Energy, Metabolism, and Enzymes

Ch 6 BaboonCh 5.1-5.8 Bat

- Energy: the ability to do work 

- Two major types of energy  1. Kinetic - energy of motion  - EX: movement, heat, electrical, radiant

  2. Potential - stored energy  - EX: positional, chemical bonds, gravitational, charge potential (battery)

- Energy is constantly being transformed from one type to another

 - EX: radiant energy from sunlight transformed into the energy of chemical bonds (kinetic to potential)

1st and 2nd Law of Thermodynamics

- 1st Law - Law of Conservation of Energy - Energy can be transformed or transferred but it can't be   created or destroyed

- 2nd Law - Law of Entropy - When energy is is transformed or transferred, some will be   "lost", usually as heat

 - Every change in Energy results in the world becoming   more disordered (chaotic)

 - Entropy - the quantitative measure of disorder

Systems- Open - when energy and matter can be transferred back and forth between the system and its surroundings EX: human body

- Closed - when energy and/or matter can  NOT be transferred back and forth between the system and its surroundings

Energy of Life- Living organisms require a constant supply of energy to

perform work that must take place in cells (powered by ATP)

 - Mechanical work - cell division, muscle     contraction, cilia movement, etc...

 - Transport work - pumping substances across membranes

 - Chemical work - breaking and forming chemical bonds

- Energy flows from the non-living world into living organisms and back

- Conversion of Radiant Energy to Chemical Energy - Photosynthesis (makes glucose) - Chemical Energy is transferred between organisms - Energy is "lost" as heat along the way

 

Metabolism

- Metabolism is the sum total of all chemical reactions in an organism (transformation of energy)

- Two types of reactions- 1. Catabolic reactions release energy by breaking   chemical bonds (complex ⇒ simple) - also known as exergonic reactions because   they release energy - EX: Cellular respiration

 2. Anabolic reactions use energy to make chemical   bonds (simple ⇒ complex)  - also known as endergonic reactions because   they require energy - EX: Photosynthesis

Exergonic vs. Endergonic (Catabolic) (Anabolic)

ΔG = amount of free energy in a system

ΔG is negative, energy is given off ΔG is positive, energy is absorbed

These reactions are usually coupled in living things - E released in exergonic is used to power endergonic

- Enzymes: proteins that act as catalysts for reactions without being permanently altered or destroyed - Catalyst: increases efficiency of reactions

- Enzymes frequently have the suffix "ase"   - Substrate: substance the enzyme acts on - EX: enzyme salivary amylase breaks down starch  

(substrate) in the food you eat - EX: enzyme glycogen synthase that builds glucose

into glycogen

Enzymes

- Enzyme - substrate relationships are specific

- Active site - point where substrate and enzyme interact (bind)

- Induced Fit Theory – active site is a crevice on the enzymes surface which interacts with the substrate. Enzyme folds around the substrate like a tight fitting glove

Enzyme - Substrate Relationships

- Reversibility - enzymes can break substances down (catabolic) or help put them together (anabolic)

Enzymes and Chemical Reactions

Enzymes and Chemical Reactions

- Catabolic (exergonic)  - Enzymes weaken bonds of substrate so   less energy is needed to break it down - lowers activation energy

- Anabolic (endergonic) - Enzymes chemically align angles of   molecules to make bonding easier

Sucrose ----------------> Fructose + Glucose

Substrates ----------------> Products(reactants)

Enzyme

(sucrase enzyme)

Catabolic

- Activation energy: initial energy required to break chemical bonds during an exergonic (catabolic) reaction  - i.e. Need to put a little E in before you can release some

Enzymes and Chemical Reactions

Enzymes and Chemical Reactions

- Enzymes act as catalysts - lower the activation energy required

Exergonic rx

Environmental Conditions

- Temperature - higher temperature result in increased molecular motion   and higher kinetic energy. More collisions between   molecules lead to faster reactions - in general an increase of 10°C doubles the rate of reactions - too much heat can, however, can cause denaturation

Environmental Conditions- pH

 - most enzymes require a neutral pH - Exceptions:

  - Pepsin (stomach) needs pH 2  - Trypsin (intestine) needs pH 7

- Concentration of substrate and product - Lots of substrate and little product = more product formed - Lots of product and little substrate = more substrate formed

- Non-protein molecules that are necessary for some enzymes to work - Usually vitamins that must be ingested   by organisms because the body does  not naturally produce them - EX: iron or zinc  - Sometimes called co-enzymes

Cofactors

Enzyme Inhibitors

1. Competitive inhibitors - molecule binds to the active site, preventing substrate from   binding - usually reversible - EX: pesticides, drugs

2. Non-competitive inhibitors - molecule binds to a region other than the active site   causing a shape change in the enzyme - EX: penicillin - prevents enzymes used by bacteria to assemble the   cell wall from working

- Cooperativity  - Enzyme becomes more receptive to   substrate molecules once one substrate   molecule has attached

 - EX: once one molecule of oxygen binds to   hemoglobin it encourages the molecule to   bind to several more molecules of oxygen

Cooperativity

- Allosteric enzymes  - enzymes have 2 kinds of binding sites

 1. one site for the substrate (the active site)

 2. one site called the allosteric site that allows the   enzyme to be controlled

- Allosteric inhibitors: bind to the allosteric site and stop the  enzyme from functioning

- Allosteric activators: bind to the allosteric site and turn the  enzyme on.

Allosteric Regulation