Transcription & Translation
In which organelle does transcription occur in eukaryotic cells?
Nucleus
Which nitrogenous base pairs with adenine in DNA?
Thymine
Which bacterium is commonly used as the example organism for the lac operon?
E. coli
What is the role of an enzyme in a chemical reaction?
To act as a biological catalyst by lowering activation energy.
State the organelle where aerobic respiration occurs in eukaryotic cells.
Mitochondria
During transcription, which enzyme builds the pre-mRNA strand?
RNA polymerase
Which enzyme unzips DNA by breaking hydrogen bonds during replication?
Helicase
What happens to the lac operon when lactose is absent?
The repressor protein binds to the operator and blocks transcription.
What is the active site of an enzyme?
The region where the substrate binds and the reaction occurs.
State the balanced equation for photosynthesis.
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Explain the difference between a codon and an anticodon.
A codon is a three-base sequence on mRNA that codes for an amino acid, while an anticodon is a complementary three-base sequence on tRNA.
State the significance of semi-conservative replication.
Each new DNA molecule contains one original strand and one newly synthesised strand.
What role does lactose (allolactose) play in the lac operon?
It binds to the repressor protein, causing it to detach from the operator.
Explain the difference between a competitive and a non-competitive inhibitor.
Competitive inhibitors bind to the active site; non-competitive inhibitors bind elsewhere and alter the enzyme's shape.
Explain the role of ATP in living cells.
ATP stores and transfers energy for cellular processes such as active transport, muscle contraction and biosynthesis.
Describe the role of RNA splicing before translation.
RNA splicing removes introns and joins exons together to form mature mRNA.
Why are insertion and deletion mutations often more serious than substitution mutations?
They cause frameshift mutations, changing all downstream codons and often producing a non-functional protein.
State the functions of the lacZ and lacY genes.
lacZ codes for β-galactosidase; lacY codes for permease.
Why does enzyme activity decrease sharply at very high temperatures?
High temperatures denature the enzyme and alter the shape of its active site.
Compare aerobic and anaerobic respiration in terms of oxygen use and ATP yield.
Aerobic respiration requires oxygen and produces 36-38 ATP; anaerobic respiration does not require oxygen and produces 2 ATP.
Explain how transcription and translation work together to produce a protein.
Transcription copies DNA into mRNA in the nucleus. Translation occurs at ribosomes where codons are read and amino acids are joined to form a protein.
Describe the roles of helicase, primase, DNA polymerase and DNA ligase during DNA replication.
Helicase unzips DNA, primase lays RNA primers, DNA polymerase adds nucleotides, and DNA ligase joins DNA fragments.
Explain why the lac operon is considered an example of gene regulation.
It switches genes on or off depending on environmental conditions, conserving energy when lactose is absent.
Explain how substrate concentration affects enzyme activity.
Increasing substrate concentration increases reaction rate until all active sites are saturated, after which the rate plateaus.
Explain how the light-dependent and light-independent reactions are linked in photosynthesis.
Light-dependent reactions produce ATP in the thylakoids, which is then used in the stroma during light-independent reactions to produce glucose.