Chapter 25: Metabolism/Nutrition

Question 1

Metabolism

Answer 1

• sum total of all the chemical reactions occurring within the cells of an organism.
• Cells need a constant supply of energy to function.
• ATP is the primary energy-carrying molecule of the cell.

Question 2

ATP

Answer 2

• ATP – adenosine triphospahte
• Has a ribose sugar, nitrogenous base (adenine) and 3 phosphate groups
• The P’s held together by higher energy stronger bonds since it needs a lot of energy to keep the negative phosphate from repelling

Question 3

Three stages occur in the processing of nutrients:

Stage 1

Answer 3

• Digestion occurs in the GIT (gastrointestinal tract) and absorbed nutrients enter the blood to reach tissue cells
• Breaking down food by chewing. Broken down nutrients is absorbed in blood and carried to tissue cells. Monomers (building blocks) if breaking down: carbs you get simple sugars [glucose, glycogen] or monosaccharides; lipids = fatty acids/glycerol, proteins = a.a

Question 4

Three stages occur in the processing of nutrients: Stage 2

Answer 4

Occurs in the cytoplasm of tissue cells. Absorbed nutrients are:
i) used to build complex molecules (lipids, proteins, glycogen) by anabolic pathways.
OR
ii) broken down by catabolic pathways to harvest their bond energy to form pyruvic acid & acetyl CoA.

[Anabolic takes simple building blocks to make more complex structure
Catabolic reactions that break things down into simpler components]

Question 5

Three stages occur in the processing of nutrients: Stage 3

Answer 5

Occurs in the mitochondria & is almost entirely catabolic (“break down”). It requires oxygen and completes the breakdown of food to CO2 and H2O, generating large amounts of ATP through oxidative phosphorylation
>Requires O2 which is why we breathe in oxygen
>Oxidative phosphorylation - gets us lots of ATP (phosphoralation is adding a phosphate to a molecure. Oxidative is stripping electrons off other compounds then passing electrons down the electron transport chain allows us to build ATP from ADP)

Question 6

How much energy from catabolic is used for cellular functions

Answer 6

Only 40% of erergy from catabolic is used for cellular functions. The other 60% is lost as heat, some of which is use to maintain body temp.

Question 7

Carbohydrate Metabolism

Answer 7

• Carbohydrates are broken down into monosaccharides: glucose (about 80%), fructose and galactose.
• Liver cells (hepatocytes) convert fructose and galactose to glucose. (fructose and galactose goes to liver to get glucose)
• Can transfer energy from glucose to ATP.
• Other nutrients (fats, amino acids) can generate ATP and are linked to glucose breakdown pathways.

Question 8

Glucose Catabolism

Answer 8

• Glucose catabolism (“break- down”) is central to ATP production.
• involves cellular respiration
• Electrons (as hydrogen atoms) are removed from various compounds in the metabolic pathways and are transferred to coenzymes (electron acceptors).
• Whole point is to take glucose striping off e- and other things in order to make ATP
• So when we strip the e- (H+) we have coenzymes that are temporary electron acceptors. They hang around and grab the H+ when they’re released. These coenzymes latch onto the e- and take them to the last step (shuttle them to where they need to go)

Question 9

Cellular respiration

Answer 9

• respiration is the process (series of catabolic reactions) that releases energy from glucose and makes it available for cellular use.
• It involves oxidation and reduction reactions (redox rxns).

Question 10

A substance is oxidized when

Answer 10

> it loses an electron (LEO) → Exergonic.
When you strip an electron the bond is broken and it looses energy

2H NADH + H+ –> (-2H) –> NAD+ (oxidized form)

Question 11

A substance is reduced when

Answer 11

> it gains an electron (GER) → Endergonic.
When you gain an electron you form a bond so you need to gain energy to trap within the bond

NAD+ –>(+2H) –>NADH + H+ (reduced form)

Question 12

Two coenzymes in the metabolic pathways that take e- are:

Answer 12

i) Nicotinamide adenine dinucleotide (NAD+)
NAD+ –>(+2H) –>NADH + H+ (reduced form)

ii) Flavin adenine dinucleotide (FAD)
FAD –> (2H+) –> FADH2 (reduced)

Question 13

Cellular respiration involves four sets of reactions:

Answer 13

1. Glycolysis
   
   2. Formation of acetyl CoA
   3. Krebs cycle (citric acid cycle)
   4. Electron transport chain reactions (ETC)

Question 14

Overall cellular respiration reaction equation

Answer 14

C6H12O6 (glucose) + 6O2 → 6CO2 + 6H2O + 32 ATP + heat

For each molecule of glucose we get 32ATP

Question 15

Glycolysis

• What step in cellular respiration?
• Where does it occur?
• how many reactions?
• input/output?

Answer 15

• Step 1
• Occurs in the cell cytoplasm.
• Is an anaerobic process (does not need O2)
• Series of 10 reactions which convert 1 glucose (6C) into • 2 molecules of pyruvic acid (3C)
• Glucose has lost 4 Hydrogen atoms which are now bound to 2 molecules of NAD+.

Inputs
1 glucose
2 NAD+
2 ATP

Outputs
2 Pyruvic acids
2 NADH + 2H+2
4 ATP

• The fate of pyruvic acid depends on oxygen availability.
If oxygen is unavailable (anaerobic conditions), then pyruvic acid will be reduced.
i.e. NADH + H+ adds H’s back to pyruvic acid to yield lactic acid, which makes more NAD+ available for glycolysis to continue.

Example of anaerobic condition: overworked skeletal muscle.

Question 16

What does the cell do with pyruvic acid - 2

Answer 16

• The fate of pyruvic acid depends on oxygen availability.

• If oxygen is unavailable (anaerobic conditions), then pyruvic acid will be reduced.
2 Pyruvate + 2NADH +2H –> 2NAD + 2 Lactic Acid

• If oxygen is available (aerobic conditions), then pyruvic acid is converted to acetyl coenzyme A (CoA)

Question 17

Formation of Acetyl CoA

• What step in cellular respiration?
• Where does it occur?
• input/output?

Answer 17

• step 2
• occurs in the matrix of the mitochondria
• If oxygen is available (aerobic conditions), then pyruvic acid is converted to acetyl coenzyme A (CoA).
• Pyruvic acid loses a C atom (as CO2) and a pair of H atoms as it enters the mitochondria.
• The 2C molecule formed (acetic acid) is attached to coenzyme A to produce acetyl CoA (form 2 for every molecule of glucose).
• H’s are transferred to NAD+ to produce NADH + H+.
• Acetyl CoA enters the Krebs cycle.
• Remember 1 glucose = 2 pyruvates!

Inputs
2 Pyruvic acids
2 NAD+

Outputs
2 CO2
2 NADH + 2H+
2 Acetyl CoA

Question 18

Krebs Cycle (Citric Acid cycle)

• What step in cellular respiration?
• Where does it occur?
• how many reactions?
• input/output?

Answer 18

• step 3
• occurs in the matrix of the mitochondria
• An aerobic process (requires O2).
• Series of 8 cyclical reactions.
• Begins with 1 acetyl CoA and results in:
- formation of 2 CO2.
- H’s are picked up by FAD to form 1 FADH2.
- H’s are picked up by NAD+ to form 3 NADH.
- formation of 1 ATP.
• Remember 1 glucose = 2 acetyl CoA
• Much of the energy originally present in the bonds of glucose is now present in the reduced coenzymes (NADH + H+ and FADH2).
• High energy electrons are handed off to the electron transport chain (last step) which couples this energy to ATP synthesis.

Inputs                     Outputs 
2 Acetyl CoA         4 CO2
6 NAD+                  6 NADH + 6H+
2 FAD                     2 FADH2
                               2 ATP

Question 19

Electron Transport Chain

• What step in cellular respiration?
• Where does it occur?
• how many reactions?
• input/output?

Answer 19

• Step 4
• Occurs on the cristae (folds) of the inner mitochondrial membrane.
• Electrons from NADH and FADH2 are transferred to a series of membrane proteins that act as acceptors.
• The proteins in the chain are electron acceptors that play hot potatoes with the electrons.
• As the electrons are passed down the line they lose energy which is used to trap in the ATP bonds
• Electrons are passed from acceptor to acceptor along the chain, and run “downhill”.
• Hydrogen atoms are split apart as they transfer from coenzymes to the ETC.
• Energy from NADH + H+ passes along the ETC and is used to pump H+ from the matrix to the intermembrane space (proton pump).
• This creates an area of high H+ concentration in the intermembrane space.
• H+ then diffuse back down the concentration gradient into the matrix through ATP synthase complexes to form ATP from ADP.
• Oxygen acts as the final electron acceptor at the end of the ETC.
- The hydrogen ions flow back into the mito matrix. H+ ions and e- recombine to make full hydrogen ions. These then combine with oxygen (O2) to give you water
- electrons are recombined with protons (H+) to form hydrogen which is combined with oxygen to form water (6 H2O).

Inputs Outputs
10 NADH + 10H+ 28 ATP
2 FADH2 10 NAD+
2 FAD

Question 20

• How much ATP is made by NADH/FADH in the ETC?

- Why is there a Dif?

Answer 20

• Each pair of electrons donated to ETC by NADH provides enough energy to pump enough protons to produce about 2.5 molecules of ATP (1.5 ATP for each FADH2).
• The dif between FAD/NADH is due to where the molecules are.
• The NADH is the first in the ETC, they go through the 3 proton pump. The FAD only gives 1.5 because it skips the first proton pump and donates the electron further down.

Question 21

Total ATP production per glucose from each step:

Answer 21

ATP
• glycolysis → 2 ATP
• Krebs cycle → 2 ATP

NADH
• glycolysis → 2 → (2.5 ATP = 5 ATP)
• acetyl CoA → 2 → (2.5 ATP = 5 ATP)
• Krebs cycle → 6 → (2.5 ATP = 15 ATP)

FADH2
• Krebs cycle → 2 → (1.5 ATP = 3 ATP)

TOTAL = 32 ATP

Question 22

Why does the textbook will give you a range of 30-32ATP per glucose molecule?

Answer 22

It has to do with glycolysis. The problem is that glycolysis takes place in the cytoplasm and everything else is in the mito. We must take the NADH and move it from the cytoplasm to the mito. In order to do that we must use one of 2 different shuttles. Different cells use dif shuttles. Shuttle #2 delivers NADH further down the ETC so instead of getting 2.5ATP your only getting 1.5ATP which will only get you 30ATP total.

Question 23

NADH + H+ Shuttles

Answer 23

• Moves NADH from cyto to mito
• Depends completely on where in the body the cellular resperaton is happening
• shuttle #2 delivers NADH further down the ETC so instead of getting 2.5ATP your only getting 1.5ATP

Shuttle #1:
• Found in liver, kidney, & heart muscle.
• NADH passes e-’s to a shuttle molecule that delivers e-’s to beginning of ETC.
• Anything that starts at the beginning generates 2.5 ATP.

Shuttle #2:
• Found in skeletal muscle & brain cells.
• NADH passes e-’s to a different shuttle that delivers e-’s farther down ETC.
• Only generates 1.5 ATP, just like FADH2.