Ch 6. Energy and Metabolism
What is the difference between kinetic and potential energy?
Kinetic energy is energy of motion, while potential energy is stored energy based on position or structure.
What is the main goal of cellular respiration?
To convert the chemical energy in glucose into ATP, which powers cellular processes
Where does photosynthesis occur and what are its main stages?
It occurs in chloroplasts; light-dependent reactions in the thylakoids capture energy, and the Calvin cycle in the stroma fixes carbon.
What are the main components required for cell signaling?
A ligand (signaling molecule) and a receptor protein that binds it, triggering a signal transduction pathway.
What is the difference between bacterial and eukaryotic cell division?
Bacteria divide by binary fission (simple replication and separation), while eukaryotes use mitosis and cytokinesis for more complex chromosome segregation.
What are the first and second laws of thermodynamics?
The first law states energy cannot be created or destroyed, only transformed. The second law says energy transformations increase entropy (disorder).
How does glycolysis contribute to cellular respiration?
It breaks glucose into two pyruvate molecules, producing a small amount of ATP and NADH in the cytoplasm without oxygen.
How do chlorophyll and accessory pigments help capture sunlight?
Chlorophyll a absorbs mainly blue and red light; chlorophyll b and carotenoids absorb additional wavelengths, broadening light absorption.
How do the four types of signaling differ from each other?
Direct contact acts locally between adjacent cells.
Paracrine acts nearby.
Endocrine travels long distances via hormones.
Synaptic uses neurotransmitters.
How is DNA packed inside a eukaryotic cell, and what are euchromatin and heterochromatin?
DNA wraps around histone proteins to form chromatin.
There are two types:
Euchromatin: is loosely packed and active in gene expression.
Heterochromatin: is tightly packed and mostly inactive.
Why is ATP called the “energy currency” of the cell?
Because ATP stores and transfers energy in its phosphate bonds, powering most cellular reactions when hydrolyzed to ADP.
What happens to pyruvate when oxygen is available versus when it is not?
With oxygen, pyruvate is oxidized to acetyl-CoA for the Krebs cycle; without oxygen, it undergoes fermentation to regenerate NAD⁺.
What is the main difference between cyclic and noncyclic photophosphorylation?
Noncyclic uses both photosystems and produces ATP, NADPH, and O₂; cyclic uses only PSI and produces ATP but no NADPH or O₂.
What is the role of intracellular receptors compared to membrane receptors?
Intracellular receptors bind small or nonpolar molecules like steroid hormones inside the cell, while membrane receptors detect larger or polar signals outside.
What happens during each stage of mitosis?
Prophase: chromosomes condense
Metaphase: align at the equator
Anaphase: chromatids separate
Telophase: nuclei reform.
How do enzymes speed up chemical reactions?
Enzymes lower the activation energy by binding substrates in a specific active site, stabilizing the transition state.
Describe the role of the electron transport chain in respiration.
It transfers electrons from NADH and FADH₂ to oxygen, using the released energy to pump protons and drive ATP synthesis through chemiosmosis.
What happens during the Calvin cycle?
CO₂ is fixed to RuBP by rubisco, producing G3P using ATP and NADPH; RuBP is regenerated so the cycle can continue.
How do receptor kinases transmit signals?
They activate by autophosphorylation and then phosphorylate other proteins, triggering cascades that affect cell growth and metabolism.
What happens during each phase of the cell cycle (G₁, S, G₂, and G₀), and what are the main checkpoints?
G₁ phase: The cell grows and performs normal functions.
* G₁ checkpoint: Checks cell size, nutrients, and DNA for damage before replication.
S phase: DNA is copied.
G₂ phase: The cell prepares for mitosis by making proteins and organelles.
* G₂ checkpoint: Ensures DNA was copied correctly and is not damaged.
* G₀ phase: The cell rests and does not divide.
* Spindle (metaphase) checkpoint: During mitosis, it makes sure chromosomes are properly attached to spindle fibers before separating.
What is the difference between competitive and noncompetitive enzyme inhibition?
Competitive inhibitors block the active site; noncompetitive inhibitors bind elsewhere, changing the enzyme’s shape and preventing substrate binding.
How do cells make sure they don’t produce too much ATP?
Cells control ATP production through feedback.
When there’s a lot of ATP, it tells enzymes to slow down respiration.
When ATP levels are low, the enzymes are activated again to make more energy.
Why is photosynthesis essential for life on Earth?
It converts solar energy into chemical energy, produces oxygen, and forms the basis of most food chains.
Explain how G-protein coupled receptors (GPCRs) work.
Ligand binding activates a G-protein by replacing GDP with GTP, which then activates an effector (enzyme or ion channel) to produce second messengers like cAMP.
What roles do cyclins and CDKs play in regulating the cell cycle?
Cyclins and CDKs work together to control when the cell moves to the next stage of the cycle. Cyclins are proteins that appear and disappear at specific times. CDKs (cyclin-dependent kinases) are enzymes that become active only when a cyclin attaches to them.