Nucleic Acids & Protein Synthesis
What is the monomer unit of a protein, and what bond links these monomers together?
Amino acid; peptide bond
Define the term "active site" of an enzyme and state what happens when an enzyme is denatured.
The active site is the specific region on an enzyme where the substrate binds. Denaturation alters the 3D conformational shape of the active site so the substrate can no longer bind.
Where in the chloroplast does the light-dependent stage of photosynthesis occur, and what is its main input that gets split?
Thylakoid membranes; water (H2O).
Name the enzyme used to cut DNA at specific recognition sites and the enzyme used to join DNA fragments back together.
Restriction enzyme (endonuclease) cuts DNA; DNA ligase joins DNA fragments.
What is biomass, and why is bioethanol considered a renewable biofuel?
Biomass is organic matter from living or recently living organisms. Bioethanol is renewable because it is produced from plant sugars/starches (e.g., crops) that can be replenished continuously through photosynthesis.
Briefly describe the key structural differences between DNA and RNA.
DNA contains deoxyribose sugar, thymine, and is double-stranded; RNA contains ribose sugar, uracil, and is single-stranded.
How do competitive inhibitors differ from non-competitive inhibitors in their mechanism of enzyme inhibition?
Competitive inhibitors bind directly to the active site (blocking the substrate), whereas non-competitive inhibitors bind to an allosteric site, altering the shape of the active site.
What are the three main stages of aerobic cellular respiration, and where in the cell does each stage take place?
Glycolysis (cytosol), Krebs cycle (mitochondrial matrix), Electron Transport Chain (mitochondrial cristae).
What is the primary purpose of the Polymerase Chain Reaction (PCR), and what are the three main steps in a single PCR cycle?
PCR amplifies DNA samples. The three steps are Denaturation (heat to separate strands), Annealing (cool to attach primers), and Extension (heat for Taq polymerase to synthesize new strands).
How does the carbon impact of burning biofuels differ from that of burning fossil fuels?
Carbon dioxide released by biofuels was recently captured from the atmosphere during plant photosynthesis (carbon neutral cycle), whereas burning fossil fuels releases carbon trapped underground for millions of years, increasing net atmospheric CO2.
What happens during the RNA processing step of eukaryotic gene expression before the mRNA exits the nucleus?
Introns are spliced out, exons are joined together, a 5' methyl-G cap is added, and a 3' poly-A tail is added.
What are coenzymes, and what role do loaded coenzymes play in biochemical pathways?
Coenzymes are non-protein organic molecules that assist enzyme function. Loaded coenzymes (like NADH, NADPH, ATP) carry high-energy electrons, hydrogen ions, or phosphate groups between metabolic reactions.
Compare the products of anaerobic fermentation in human muscle cells versus yeast cells.
Human muscle cells produce lactate (lactic acid); yeast cells produce ethanol and carbon dioxide (CO2).
In the CRISPR-Cas9 defense system in bacteria, what are the distinct roles of the gRNA (guide RNA) and the Cas9 endonuclease?
The gRNA guides the complex to a specific complementary target DNA sequence, while Cas9 acts as molecular scissors to cut the double-stranded DNA.
Name two agricultural applications where CRISPR-Cas9 gene editing is used to improve plant or livestock traits.
In crops: creating disease resistance, heat/drought tolerance, or non-browning produce. In livestock: conferring resistance to diseases (e.g., tuberculosis), increasing milk production, or generating leaner meat.
Explain the difference between coding and regulatory genes, and state the function of an operator in an operon model (e.g., trp operon).
Coding genes code for structural or functional proteins;
regulatory genes code for proteins that control gene expression.
An operator is a DNA sequence where a repressor protein binds to block or allow transcription.
Describe how increasing substrate concentration affects the rate of an enzyme-catalysed reaction in the presence of a competitive inhibitor.
Increasing substrate concentration can overcome competitive inhibition by outcompeting the inhibitor for active sites.
How does Rubisco's affinity for oxygen (O2) lead to photorespiration, and how do C4 and CAM plants structurally/temporally minimise this issue?
Rubisco can bind O2 instead of CO2, wasting energy and reducing glucose yield.
C4 plants spatially separate initial CO2 fixation (mesophyll) from the Calvin cycle (bundle-sheath), while CAM plants temporally separate them (stomata open at night).
Explain the difference between a Transgenic Organism (TGO) and a Genetically Modified Organism (GMO).
All TGOs are GMOs, but a TGO specifically contains foreign DNA inserted from a different species, whereas a GMO has had its genome altered (e.g., gene silenced, knock-out, or modified) regardless of whether foreign DNA was introduced.
Outline the major steps involved in producing bioethanol from plant starch or crop waste via anaerobic fermentation.
Break down complex carbohydrates (starch/cellulose) into simple glucose sugars (saccharification). 2. Yeasts/bacteria ferment glucose anaerobically to produce ethanol and CO2. 3. Distill and purify the ethanol to use as fuel.
Outline how the trp operon regulates transcription in E. coli via both repression and attenuation when tryptophan levels in the cell are high.
Tryptophan bind to repressor protein which binds to operator region to stop transcription.
Ribosome do not stall at the tryp codons causing the formation of terminator hairpin look causing RNA polymerase to detach from DNA.
Explain why temperature above the optimal level drastically reduces enzyme activity, whereas temperatures below optimal only slow down the rate without permanently altering the enzyme.
High temperatures disrupt bonds (hydrogen/ionic), causing irreversible denaturation. Low temperatures lower kinetic energy, reducing collisions between enzyme and substrate without altering the active site's structure.
Explain how scientists can use CRISPR-Cas9 gene editing technology to overcome the limitations of Rubisco and enhance crop yield during photosynthesis.
Scientists can target and edit the gene encoding the Rubisco enzyme to increase its specificity for CO2 over O2, or knock out/modify genes involved in photorespiratory pathways to make carbon recovery more energy-efficient.
Describe how recombinant plasmids are created and transformed into bacteria.
Plasmids and target genes are cut with the same restriction enzyme and joined with ligase. Bacteria are transformed via heat-shock or electroporation.
Explain how Australia avoids land-use conflict between food crops and biofuel production compared to other international markets.
Australia predominantly utilizes agricultural waste, feed residues, and starch by-products (such as sorghum waste) rather than dedicating prime arable farmland exclusively to growing bioenergy crops.