Introduction to Metabolism

Artika Nath Biochemistry

School of Health Sciences

ObjectivesObjectives

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 …………………………

MetabolismMetabolism

Divided into two categories

1.1.Catabolism Catabolism – break down of molecules to obtain energy

2.2.AnabolismAnabolism- the synthesis of all molecules needed by cells e.g. DNA, protein etc.

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

• 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)

Thermodynamics of Metabolism

Major purpose living things require Major purpose living things require

energy forenergy 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

What carries energy????What carries energy????

• 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

The energy currency in combustion engines is heatheat: heat is produced and used to expand the volume of a gas

A large amount of energy is liberated A large amount of energy is liberated

whenwhen 1.

2. ATP → AMP + PPi (pyrophospahte)

ATP → ADP + Pi (orthophosphate)

The free energy liberated with the hydrolysis of ATP is used to drive reactions that require input f free energy

• ATP is continuously formed and consumed

• It’s 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.

ADP ATP

Motion, Active transport, Biosynthesis, Signal amplification

Photosynthesis or oxidation of fuel molecules

Basic model of energy exchange in biological systems

How do cells make ATPHow do cells make ATP • By PHOSPHORYLATION...PHOSPHORYLATION...    adding a phosphate to ADP         ADP   +   P    ------>    ATP

3 mechanisms of phosphorylation:

1.1. substrate level phosphorylation- substrate level phosphorylation- where a substrate molecule ( X-p ) donates its high energy P to ADP making ATP

2. Oxidative phosphorylation    e- transferred from organic

molecules and passed through a series of acceptors to O2

3. PhotophosphorylationPhotophosphorylation    Occurs during photosynthesis –light

energy used to make ATP    

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 > ATP generated in this process

How does the e- get to oxygen???????

Stage 1Large molecules broken int o

smaller units

Stage 2The 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 3Kreb cycle and oxidative

phosphorylation Most energy generated

here

Carbohydrates

•2-3% of your total body weight •Monosaccharides – the building blocke.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

•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

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

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?