BIOLOGY 1A03 Exam Review: Macromolecules, Membranes, Metabolism and Gene Expression

Terms in this set (27)

1. Name the four major classes of biological macromolecules and their monomers.Proteins (amino acids), nucleic acids (nucleotides), carbohydrates (monosaccharides) and lipids (not true polymers; fats are built from glycerol and fatty acids).
2. What type of bond links amino acids, and how is it formed?A peptide bond, formed by a dehydration (condensation) reaction between the carboxyl group of one amino acid and the amino group of the next.
3. Four levels of protein structurePrimary: amino acid sequence. Secondary: alpha helices and beta sheets held by backbone H-bonds. Tertiary: 3D fold from side-chain interactions. Quaternary: assembly of multiple polypeptides.
4. Why does a protein denature at high temperature or extreme pH?Heat and pH disrupt the hydrogen bonds, ionic interactions and hydrophobic interactions that hold its shape, causing loss of function; the primary sequence is unchanged.
5. DNA vs RNA structureDNA: deoxyribose, bases A, T, G, C, usually double-stranded. RNA: ribose (with 2' OH), bases A, U, G, C, usually single-stranded.
6. What does antiparallel mean for DNA strands?The two strands run in opposite directions: one 5' to 3', the other 3' to 5'. A pairs with T (2 H-bonds) and G pairs with C (3 H-bonds).
7. What did the Meselson-Stahl experiment show?Using heavy (15N) and light (14N) nitrogen, they showed DNA replication is semiconservative: each new double helix has one parental and one new strand.
8. Leading vs lagging strand synthesisDNA polymerase only adds nucleotides to a 3' end. The leading strand is made continuously toward the fork; the lagging strand is made discontinuously as Okazaki fragments that ligase joins.
9. Roles of helicase, primase and DNA ligaseHelicase unwinds the double helix, primase lays down a short RNA primer to give a 3' OH, and ligase seals nicks between Okazaki fragments.
10. State the central dogma of molecular biology.Genetic information flows from DNA to RNA (transcription) to protein (translation). Reverse transcriptase in retroviruses is a notable exception (RNA to DNA).
11. Where does transcription start and what enzyme carries it out?RNA polymerase binds a promoter upstream of the gene (in eukaryotes with the help of transcription factors, e.g. at a TATA box) and synthesizes RNA 5' to 3' from the template strand.
12. Three main eukaryotic pre-mRNA processing stepsAdding a 5' cap, adding a 3' poly-A tail, and splicing out introns (joining exons) by the spliceosome.
13. What is alternative splicing?Different combinations of exons are joined from the same pre-mRNA, allowing one gene to produce several different proteins.
14. Mini-problem: the mRNA codon is 5'-AUG-3'. What is the tRNA anticodon?3'-UAC-5' (usually written 5'-CAU-3'). AUG codes for methionine and is the start codon.
15. Name the three stop codons.UAA, UAG and UGA. They are recognized by release factors, not tRNAs.
16. What happens at the A, P and E sites of the ribosome?A site: incoming aminoacyl-tRNA binds. P site: holds the tRNA with the growing chain; peptide bond forms. E site: empty tRNA exits.
17. What is the genetic code's redundancy?Most amino acids are coded by more than one codon (64 codons for 20 amino acids), often differing at the third position (wobble), which reduces the impact of some mutations.
18. Missense vs nonsense vs frameshift mutationMissense changes one amino acid. Nonsense creates a premature stop codon. Frameshift (insertion or deletion not a multiple of 3) shifts the reading frame and changes all downstream codons.
19. How does the lac operon respond when lactose is present and glucose is absent?Allolactose binds the lac repressor so it leaves the operator, and high cAMP-CAP boosts RNA polymerase binding, so the lac genes are strongly transcribed.
20. What is a signal sequence and what does it do?A short stretch of hydrophobic amino acids at the N-terminus that is recognized by SRP, which directs the ribosome to the rough ER so the protein enters the secretory pathway.
21. Exergonic vs endergonic reactionsExergonic reactions release free energy (delta G < 0) and are spontaneous. Endergonic reactions require free energy input (delta G > 0) and are often coupled to ATP hydrolysis.
22. Why is ATP called the energy currency of the cell?Hydrolysis of its terminal phosphate bond (ATP -> ADP + Pi) releases usable free energy that is coupled to endergonic reactions, often via phosphorylation of a substrate or protein.
23. Oxidation vs reduction (OIL RIG)Oxidation is loss of electrons; reduction is gain. In respiration glucose is oxidized and O2 is reduced; NAD+ is reduced to NADH as it carries electrons.
24. What is osmosis, and what happens to an animal cell in a hypotonic solution?Osmosis is diffusion of water across a selectively permeable membrane toward higher solute concentration. In a hypotonic solution water enters and an animal cell swells and may lyse.
25. Light reactions vs Calvin cycle in photosynthesisLight 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 via rubisco.
26. What is a receptor tyrosine kinase?A membrane receptor that dimerizes when a signal binds, then phosphorylates tyrosines on itself, creating docking sites that start intracellular signalling cascades such as Ras/MAP kinase.
27. What is a second messenger? Give an example.A small intracellular molecule that relays and amplifies a signal from a membrane receptor, e.g. cAMP made by adenylyl cyclase after G protein activation, or Ca2+.