Metabolism

Question 1

What is ATP

Answer 1

ATP is the cell’s energy currency, it is known as adenosine triphosphate, it is generated via cellular respiration, it is a temporary store formed from ADP + P, it is released during 1-6 seconds of exercise
Function: ATP phosphorylates contractile proteins in the muscle allowing them to shorten, phosphorylates transport proteins, allowing passage of substances through cell membrane. ATP is always being broken down releasing free P groups

Question 2

What is creatine

Answer 2

used to convert ADP to ATP by direct phosphorylation, it is stored in the muscles which have limited stores so they cannot provide for all muscle activities, they are reusable & recombine with P to regenerate a CP molecule
Chemical pathways break the chemical bonds between nutrient molecules and convert potential energy into ATP

Question 3

What is creatine kinase

Answer 3

An enzyme found in healthy muscle that catalyzes direct phosphorylation
Damage to muscle results in subtype of CK entering the bloodstream, this is used as an indicator of heart attacks,
Exercise, damage & trauma can increase CK concentrations

Question 4

Define coenzyme

Answer 4

a non-protein compound that is vital for the functioning of an enzyme

Question 5

Name 3 coenzymes and their function in respiration

Answer 5

NAD: is a hydrogen atom acceptor, reduced during cellular RS, they are oxidised in OD
FAD: Reduced during the krebs cycle, is a hydrogen acceptor, it is bound to cristae
Acetyl coenzyme A: carriers an acetyl group from the links reaction to the krebs cycle

Question 6

Describe the process of glycolysis

Answer 6

Occurs in aerobic & anaerobic RS, occurs in cell cytoplasm

Glucose is converted into hexose bisphosphate, this uses 2 ATP molecules

hexose bisphosphate is unstable and so is broken into 2 3 carbon triose molecules

Triose phosphates are oxidized via coenzyme NAD accepts H atom, which produces 2 molecules of ATP, NAD has been reduced via dehydrogenase enzyme to form NADH. This forms 2 pyruvate molecules (3C)

Phosphates are transferred to form 4 ATP molecules via substrate-level phosphorylation

Net gain of 2 ATP, 2NADH, 2 ATP used, 2 pyruvate molecules

NAD acts as an electron carrier

Question 7

Describe the process of the links reaction

Answer 7

Takes place in mitochondria matrix, no ATP made in this phase
It is referred to as the link reaction because it links glycolysis to the Krebs cycle

The steps are:

Pyruvate is decarboxylated to form acetate via enzyme decarboxylase, CO2 is released, NAD becomes reduced to NADH, accepts hydrogen atom

This is a redox reaction as pyruvate is oxidized and NAD is reduced

Acetate combines with acetyl coenzyme A to form acetyl coenzyme A acetate

Acetyl coenzyme A enters Krebs cycle

2 NADH produced, NO ATP

Question 8

Describe the process of the Krebs cycle

Answer 8

Acetyl coenzymes enter krebs cycle which takes place in the mitochondrial matrix,it combines with oxaloacetate (4C) to form citrate (6C),

Citrate is decarboxylated & dehydrogenated via enzymes causing release of CO2 and NAD to accept H+ to form NADH, NAD is reduced producing ketoglutarate (5C)

ketoglutarate (5C) is dehydrogenated & decarboxylated via enzymes decarboxylase & dehydrogenase, this forms intermediate compound of succinate, this generates phosphorylation of ADP + P to form 1 molecule of ATP, as well as producing CO2 & NADH

Succinate is oxidised to form fumurate, FAD is reduced as it accepts H+ forming FADH

Fumarate is converted to malate, this releases a H2O molecule

Final NADH is formed when malate is oxidized to reform oxaloacetate

In total in one cycle of krebs 1 ATP produced, 2CO2 released, 3NADH, 1 FADH

For 1 molecule of glucose 2 ATP, 4CO2, 6NADH, 2FADH

Question 9

Describe the process of oxidative phosphorylation

Answer 9

This occurs in the cristae of the mitochondria and involves ATP synthase
1. NADH & FADH release Hydorgen atom into mitochondrial matrix, are regenerated and re-enter glycolysis.
2. Hydrogen atoms split into electrons & H+, electrons are used in the ETC, H+ stays in matrix
3. Electrons are carried via electron carriers in ETC, as they move along ETC, electrons lose energy & is released
4. Energy released is used to actively pump H+ into intermembrane space via active transport, establishing an electrochemical gradient, H+ builds up in Intermembrane space
5. H+ concentration os greater outside matrix & so rapidly diffuse in down EC gradient, known as chemiosmosis
6. H+ triggers ATP synthase to phosphorylate ADP + P to ATP
7. H+ and electrons recombine to form H atoms, which are accepted by O2 (final electron acceptor) to produce water a product of respiration

Question 10

Describe the anaerobic respiration

Answer 10

anaerobic is where glucose is oxidised in not enough oxygen, only glycolysis occurs in which pyruvate is converted to lactic acid (cramps), NAD is regenerated, only 2 ATP made, is an insufficient process, we cannot anaerobically respire for long.
Lactic acid is converted back to pyruvate in the liver, which is then converted to glycogen, NAD is regenerated so coenzymes can continuously accept hydrogen atoms form triose phosphate

Question 11

How much ATP is generated from each process and what is the total ATP generated?

Answer 11

Overall 38 ATP generated
In glycolysis there is a production 4 ATP is produced
No ATP produced in Links reaction only acetyl coenzyme A
Krebs produces per 1 molecule of glucose: 2 ATP

Question 12

Why do we catabolize lipids?

Answer 12

We catabolise lipids when suffcient carbohydrates are not available. Fatty acids produce more ATP than glucose, but therefore have a higher oxygen demand. Abscence of glucose enables glycerol to enter glycolysis if enough O2 Avaliable it will continue to krebs & OP.
2 carbons are split off in a process called beta-oxidation in the mitochondria, each fragment is converted into acetyl coenzyme A.

Question 13

What does RER mean?

Answer 13

Stands for respiratory exchange ratio, it allows us to identify which food group is being used as the predominant energy source by measuring O2 consumption & CO2 production
fats: 0.7
Glucose: 1
Amino acids: 0.8

Question 14

How much ATP does a triglyceride yield compared to glucose

Answer 14

Per molecule of triglyceride 129 ATP produced compared to glucose of 38 ATP

Question 15

What are the dangers of a high fat diet & how does it happen?

Answer 15

A high-fat diet can cause acetyl A to convert to ketones, which causes ketoacidosis, which makes the blood acidic due to reduced carbohydrates.
This occurs due to a low-carb diet, starvation or uncontrolled diabetes
Causes Kussmaul breathing (deep & rapid)
ketone breath
ketones in urine
coma->death

Question 16

Why & how do we catabolize proteins?

Answer 16

We catabolise proteins when neither carbs nor fat are available, through gluconeogenesis. This is likely to occur during periods of starvation or prolonged exercise e.g., marathon running.
Amino acids are deaminated in the liver forming NH2 which is converted to urea to be excreted. Keto acid remains which can be converted to pyruvate or acetyl coenzyme A which can enter aerobic RS

Question 17

Describe the release of ATP during short duration exercise

Answer 17

S1: in the first 6 seconds, ATP is stored in the muscles is used first
S2: At 10 seconds ATP is phosphorylated from ADP + creatine phosphate
S3: At 30-40 seconds glycogen stored in the muscles is broken down to glucose which is oxidized to generate ATP

Question 18

Describe the release of ATP during long duration exercise

Answer 18

ATP is broken down via several different nutrient fuel sources via aerobic pathways, this pathway uses oxygen released from myoglobin or haemoglobin. When exercise ends oxygen debt is repaid

Question 19

What is a redox reaction

Answer 19

Where oxidation & reduction reactions are occurring simultaneously
Reduction is gaining of election whereas oxidation is losing of electrons (removal of hydrogen)

Question 20

What are the factors that influence metabolism

Answer 20

• Diet
• exercise
• stress
• disease

Question 21

Define cellular respiration

Answer 21

Respiration that occurs within the cells itself of cytoplasm & mitochondria, produces ATP from stored nutrients

Question 22

Describe the differences between glycolysis & oxidative phosphorylation

Answer 22

Glycolysis: occurs in aerobic & anaerobic RS, produces 2 ATP, occurs in cytoplasm of cell, uses enzymes of dehydrogenase and decarboxylase, substrates of glucose, short term energy

OD: Occurs in aerobic RS, occurs in mitochondrial matrix, produces 38 ATP, uses enzymes of ATP synthase, substrates of fatty acids, glucose & proteins, long term energy

Question 23

Describe the absorptive state

Answer 23

Absorptive state: the fed state following digestion where nutrients are absorbed into the bloodstream. Insulin is a key hormone involved

A typical meal takes 4hrs to digest & absorb completely, eating 3 times a day leaves us with a 12hr absorptive state. At rest free glucose is used to make ATP, lipids are used for synthesis, amin acids used for protein synthesis

Excess glucose stored as glycogen, excess is stored as fat (adipose tissues) via lipogenesis

Question 24

Describe the post-absorptive state

Answer 24

Post absorbative state: the fasting state, occurs overnight, where stored nutrients are being used up, the body relies on these stored nutrients as fuel to maintain a blood glucose level of 4-7mmol. Key hormone involved is glucagon

The brain has a high energy demand relying on carbohydrates and not fats

RBC relies on anaerobic glycolysis

Stored glycogen broken down via glycogenolysis to produce free glucose, stored triglycerides are broken down via lipolysis to produce fatty acids & glycerol, during a prolonged fast when glycogen stores are depleted glucose is synthesized via other stores by gluconeogenesis.

Question 25

Define glycogenesis, glycogenolysis & gluconeogenesis

Answer 25

glycogenesis: excess glucose stored as glycogen in the liver & muscles
Glycogenolysis: glycogen stores are broken down to form glucose to enter the bloodstream
Gluconeogenesis: production of glucose from non-carbohydrate molecules e.g., AA’s & FA’s

Question 26

What is the normal blood glucose range in the blood?

Answer 26

4-7mmol

Question 27

What is hyperglycemia & hypoglycemia?

Answer 27

Hyperglycemia: blood glucose levels above normal range of 4-7mmol
Hypoglycemia: blood glucose levels are below normal range, below 4mmol

Question 28

Define lipolysis & lipogenesis

Answer 28

Lipogenesis: ingested glucose, fatty acids & amino acids are stored as fat influenced by prescence of insulin
Lipolysis: breakdown of fat stores, broken into fatty acids & glycerol, fatty acids can be used for oxidation in krebs cycle & ETC. Glycerol can be converted into pyruvate to generate ATP or undergo gluconeogenesis to maintain blood glucose via liver

Question 29

What occurs to excess protein?

Answer 29

Surplus of protein is stored as fat, amino acids deaminated to form NH2 which is converted to urea to be excreted by the kidneys. Amino acids are also used to make plasma proteins, clotting proteins, albumin, most amino acids remain in bloodstream to be taken up by other cells

Question 30

Describe the breakdown of proteins in the liver

Answer 30

1. during transamination an amine group is switched from an AA to a ketone acid
2. in oxidative deamination, the amine group of glutamic acid is removed as NH2 + CO2 forms urea
3. Keto acid modification, keto acids are modified so they can enter krebs cycles pathway

Question 31

Describe the hormonal control of the absorptive state

Answer 31

After eating a meal, blood glucose levels & amino acids levels rise, stimulating the beta cells in the pancreas to secrete insulin

GI tract hormone GIP & parasympathetic stimulation also stimulates secretion of more insulin

Insulin binds to complementary receptors on target cells, receptors are specific in shape. Stimulating the shuttling of glucose inside the cell via transport proteins

Facilitated diffusion of glucose into the cell increases causing blood glucose levels in the blood to decrease, active transport of amino acids into tissues decreases amino acids concentration in blood. This stops secretion of insulin from pancreas

Amino acids are used for protein synthesis

Once glucose enters the tissue cells insulin enhances glucose oxidation in adipose tissue to triglycerides (glycerol + fatty acids)

Enzymes involved in glyconeogenesis are inhibited

Question 32

Describe hormonal & neuronal control of post-absorptive state

Answer 32

Glucagon is released from alpha cells when blood glucose levels fall below 4mmol, glucagon is a hyperglycemic hormone, promotes glucose release to blood

Glucagon targets liver & adipose tissues

Hepatocytes respond to glucagon by stimulating glycogenolysis & gluconeogenesis

Adipose tissues release FA’s & glycerol to the bloodstream via lipolysis, aipose tissue contains sympathetic fibres, this causes adrenaline release from adrenal medulla due to sympathetic activation on liver, providing lots of fuel for ATP

Injury. Stress, exercise will trigger this pathway

FA’s used by cells to respire

In some cases, persistent low glucose levels lead to formation of ketones

Glucagon is inhibited when blood glucose levels begin to rise & insulin secretion begins again

Rising amino acids stimulate release of glucagon & insulin