BIOL 102 Midterm Review: Biomolecules, Metabolism and Molecular Genetics

Terms in this set (31)

1. What are the four major classes of biological macromolecules?Carbohydrates, lipids, proteins and nucleic acids. All except lipids are true polymers built from repeating monomers.
2. Dehydration synthesis vs hydrolysisDehydration synthesis joins monomers by removing a water molecule, forming a covalent bond. Hydrolysis breaks the bond by adding water.
3. Why is water such a good solvent for biological molecules?Water is polar and forms hydrogen bonds, so it surrounds and dissolves ions and other polar molecules. Nonpolar molecules are excluded, which drives hydrophobic interactions.
4. The four levels of protein structurePrimary: amino acid sequence. Secondary: alpha helices and beta sheets held by backbone hydrogen bonds. Tertiary: overall 3D fold from side-chain interactions. Quaternary: assembly of multiple polypeptide subunits.
5. Phospholipid structure and why it forms bilayersA hydrophilic phosphate-containing head attached to two hydrophobic fatty acid tails. Being amphipathic, phospholipids in water arrange with heads facing out and tails tucked inward, forming a bilayer.
6. Saturated vs unsaturated fatty acidsSaturated fatty acids have no C=C double bonds, pack tightly and are solid at room temperature. Unsaturated fatty acids have one or more cis double bonds that kink the chain, so they pack loosely and are usually liquid.
7. Three structural differences between DNA and RNADNA uses deoxyribose sugar, RNA uses ribose. DNA uses thymine, RNA uses uracil. DNA is usually double-stranded, RNA is usually single-stranded.
8. How do enzymes speed up reactions?They lower the activation energy by stabilizing the transition state. They do not change the overall free energy change (delta G) or the equilibrium position, and they are not consumed.
9. Competitive vs noncompetitive inhibitionA competitive inhibitor binds the active site and can be overcome by adding more substrate (Vmax unchanged, apparent Km rises). A noncompetitive inhibitor binds elsewhere, changes the enzyme's shape and lowers Vmax.
10. What does a negative delta G tell you about a reaction?The reaction is exergonic and spontaneous: it releases free energy. It says nothing about speed; a spontaneous reaction can still be very slow without a catalyst.
11. How does ATP power endergonic reactions?Hydrolysis of ATP to ADP + phosphate releases free energy. Cells couple this to unfavourable reactions, often by transferring the phosphate to a reactant (phosphorylation) to make the overall process spontaneous.
12. Overall equation for aerobic cellular respirationC6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + energy (captured as ATP). Glucose is oxidized and oxygen is reduced.
13. Glycolysis: location and net products per glucoseOccurs in the cytosol and does not require oxygen. One glucose becomes 2 pyruvate, with a net gain of 2 ATP and 2 NADH.
14. Pyruvate oxidation and the citric acid cycle: where and what?In the mitochondrial matrix. Pyruvate is converted to acetyl-CoA, which enters the citric acid cycle. Per glucose: CO2 is released and the cycle yields 2 ATP (or GTP), 6 NADH and 2 FADH2, plus 2 NADH from pyruvate oxidation.
15. How does oxidative phosphorylation make ATP?The electron transport chain in the inner mitochondrial membrane uses electrons from NADH and FADH2 to pump H+ into the intermembrane space. H+ flows back through ATP synthase, driving ATP production (chemiosmosis). O2 is the final electron acceptor, forming water.
16. What is the purpose of fermentation?To regenerate NAD+ from NADH so glycolysis can continue without oxygen. Animal muscle cells produce lactate; yeast produce ethanol and CO2. Only the 2 ATP from glycolysis are made.
17. Photosynthesis: light reactions vs Calvin cycleLight reactions (thylakoid membranes) split water, release O2 and make ATP and NADPH. The Calvin cycle (stroma) uses that ATP and NADPH to fix CO2 into sugar, with rubisco catalyzing carbon fixation.
18. State the central dogma of molecular biologyGenetic information flows from DNA to RNA (transcription) to protein (translation). DNA is also copied to DNA during replication.
19. What does semiconservative replication mean, and which experiment supported it?Each new DNA double helix contains one original strand and one newly made strand. Meselson and Stahl showed this using heavy (15N) and light (14N) nitrogen and density gradient centrifugation.
20. Leading vs lagging strandDNA polymerase only adds nucleotides to a 3' end, so it builds new DNA 5' to 3'. The leading strand is made continuously toward the fork; the lagging strand is made in short Okazaki fragments that DNA ligase joins.
21. Role of primase in DNA replicationPrimase makes a short RNA primer that provides the free 3' OH group DNA polymerase needs to start synthesis. The primers are later removed and replaced with DNA.
22. Transcription: what happens?RNA polymerase binds a promoter, unwinds the DNA and builds an RNA strand 5' to 3' that is complementary to the template strand. The RNA matches the coding strand, with U in place of T.
23. Three processing steps for eukaryotic pre-mRNAAddition of a 5' cap, addition of a 3' poly-A tail, and splicing to remove introns and join exons. These steps occur in the nucleus before export.
24. Start and stop codonsStart codon: AUG, which codes for methionine. Stop codons: UAA, UAG and UGA, which code for no amino acid and end translation.
25. Mini-problem: a template DNA strand reads 3'-TAC GGA-5'. What are the mRNA and amino acids?mRNA: 5'-AUG CCU-3'. This codes for methionine (AUG) then proline (CCU).
26. Silent vs missense vs nonsense mutationsSilent: a base change that still codes for the same amino acid. Missense: codes for a different amino acid. Nonsense: creates a premature stop codon, usually producing a truncated protein.
27. Why are frameshift mutations usually severe?Inserting or deleting a number of bases that is not a multiple of three shifts the reading frame, changing every codon downstream and often creating an early stop codon.
28. Mitosis vs meiosisMitosis: one division producing two genetically identical diploid cells, used for growth and repair. Meiosis: two divisions producing four genetically different haploid gametes, with crossing over and independent assortment.
29. Mendel's laws of segregation and independent assortmentSegregation: the two alleles of a gene separate into different gametes. Independent assortment: alleles of different genes (on different chromosomes) sort into gametes independently of one another.
30. Mini-problem: cross Aa x Aa where A is dominant. Expected ratios?Genotypes: 1 AA : 2 Aa : 1 aa. Phenotypes: 3 dominant : 1 recessive.
31. What is a test cross?Crossing an individual with a dominant phenotype to a homozygous recessive individual. If any recessive offspring appear, the unknown parent must be heterozygous.