lecture 6 - cellular energy

Question 1

in living organisms, what are energy conversions linked to ?

Answer 1

chemical reactions called metabolism.

• the totality of an organism’s chemical reactions
• arises from interactions between molecules
• transforms matter and energy, subject to the laws of thermodynamics

Question 2

how does the second law of thermodynamics relate to biology?

Answer 2

an open system (living organism) needs constant energy input to maintain itself, because it is always losing energy to the universe.

Question 3

what is Gibbs free energy?

Answer 3

• amount of energy in a system that can be used to do work while pressure and temperature remain constant
• for a chemical reaction, the most important parameter is the CHANGE in Gibbs free energy (delta G) that occurs during a reaction.
• delta G = G(final state) - G(initial state)

Question 4

how can metabolic reactions be classified?

Answer 4

based on the change in free energy (G) during the reaction

• the can break down molecules/release energy (catabolic reactions = negative delta G)
• or the can synthesise molecules/ consume energy (anabolic reactions = positive delta G)

Question 5

what are exergonic reactions?

Answer 5

• negative change in Gibbs free energy (G)
• energy level of reactants is higher than the energy level of the products, therefore delta G is -ve
• know diagram

Question 6

describe exergonic reaction in catabolism

Answer 6

• enzymes, e.g., DNA polymerase, lower the activation energy, which makes the reaction more likely to proceed.

Question 7

what is activation energy?

Answer 7

activation energy (barrier) is what prevents reactions from proceeding as soon as the reactants are present

Question 8

what are the properties of exergonic reactions?

Answer 8

• negative delta G
• releases energy during reaction
• has activation energy barrier
• reactant energy level = HIGH
  product energy level = LOW
• typical for catabolism/energy generation

Question 9

describe endergonic reactions

Answer 9

• low reactant energy level
• high product energy level
  requires energy input to drive reaction, but still has an activation energy barrier
• +ve delta G

Question 10

what cellular materials are synthesised from endergonic reactions?

Answer 10

pretty much all of them.

- DNA, lipids, amino acids

Question 11

what are the properties of endergonic reactions?

Answer 11

• positive delta G
• consumes energy during reaction
• has an activation energy barrier
• reactant energy level = LOW
• product energy level = HIGH
• used in anabolism/

Question 12

why is metabolism important?

Answer 12

• without metabolism cells cannot survive
• metabolic pathways and enzymes determine the ‘lifestyles’ that an organism can adopt.
• interactions between human cells and microbes are based on the exchange of the product of metabolism.

Question 13

what reaction releases the energy stored in bonds of ATP?

Answer 13

hydrolysis
- because the phosphate groups want to get away from each other. because ADP has less electrostatic repulsion and therefore has a lower potential energy

Question 14

what is a couple reaction?

Answer 14

• in cells reactions that release energy (exergonic) are used to provide the energy fo energy requiring reactions (endergonic)
• the energy is usually provided by ATP or related compounds

Question 15

Explain and describe DNA synthesis

Answer 15

• DNA polymerisation combines two exergonic reactions
  1) the breaking of phosphoanhydride bond in a nucleotide of an O-H bond. and one
  2) energonic reaction
• the formation of a new phosphodiester bond between two nucleotides