Nucleic Acids & ATP

What are the three components of a nucleotide?

A phosphate group, a pentose sugar, and a nitrogenous base.

What is the difference between DNA and RNA nucleotides?

DNA contains deoxyribose and thymine

RNA contains ribose and uracil.

Which bases are purines and which are pyrimidines?

Purines: A + G

Pyrimidines: C + T (or uracil in RNA).

What are the base pairing rules in DNA and RNA?

In DNA:

A pairs with T

G pairs with C

In RNA:

A pairs with U.

How many hydrogen bonds form between complementary bases?

A–T (or A–U): 2 hydrogen bonds; G–C: 3 hydrogen bonds.

Why are mRNA molecules shorter than DNA?

Because only one gene is transcribed into a short mRNA strand

(not the entire chromosome)

Why can RNA leave the nucleus but DNA cannot?

RNA is small and single-stranded; DNA is large and double-stranded, remaining in the nucleus.

How are polynucleotides formed from nucleotides?

By condensation reactions forming phosphodiester bonds between the phosphate of one nucleotide and the sugar of the next.

What happens to RNA after protein synthesis?

Broken down by hydrolysis of phosphodiester bonds

nucleotides are recycled

What is uracil and how does it pair?

Uracil is a pyrimidine base in RNA that pairs with adenine via two hydrogen bonds.

Why is transcription described as a short copy of a gene?

Only the section of DNA coding for 1 protein is copied into mRNA.

Why is DNA kept cold during extraction?

Low temperature slows down DNases , preventing DNA degradation.

Why is detergent used in DNA extraction?

It disrupts the phospholipid bilayer and releases cellular contents.

What role does salt play in DNA extraction?

It neutralises the DNA charge and helps it clump together for precipitation.

Why is protease used in DNA extraction?

It digests proteins (like histones) bound to DNA, freeing it

Why does alcohol cause DNA to precipitate?

Alcohol is less polar than water, so DNA becomes insoluble and forms visible strands.

How is DNA’s structure suited for storing genetic information?

• Double helix + strong sugar-phosphate backbone provide stability

• Base sequences store information and allow accurate replication.

How does complementary base pairing ensure accurate replication?

Each strand acts as a template for correct nucleotide pairing + copying

Why is DNA more stable than RNA?

• Deoxyribose lacks the 2′-OH group of ribose, making it less reactive

• The double helix protects the bases

Why is it useful that DNA is a long polymer?

It can store a large quantity of information — many genes across long base sequences.

What are the three main cellular uses of energy?

• Synthesis (building macromolecules)

• Transport (active transport)

• Movement (muscle contraction)

What is ATP made of?

Adenine, ribose, and three phosphate groups.

Why is ATP known as the universal energy currency?

It is used by all living cells to transfer energy for biological processes.

How does ATP release energy?

By hydrolysis: breaking the bond of the final phosphate group releases energy.

What enzyme catalyses ATP hydrolysis? (state the reaction)

ATPase

(ATP to ADP + Pi)

Why does ATP hydrolysis release more energy than it requires to start?

The weak bond between the final phosphate is easily broken so new bonds formed during reactions release much more energy.

What is the reaction for ATP hydrolysis?

ATP + H₂O → ADP + Pi + energy.

Why is ATP hydrolysis described as a coupled reaction?

It happens alongside energy-requiring reactions, transferring released energy directly.

Why isn’t ATP used for long-term energy storage?

It is unstable; carbohydrates and fats are used instead

How is ATP regenerated from ADP?

By phosphorylation: ADP + Pi → ATP using energy from respiration or photosynthesis.

What type of reaction forms ATP from ADP and Pi?

A condensation reaction, as water is removed when the phosphate reattaches.

Why do cells not store much ATP?

It’s an unstable, short-term energy carrier, and its bonds are easily broken to release energy for immediate use

What properties make ATP well suited for energy transfer?

• Small

• Water-soluble

• Releases moderate amounts of energy

• Releases energy in small quantities

• Easily regenerated

Why is ATP described as a phosphorylated nucleotide?

It has the same base and sugar structure as nucleotides, but with three phosphate groups instead of one.