Bioenergetics

Question 1

Physio chemical characteristics of triacylglycerols

Answer 1

Extreme insolubility in water
Inert

Question 2

Where can cells obtain fatty acids

Answer 2

Fats in the diet
Fats stored in cells as lipid droplets in adipocytes
Fats synthesised in the liver
Fats obtained by autophagy (degradation of cells own organelles) during starvation

Question 3

What must happen to triaculglycerols before they can be absorbed

Answer 3

Converted from insoluble macroscopic fat particles to microscopic droplets (micelles)

Question 4

Bile salts

Answer 4

Biological detergents
Emulsify dietary fats

Question 5

What happens after lipase converts triacylglycerols to mono and di acylglycerols and free fatty acids

Answer 5

Diffuse or are transported into the epithelial cells where they are reconverted to triacylglycerols and packaged with dietary cholesterol and specific apolipoproteins (proteins in lipid free form) into aggregates called chylomicrons

Question 6

What happens when the diet contains too many fatty acids

Answer 6

Liver converts them to triacylglycerols which are packaged with specific proteins into Very-low-density lipoproteins

Question 7

Transport of triacylglycerols

Answer 7

Hormones (epinephrine and glucagon) signal for energy
Triacylglycerols stored in adipose tissue mobilise and transported to tissue
Oxidised for energy production
Release free fatty acids into blood stream
Bind to blood proteins serum albumin
Fatty acids are carried to skeletal muscles, heart and renal cortex
Dissociate from albumin

Question 8

Carnitine shuttle

Answer 8

System that moves long chain fatty acids into the mitochondria for energy production and b-oxidation

Question 9

Mitochondrial oxidation of fatty acids

Answer 9

B- oxidation= fatty acids undergo oxidative removal of successive two carbon units in the form of acetyl-coA
Citric acid cycle= acetyl groups of acetyl- coA are oxidised to co2
Respiratory chain= NADH AND FADH2 donate electrons to the mitochondrial respiratory chain with production of atp and h2o

Question 10

Palmitic acid process

Answer 10

Palmitic acid (palmitate salt at pH7)
Palmitoyl- CoA
8 molecules of Acetyl CoA
80 ATP

Question 11

In the liver, what are the two pathways acyl- CoA go through

Answer 11

B oxidation in mitochondria
Or conversion into triacylglycerols and phospholipids in the cytosol

Question 12

Ketone bodies

Answer 12

Produced by liver
Used peripherally as an energy sours when glucose is not available

Question 13

Brain and ketones

Answer 13

The brain can adapt to the use of ketones under starvation conditions when glucose is unavailable
Cannot use free fatty acids because they cannot cross the blood brain barrier

Question 14

Digestion of dietary proteins

Answer 14

Dietary protein in stomach stimulates gastric mucosa to secrete the hormone gastric which stimulates secretion of hydrochloride acid and pepsinogen
Ph of stomach goes down= acidic
The acidic gastric juice starts killing bacteria and a denaturing agent, unfolding proteins
Pepsinogen is converted to active pepsin at low pH
Contents pass into small intestine, triggers secretion of hormone secretin
Stimulates pancreas to secrete bicarbonate to neutralise gastric HCl increasing pH to 7
Cholecystokinin released into blood in the upper part of intestines
Stimulates secretion of trypsin
Mixture of free amino acids transported into epithelial cells lining the small intestine, enters blood capillaries in villi and travel to liver

Question 15

What happens to the amino acids in the liver

Answer 15

A amino groups are removed by enzymes called aminotransferases or transaminases
Collected in the form of L-glutamate
Glutamate releases amino groups as ammonia in liver
Undergoes oxidative deaminatiion to a- ketoglutarate

Question 16

What causes an increase in transaminases

Answer 16

Metabolic dysfunction
Alcohol consumption
Medications
Hepatitis virus
Other infections

Question 17

Function of pyridoxal phosphate (PLP)

Answer 17

Coenzyme form of pyridoxine
Intermediate carrier of amino groups at the active site of aminotransferases

Question 18

Glutamine

Answer 18

Second major source of ammonia in hepatocyte mitochondria
Important for intercellular transport of ammonia

Question 19

How is ammonia transported

Answer 19

Ammonia is toxic
Free ammonia is converted to a non toxic compound before export into blood and transport to kidneys
Glutamate is replaced by glutamine
Free ammonia is combined with glutamate to yield glutamine

Question 20

How does a brain oedema occur

Answer 20

Increased ammonium ion (NH4+) alters the capacity of astrocytes to maintain potassium homeostasis across the membrane
Cells swell

Question 21

Astrocytes

Answer 21

Detoxification of ammonia in the brain
Express necessary enzymes to produce glutamate

Question 22

When do urea levels increase

Answer 22

Dietary intake is primarily protein
During prolonged starvation when muscle proteins are broken down

Question 23

Where does oxidative phosphorylation occur

Answer 23

Mitochondrial membranes

Question 24

Chemiosmotic theory

Answer 24

Transmembrane differences in proton concentration are the reservoir for the energy extracted from biological oxidation reactions

Question 25

Mitochondrial matrix

Answer 25

Contains pyruvate dehydrogenase complex and enzymes of citric acid cycle, fatty acid oxidation pathway and pathway of amino acid oxidation

Question 26

Outer membrane of mitochondria

Answer 26

Freely permeable to small molecules and ions

Question 27

Inner membrane of mitochondria

Answer 27

Impermeable to most small molecules and ions including H+
Contains respiratory electron carriers
STP synthase
Other membrane transporters

Question 28

Matrix of mitochondria

Answer 28

Contains pyruvate dehydrogenase complex
Citric acid cycle enzyme
Fatty acid b-oxidation

Question 29

3 types of electron carrying molecules function in the respiratory chain

Answer 29

Ubiquinone
Cytochromes
Iron-sulfur proteins

Question 30

Ubiquinone/ coenzyme Q

Answer 30

Lipid soluble benzoquinone
Can accept one electron or two electrons

Question 31

Cytochromes

Answer 31

Proteins
Strong absorption of visible light (makes blood red)
Iron containing heme groups
Three classes= a,b,c

Question 32

Iron sulfur proteins

Answer 32

Iron is present in association with inorganic sulfur atoms
Cys residues

Question 33

Net reaction of respiratory chain

Answer 33

Highly exergonic
Energy is used to pump proteins out of the matrix

Question 34

Protons and complex for each 2 electrons transferred to O2

Answer 34

4 protons by complex I
4 protons by complex III
2 protons by complex IV

Question 35

What is the electrochemical energy stored in a gradient of

Answer 35

1) the chemical potential energy due to the difference in concentration of H+ in the re regions separated by the membrane
2) the electrical potential energy that results from the separation of charge when a proton moves across the membrane without a counter ion

Question 36

ATP synthase

Answer 36

Two major components Fo and F1
F1= atp bound to empty conformations

Question 37

Rotational catalysis

Answer 37

The flow of protons through Fo causes the ring to rotate and in turn triggers the subunit conformational changes in F1

Question 38

ATP synthesised per 1/2 O2

Answer 38

2.5 ATP when electrons enter the respiratory chain at Complex I
1.5 ATP when electrons enter at Ubiquinone

Question 39

ATP per FADH2 AND NADH

Answer 39

1.5 atp per FADH2
2.5 ATP per NADH

Question 40

Hypoxic cells (deprived of oxygen)

Answer 40

Imbalance between the input of electron from fuel oxidation in the mitochondrial matrix and transfer of electrons to oxygen
Increased formation of reactive oxygen species