Basic Metabolism

Question 1

What are the 3 energy sources

Answer 1

Carbohydrates;
Lipids;
Proteins;

Question 2

Carbohydrate, proteins and lipids yield how much energy per gram?

Answer 2

Carb, protein - 4kcal (17kJ);

Lipid - 9kcal;

Question 3

Recommended intake of the 3 energy sources

Answer 3

Carbohydrate - 55%;
Lipids - 30%;
Proteins - 15%;

Question 4

What is ATP

Answer 4

Adenosine triphosphate;

Energy currency of the cell;

Question 5

ATP hydrolysis to ADP and Pi is?

Phosphorylation of ADP to form ATP is?

Answer 5

Exergonic;

Endergonic;

Question 6

Gamma-phosphate bond of ATP is?

Answer 6

High energy bond

Question 7

Catabolism

Answer 7

Energy yielding nutrients (fats, carbs, proteins) converted to energy poor products (CO2, H2O, NH3);

Question 8

Anabolism

Answer 8

Precursor molecules (amino acids, sugars, fatty acids, nitrogenous bases) converted to complex molecules (protein, polysaccharides, lipids, nuclei acids);
Needs ATP and NADH;

Question 9

3 stages

Answer 9

1. Hydrolysis of complex molecules to component building blocks;
2. Conversion of building blocks to Acetyl CoA (or other simple intermediates);
3. Oxidation of acetyl CoA (oxidative phosphorylation)

Question 10

Carbohydrate

Answer 10

CH2On;
Contains C combined with hydroxyl, keto, aldehyde and hydrogen;
Simple carbohydrates (monosaccharides);
Complex polymers (polysaccharides);

Question 11

Simplest carbohydrate has?

Answer 11

3C;
Aldehyde or ketone group;

Example: glyceraldehyde - asymmetric C2 - has D and L enantiomers;

Question 12

Generic names for:
3C;
4C;
5C;
6C;
7C;
9C;

Answer 12

Trioses;
Tetroses;
Pentoses;
Hexoses;
Heptoses;
Nonoses;

Question 13

Glucose

Answer 13

Most abundant carbohydrate;
C6,H12,O6;
Exists in D and L enantiomers;
Found in plasma, cellls;
Stored as insoluble glycogen;
Comes from diet or body stores;

Question 14

In solution glucose forms a 6 membered ring called? 5 membered is are called?

Answer 14

Pyranose;

Furanose;

Question 15

Polysaccharides

Answer 15

Assembled from monosaccharide units joined by glycosidic bonds;
Same/diff monosaccharides;
May be branched - glycogen;

Question 16

Major transported carbohydrate in blood

Answer 16

Glucose

Question 17

Blood concentration of glucose is tightly controlled by

Answer 17

Hormones

Question 18

Fasting conc of glucose;

Following a high carb meal;

Answer 18

4mM;

8mM;

Question 19

Glusose is required by?

Answer 19

Brain and RBCs

Question 20

Majority of carbohydrates in diet are

Answer 20

Polysaccharides

Question 21

Digestion of carbohydrates

Answer 21

Salivary amylase in mouth (to oligosaccharides);
Pancreatic amylase in small intestine;
Final digestion my mucosal cells (disaccharides to monosaccharides);
Glucose taken into cells with Na+ by active transport;

Question 22

Glucose uptake

Answer 22

Taken into cells from blood by facilitated diffusion mediated by hexose transporter proteins in PM (GLUTs);
Tissue specific expression of different gluts;
Insulin increases activity/expression of GLUT 4, regulated uptake by muscle, adipose, heart;
Glucose uptake by brain GLUT3;
Kidney, pancreas, liver - GLUT 2;
RBCs - GLUT 1 - Insulin independent

Question 23

Hyperglycaemia

Hypoglycaemia

Answer 23

High blood glucose conc;

Low blood glucose conc;

Question 24

Glycolysis location. Yields?

Answer 24

Cytosol of every cell in the body;

ATP and intermediates;

Question 25

Glycolysis converts 6C glucose into

Answer 25

2 molecules of 3C pyruvate -aerobic;

Lactate - anaerobic

Question 26

Glucose conversion to glucose 6 phosphate

Answer 26

Glucose taken up by cell;
Rapidly phosphorylated to glucose 6 phosphate;
Traps glucose in cell;
Energy investment reaction
Isoenzymes responsible are - hexokinase (all tissues) and glucokinase (liver and pancreatic B cells);

Question 27

Hexokinase

Answer 27

Low Km -high affinity for glucose - provides glucose to all cells but easily saturated;
Low Vm - at high blood glucose enzyme saturated so all cells do not trap high levels of glucose;
Inhibited by high G6P;

Question 28

Glucokinase

Answer 28

High Km (Low affinity) - only traps glucose when blood glucose high (post prandial);
High Vm - liver sequesters glucose at high blood glucose (prevents hyperglycaemia);
Not inhibited by G6P; stimulated by glucose via a regulatory protein;
High insulin increases glucokinase levels;

Question 29

Glucose 6 phosphate to fructose 6 phosphate

Answer 29

Isomerized;
Enzyme: phosphoglucose isomerase;
Readily reversible, not regulatory;

Question 30

Fructose 6 phosphate to fructose 1 6 biphosphate

Answer 30

First committed step in glycolysis;
Energy investment step;
Highly regulated enzyme - phosphofructokinase-1 (PFK-1);
Inhibited allosterically by high ATP and citrate;
Activated allosterically by ADP and AMP;
In liver - allosterically regulated by fructose 2 6 biphosphate;

Question 31

Fructose 1 6 biphosphate to glyceraldehyde 3 phosphate

Answer 31

F 1 6 biphosphate cleaved by aldolase;
Products are glyceraldehyde 3 phosphate (GAP) and dihydroxyacetone (DHAP);
DHAP converted to GAP by triose phosphate isomerase;

Question 32

GAP to 1, 3 bis phosphoglycerate

Answer 32

Oxidation and phosphorylation;
Transfer of H+ and 2 electrons from GAP to co-factor NAD+ which is reduced to NADH (catalysed by GAP dehydrogenase);

H+ is also lost from GAP and a phosphate is added from Pi;
The coupling of oxidation of GAP (exergonic) and the formation of the bond with phosphate (endergonic) yields a high energy phosphate bond;

Question 33

1, 3 bis phosphoglycerate to 3-phosphoglycerate

Answer 33

High energy phosphate is transferred from 1,3 bPG to ADP to yield 3PG and ATP;
Substrate level phosphorylation;
2 ATP generated for each glucose;

Question 34

3 -posphoglycerate to 2-phosphoglycerate to phosphophenylpyruvate

Answer 34

Phosphate moved from C3 to C2 to yield 2-phosphoglycerate;
2PG dehydrated to PEP;
This re-arrangement generates a new high energy bond in PEP;

Question 35

PEP to Pyruvate

Answer 35

Pyruvate kinase converts PEP to pyruvate and at the same time transfers phosphate from PEP to ADP to form ATP;
Substrate level phosphorylation;
PK activated allosterically by fructose 1, 6 biphosphate;
When glucose Low, insulin/glucagon Low, cAMP high, PK phosphorylated and inactive;
In aerobic conditions pyruvate converted to Acetyl CoA and enter TCA cycle;

Question 36

Anaerobic glycolysis

Answer 36

Eg. strenuous exercise;
Respiratory chain cannot oxidise NADH to regenerate NAD+ (requires O2);
Glycolysis will convert NAD+ to NADH but NAD+ required for glycolysis to continue (GAPDH) step;
Pyruvate reduced to lactate by lactate dehydrogenase (LDH) to regenerate NAD+;
Different LDH isozymes in different tissues;

Question 37

Lactate and the Cori cycle

Answer 37

Lactate produced by erythrocytes normally; used by heart;
Heart LDH Low Km for lactate;
Converted to Pyruvate - TCA cycle;

Skeletal muscle produces high levels of lactate during anaerobic exercise, released to blood;
Live LDH (high Km for lactate) converts to pyruvate;
Converts pyruvate back to glucose (gluconeogenesis) and releases it to blood;

Question 38

Lactate acidosis

Answer 38

High blood lactase produced by:
Strenuous physical exercise, severe lung disease, high altitude, severe anaemia, CO poisoning;
Alcohol intoxication - reduction of NAD+ to NADH;
Von gierke’s disease - excess glycolytic activity;

High levels of blood lactate (lactic acid) - reduce blood pH - Hyperlactatemia

Question 39

Creating phosphate

Answer 39

High energy intermediate in muscle;
Can transfer phosphate to ADP;
Replenishes ATP;
Lasts few seconds;

Question 40

Adenylate kinase

Answer 40

ATP can be regenerated by adenylate kinase;
ATP:ADP:AMP 50,5,1;
Small fall in ATP leads to large rise in AMP;
Large changes in AMP regulate PFK etc;

Question 41

Other fates of Glucose 6 phosphate

Answer 41

Glycogen synthesis;
Converted back to glucose (liver only);
Pentose phosphate pathway (PPP) -
Generates ribose for nucleotide synthesis;
Generates NADPH for fatty acid synthesis;
NADPH required to prevent oxidative damage to proteins;