Introduction to Metabolism

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Introduction to Metabolism

• Artika Nath
• Biochemistry
• School of Health Sciences

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Objectives

• We are now going to look at two major
  questions in Biochemistry
• How do cells extract energy from their
  environment
• How do cells synthesize the building blocks of
  their macromolecules
• This leads to the study of

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Metabolism

• Is the sum total of all chemical reactions
  involved in maintaining the living state of the
  cells, and thus the organism.

• Divided into two categories
• Catabolism break down of molecules to obtain
  energy
• Anabolism- the synthesis of all molecules needed
  by cells
• e.g. DNA, protein etc.

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Thermodynamics of Metabolism

• Metabolic reactions are catalyzed by enzymes and
  obey the laws of thermodynamics  
• (1) First Law of Thermodynamics (conservation of
  energy) energy can be transformed from one form
  to another but cannot be created nor destroyed.
  Energy in the universe is constant.
• 2) Second Law of Thermodynamics energy
  transformations are never 100 efficient (some
  energy is lost as heat)

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Major purpose living things require energy for

• 1. mechanical work in muscle contraction and
  other cellular movement

• 2. Active transport of molecules and ions

• 3. Synthesis of bio-molecules and simple
  precursors proteins, glycogen, fat

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What carries energy????
The energy currency in combustion engines is
heat heat is produced and used to expand the
volume of a gas

• The energy currency or coin of the cell
• Energy rich molecule
• Triphosphate contains 2 phosphoanhydride bonds

The 2 phosphate bonds (phosphoanhydride) bond) is
here the energy is stored in ATP
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A large amount of energy is liberated when
1.
ATP ? ADP Pi (orthophosphate)
2.
ATP ? AMP PPi (pyrophospahte)
The free energy liberated with the hydrolysis of
ATP is used to drive reactions that require input
f free energy
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• ATP is continuously formed and consumed
• Its the principal immediate donor and not long
  term storage of energy
• Rate of turnover of ATP is high. A molecule of
  ATP is consumed within a minute it is formed
• Resting person consumes 40kg of ATP/ 24 hr.

Motion, Active transport, Biosynthesis, Signal
amplification
ATP
ADP
Photosynthesis or oxidation of fuel molecules
Basic model of energy exchange in biological
systems
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How do cells make ATP

• By PHOSPHORYLATION...    adding a phosphate to
  ADP
•          ADP      P    ------gt    ATP

3 mechanisms of phosphorylation

• substrate level phosphorylation- where a
  substrate molecule ( X-p ) donates its high
  energy P to ADP making ATP
• Oxidative phosphorylation   
• e- transferred from organic molecules and
  passed through a series of acceptors to O2
• 3. Photophosphorylation   
• Occurs during photosynthesis light energy
  used to make ATP    

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Electron carriers

• When food molecule oxidized electrons are
  removes
• These electrons are carried to oxygen
• e-
  O2
• ANS Electron carriers
• NAD (nicotinamide adenine dinucleotide) and
• FAD (flavin adenine dinucleotide)
• Reduced form (with electrons bound) is
• NADH and FADH2
• NADH and FADH2 transfer e- to O2 in the
  mitochondria by means of ETC gt ATP generated in
  this process

How does the e- get to oxygen???????
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Stage 1 Large molecules broken int o smaller
units
Stage 2 The numerous small units are degraded to
a few simple units that play a central role in
metabolism. Most re converted to the acetyl unit
of acetyl CoA. Some ATP generated
Stage 3 Kreb cycle and oxidative phosphorylation
Most energy generated here
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Carbohydrates

• 2-3 of your total body weight
• Monosaccharides the building block
• e.g. glucose (the main energy supplying molecule
  of the body
• Fructose- found in fruits Galactose present
  in milk Deoxyribose in DNA Ribose- RNA
• Glycogen main storage (liver and skeletal
  muscle) form of carbohydrate.
• Starch main carbohydrate in food
• Cellulose- no digested by humans

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• 18-25 of body weight in lean adults
• Hydrophobic
• Usually combine with proteins (lipoproteins) and
  move in the blood
• Hydrophobic , so cannot exert osmotic pressure on
  cell walls therefore stored easily.
• Triglycerides most plentiful lipid in your body.
  Each gram can produce twice as much as energy
  compared to carbohydrates and proteins
• Triglycerides stored unlimited in adipose tissues
  

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Proteins

• 12-18 body weight
• Many functions
• catalyst, transport and storage, movement,
  structural, immune system and regulatory role
• Amino acids building blocks
• Cannot store proteins

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1. What is a polysaccharide? A disaccharide? A
   monosaccharide? Give some examples of
   monosaccharides. Which monosaccharide does the
   body use for energy production?
2. How is carbohydrate stored in the body?
3. What is a polypeptide? A dipeptide? An amino
   acid? What distinguishes an amino acid from a
   carbohydrate?
4. What does the body use proteins for?
5. What is a triglyceride? A fatty acid? Glycerol?
   Name some uses of lipids in the body. How are
   excess fatty acids stored in the body?
6. Define metabolism.
7. Distinguish between anabolism and catabolism.
8. ATP is the cell's storehouse of energy. Where,
   within the ATP molecule, is this energy stored?
   Where does that energy come from?
9. Which of the three nutrients produces more
   energy, gram for gram, when oxidized?
10. What is the difference between glycogenesis and
    glycogenolysis?