Unit 1
What is the difference between a covalent and an ionic bond?
ionic bonds transfer electrons whereas covalent shares electrons
Describe passive vs. active transport
Passive transport:
Requires no energy
Moves down a concentration gradient
Includes: diffusion, osmosis, facilitated diffusion (via channels or carriers)
Active transport:
Requires energy input (usually ATP)
Moves against the concentration gradient
Uses protein pumps (e.g., Na⁺/K⁺ ATPase)
How does an enzyme interact with a substrate?
Substrate binds to active site
Enzyme undergoes induced fit
Lowers activation energy by stabilizing transition state
Enzyme emerges unchanged at the end
What happens in mitosis? (What are the phases and what happens in them?)
Prophase: chromosomes condense, spindle forms
Prometaphase: nuclear envelope breaks
Metaphase: chromosomes line up
Anaphase: sister chromatids separate
Telophase: nuclei reform
Cytokinesis: cell splits
What type of bond forms between amino acids?
Peptide bond
What is the endosymbiotic theory?
The theory that mitochondria and chloroplasts originated when ancient eukaryotic cells engulfed bacteria, which then lived symbiotically inside the host.
Evidence includes:
Own circular DNA
Double membranes
Divide independently by fission
Ribosomes resemble bacterial ribosomes
What is a way for enzyme reactions to be regulated?
Competitive inhibition
Allosteric inhibition/activation
Covalent modification (phosphorylation)
Feedback inhibition (product shuts down pathway)
Changes in temperature or pH
How can DNA be template for replication?
Complementary base pairing (A–T, G–C).
What is the difference between a condensation reaction and a hydrolysis?
Condensation: builds polymers, releases water
Hydrolysis: breaks polymers, uses water
How can cells in different animal and plant tissues be connected and/or communicate?
Animal cells:
Tight junctions: seal cells together
Desmosomes: strong adhesions, link cytoskeletons
Gap junctions: channels for ion/small molecule exchange
Plant cells:
Plasmodesmata: cytoplasmic channels that connect cells directly
What are key regulatory step in glycolysis?
Phosphofructokinase (PFK) and ATP
Phosphofructokinase (PFK) converts fructose-6-phosphate → fructose-1,6-bisphosphate.
ATP allosterically inhibits it (feedback regulation).
Dominant vs recessive (using Mendel ratios)
Monohybrid cross → 3:1 phenotype
Dihybrid cross → 9:3:3:1 ratio
What are the differences between RNA and DNA? Which molecule is most likely the first “living” molecule, and why?
RNA: ribose sugar, uracil, usually single-stranded
DNA: deoxyribose, thymine, double-stranded
RNA is likely the earliest molecule because it can store information and catalyze reactions (ribozymes).
What do hypertonic, hypotonic, and isotonic mean? What happens to cells?
Hypertonic solution: Higher solute outside → water leaves the cell → cell shrinks (crenates)
Hypotonic solution: Lower solute outside → water enters → cell swells or bursts (lysis)
Isotonic solution: Equal solute inside and out → no net water movement
What is the purpose of fermentation? What types are there?
Regenerate NAD⁺ when oxygen is unavailable.
Lactic acid fermentation – used by animals and bacteria.
Alcohol fermentation – used by yeast and some plants; produces ethanol + CO₂.
Main difference between meiosis I and II; comparison to mitosis
Meiosis I: separates homologous chromosomes
Meiosis II: separates sister chromatids (like mitosis)
What is special about carbohydrates that makes them “energy molecules”?
They contain many C–H and C–C bonds, which release significant energy when oxidized.
What are the major cytoskeletal components and their composition/functions? (Just explain one)
Actin filaments (microfilaments)
Composition: actin protein
Functions: cell shape, muscle contraction, cytokinesis, cell crawling
Intermediate filaments
Composition: various proteins (keratin, lamin)
Functions: structural stability, resist tension, nuclear lamina
Microtubules
Composition: tubulin dimers
Functions: vesicle transport, chromosome movement (spindle), cilia/flagella structure
What complexes are used in light reactions, and what do they contribute?
Photosystem II (PSII):
Splits water
Sends high-energy electrons through ETC
Generates proton gradient → ATP
Photosystem I (PSI):
Re-excites electrons
Produces NADPH
Major parts of replisome
Helicase: unwinds DNA
Primase: makes RNA primers
DNA polymerase III: main synthesis
Sliding clamp: holds polymerase on DNA
DNA polymerase I: removes primers
Ligase: seals fragments
Topoisomerase: relieves tension