STEM Readiness: Biology Readiness - Chemistry of Life: Enzyme Kinetics - Km Vmax, Michaelis-Menten Competitive, vs. Non-competitive, Inhibition

Must?Know (20–25 detailed bullets)

• Prokaryotic cells range from 0.1–5.0 ?m in diameter; eukaryotic cells range from 10–100 ?m.
• Prokaryotes include Bacteria and Archaea; eukaryotes include animals, plants, fungi, and protists.
• DNA in prokaryotes is located in the nucleoid, a region without a membrane; eukaryotes house DNA within a membrane-bound nucleus.
• Prokaryotes lack membrane-bound organelles; eukaryotes contain endoplasmic reticulum, Golgi apparatus, mitochondria, and lysosomes.
• Both prokaryotes and eukaryotes have a phospholipid bilayer plasma membrane.
• Prokaryotic ribosomes are 70S (50S + 30S subunits); eukaryotic cytoplasmic ribosomes are 80S (60S + 40S subunits).
• Mitochondria and chloroplasts in eukaryotes contain 70S ribosomes, similar to prokaryotes, supporting endosymbiotic theory.
• Bacterial cell walls contain peptidoglycan; archaeal cell walls lack peptidoglycan and instead have pseudopeptidoglycan or other polysaccharides.
• Plant cell walls are composed of cellulose; fungal cell walls contain chitin; animal cells lack a cell wall.
• Prokaryotes reproduce by binary fission; eukaryotes undergo mitosis and meiosis.
• Prokaryotic DNA is typically a single circular chromosome; eukaryotic DNA is linear and organized into multiple chromosomes.
• Plasmids are small, circular extrachromosomal DNA molecules common in prokaryotes, rare in eukaryotes.
• Eukaryotic cells contain internal membrane systems (nuclear envelope, ER, Golgi); prokaryotes lack internal membranes.
• Cytoskeleton elements (actin, tubulin homologs) exist in both prokaryotes and eukaryotes, though more complex in eukaryotes.
• Flagella in prokaryotes are made of flagellin and rotate; eukaryotic flagella are composed of microtubules (9+2 arrangement) and undulate.
• Mycoplasma species are bacteria without a cell wall, making them resistant to antibiotics like penicillin.
• Human red blood cells lack a nucleus and mitochondria in maturity, limiting their lifespan and metabolic capacity.
• Plant cells contain chloroplasts for photosynthesis; animal cells do not.
• Lysosomes are membrane-bound organelles in animal cells that contain hydrolytic enzymes; plants use vacuoles for similar functions.
• Peroxisomes in eukaryotes detoxify substances like hydrogen peroxide; prokaryotes lack peroxisomes.
• Nuclear pores in the nuclear envelope regulate transport between nucleus and cytoplasm; prokaryotes lack nuclear pores.
• Endosymbiotic theory is supported by mitochondria and chloroplasts having their own DNA, 70S ribosomes, and double membranes.
• Chloroplasts are found in plants and some protists; absent in fungi and animals.
• Archaea are prokaryotes but share some molecular features with eukaryotes (e.g., RNA polymerase, histones).
• Gram-positive bacteria have thick peptidoglycan layers; Gram-negative bacteria have thin peptidoglycan and an outer membrane.

Difficulty Level

Intermediate – requires distinguishing structural and functional differences across domains and organelle roles.

Common Traps (3–5 factual traps)

Trap: All cells with cell walls have peptidoglycan – Fact: Only bacteria have peptidoglycan; plants (cellulose), fungi (chitin), and archaea (no peptidoglycan) differ.

Trap: Ribosome size is the same across all cells – Fact: Prokaryotes use 70S ribosomes; eukaryotic cytoplasmic ribosomes are 80S, though mitochondria and chloroplasts retain 70S.

Trap: Prokaryotes have no internal structure – Fact: Prokaryotes lack membrane-bound organelles but have nucleoids, ribosomes, and cytoskeletal proteins.

Trap: The nucleus is the only organelle with a double membrane – Fact: Mitochondria and chloroplasts also have double membranes; nucleus, mitochondria, and chloroplasts all have two lipid bilayers.

Practice MCQs (5–7 questions)

Question: Which of the following is a defining feature of eukaryotic cells but absent in prokaryotic cells?
A) Plasma membrane
B) Ribosomes
C) Mitochondria
D) Circular DNA
Answer: C
Explanation: Mitochondria are membrane-bound organelles found only in eukaryotic cells.
Why the top distractor is wrong: Circular DNA is common in prokaryotes but also present in mitochondria and chloroplasts, so it is not exclusive to prokaryotes.

Question: A cell is observed to have a nucleus, 80S ribosomes, and a cell wall made of cellulose. This cell is most likely from which organism?
A) Fungus
B) Bacterium
C) Animal
D) Plant
Answer: D
Explanation: Cellulose cell walls and 80S ribosomes with a nucleus are characteristic of plant cells.
Why the top distractor is wrong: Fungi have chitin in cell walls, not cellulose.

Question: Which structure is found in both prokaryotes and eukaryotes?
A) Nucleoid
B) 80S ribosomes
C) Phospholipid bilayer
D) Golgi apparatus
Answer: C
Explanation: Both cell types have a plasma membrane made of a phospholipid bilayer.
Why the top distractor is wrong: The nucleoid is only in prokaryotes; eukaryotes have a nucleus.

Question: Which of the following provides the strongest evidence for the endosymbiotic origin of mitochondria?
A) Presence of a double membrane
B) Ability to synthesize proteins using 80S ribosomes
C) Linear DNA organized with histones
D) Use of binary fission for replication
Answer: A
Explanation: The double membrane and presence of 70S ribosomes and circular DNA support endosymbiosis; binary fission is also key.
Why the top distractor is wrong: Mitochondria use 70S ribosomes, not 80S; 80S are cytoplasmic in eukaryotes.

Question: Which organism lacks a cell wall entirely?
A) Escherichia coli
B) Saccharomyces cerevisiae
C) Mycoplasma pneumoniae
D) Arabidopsis thaliana
Answer: C
Explanation: Mycoplasma is a bacterium without a cell wall.
Why the top distractor is wrong: E. coli has a peptidoglycan cell wall and is Gram-negative.

Question: Where is DNA located in a prokaryotic cell?
A) Within the nucleus
B) In mitochondria
C) In the nucleoid region
D) Bound to the Golgi apparatus
Answer: C
Explanation: Prokaryotes lack a nucleus; DNA resides in the nucleoid.
Why the top distractor is wrong: Prokaryotes do not have a nucleus.

Question: Which of the following organelles is responsible for protein modification and sorting in eukaryotic cells?
A) Rough endoplasmic reticulum
B) Smooth endoplasmic reticulum
C) Golgi apparatus
D) Lysosome
Answer: C
Explanation: The Golgi apparatus modifies, sorts, and packages proteins for secretion or delivery.
Why the top distractor is wrong: The rough ER synthesizes proteins but does not sort or modify them for final destination.

Last?Minute Revision (20–25 one?liners)

• Prokaryotic cell size: 0.1–5.0 ?m; eukaryotic: 10–100 ?m.
• Prokaryotes: nucleoid; eukaryotes: nucleus with nuclear envelope.
• Prokaryotic ribosome = 70S; eukaryotic cytoplasmic ribosome = 80S.
• Mitochondria and chloroplasts have 70S ribosomes and circular DNA – evidence of endosymbiosis.
• Bacteria: peptidoglycan cell wall; Archaea: no peptidoglycan.
• Plants: cellulose cell wall; fungi: chitin; animals: no cell wall.
• Mycoplasma – only bacteria without cell wall.
• Human red blood cells: no nucleus, no mitochondria.
• Prokaryotes lack membrane-bound organelles (ER, Golgi, lysosomes).
• Both cell types have plasma membrane (phospholipid bilayer).
• Eukaryotes have internal membranes (ER, nuclear envelope, Golgi).
• Prokaryotic DNA: single circular chromosome; eukaryotic: multiple linear chromosomes.
• Plasmids: common in bacteria, rare in eukaryotes.
• Flagellin = prokaryotic flagella protein; 9+2 microtubule array in eukaryotes.
• Cytoskeleton present in both, but more complex in eukaryotes.
• Lysosomes: animal cells only; plants use central vacuole for degradation.
• Peroxisomes: eukaryotic organelles for detoxification (e.g., H?O? breakdown).
• Nuclear pores: regulate nucleocytoplasmic transport; absent in prokaryotes.
• Chloroplasts: in plants and some protists; absent in fungi and animals.
• Archaea: prokaryotic cell structure but share transcription machinery with eukaryotes.
• Gram-positive: thick peptidoglycan; Gram-negative: thin peptidoglycan + outer membrane.
• Endosymbiotic theory: mitochondria/chloroplasts reproduce via binary fission independently.
• Mitochondria have double membrane, 70S ribosomes, circular DNA.
• Verify from standard textbook: exact composition of archaeal cell walls varies widely.
• Eukaryotic organelles with double membranes: nucleus, mitochondria, chloroplasts.