Nucleic Acids
What missing nucleotide component would prevent the molecule from forming nucleic acid polymers or storing chemical energy?
The phosphate group
The presence of many polar and charged amino acids on a protein’s surface suggests what type of cellular environment?
aqueous (water-based) environment
What does the First Law of Thermodynamics state?
Energy cannot be created or destroyed
What symbol represents free energy?
G
What molecule is the primary carrier of high-energy phosphate groups in cells?
ATP
What structural feature makes DNA more chemically stable than RNA under cellular conditions?
lack of a hydroxyl group on the 2′ carbon of deoxyribose
How can 2 proteins with identical amino acid composition fold into different structures?
difference in amino acid sequence
According to the Second Law of Thermodynamics, what always increases when anything happens?
Entropy
What does a negative ΔG indicate about a reaction?
spontaneous/energetically favorable
What is meant by a coupled reaction?
Linking unfavorable reactions to favorable ones
Would more A-T base pairs cause an increase or decrease in the energy required to separate a DNA double helix?
decrease
Replacing cysteine with serine disrupts what stabilizing interaction in an protein's tertiary structure?
disulfide bonds
Why does the Second Law still apply even though cells are highly ordered?
Entropy increases in the surroundings
Write the equation used to calculate ΔG in a closed system.
ΔG = ΔH − TΔS
Why are condensation reactions energetically unfavorable on their own?
They have a positive ΔG
How could two DNA molecules with the same nucleotide composition store different genetic information?
Because the order (sequence) of nucleotides differs, allowing different genetic instructions even if the overall composition is the same
If protein structure were stabilized only by covalent bonds, what essential functional property would be lost?
conformational flexibility required for protein function
How can cells maintain internal order while still obeying the Second Law of Thermodynamics?
Cells maintain order by exporting entropy to their surroundings, primarily through the release of heat.
How do reactant and product concentrations influence ΔG inside a cell?
Through the RT ln(products/reactants) term
makes G more negative or more positive
Why does coupling an unfavorable reaction to a favorable one allow the overall process to proceed?
Because the negative ΔG of the favorable reaction offsets the positive ΔG of the unfavorable one.
Why are hydrogen bonds between base pairs strong enough to stabilize DNA but weak enough to allow replication and transcription?
Hydrogen bonds are weak individually but strong collectively, providing stability while still allowing strands to separate when needed.
Why do proteins rely on many weak noncovalent interactions rather than a few strong covalent bonds to maintain their structure?
Because weak interactions allow flexibility and reversibility, which are essential for protein folding, conformational changes, and function.
According to the laws of thermodynamics, why must living systems continuously acquire energy from their environment?
Because maintaining order opposes the spontaneous dispersal of energy, requiring constant energy input.
Why can a reaction with a negative ΔG° become unfavorable inside the cell?
Because actual reactant and product concentrations inside the cell can change ΔG, overriding ΔG°.
How does reaction coupling relate to the overall change in free energy (ΔG) for a cellular process?
Reaction coupling ensures that the net ΔG of the combined process is negative, allowing the reaction to occur spontaneously.