Enzymes and Photosynthesis : BIOL 107

Lec 21 - 25

Metabolism

The chemical reactions taking place within a cell / organism

First law of thermodynamics

Energy can be transfered or transformed but not created or destroyed (it is constant)

Second law of thermodynamics

When energy is transfered or transformed some useful energy is lost as heat

Free energy

Amount of energy available to do work

Changes in free energy

The types of covalent bond

The number of atoms

The number of covalent bonds

Exergonic reactions are

spontaneous

Exergonic reactions definition

Energy is released by breaking bonds: G < 0

Endergonic reactions are

not spontaneous

Endergonic reactions definition

Energy is absorbed by forming bonds: G > 0

Reaction with Sucrose

disaccharide // made by plants

Glucose enters with SGLT

low to high

Fructose enters with GLUT

high to low

What limits exergonic (–𝚫G) reactions?

Requires an initial input of energy (EA = barrier) therefore requires enzyme

Enzymes ____ so that a reaction can occur

decrease EA

decrease G

increase G

increase EA

What allows endergonic (+𝚫G) reactions?

requires enzymes (input of energy) to make it energetically favourable

Why are endergonic reactions not spontaneous

G > 0 // energy of the products is higher than the energy of the reactants therefore requires energy to be absorbed to proceed

ATP function #1

A monomer used to make RNA

ATP function #2

source of energy // it links endergonic and exergonic reactions together

ATP hydrolysis

ATP broken down into ADP // it releases free energy

Reactions with Ethanol

Made by yeast as they feed on fruit //

ADH (enzyme)

breaks down ethanol into acetaldehyde

Food allergy

when a person's immune system overreacts to a harmless molecule

Food intolerance

when a person doesn't make the enzyme needed to digest a molecule

Electron shuttle table

NAD+ ←→ NADH

NADP+ ←→ NADPH

FAD ←→ FADH2

Photosynthesis products

sugars + O2

Photosynthesis reactants

solar energy + water + CO2

Why is photosynthesis the most important chemical reaction on Earth?

it is fundamental to nearly all life forms

Why is visible light used for both vision and for photosynthesis?

its wavelengths contain the ideal amount of energy for these processes AND most abundant form of light reaching Earth's surface

UV is blocked by

ozone

IR is blocked by

atmosphere (CO2 + H20)

Where does photosynthesis occur? (Eukaryotes)

Plants, algae, and Euglena

Where does photosynthesis occur? (Mesophyll cells)

Cells in the middle of leaves

Where does photosynthesis occur? (Chloroplast)

Each mesophyll cell contains 30 - 40 chloroplasts

How does photosynthesis occur? (simple)

Calvin cycle and light reaction

How is solar energy harvested?

chlorophyll pigments

Photosynthesis light reaction

occurs in the thylakoid membrane (chloroplast)

Photosystems

Light capturing machines located in a membrane

Photosystems input and output

input: photon (low energy electron)

output: high energy electron

ETC

found in the membrane // are proteins

ETC input and output

input: high energy electron

output: low energy electron

allows: H+ (transfer protons) to enter

Water-splitting enzymes

Peripheral membrane proteins that supply electrons

Water-splitting enzymes are

below the membrane

NADP+ Reductase

Peripheral membrane proteins that make NADPH

NADP+ Reductase are

above the membrane

ATP synthase

Membrane proteins that make ATP

Cyclic electron flow

electrons leaving PSI make photon gradient

photon gradient is acidic

stroma: pH 8 // thylakoid space: pH 5

stroma: pH 5 // thylakoid space: pH 8

What is the purpose of cyclic electron flow?

to produce additional ATP without generating NADPH or releasing oxygen

What is the purpose of linear electron flow?

Uses sunlight to make ATP and NADPH, which is required to power the Calvin cycle

PS II is

only in linear flow

PS I is

both in linear and cyclic flow

Photosynthesis Calvin cycle

occurs in the thylakoid membrane

Rubisco

fixes carbon // converts CO2 + C5 into C6

Phase 1: Carbon fixation

Attach CO2 to organic molecule

Phase 2: Synthesis of sugar

Turn the organic molecules into sugars

Phase 3: Regeneration of CO2 acceptor

5 G3P stay in cycle AND 1 G3P leaves

Calvin cycle input #1

3 CO2

Calvin cycle output #1

G3P (sugar)

Calvin cycle input #2

6 ATP

Calvin cycle output #2

6 ADP

Calvin cycle input #3

6 NADPH

Calvin cycle output #3

6 NADP+

Calvin cycle input #4

3 ATP

Calvin cycle output #4

3 ADP

What happens to the G3P? #1

Storage (glucose → starch)

What happens to the G3P? #2

makes ATP (in cytosol and mitochondria)

What happens to the G3P? #3

makes organic molecules

What happens to the G3P? #4

export

How many CO2 to make a sucrose?

12