the Krebs Cycle

Question 1

What does ATP stand for and is its structure?

Answer 1

Adenosine Triphosphate; its a nucleotide which contains the sugar ribose, the base adenine and 3 phosphate groups

Question 2

What does ATP do?

Answer 2

its the energy currency of the body; it is used to capture the energy released by reactions in the body such as burning glucose or fat.

Question 3

What is the energy producing formula?

Answer 3

ATP + H2O and ATPase = ADP + P Group + energy

Question 4

what is phosphorylation?

Answer 4

the addition of a phosphate group like when storing energy i.e. ADP + P + E via ATP synthase = ATP + H2O

Question 5

What mineral is always present in ATP?

Answer 5

Magnesium binds to phosphate group in ATP and holds the molecule in a particular shape.

Question 6

What are the functions of ATP?

Answer 6

• capture the energy from oxidation reactions
• drive synthetic reactions
• fuel movement
• transport substances across the cell membranes
• cell division

Question 7

What are the two ways of making ATP?

Answer 7

1. Substrate level phosphorylation - happens in the cytosol and can occur with or without Oxygen for a limited time
2. Oxidative phosphorylation and the electron transport chain - occurs in the mitochondria of cells (better place)

Question 8

What is NAD, what does it stand for and how is it derived?

Answer 8

Nicotinamide adenine dinucleotide; its an intermediate energy carrying molecule. instead of trapping energy in oxygen-phosphate bonds, it steals hydrogen and two high energy electrons and becomes NADH. it is derived from niacin which can be made in the liver from tryptophan or aspartic acid.

Question 9

What is FAD, what does it stand for and how is it derived?

Answer 9

flavin adenine dinucleotide; an intermediate energy carrying molecule that steals Hydrogens and electrons to become FADH2; derived from riboflavin B2.

Question 10

what are the 4 steps in cellular respiration?

Answer 10

1. glycolysis or anaerobic cellular respiration (in cytoplasm)
2. formation of acetyl CoA
3. Krebs cycle or the citric acid cycle (mitochondrial matrix)
4. electron transport chain

Question 11

What does glycolysis yield?

Answer 11

one glucose molecule is transformed into two pyruvate molecules; input of 2 x ATPs and output of 4 x ATPs; yields net 2 x ATPs and 2 x NADHs 2 x pyruvates.

Question 12

What micronutrients are needed during glycolysis?

Answer 12

Magnesium and B3 (niacin)

Question 13

what happens if no oxygen is available during glycolysis?

Answer 13

when no oxygen is available the NADH cannot be recycled in the ETC, so NAD+ supplies will run low. in order for energy production to continue, the NADH reacts with the pyruvate, turning it into lactic acid. this allows small amounts of ATPs to continue until acidity becomes too high. lactic acid will then go to the liver and gets recycled in the cori cycle.

Question 14

what is coenzyme A and how is it synthesised?

Answer 14

CoA is a vital carrier molecule to transport the acetyl group (2Cs) in to the mitochondria so it can participate in the Krebs cycle. it is naturally synthesized from pantothenate (Vitamin B5) which is found in meat, vegetables, cereal grains, legumes, eggs and milk.

Question 15

How does acetyl coA gets formed?

Answer 15

Acetyl CoA is catalysed by pyruvate dehydrogenase. the pyruvate loses a carbon with the help of Thiamine (B1) and lipoic acid. once the carbon has been lost, NAD
is able to steal H and some e- to make another NADH. what is left of pyruvate is joined to a carrier molecule called CoA.

Question 16

What micronutrients are required for the Krebs Cycle?

Answer 16

Magnesium, Riboflavin (B2), Niacin (B3) because most of its energy is trapped in NADH and FADH2.

Question 17

How much energy do you get from the Krebs Cycle per glucose molecule?

Answer 17

the Krebs Cycle turns twice with each molecule of glucose. for each glucose you get 2 x ATP, 6 x NADH and 2 FADH2.

Question 18

what is the net result for 1 molecule of glucose from aerobic respiration?

Answer 18

10 x NADH and 2 x FADH2 + 4x ATPs arrive at the ETC = 38 ATPs.

Question 19

What cofactors do each of the enzyme complexes in the ETC need?

Answer 19

Complex I = Iron and Sulphur
Complex II = CoQ10
Complex III = Iron
Complex IV = copper to make water at the end of chain
ATP Synthase at the end channel needs magnesium

Question 20

what is the formula to convert 1 x glucose molecule into ATP?

Answer 20

C6H1206 + 6 x O2 + 38 x ADP’s + 38 P = 38 ATPs plus 6 x COs plus 6 x H20.

Question 21

How does the Krebs cycle begin?

Answer 21

Acetyl CoA will transfer two carbons to a four carbon molecule called oxaloacetate making citrate (6Cs).

Question 22

where are the series of enzymes complexes in the ETC embedded?

Answer 22

mitochondrial cristae

Question 23

how does the ETC work?

Answer 23

the molecules give their electrons to the enzyme complexes at the beginning of the chain. the electrons are then passed along the chain, releasing energy that pumps H+ into the intermembrane space from the matrix creating a concentration gradient. as they come back into the matrix they pass through another enzyme complex that has ATP synthase embedded.

Question 24

How to you obtain energy from Fats?

Answer 24

Lipases split triglycerides; glycerol enters the glycolysis pathway; fatty acids are carried to the liver where through a process called beta oxidation they get converted into acetyl CoA and enters the Krebs Cycle.

Question 25

What nutrients are required for fatty acids to get into the mitochondria?

Answer 25

magnesium (for ATP) and the amino acid carnitine

Question 26

what is carnitine made of?

Answer 26

lycene and methiodine

Question 27

what is the aim of beta oxidation?

Answer 27

the aim is to chop the fatty acid chain into two carbon chunks, that can react with coA to go into the Krebs Cycle.

Question 28

what are the 4 steps in beta-oxidation?

Answer 28

1. Oxidation by FAD
2. Hydration
3. Oxidation by NAD+
4. Thiolysis

each cycle will cleave off 2 carbons at a time.

Question 29

What are the products of beta-oxidation?

Answer 29

Acetyl CoAs - Krebs Cycle
NADHs - ETC
FADH2 s - ETC

amount of energy produced depends on length of fatty acid chain.

Question 30

What are ketone bodies?

Answer 30

in the absence of carbs, the liver can convert acetyl CoA from fatty acid oxidation or proteins as a last resort into ketone bodies.

Question 31

Three examples of ketone bodies

Answer 31

acetone, acetoacetic acid and beta-hydroxybutyrate.

Question 32

what is Ketosis?

Answer 32

accumulation of ketone bodies during high fat diets or fasting; normally not harmful.

Question 33

what is ketoacidosis?

Answer 33

if levels of acetoacetic acid and beta-hydroxybutyrate (which are acidic) get too high, the blood pH drops, resulting in Ketoacidosis. It’s dangerous and only happens in disease states like diabetes and alcoholism.

Question 34

What is lost when amino acids are broken down to enter the Krebs Cycle ? and what co factors are needed? what is the result?

Answer 34

Nitrogen; Vitamins B3 and B6 are important cofactors; Ammonia NH3 either excreted as urine or converted to urea in the urea cycle.

Question 35

What is gluconeogenesis?

Answer 35

the synthesis of new glucose from non carb sources
- pyruvate
- lactic acid
- glycerol
- some amino acids like glutamine
requires ATP; it’s glycolysis in reverse.

Question 36

where does gluconeogenesis take place?

Answer 36

in the liver and to a lesser degree in the kidneys

Question 37

when does gluconeogenesis happen?

Answer 37

periods of fasting, starvation or intense exercise

Question 38

what cofactor is needed for gluconeogenesis?

Answer 38

Biotin (and ATP)

Question 39

where will adults in a fed state obtain their energy from?

Answer 39

47% carbs, 38% fat and 15% from protein.