Molecular and Cellular Biology
What to know
Molecular and cellular biology asks how information and energy move through cells. At the molecular level, know the structure of DNA (antiparallel double helix, complementary base pairing A-T and G-C, hydrogen bonds between strands), the central dogma (DNA to RNA to protein), and the three RNA types: mRNA carries the message, tRNA brings amino acids, rRNA builds the ribosome. Understand transcription in the nucleus and translation at the ribosome, including codons, anticodons, start and stop signals, and that the genetic code is redundant but not ambiguous.
At the cellular level, know the differences between prokaryotic and eukaryotic cells, the roles of major organelles (mitochondria for aerobic respiration, chloroplasts for photosynthesis, ribosomes for protein synthesis, the rough and smooth ER, Golgi, lysosome), and the fluid mosaic model of the membrane. Movement across membranes (diffusion, osmosis, facilitated diffusion, active transport, endocytosis) and enzyme kinetics (substrate specificity, effect of temperature and pH, denaturation) are frequent topics. Also review the stages of mitosis and the cell cycle checkpoints.
Traps
Questions often confuse transcription with translation, or claim that DNA is directly translated. Watch for items implying that active transport requires no energy, that osmosis moves solute rather than water, or that enzymes are consumed in reactions. A common distractor is that the lagging strand is synthesized continuously.
Worked example
A DNA template strand reads 3'-TAC GGA-5'. The mRNA is 5'-AUG CCU-3', and the anticodon on the incoming tRNA is complementary to the codon. Rule of thumb: transcribe by base-pairing (A pairs with U in RNA), then read codons in the 5'-to-3' direction on mRNA.