(WIP) Ch 6 - How Cells Utilize Energy

Bio 190A

Energy

the ability to promote change or do work; various form of energy are common in biological systems

There are two forms of general energy

kinetic and potential

Kinetic energy

associated with movement

Potential energy

due to structure or location

Chemical potential energy

the energy in bonds between atoms; is a biologically important form of potential energy

First law of thermodynamics

states that energy cannot be created or destroyed, but can be transferred from oen place to another and can be transformed from one type to another

Second law of thermodynamics

Affinity

the attraction of an enzyme for a substrate

For a given concentration of n enzyme, as substrate concentration is increased…

reaction velocity increases until it plateaus

V_max

the maximal rate of the reaction

K_M

the substrate concentration where velocity is half the max

Reversible inhibitors

often used by cells to regulate enzyme activity

Competitive inhibitors

bind noncovalently to the active site

Noncompetitive inhibtors

bind to a distinct regulatory site, called an allosteric site, that is different than the active site

Some enzymes may require various types of __-___ ___ or ___ to function

non-protein molecules or ions

Prosthetic group

a small molecule permanently attached to the enzyme (e.g. heme, found in hemoglobin)

Cofactor

an ion that temporarily binds to enzyme (e.g. Fe³⁺, Zn²⁺)

Coenzyme

an organic molecule that participates in reaction but is left uncharged afterword (e.g. NAD⁺/NADH, an electron carrier)

Temperature, pH, and ionic conditions

influence enzyme structure and function

Metabolic pathway

a series of steps the occur in living cells, where chemical reactions coordinated with each other often occur as

Catabolic reactions

break down larger molecules into smaller ones and are typically exergonic

Anabolic reactions

synthesize larger molecules from smaller ones and are typically endergonic

As a larger molecule (e.g. glucose) is broken down, energy is often stored in an ___ ___ such as ATP or NADH

energy intermediate

Oxidation

the removal of electrons

Reduction

the addition of electrons

OIL RIG

oxygen is lost, reduction is gained

Reduction-oxidation (redox) reactions

are coupled; the electron removed from one molecule is added to another

In general, a substance that has been oxidized has ___ energy stored in its bonds, whereas a substance that has been reduced has ___ energy

less; more

Cells use NAD⁺/NADH in many important redox reactions, including the reactions that

breakdown “food” molecules like glucose or fat

The regulation of catabolic pathways occurs at the

genetic, cellular, and biochemical levels

Gene regulation

involves increasing/decreasing the level of gene expression for the genes that encode certain enzymes

Cells integrate signals from

their environment (through various signaling pathways) and adjust their metabolic activity

Feedback inhibition

frequently used: a product of a pathway binds a pathway enzyme at an allosteric site and decreases its activity

Cellular respiration

a process by which living cells obtain energy from organic molecules and release waste products (a primary aim is to make ATP)

Aerobic reaction

uses O₂ during the process of oxidizing organic molecules (carbohydrates, proteins, fats) and generates CO₂

The aerobic respiration of glucose involves 4 metabolic pathways

1. Glycolysis

2. Breakdown of pyruvate to an acetyl group (Pyruvate oxidation)

3. Citric acid cycle

4. Oxidative phosphorylation

C₆H₁₂O₆ + 6O₂ —>

6CO₂ + 6H₂O

Glycolysis

the first stage of cellular respiration

Three groups of glycolysis:

1. Energy investment phase

2. Cleavage phase

3. Energy liberation phase

Overall, 1 molecule of glucose is transformed into

2 molecules of pyruvate and a net of 2 ATP and 2 NADH are generated

Pyruvate oxidation

the second stage of cellular respiration

For 1 glucose (in pyruvate oxidation):

2 pyruvate yield a total of 2 acetyl CoA, 2 HADH, and 2 CO₂

Citric acid cycle

the third stage of cellular respiration

In citric acid cycle, one glucose yields

2 acetyl CoA

The processing of 2 acetyl groups through the citric acid cycle yields a total of

4 CO₂, 6 NADH, 2 FADH₂, and 2 ATP (via GTP)

Upon completion if glycolysis, pyruvate oxidation, and the citric acid cycle (CAC), the following products have been generated:

• 6 CO₂ —> 2 during pyruvate oxidation, 4 during CAC

• 4 ATP —> 2 during glycolysis, 2 during CAC

• 10 NADH —> 2 during glycolysis, 2 during pyruvate oxidation, 6 during CAC

• 2 FADH₂ —> during CAC

Oxidative phosphorylation

final stage of cellular respiration; utilizes the high energy electrons stored in NADH and FADH₂ to generate a H⁺ gradient

Th enzyme ATP synthase uses

the H⁺ gradient to synthesize ATP

Electron transport chain (ETC)

consists of a group of protein complexes and small organic molecules embedded in the inner mitochondrial membrane

Final electron acceptor

oxygen receives electrons at the end of the chain

H⁺ electrochemical gradient

established by some of the energy that is released during the movements of the electrons is used to pump H⁺ across the membranes

H⁺ gradient is a source of

potential energy

The flow of H⁺ through the ATP synthase enzyme cuases

conformational changes that result in the synthesis of ATP (from ADP + P_i)

Chemiosmosis

the chemical synthesis of ATP as a result of pushing H⁺ across the membrane

Substrate-level phosphorylation

distinct from chemiosmosis; produce ATP during glycolysis and the CAC

NADH oxidation substantially contributes to the

H⁺ electrochemical gradient to synthesize ATP

Cell rarely achieve this maximal amount of ATP because

NADH is also used in anabolic pathways and H⁺ gradient is also used for other purposes

The actual amount of ATP synthesized with be ___ than maximal (___), but still substailyy ___ than the amount of ATP generated by glycolysis or the CAC

less; ~25; greater

ATP synthase

can be considered a rotary machine; it has moving parts powered by an energy source

As proteins and fats are broken down into smaller molecules, those smaller components can

enter glycolysis or the CAC at different points

Anaerobic

an environment without oxygen

Cells can use two different strategies to metabolize organic molecules in the absence of oxygen

1. Anaerobic respiration - uses a substrate other than O₂ as the final electron acceptor of the ETC

2. Fermentation - produces ATP through substate-level phosphorylation without any net oxidation of organic molecules

Under anaerobic conditions, E. coli produces

nitrate reductase; this enzyme uses nitrate (NO₃-) as the final electron acceptor

One straegy to produce ATP under anaerobic conditions is to

make ATP only via glycolysis

Glycolysis requires ___ and generates ___

NAD+; NADH

Under anaerobic conditions,

NADH builds up and NAD+ decreases

NAD+ must be regenerated to

keep glycolysis running

Lactic acid production in muscle and ethanol production in yeast are both examples of

fermentation processes that oxidize NADH to NAD+, thus allowing glycolysis to continue