Topic 7 - Energy (Part II)

where does glycolysis occur?

cytosol

Where do pyruvate oxidation and the citric acid cycle occur?

in the mitochondrial matrix

Where are the electron transfer system and ATP synthase enzymes located?

inner mitochondrial membrane

glycolysis

breaks a 6-carbon glucose molecule into two 3-carbon pyruvate (pyruvic acid) in 10 sequential enzyme-catalyzed reactions

Do the initial steps of glycolysis require energy?

yes, 2 ATP

How many ATP are formed from the substrate level phosphorylation in glycolysis?

4 with a net gain of 2 

What happens to NAD+ in glycolysis?

it gets reduced to NADH which carries 2 electrons and a proton (H+) removed from the fuel molecules

What do the first 5 reactions in glycolysis do?

generate 2 molecules of G3P with 2 ATP

What to the last 5 reactions in glycolysis do?

convert the G3P to pyruvate, producing 4 ATP and 2 NADH

What is the chemical formula for glycolysis

glucose + 2ADP + 2P_i + 2 NAD⁺ + 4e^- + 4 H⁺ → 2 pyruvate + 2 ATP + 2NADH + 2H⁺ + 2H₂O

How does pyruvate get moved into the mitochondrial matrix?

active transport

What does pyruvate oxidation produce?

CO₂, acetyl-coenzyme A (acetyl-CoA), and NADH

What product of pyruvate oxidation enters the citric acid cycle?

the acetyl group of the acetyl-CoA

pyruvate oxidation

removed CO₂ from pyruvate and oxidizes the remaining 2-carbon fragments into an acetyl group (CH₃CO) which is carried by acetyl-CoA to the citric acid cycle

pyruvate oxidation chemical equation 

pyruvate + CoA + NAD⁺→ acetyl-COA + NADH + H⁺+ CO₂

citric acid cycle

carbon products of pyruvate oxidation are oxidized to CO₂

In the citric acid cycle, where are all available electrons transfer to?

to 3 NAD+ (NADH) and 1 FAD (FADH₂)

How much ATP does one turn of the citric acid cycle produce and how?

produces 1 ATP per turn through substrate level phosphorylation

What are other names for the citric acid cycle?

Krebs cycle or tricarboxylic acid cycle

chemical equation of the citric acid cycle?

1 acetyl-CoA + 3NAD⁺ + 1FAD + 1ADP + 1P_i + 2H₂O → 2CO₂ + 3NADH + 1FADH₂ + 3H⁺ + 1ATP + 1CoA

Why is the citric acid cycle regulated at several steps?

to match the cell’s requirements for ATP

citrate synthase 

enzyme apart of step one of the citric acid cycle, inhibited by elevated ATP concentrations 

Where are high energy electrons that are removed from fuel molecules and picked up by carrier molecules released?

the electron transfer system of the mitochondria

mitochondrial electron transfer system (ETS)

a series of electron carriers that alternately pick up and release electrons and ultimately transfer them to their final acceptor, oxygen 

What do the electrons of the ETS release and what does this cause?

free energy used to build a H+ gradient across the inner mitochondrial membrane (higher H+ concentration in the intermembrane compartment and lower H+ concentration in the matrix) 

What does the H+ gradient in the ETS supply?

supplies energy that drives ATP synthesis by mitochondrial ATP sythanse

What are the three major protein complexes and what do they do?

complexes I, III, and IV; serve as electron carriers

What is the smaller protein complex and how is it different?

complex II; only bound to the inner mitochondrial membrane on the matrix side 

Where do electrons carried by NADH enter the ETS?

complex I

Where do electrons carried by FADH₂ enter the ETS?

complex II

What shuttles electrons between major complexes?

two small, mobile electron carriers, cytochromes and ubiquinone

cytochromes

proteins with a heme prosthetic group that contains an iron atom that accepts and donates electrons 

How are individual electron carriers in ETS organized?

organized specifically from high to low free energy

NADH and FAD contain ____ free energy and are ____ oxidized

abundant; easily

the terminal acceptor (oxygen) is ____ reduced

easily

What does the higher concentration on H+ in the intermembrane compartment generate?

electrical and chemical gradient across the inner mitochondrial membrane

proton-motive force

• stored energy produced by proton and voltage gradient

• energy is used for ATP synthesis and cotransport of substances to and from the mitochondria

How does the H⁺ gradient power ATP synthesis?

by chemiosmosis

How does ATP synthase use proton-motive force?

uses it to add a phosphate to ADP to make it ATP (phosphorylation)

a _______ in the inner membrane is connected by a _____ to a ________located at the matrix

basal unit; stalk; headpiece

What bridges the basal unit and the head piece

a peripheral stalk

How does proton-motive force move enzymes?

through the basal unit to the matrix 

chemiosmosis causes….

the rotation of the ATP synthase headpiece

How many ATP are produced from 1 oxidized molecule of glucose?

32 (abt 2.5 from NADH and 1.5 from FADH₂)

How many ATP are produced from pyruvate oxidation?

5 ATP from 2 NADH

How many ATP are produced from the citric acid cycle?

2 ATP + 15 ATP from 6 NADH + 3 ATP from 2 FADH₂ = 20

What does the hydrolysis of ATP to ADP yield?

abt 7.0 kcal/mole

What is the efficiency of cellular glucose oxidation?

33%

How many kcal/mol are released when glucose is burned?

686 kcal/mol

What is the total energy conserved by 32 ATP?

224 kcal/mol

How is the rest of chemical energy release?

as body heat 

What happens when oxygen is absent or limited?

electrons carried by the 2 NADH produced by glycolysis may be used for fermentation

fermentation

• electrons carried by NADH are transferred to an organic acceptor molecule (converts NADH to NAD+)

• glycolysis continues to supply ATP by substrate-level phosphorylation

How does fermentation differ from anaerobic respiration?

in fermentation, electrons carried by NADH are transferred to an organic acceptor molecule, while in anaerobic respiration, electrons are transferred to an ETS in which in the final acceptor is not oxygen

what are the two types of fermentation?

• lactate fermentation 

• alcoholic fermentation

lactate fermentation 

• converts pyruvate to lactate

• occurs in some bacteria, plant tissues, and skeletal muscles 

• used to make buttermilk, yogurt, and dill pickles 

alcoholic fermentation

• converts pyruvate to ethyl alcohol and CO₂

• occurs in some plant tissues, invertebrates, protasis, and bacteria

• used to make bread and alcoholic beverages

oxidation of fats

• oxidation created more than twice the energy of oxidation of proteins and carbohydrates 

• before entering oxidative reactions, triglycerides are hydrolyzed into glycerol and individual fatty acids 

oxidation of proteins

• amino group is removed 

• the remainder enters oxidative pathways as pyruvate, acetyl-CoA, or intermediates of the citric acid cycle 

gluconeogenesis

when the body synthesizes glucose from the glycolysis and citric acid cycle pathways when energy is needed by the body; consumes ATP rather than producing it