesis is to supply electrons for carbon fixation

• NADPH supplies the electrons (as H atoms) to reduce CO₂ to carbohydrates.

• This is essentially the reverse of respiration where carbohydrates are oxidized to CO₂ and the electrons are captured in NADH.

where does the calvin cycle occur

in the stroma of the chloroplast

3 steps of calvin cycle/dark reactions:

1. carbon fixation

2. reduction and sugar production

3. regeneration of RuBP

carbon fixation

• CO₂ is added to 5-C backbone ribulose 1,5-bisphosphate (RuBP).

• Ribulose bisphosphate carboxylase/oxygenase (rubisco) catalyzes the reaction.

• A 6-C molecule results, which quickly breaks into two 3-carbon molecules: 3-phosphoglycerate (3PG)

reduction and sugar production

• 3PG is reduced to form glyceraldehyde 3-phosphate (G3P).

• 3PG is used to make sugars

• When glucose accumulates, it is linked to form starch, a storage carbohydrate

regeneration of RuBP

• The CO₂ acceptor, RuBP, is regenerated from G3P.

  • 1/6^th of the G3P is used to form sugars

  • The rest is used to regenerate RuBP

light reactions

a) two photosystems

  photons, pigments (chl)

  cyclic, noncyclic PS

    b) electron transport chain

        c) light energy à chemical energy

  NADPH, ATP

dark reactions

a) C-fixation

  rubisco, ribulose-1,6-bisphosphate (RuBP),

  and 3-phosphoglycerate (3GP)

    b) reduction

   glyceraldehyde-3-phosphate (G3P)

    c) regeneration of RuBP