BIOLOGY 1111

CHAPTER 6

METABOLISM

Instructor Terry Wiseth

Northland College 

METABOLISM

Metabolism - the capacity to acquire energy and use it to build, store, break apart and eliminate substances in controlled ways

Energy - the capacity to make things happen

METABOLISM

cells secure, use and lose energy

cells cannot create energy

cells must get energy from somewhere else

Most energy available for energy conversion is stored in covalent bonds

glucose, starch, glycogen and fatty acids are rich in covalent bonds

When molecules are broken apart there is a release of energy which is available to make things happen

ENTROPY

Organized systems (cells) become disorganized without energy to maintain it

Entropy - measure of the degree of a system’s disorder

maximum entropy is reached when disorder is at its greatest least organized

the cell is a pocket of resistance to the flow toward maximum entropy

Cells organize and concentrate molecules and energy

Any energy gain is an energy loss from some other source

METABOLIC REACTIONS

Metabolic reactions can be classified as:

1) Exergonic reaction

2) Endergonic reaction

EXERGONIC REACTIONS

Exergonic reaction - a reaction that ends with a net loss in energy

ex:  Cellular respiration                

ENDERGONIC REACTIONS

Endergonic reaction - a reaction that ends with a net gain in energy

ex:  Photosynthesis

synthesis of complex molecules from simple raw materials

METABOLIC PATHWAYS

Orderly sequence of reactions with specific enzymes acting at each step

BIOSYNTHETIC PATHWAY

Biosy nthetic (anabolism) - small molecules are assembled into large molecules of higher energy content

ex:  amino acids--------------proteins

        fatty acids-----------------lipids

       glucose--------------------starch

BIODEGRADATIVE PATHWAY

Biodegradative (catabolism) - large molecules are broken down to smaller molecules of lower energy content

ex: starch-----------glucose

       protein----------amino acids

       lipids-------------fatty acids

METABOLIC REACTION PARTICIPANTS

All reactions have these participants:

Substrates - enter into reactions (reactants)

End products - substance at the end of a reaction

Intermediates - compounds formed between the start and the end of a metabolic pathway

Enzymes - proteins that catalyze reactions

Cofactors & Coenzymes - metal ions or organic molecules that assist enzymes

Energy carriers - move or temporarily store energy

ENZYMES PROPERTIES

1)  Able to speed up reactions (million fold)

described as catalytic molecules

2)  Enzymes are not used up in the reactions they mediate

3)  Enzymes are highly specific about the reactions they will affect

ex:  thrombin  (enzyme) essential for blood clotting

breaks only a peptide bond between two amino acids (arginine and glycine)

4)  Enzymes are used in both directions of a reaction

6) Enzymes are able to lower the Activation energy necessary to make its substrates react

7) Enzyme function is based on shape

EFFECTS OF TEMPERATURE ON ENZYME ACTIVITY

Enzymes function best within a certain temperature range

Enzymes lose their 3-dimensional shape when exposed to high heat

ex:  human cell death - 112 degrees F

ex:  Siamese cat

Siamese cat-- ears and paws are the darkest part of the body

Heat sensitive enzyme is less active in warmer regions of the body

Enzyme influences higher melanin production

EFFECTS OF pH ON ENZYME ACTIVITY

Enzymes function best within a certain pH range

most function best at pH=7 (neutral)

exception:  pepsin (a stomach cell enzyme) works best at low pH

ALLOSTERIC ACTIVATION

Factors which assist the action of enzymes are called Cofactors

1) Coenzymes

2) Metal ions

3) Effectors

COFACTORS

1)  Coenzymes - complex organic molecules

most are derived from vitamins

ex:  NAD+ and FAD

2)  Metal ions

ex:  Fe++, Cu+

3) Effectors

Effectors are factors which may affect how an active site functions

Ex. Change shape

COMPETITIVE AND NON-COMPETITIVE INHIBITION

Inhibition at the active site prevents an enzyme substrate complex from forming

ELECTRON TRANSFERS

Glucose molecules are broken down in a series of steps by the cell

The glucose breakdown leaves energy released and intermediate by-products at each step

energy release is accomplished by electron transport systems  (ets)

electrons are accepted (reduced) at higher energy levels and released (oxidized) to lower energy levels

as electrons move down the staircase energy is released at each step

as electrons move down the staircase energy is released at each step

STRUCTURE AND FUNCTION OF ATP

ATP - Adenosine TriPhosphate

energy from glucose breakdown or light is converted to ATP

phosphate groups with covalent bonds are unstable and easily broken

END

CHAPTER 6