Glycolysis, Krebs Cycle, and Oxidative Phosphorylation

metabolism

all reactions of the body

anabolism

building reactions

catabolism

breakdown reactions

pathways

sets of chemical reactions that begin with a specific set of reactants and sequentially lead to a specific products

energy metabolism

the catabolic pathways used to generate ATP

burning of carbs, fats, and proteins

anaerobic or aerobic

also called respiration

anaerobic respiration

does not use oxygen

glycolysis is a catabolic pathway that is anaerobic

aerobic respiration

uses oxygen

the Krebs Cycle and electron transport are two catabolic pathways that are aerobic

begins with glycolysis (which is anaerobic)

what is the starting reactant of glycolysis and what does it turn into?

glucose (a 6 carbon sugar) → 2 pyruvic acid (pyruvate: a 3-carbon moelcule)

where does glycolysis occur?

in the cytoplasm of cells

for each glucose consumed, what is the net ATP?

2 ATP produced by substrate-level phosphorylation

for each glucose consumed, how many coenzymes are made?

2 reduced coenzymes (NADH + H⁺) are formed

if O₂ is present, where does glycolysis lead to?

aerobic metabolism

what happens to pyruvate after glycolysis when O₂ is present?

each pyruvate is first transported from the cytoplasm into a mitochondrion

each acetate is then combined with coenzyme A to form acetyl-Coenzyme A (acetyl-CoA)

coenzyme A

dervied form pantothenic acid, which is one of the “B vitamins”

products of turning pyruvate into acetyl-CoA

acetyl-Coenzyme A (acetyl-CoA)

1 CO₂

2 NADH + H⁺

enzymes

organic proteins that act as catalysts in chemical reactions, usually specific for one or a few reactions

catalyst

chemical that causes a reaction to occur faster

coenzymes

vitamin derivatives

low specificity

organic

nonprotein catalysts

vitamin

organic molecules needed for life that we can’t make

taken to supply body with certain chemicals that diet doesn’t fulfill

cofactors

inorganic minerals that act as catalysts that help enzymes work

Zn⁺⁺, Fe⁺⁺, Cu⁺⁺, etc

coenzymes are used in what type of reactions?

redox

why are coenzymes used in redox reactions?

shuttle electrons/protons from fuel reactions to oxidative phosphorylation (electron transport) for ATP synthesis

Krebs Cycle names

Citric Acid Cycle

Tricarboxylic Acid Cycle

reaction for turning pyruvate into acetyl-CoA

2 pyruvate → 2 acetyl-CoA + 2 CO₂

where does Krebs cycle occur?

in the mitochondria

does Krebs cycle use O₂?

it does not but it’s linked to e^- transport

how many times does the Krebs cycle run per glucose molecule?

2 (once for each acetyl-CoA entering the cycle

reaction for each acetyl-CoA entering the cycle

Acetyl CoA → 2CO₂ + (3 NADH + H⁺) + 1 FADH₂ + 1 GTP (is used later to recycle a new ATP through substrate-level phosphorylation) + 1 Reduced CoA

reaction for oxidative phosphorylation

a lot of H⁺ a lot of ½ O₂ → H₂O

where does oxidative phosphorylation occur?

in the mitochondria, and uses O₂ (aerobic)

process of oxidative phosphorylation

the two NADH + H⁺ formed during glycolysis must have their H+ shuttled into the mitochondria

this process USUALLY results in a new FADH₂ being formed in the mitochondria, not another NADH + H⁺

But some cells can shuttle the H⁺ to NADH + H⁺ inside the mitochondria. Thus, the efficiency of this step is variable.

what happens to the reduced coenzymes in oxidative phosphorylation?

NADH + H⁺ and FADH₂ are oxidized (recycled) into NAD⁺ and FAD

how much ATP is formed for every NADH + H⁺?

up to 3 ATP

more like 2.5 ATP

how much ATP is formed for every FADH₂?

up to 2 ATP

more like 1.5 ATP

what is the final recipient (acceptor) of the H⁺ and e^- from the coenzymes and what is formed?

O₂ is the final recipient and is reduced to H₂O

maximum total aerobic ATP production per glucose

38 ATP

By substrate-level phosphorylation: 2 ATP (from glycolysis) + 2ATP (from 2 turns of Krebs cycle)

By oxidative phosphorylation: 4 ATP (2 FADH2 formed from 2 NADH+H+ from glycolysis) + 6 ATP (2 NADH+H+ from pyruvate oxidation) + 18 ATP (6 NADH+H+ from K.C.) + 4 ATP (2 FADH2 from K.C.)

what acts as catalysts for chemical reactions?

enzymes, coenzymes and cofactors

are coenzymes and cofactors reaction-specific?

they are not

they can be used in many different reactions

oxidation reactions

remove H⁺ or e^- from a molecule

reduction reactions

add H⁺ or e^- to a molecule

to reduce one molecule requires ____

the oxidation of another

with limited O₂, what occurs?

anaerobic metabolism

reaction for anaerobic metabolism

2 pyruvate → 2 lactic acid (lactate)

process of anaerobic metabolism

without more O2 to recycle the coenzymes, the rates of e-transport and Krebs Cycle peak. Excess acetyl-CoA and pyruvate accumulate. To balance this, excess pyruvate is reduced to form lactate. Lactate is toxic, so it must be excreted or recycled aerobically (at a later time) into glucose.

ATP production from anaerobic metabolism

none, but each lactate formed recycles NADH + H⁺ into NAD⁺

what is the NAD⁺ produced (1 per each pyruvate) from anaerobic metabolism used for?

enough to sustain continued glycolysis, therefore more ATP is produced

can the NAD⁺ produced from anaerobic metabolism be used in Krebs Cycle?

NAD⁺ formation isn’t adequate to sustain Krebs cycle and lactate is toxic, so endurance decreases

how are fats (triglycerides) used in aerobic metabolism?

they are hydrolyzed by lipolysis to glycerol and fatty acids

glycerol can be converted to dihydroxyacetone phosphate and enter glycolysis

fatty acids are degraded to many acetates that are used to make acetyl-CoA through β-oxidation

what is the net gain of using fats as fuel?

146 ATP for a C18 fatty acid

how are proteins used as fuel?

they are hydrolyzed by proteolysis to amino acids

what happens to amino acids that were formed from proteolysis of proteins?

amino acids are deaminated to form keto acids

what happens to dihydroxyacetone phosphate?

enters glycolysis

what happens to acetyl-CoA and keto acids?

enter the Krebs cycle

glycolysis (with glycogenolysis)

pyruvate to acetyl-CoA

Krebs Cycle

oxidative phosphorylation

anaerobic metabolism (accelerated glycolysis)

pyruvate to lactate (lactic acid)

anaerobic metabolism (accelerated glycolysis)

intermediary metabolism

aerobic metabolism with other fuels

fats as fuels

β-oxidation of fatty acids

proteins as fuel

oxidative deamination

proteins as fuel

transamination

intermediary metabolism

the metabolism of a “common pool” of short-chain (~2-4 carbon) organic molecules that can be used to produce carbohydrates, proteins, and lipids

anabolism of glycogen

glycogenesis

catabolism of glycogen

glycogenolysis

anabolism of glucose

gluconeogenesis

catabolism of glucose

glycolysis

anabolism of protein

protein anabolism

catabolism of protein

proteolysis

anabolism of triglyceride

lipogenesis

catabolism of triglyceride

lipolysis