Metabolism and Nutrition Flashcards
1
Q
Catabolism
A
Breakdown of complex organic molecules into simpler ones.
Exergonic
About 40% E released in catabolism used for cellular function; the rest is converted to heat
Ex. glycolysis, Kreb’s cycle
2
Q
Anabolism
A
Reactions that combine simple molecules to form complex structural and functional components of the body.
Endergonic
3
Q
Adenosine TriPhosphate
A
ATP.
Adenine molecule + ribose molecule + three phosphate groups bonded to each other
Energy currency of the body
ADP + Phospate + E –> ATP
About a billion molecules in each cell, each used up within a minute of being created.
4
Q
Phosphorylation
A
Addition of a phosphate group to a molecule, increasing its potential energy.
5
Q
Phosphate
A
PO4(-3)
One phosphorus (P) atom surrounded by 4 oxygen atoms in a tetrahedral arrangement.
Carries
An ester of phosphoric acid
6
Q
Oxidation
A
Removal of an electron from a molecule.
Usually exergonic
DECREASES potential energy
7
Q
Dehydrogenation reaction
A
The form of oxidation which occurs in almost all biological oxidation reactions.
Hydrogen atom is removed.
Example: Lactic acid –> Pyruvic acid
C3H6O3 –> C3H4O3 + 2H (one neg, one pos)
8
Q
Reduction
A
Addition of electrons to a molecule. Makes it less positive.
INCREASE in potential energy
Ex: Pyruvic acid –> Lactic acid
C3H2O3 + 2H –> C3H6O3
9
Q
What happens to the H atoms liberated in oxidation?
A
Immediately transferred by coenzymes to another compound.
10
Q
Coenzyme
A
Organic nonprotein molecules that bind with protein molecule (apoenzyme) to form an active enzyme (holoenzyme)
11
Q
What two coenzymes are commonly used to carry H atoms after oxidation?
A
NAD (nicotinamide adenine dinucleotide) – derived from niacin. NAD+ reduced to (NADH) + (H+)
FAD (flavin adenine dinucleotide) FAD – derived from riboflavin (B2). FAD reduced to FADH2
12
Q
Redox Reactions
A
Oxygen-Reduction Reactions
Each time one substance is oxidized, another one is automatically reduced.
Ex. Lactic acid reduced to Pyruvic acid; NAD+ is oxidized to (NADH) + (H+)
13
Q
3 Mechanisms of ATP Production
A
- Substrate level phosphorylation. (anaerobic). Occurs in cytosol.
- Oxidative phosphorylation (aerobic) [Electron Transport Chain]
- Photophosphorylation (requires chlorophyll)
14
Q
Glucose, Fructose, Galactose
A
C6H12O6
Monosaccharides
Structural isomers.
Glucose is the body’s preferred source of ATP
15
Q
Functions of Glucose
A
- ATP synthesis
- Glycogen synthesis
- Amino acid synthesis
- Triglyceride synthesis
16
Q
Glycogenesis
A
Hundreds of glucose molecules are combined (by hepatocytes and muscle fibres) to form glycogen for storage
17
Q
Lipogenesis
A
When glycogen stores are filled up, excess glucose are transformed by hepatocytes to glycerol and fatty acids, which are used to make triglycerides, which are stored in adipose tissue.
18
Q
How does glucose enter cells?
A
In GI tract and kidney tubules: secondary active transport (with Na+ symporter)
Most of the rest of the body via GluT molecules/facilitated diffusion
19
Q
GluT molecules
A
Family of transporter molecules which facilitate diffusion of glucose through a plasma membrane.
High insulin increases number off GluT4 molecules (increasing rate of facilitated diffusion)
Neurons and hepatocytes have GluT molecules that don’t ever turn off.
20
Q
What happens once glucose enters a cell?
A
It becomes phosphorylated.
GluT can’t transport it once the phosphate group is added, so it ends up trapped in the cell.
21
Q
Four steps of glucose catabolism
A
- glycolysis
- formation of acetyl coenzyme A
- Krebs cycle
- Electron Transport Chain
Start with one glucose, end up with 30-32 ATP
22
Q
Glycolysis in a nutshell
A
1 glucose –> 2 pyruvic acid + 2 ATP + 2NADH + (2H+)
2 ATP used –> 4 ATP created –>2 ATP net
10 steps
23
Q
Formation of Acetyl Coenzyme A in a nutshell
A
2 pyruvic acid –> 2 Aceyl Coenzyme A + 2CO2 + 2NADH +(2H+)
24
Q
Krebs Cycle in a nutshell
A
2 Acetyl Coenzyme A –> 2ATP + 4CO2 + 6NADH + (6H+) +2FADH2
25
Electron Transport Chain in a Nutshell
3ATP from 2 x FADH2 + 23-25 ATP from 10 x NADH --> 25 or 28 ATP + 6H2O
26
Where does glycolysis occur?
Cytoplasm
27
What does ~ic acid mean?
It's a carboxylic acid (contains a COOH group)
28
What is involved in the first half of glycolysis?
2 ATP are used to break glucose down, eventually forming 2 x glyceraldehyde 3-phospate
29
Phosphofructokinase
The enzyme involved in the phosphorylation of Fructose 6phosphate into Fructose 1, 6-biphosphate (which then splits into 2 x glyceride 3phosphate)
Key regulator of the rate of glycolysis.
Involved in Step 3: the first irreversible stage of glycolysis
30
What happens when levels of phosphofructokinase are high? Low?
When ATP and citrate (and thus phosphofructokinase) levels are high, glucose is converted to glycogen for storage.
When ADP is high (and phosphofructokinase low), rate of glycolysis increases
31
What happens in the second half of glycolysis
Start with 2 x gyceride 3phosphates
| Create 2 pyruvate molecules, plus 4 ATP, plus 2 NADH + (H+)
32
Sequence of substrates in glycolysis
Glucose
1. (phosphorylized)
Glucose 6phosphate
2. (isomerized)
Fructose 6phosphate
3. (phosphorylized by Phosphofructokinase)
Fructose 1, 6-biphosphate
4. split into:
```
Dihydroxyacetone Phosphaten (DHAP), and
Glyceraldehyde 3phospate (G3P).
(DHAP isomerizes into G3P, so now we have 2 x G3P)
```
5.( oxidation) and 6. (phosphorylation)
1, 3-biphosphateglycerate (BPG)
7. (dephosphorylation)
3phosphoglyceric acid
8. (Isomerization - Phosphate repositioned)
2phosphoglyceric acid
9. (Dehydration)
Phophoenolpyruvate (PEP)
10. (dephosphorylation)
PYRUVATE
33
What happens to pyruvate in anaerobic conditions?
Homolactic fermentation
In cytosol
Pyruvate is reduced to lactate; NADH produced by glycolysis oxidized into NAD).
Lactate is oxidized back to pyruvate by the hepatocytes
34
What happens to pyruvate in aerobic conditions?
Enters mitochondria to form acetyl-CoA.
2 Pyruvate in --> 2 CO2, 2 NADH + 2(H+), 2 Acetyl CoA out.
Pyruvate acted on my pyruvate dehydrogenase
(Decarboxylation -- CO2 removed)
(Oxidation by NAD --> NadH + H+)
Acetyl Group COCH3
Attaches to CoA to become ACETYL CoA
35
How do red blood cells produce energy?
Glycolysis (no mitochondria)
36
Krebs Cycle
Acetyl CoA goes through a series of redox reactions and forms 3NADH + 3(H+), FADH2, plus one ATP (via GTP)
Since two Acetyl CoA created per glucose --> 6 NADH + 6(H+), plus 2 FADH2, plus 2 ATP
37
Pyruvate dehydrogenase
In formation of Acetyl CoA, converts pyruvic acid into an acetyl group (decarboxylation and oxidation via NAD reduction)
Exclusive to mitochondrial matrix.
38
At what point is CO2 produced during glucose catabolism?
1 during Acetyl-CoA production (when pyruvate transformed to acetyl)
2 during Kreb's Cycle (conversion of isocitric acid --> alpha-ketoglutaric acid, and from alphaketoglutaric acid --> succinyl CoA)
Thus 6 CO2 produced per glucose
39
When is the only point that oxygen is used during glucose catabolism?
During the Electron Transfer Chain.
Oxygen has a high affinity for electrons, and acts as the final electron acceptor in the chain. One O2 accepts 4 electrons, is now negatively charged and attractive to H+, and two H2O are formed
40
Chemiosmosis
The linking of chemical reactions (passage of electrons along transport chain) with the pumping of hydrogen ions.
41
Oxidative Phosphorylation
Removal of electrons from organic compounds, passing them through electron acceptors to molecules of oxygen.
The combination of chemiosmosis and the electron transport chain.
42
Proton Motive Force
The electrochemical gradient built up across the inner mitochondrial membrane, whose potential energy is used to create ATP in the Electron Transport Chain.
43
The types of glucose anabolism
1. glycogenesis
2. glycogenolysis
3. gluconeogenesis
44
Glycogenesis
Many molecules of glucose put together to form glycogen for energy storage.
Carried out by liver and muscle cells, stimulated by insulin
Body can store 500g of glycogen, mostly in skeletal muscle
1. Glucose phosphorylated to Glucose 6-Phosphate by hexokinase [*in T&D just hexokinase; other sources say hexokinase in muscle, glucokinase in muscle*]
2. Glucose 6-P converted to Glucose 1-P
3. Glucose 1-P converted to Uridine diphosphate glucose
4. Uridine diphosphate glucose converted to GLYCOGEN
45
Glycogen
Polysaccharide -- only storage form of carbohydrate in the body
46
Glycogenolysis
When energy required, the breakdown of glycogen into glucose.
Stimulated by epinephrine (adrenal medulla) and glucagon (pancreas)
1. Glycogen converted into Glucose 1-Phosphate by Phosphorylase
2. Glusose 1-P isomerized into Glucose 6-P
3. IN LIVER: Glucose 6-P converted to Glucose by Phosphatase IN MUSCLE no phosphatase, no dephosphorylation
4. IN LIVER: Glucose exits cell into blood stream. IN MUSCLE: Glucose 6-phosphate enters glycolsis
47
Kinase
An enzyme that catalyzes phosphorylation
48
Phosphatase
In liver, enzyme that catalyzes dephosphorylation of glucose 6-phospate into glucose.
49
Phosphorylase
Part of glycolysis
In muscle and liver cells.
Enzyme that converts glycogen into glucose 1-phosphate
50
Hexokinase
Enzyme that catalyzes phosphorylation of glucose into glucose 6-phosphate.
Involved in glycolysis and glycogenesis.
51
Gluconeogenesis
Formation of glucose from non-carbohydrates
Occurs in liver
Stimulated by cortisol (adrenal cortex), glucagon (pancreas), and thyroid hormones.
Glycerol portion of fatty acids --> Glyceraldehyde 3P
60% of amino acids and lactic acid --> Pyruvate
Products can be used to synthesize glucose, or enter cellular respiration
52
Cortisol
Main glucocorticoid hormone of adrenal cortex
Stimulates lipolysis
53
At what point in Kreb's Cycle is ATP produced?
Step 5: A free phosphate knocks CoA off Succinyl-Co A, attaches briefly, then phosphorylates GDP->GTP, which then phosphorylates ADP-->ATP
Succinyl CoA is thus transformed into Succinic Acid
54
How are lipids transported in blood?
Because most non-polar and hydrophobic, they combine with proteins to form lipoproteins.
55
Lipoproteins
Proteins produced by liver and intestine combine with lipids to created spherical particles for transport in blood.
Function as transport vehicles
Outer shells: proteins, phospholipids, cholesterol
Inner core: triglycerides and other lipids
56
Apoproteins
Proteins on outer shell of lipoproteins that help solubilize the lipoprotein, plus each has a specific function.
Designated by ABCDE plus a nubmer
57
Categories of lipoproteins
Categorized by fat:protein
From largest and lightest, to heaviest and smallest:
Chylomicrons
VLDL
LDL
HDL
58
Chylomicrons
Form in mucosal epithelial cells
Transports dietary fat to adipose tissue for storage
85% triglycerides, 7% phospholipids, 6-7% cholesterol, some fat soluble vitamins, and only 1-2% protein
Enter intestinal villi, travel in lymph to venous blood, then systemic circulation to liver and then adipose tissue
59
Adventures of Chlyomicrons
Form in absorptive cells in intestinal villi
```
Exocytosed into lacteals
Lymphatic vessels to thoracic duct
Enter circulation (stay in blood for only a few minutes)
```
One in circulation (in capillaries of adipose), apoprotein C2 activates endothelial lipoprotein lipase, which remove fatty acids from triglycerides.
60
Lipoprotein lipase
Enzyme that acts on chylomicrons, removing fatty acids from triglycerides
61
What happens to deconstructed chylomicrons
The free fatty acids taken up by adipocytes for synthesis and storage as triglycerides, and by muscle cells for ATP production
Glycerol transported to liver and/or kidneys and converted to Glyceraldehyde 6P
Remaining portion removed by hepatocytes from blood (receptor-mediated endocytosis -- apoE)
62
Very Low Density Lipoproteins
Formed in hepatocytes, and carry endogenous lipids (synthesized in hepatocytes) to adipocytes
50% triglycerides, 20% phospholipids, 20% cholesterol, and 10% protein
Deconstructed like chylomicrons (C2/lipoprotein lipase)
Once triglycerides deposited, converted to LDL
63
Low Density Lipoproteins
"Bad Cholesterol"
5% triglycerides, 20% phospholipids, 50% cholesterol, 25% protein
Carry about 75% of the total cholesterol in the body
Negative feedback mechanism limits number of LDL receptors when body's needs met; this means that unneeded cholesterol has nowhere to go, so gets deposited in and around smooth muscle in arteries, forming fatty plaques.
64
High Density Lipoproteins
5-10% triglycerides, 30% phospholipids, 20% cholesterol, and 40-45% protein
Remove excess cholesterol from cells and blood, and transport it to liver for elimination
"Good Cholesterol"
65
Cholesterol
Sterol; lipid with 4 carbon-rings
Used for repairing cell membranes, synthesis of steroid hormones and bile salts
2 sources: dietary and endogenous (synthesized by hepatocytes)
When cholesterol above 200 mg/dL, risk of heart attack doubles with every 50 mm/dl
HDL:cholesterol ration--> 4:1 or above indicated increased risk
66
How can fatty, cholesterol-free foods still increase blood cholesterol?
1. High intake of fat --> stimulates reabsorption of bile back into blood --> decreased elimination of cholesterol in feces
2. When saturated fats broken down, hepatocytes make cholesterol out of some of the products
67
What are the essential fatty acids?
Linoleic and linolenic acids
68
Structural molecules created from lipids
Phosolipids
Lipoproteins
Thromboplastin
Myelin sheaths
69
Triglyceride storage
Adipose tissues removes triglycerides from VLDLS and chylomicrons and stores them
98% energy reserves
```
50% subQ
12% around kidneys
10-15% omenta
15% genitals
5-8% behind muscles
5% behind eyes, sulci of heart, and outside of LI
```
70
Why store 98% energy as fat?
Lipids are hydrophobic, and so do not exert osmotic pressure on cell membranes (unlike glycogen)
71
Lipolysis
Splitting fats into glycerol and fatty acids
| Catalyzed by lipases
72
What hormones stimulate lipolysis?
```
Norepinephrine
Epinephrine
Cortisol
Thyroid hormones
Insuline-like growth hormones
```
73
What happens to the glyceride after it has been cleaved from the fatty acids?
Converted to glyceraldehyde 3-P
If ATP levels high --> glucose
If ATP levels low --> onward to pyruvic acid
74
What happens to the fatty acids after lipolysis?
In mitochondrial matrix:
| Beta oxidation -- 2 carbon removed at a time and attached to CoA --> AcetylCoA --> Krebs Cycle
75
How much ATP can one 16-carbon fatty acid yield?
129 ATP
76
Beta oxidation
A catabolic process in which fatty acids are broken down in the mitochondrial matrix and made into Acetyl CoA
77
Ketogenesis
Hepatocytes take 2 AcetylCoA -[3 steps]-> 1 x acetoacetic acid + CoA
CoA cannot diffuse out of cell
Remaining ketone bodies diffuse out of cell, enter bloodstream.
Heart and renal cortex muscle pick them up, attach 2 acetylCoA --> Krebs Cycle
Hepatocytes make ketone bodies but can't use them.
78
Ketone Bodies
Acetoacetic acid
Acetone
Beta-hydroxybutyric acid
Product of ketogenesis -- condensed/transformed acetylCoa with CoA cleaved off --> can enter blood stream and be transformed into acetyl CoA by other cells (especially renal cortex and cardiac muscle)
79
Lipogenesis
Synthesis of lipids by liver and adipose cells, out of glucose or amino acids
Stimulated by insulin
1) Amino acids --> acetyl CoA --> fatty acids --> triglycerides
2a) Glucose --> glyceraldehyde 3P --> glycerol
2b) Glucose --> glyceraldehyde 3P --> acetylCoA --> fatty acids --> triglycerides
Can now be anabolized to be stored as triglycerides, or produce lipoproteins, phospholipids, cholesterol
80
Protein Metabolism
Protein broken down into amino acids, which can't be stored
Amino acids either:
- -> oxidized into ATP
- -> used to synthesize new structural proteins
- -> converted into glucose (gluconeogenesis) or triglycerides (lipogenesis)
81
Uses of protein
```
Most function as enzynes
Also transportation (hemoglobin)
Antibodies
Clotting (fibrinogen)
Hormones (insulin)
Contractile elements (actin, myosin)
Structural components (collagen, elastin, keratin)
```
82
Active transport of amino acids into body cells stimulated by
Insulin-like growth factors (IGHs)
| Insulin
83
Protein catabolism
Amino acids may be:
- - converted into other amino acids
- - synthesized into new proteins (new peptide bonds)
- - converted into fatty acids, ketone bodies or glucose by hepatocytes
84
What must occur to amino acids before they enter Krebs Cycles?
Deamination
Amino group removed --> converted to urea --> excreted
Remaining part of molecule can be oxidized to enter Krebs
85
Protein anabolism
Formation of peptide bonds between amino acids to produce proteins
Occurs on the ribosomes of almost ever cell
Stimulated by IGFs, T3 andT4, insulin, estrogen, testosterone
86
How many amino acids? How many essential?
20 and 10
ish.
87
Roles of Glucose 6 Phosphate
1. Glycogenesis (mostly in skeletal muscle and hepatocytes)
2. Release of glucose into bloodstream (in liver; in presence of glucose 6-phosphatase, which dephosphoralates glucose6P into glucose)
3. Synthesis of nucleic acid (precursor for ribose 5-P -- needed for RNA and DNA); creates NADPH in same reaction
4. Glycolysis
88
Roles of Pyruvic Acid
1. Production of lactic acid
2. Production of alanine (amino acid)
3. Gluconeogenesis (converted to oxaloacetic acid --> glucose 6P --> glucose)
4. Conversion to acetyl CoA
89
Roles of Acetyl CoA
1. Low ATP, high O2 --> Krebs cycle and ETC --> ATP production
2. Lipogenesis (acetyl CoA --> fatty acids --> triglycerides)
90
Main metabolic events during absorptive state
Oxidation of glucose for ATP
| Storage of fuel molecules just in case
91
What happens to Glucose in absorptive state:
50% oxidized to ATP
40% lipogenesis by adipocytes
10% glycogenesis (most glucose that enters hepatocytes)
92
What happens to Lipids in absorptive state
Most packaged into VLDL by hepatocytes, and carried to adipose tissue
93
What happens to amino acids in absorptive state?
Many deaminated to keto acids (either Krebs or used to synthesize glucose or fatty acids)
Some used in protein synthesis by hepatocytes
Others taken up by non-liver cells to make proteins or regulatory chemicals (enzymes and hormones)
94
Insulin
Released by pancreatic beta cells after a meal
Stimulates anabolism and synthesis of storage molecules
Promotes entry of glucose and amino acids into many cells
(-->glycogen, triglyceride and protein synthesis)
95
Main focus of postabsorptive state
About 4 hours after meal
Maintain normal blood glucose level (70-110 mg/100 ml)
Two foci:
1. Glucose production
2. Glucose conservation
96
Why is the dominant fuel for ATP production in CNS and RBCs?
Fatty acids can't cross BBB
RBC's don't have mitochondria, so can only do glycolysis
97
How is glucose produced in the postabsorptive state?
1. breakdown of liver glycogen (4 hour supply)
2. lipolysis (glycerol --> glucose)
3. gluconeogenesis using lactic acid
4. gluconeogenesis using amino acids (in liver --> glucose)
98
How is glucose conserved while ATP produced in postabsorptive state?
1. oxidation of fatty acids
2. oxidation of lactic acid (cardiac muscles produce ATP aerobically from lactic acid)
3. oxidation of amino acids (in hepatocytes, oxidized directly into ATP)
4. oxidation of ketone bodies
5. breakdown of muscle glycogen (--> glucose 6P)
99
Glucagon
Released by pancreatic alpha cells in response to dropping blood glucose levels
Stimulates glycogenolysis and gluconeogenesis
100
Role of ANS blood glucose levels
Low blood glucose --> sympathetic NS
--> NE (hypothalamus), adrenal medulla (epinephrine and norepinephine)
=> lipolysis
101
Most dramatic metabolic change during fasting/starving
Formation of ketone bodies by hepatocytes
102
Heat
Form of energy that can me measured as temperature and expressed as calories
103
Calorie
The amount of energy needed to raise 1 gram of water by 1 degree celsius
Expressed as calories (small c -- very small), or Kcal=Cal (big C)
104
Conduction
Heat exchange between two molecules in direct contact with each other
105
Convection
Transfer of heat by movement of a fluid (gas or liquid) between areas of different temperatures.
106
Radiation
Transfer of heat in the form of infrared rays (or any electromagnetic wave) between a warmer and a cooler object.
107
Evaporation
Combination of convection and conduction
Conversion of a liquid to a vapour; as water evaporates it takes heat with it.
108
Insensible water loss
At rest 22% heat loss occurs through evaporation of about 700ml of H2O (300ml exhaled, 440mL sweat).
Not aware of it.
109
Body's thermostat
Preoptic area of the anterior hypothalamus
sends impulses to heat-losing and heat-promoting centres
110
Minerals
Inorganic
Help regulate enzymatic reactions
Extra is usually excreted
111
Vitamins
Organic. needed in small amounts
Do not provide energy or building blocks
Mostly co-enzymes
Fat soluble: ADEK
112
Antioxidant vitamins
C, E, beta carotene
Inactivate dangerous free radicals.
