7/23 Cellular Biology Lecture: Organelles, Membranes & Energetics

60 question-and-answer flashcards covering key topics from the lecture: organelles, membrane structure, transport mechanisms, cell junctions, energetics, and thermodynamics.

Why are mitochondria called the powerhouse of the cell?

They efficiently produce large amounts of ATP from food molecules.

Do cells absolutely need mitochondria to make ATP?

No; glycolysis and fermentation can make ATP without mitochondria, but far less efficiently.

How many membranes does a mitochondrion possess?

Two – an outer membrane and a highly infolded inner membrane.

What are the infoldings of the mitochondrial inner membrane called?

Cristae.

What is the functional purpose of cristae?

They greatly increase inner membrane surface area for cellular respiration reactions and ATP synthesis.

Describe the shape dynamics of mitochondria.

They can elongate, branch, and form dynamic networks rather than being static bean-shapes.

What genetic feature distinguishes mitochondria from most other organelles?

They have their own circular DNA separate from nuclear DNA.

Which theory explains the origin of mitochondria and chloroplasts?

The endosymbiotic theory.

Name two key pieces of evidence supporting endosymbiotic theory.

Their double membranes and possession of their own DNA/ribosomes.

What medical condition shows mitochondrial DNA can trigger immune reactions?

Sterile shock after tissue damage releases mitochondrial DNA.

From which parent is mitochondrial DNA typically inherited?

The mother (maternal lineage).

What structure within chloroplasts contains photosynthetic pigments?

Thylakoids.

What is a stack of thylakoids called?

A granum (plural grana).

What is the primary function of chloroplasts?

Transforming light energy into chemical energy in the form of sugars.

What structural feature do mitochondria and chloroplasts share?

Both have double membranes and extensive internal membrane infoldings.

What network of proteins gives eukaryotic cells shape and transport rails?

The cytoskeleton.

List three main roles of the cytoskeleton.

Structural support, intracellular transport, and organelle/membrane anchoring.

Which extracellular structure compensates for the lack of a cell wall in animals?

The extracellular matrix (ECM).

What are plasmodesmata?

Cytoplasmic channels through plant cell walls that connect adjacent plant cells.

Which junction ‘stitches’ adjacent animal cells together to prevent leakage?

Tight junctions.

Which junction anchors cells together via intermediate filaments?

Desmosomes.

Which junction forms ion channels allowing direct electrical signals between cells?

Gap junctions.

Which human organ relies heavily on gap junctions for synchronized activity?

The heart (cardiac muscle).

What term describes molecules with both hydrophilic and hydrophobic regions?

Amphipathic.

In a phospholipid, which part is hydrophilic?

The phosphate head group.

In a phospholipid, which part is hydrophobic?

The fatty-acid tails.

What model describes the dynamic nature of biological membranes?

The fluid mosaic model.

What role do integral membrane proteins often play?

They act as transport channels spanning the bilayer.

How does cholesterol influence membrane properties?

It fits between phospholipids, modulating membrane fluidity.

What is the function of cell-surface glycoproteins?

They serve in cell identification, communication, and pathogen recognition.

Which immune-cell receptor is exploited by HIV for entry?

The CD4 receptor on T cells.

Define diffusion.

Passive movement of molecules from high to low concentration.

Define osmosis.

Diffusion of water across a selectively permeable membrane from high to low water concentration.

During osmosis, toward which side does water move relative to solute concentration?

Toward the side with higher solute concentration (to dilute it).

Describe a hypotonic solution relative to a cell.

Lower solute concentration outside than inside the cell.

What happens to an animal cell placed in hypotonic solution?

It gains water and may lyse (burst).

Describe a hypertonic solution relative to a cell.

Higher solute concentration outside than inside the cell.

What happens to an animal cell in hypertonic solution?

It loses water and shrivels (crenates).

What is an isotonic solution?

Solute concentration equal inside and outside; no net water movement.

What everyday solution is roughly isotonic to human cells?

Physiological saline (0.9 % NaCl).

Why is seawater dangerous to drink?

Its hypertonic salt concentration draws water out of body cells, causing dehydration.

What ion concentration pattern is maintained by most animal cells?

High Na⁺ outside and high K⁺ inside.

What membrane protein establishes the Na⁺/K⁺ gradient?

The sodium-potassium ATPase pump.

What is the exchange ratio of the Na⁺/K⁺ pump per cycle?

Three Na⁺ ions out for two K⁺ ions in.

Does the Na⁺/K⁺ pump require energy?

Yes, it hydrolyzes ATP to move ions against their gradients.

Define electrochemical gradient.

Combined influence of a concentration gradient and an electrical charge difference across a membrane.

Name three forms of endocytosis.

Phagocytosis, pinocytosis, and receptor-mediated endocytosis.

What is phagocytosis?

Cellular engulfment of large particles into a vesicle.

What distinguishes receptor-mediated endocytosis?

Cargo must bind specific surface receptors before vesicle formation.

What is exocytosis?

Fusion of an internal vesicle with the plasma membrane to release contents outside the cell.

Differentiate kinetic and potential energy.

Kinetic is energy of motion; potential is stored energy, e.g., in chemical bonds.

Which covalent bond stores more potential energy: C–H or O–H?

C–H, because it is longer and weaker.

State the first law of thermodynamics.

Energy cannot be created or destroyed, only transformed or transferred.

What does entropy measure?

The degree of disorder in a system.

According to the second law of thermodynamics, how does entropy change overall?

The total entropy of the universe tends to increase.

What does a negative ΔG indicate about a reaction?

It is exergonic and can proceed spontaneously.

What does a positive ΔG signify?

The reaction is endergonic and requires input of energy.

How do temperature and reactant concentration affect reaction rate?

Increasing either raises collision frequency, accelerating the reaction.

What role do enzymes play in cellular reactions?

They speed reactions by bringing reactants together and lowering the energy barrier.