Enzymes
Define metabolism and catalysis, and explain the role of enzymes in metabolism.
Metabolism: the sum of all chemical reactions occurring in a cell or organism.
Catalysis: the speeding up of a chemical reaction without the catalyst being consumed.
Role of enzymes: enzymes act as biological catalysts that control and accelerate metabolic reactions by lowering activation energy
Define cell respiration and state the word equation for aerobic respiration.
Cell respiration: the controlled release of energy from organic compounds to produce ATP.
Word equation:
glucose + oxygen → carbon dioxide + water (+ energy/ATP)
Define photosynthesis and state the balanced chemical equation.
Photosynthesis: the process by which light energy is converted into chemical energy stored in glucose.
6CO2 + 6H2O --> C6H12O6 + 6O2
State at least 3 reasons that DNA replication is needed for life.
Growth, repair, development.
Define transcription and translation, and state where each occurs in eukaryotic cells.
Transcription: synthesis of RNA from a DNA template (occurs in the nucleus).
Translation: synthesis of a polypeptide from mRNA (occurs at ribosomes in the cytoplasm or on rough ER).
Explain enzyme specificity and describe the relationship between an enzyme’s active site and its substrate. Also state one example each of an anabolic and catabolic reaction.
Specificity: enzymes bind only particular substrates because the active site has a complementary shape and chemical properties.
The active site is a pocket formed by the enzyme’s tertiary structure; substrate binding depends on shape and intermolecular forces.
Anabolic example: synthesis of proteins from amino acids.
Catabolic example: breakdown of glucose during respiration
Explain how the following can be used to measure the rate of cellular respiration:
https://docs.google.com/presentation/d/14_JrrACDeHpywtBRqFqnsgKq36vMinYdsrussHoTEE4/edit?usp=sharing
Oxygen uptake by respiring organisms causes a decrease in gas volume or pressure.
CO2 is absorbed, so changes reflect oxygen consumption only.
The movement of liquid in the capillary tube / manometer over time is used to calculate respiration rate.
Give an overview of how light energy is transformed into chemical energy during photosynthesis, including the role of pigments, ATP, and electron carriers.
*Just an overview! 2-3 steps is fine.
Pigments absorb light, exciting electrons.
This energy is used to produce ATP and reduced NADP in the light-dependent reactions.
These molecules provide energy and reducing power to synthesize glucose in the Calvin cycle
State the base pairing rules AND outline what is meant by semi-conservative replication.
Base pairing rules: Adenine and Thymine pair; cytosine and guanine pair
Semi-conservative replication means that each new DNA molecule contains one original strand and one newly synthesized strand.
Define codon and anticodon, where you might find them in a cell, and the type of bond that forms between them.
A codon is a three-nucleotide sequence on mRNA that codes for an amino acid.
An anticodon is a complementary three-nucleotide sequence on tRNA.
They pair via hydrogen bonds.
Identify and explain the model shown:
https://docs.google.com/presentation/d/1dURVyOIuTUtez_VIgXDKQCumxNv4zJAC7qP4PWbI1rI/edit?usp=sharing
This is the induced-fit model.
Substrate binding causes a conformational change in the enzyme, improving fit and straining substrate bonds, lowering activation energy.
Explain why NAD must be regenerated during anaerobic respiration and describe how this occurs in humans.
NAD⁺ is required for glycolysis to continue (acts as electron carrier).
Without regeneration, glycolysis stops due to lack of NAD⁺.
In humans, pyruvate is reduced to lactate, oxidizing NADH back to NAD⁺.
Outline why pigment molecules are arranged into photosystems, and state the basic function of photosynthetic pigments.
Photosystems contain arrays (multiple types of) of different pigments that absorb a wider range of wavelengths, increasing light capture.
Pigments excit electrons (in the presence of light), which enters the electron transport chain to drive ATP and reduced NADP production.
Describe the roles of helicase, DNA polymerase III, and DNA polymerase I during DNA replication.
Helicase separates the DNA strands by breaking hydrogen bonds.
DNA polymerase III synthesizes most of the new DNA by adding nucleotides in the 5′ → 3′ direction.
DNA polymerase I removes RNA primers and replaces them with DNA.
Explain how a point mutation in DNA can alter protein structure, using translation to justify your answer.
A point mutation changes a DNA base sequence.
This can alter the mRNA codon during transcription.
A different amino acid may be incorporated during translation, potentially altering protein structure and function (e.g., sickle-cell hemoglobin).
Explain why increasing substrate concentration overcomes competitive inhibition but not non-competitive inhibition.
Competitive inhibition: inhibitor binds reversibly to the active site.
Non-competitive inhibition: inhibitor binds to an allosteric site, changing active-site shape.
Competitive inhibition can be reduced by adding more substrate (outcompetes inhibitor).
Non-competitive inhibition lowers maximum enzyme activity because enzyme structure is altered regardless of substrate concentration.
Identify the structure and explain at least 2 adaptations for its function:
https://docs.google.com/presentation/d/11Nx9TY0Lg75LLkVQNQBHIZLJ_rJKx3ftSM-cNeNbqOY/edit?usp=sharing
Mitochondrion
Double membrane creates separate compartments for proton gradient formation.
Inner membrane folds (cristae) increase surface area for electron transport chains and ATP synthase.
Matrix contains enzymes for link reaction and Krebs cycle
Identify the structure, all labels and explain at least 2x of its adaptations:
https://docs.google.com/presentation/d/1gwlYwCq1VEn4kxHO9nVNFveagdP85zFoWvAEEq3MopM/edit?usp=sharing
A chloroplast.
Thylakoid membranes provide large surface area for light-dependent reactions.
Small thylakoid spaces allow rapid proton accumulation for chemiosmosis.
Stroma contains enzymes for the Calvin cycle, keeping substrates close together.
Identify each of the labeled units in this diagram of DNA replication:
https://docs.google.com/presentation/d/15Gm4I4TrUWighghvLJJU98F9T9K728-jlDOSfskBJYs/edit?usp=sharing
Answer on slide
Explain how alternative splicing increases protein diversity in eukaryotes.
Introns are removed and exons are joined [exons are expressed!] during RNA processing.
Different combinations of exons can be spliced together.
This allows one gene to produce multiple protein variants.
A metabolic pathway converts threonine → isoleucine (in plants/bacteria) using several enzymes.
Define end-product (feedback) inhibition and explain how it regulates this pathway. Then state why this is necessary in the first place.
End-product inhibition: the final product (isoleucine) binds allosterically to the first enzyme, reducing pathway activity when product is abundant.
This is necessary to not let the pathway consume all available threonine, which has several other uses for plants/bacteria.
Using at least 4 key steps, explain how oxidative phosphorylation produces ATP and why oxygen is essential to this process.
NADH and FADH₂ donate electrons to the electron transport chain in the inner membrane.
Electron flow drives proton pumping into the intermembrane space, creating a proton gradient.
Protons flow back through ATP synthase (chemiosmosis), generating ATP.
Oxygen acts as the final electron acceptor, forming water; without oxygen, the chain stops.
Explain the interdependence of the light-dependent reactions and the Calvin cycle.
Light reactions produce ATP and reduced NADP.
The Calvin cycle uses ATP and reduced NADP to fix CO₂ and make triose phosphate.
ADP, Pi, and NADP⁺ are returned to the light reactions, so neither stage can function independently.
Explain why DNA replication differs on the leading and lagging strands, including the roles of primers and Okazaki fragments.
DNA polymerase III can only add nucleotides in the 5′ → 3′ direction.
The leading strand is synthesized continuously toward the replication fork.
The lagging strand is synthesized discontinuously as Okazaki fragments, each started by an RNA primer.
DNA ligase joins fragments to form a continuous strand.
Outline types of post-translational modifications of polypeptides that may be required to form a functional protein, giving at least one practical example to support one.
1) The formation of disulphide bridges. (e.g. insulin)
2) Conjugation with other proteins or inorganic cofactors (e.g. the heme group in hemoglobin).
3) Chemical modifications (e.g. glycosylation or phosphorylation) to improve structural stability, signal recognition, etc. (e.g. glycolysation of membrane receptors).