Week 8: Obtaining energy

Question 1

what is metabolism

Answer 1

the sum of all chemical reactions

Question 2

what is catabolism

Answer 2

the breakdown of nutrients to release energy

Question 3

what is anabolism

Answer 3

synthesis of molecules within cells

Question 4

Catabolic pathways

Answer 4

breakdown fuel molecules to produce H2O, CO2

Question 5

Anabolic pathways

Answer 5

build macromolecules from building blocks

Question 6

Metabolic pathway

Answer 6

transforming substrates into products, via specific intermediates/metabolites

Question 7

Chemical reaction

Answer 7

loss of free energy

molecules move to a lower energy state

Question 8

Activation energy

Answer 8

The energy required to overcome the hill is called the activation energy

Question 9

Why do we need enzymes

Answer 9

Enzymes act by lowering the activation energy & making it easier for a reaction to occur

Enzymes increase reaction rates

They allow reactions to occur under much milder conditions: low temperature, atmospheric pressure, approx. neutral pH…ie. physiological conditions!

Question 10

How does an enzyme work

Answer 10

Enzymes have an active site, a cleft into which substrate molecules fit
They are highly selective

Question 11

How to obtain energy from food

Answer 11

food is oxidised by chemical reactions

energy is converted into ATP

Question 12

Indirect synthesis of ATP

Answer 12

Co-enzymes “trap” the packets of energy from the reactions as electrons & an H+ (= H-) eg. NAD+ accepts electrons and hydrogen to become NADH

Energy trapped in NADH is then used to synthesize ATP

Question 13

Direct ATP synthesis

Answer 13

substrate - level phosphorylation

High-energy phosphate groups are directly transferred from phosphorylated substrates to ADP (adenosine diphosphate)
Occurs in glycolysis and the Krebs cycle

Question 14

what is NAD+

Answer 14

nicotinamide adenine dinucleotide
a carrier molecule (like ATP)
a coenzyme
carries electrons

Question 15

what has a lower chemical potential energy NADH or NAD+

Answer 15

NADH

Question 16

How are macronutrients broken down to acetyl CoA

Answer 16

Glucose is broken down to acetyl CoA via the glycolysis pathway, generating NADH

Fatty acids are broken down to acetyl CoA via the β-oxidation pathway, generating NADH

Amino acids are broken down to acetyl CoA via a variety of pathways

Question 17

What is the breakdown of macronutrients

Answer 17

Glycolysis, breakdown of fats or amino acids all can produce acetyl CoA

Citric acid cycle in the mitochondria

Electron transfer &
Oxidative phosphorylation in the mitochondria

Question 18

how to convert pyruvate to acetyl CoA in the mitochondria

Answer 18

The ‘bridge reactions between glycolysis and Krebs cycle - via pyruvate dehydrogenase enzyme complex

Occurs in the mitochondrial matrix

Each pyruvate yields: 1x Acetyl CoA, 1x NADH, 1x CO2

Question 19

what is the citric acid cycle

Answer 19

Acetyl CoA combines with oxaloacetate
Gradual oxidation of citrate

Each acetyl CoA yields:
3x NADH (yield 3 ATP each)
1x FADH2 (yield 2 ATP each)
1x ATP
2x CO2

The initial acceptor molecule oxaloacetate is also reformed

Question 20

Glycolysis vs Citric Acid Cycle

Answer 20

Glycolysis:

• linear pathway
• cytosol
• no oxygen

Krebs

• cyclic
• mitochondria
• aerobic

Question 21

Oxidative phosphorylation

Answer 21

NADH & FADH2 are used to drive the synthesis of ATP from ADP & Pi (inorganic phosphate)

Consists of 2 processes:
Electron transport chain
ATP synthesis

In eukaryotic cells this takes place in the mitochondria

Question 22

Electron Transport Chain

Answer 22

Re-oxidation of NADH to NAD+

Releases 2 “high energy” electrons which are passed along the electron transport chain, which is a series of membrane-bound proteins/enzymes that accept the electrons (are reduced).

The electrons lose energy as they pass through the chain of proteins

This energy is then used to pump H+ ions across the inner mitochondrial membrane into the intermembrane space

This generates an H+ gradient which is used to drive ATP synthesis

At the end of the chain, electrons combine with O2 to form H20

Question 23

what is ATP synthase

Answer 23

Large multi-subunit proteins in inner mitochondrial membrane

Act as energy generating molecular motors

Converts energy from the flow of H+ (protons) down the concentration gradient into mechanical energy

ATP synthase has 2 sets of proteins – rotating stalks that push against stationary heads and cause a change in conformation of the subunits of the heads

the mechanical energy is converted into chemical bond energy – ie. a bond is formed between ADP & Pi & ATP is produced

100 molecules of ATP produced per second
approx. 3 H+ moved to produce 1 ATP