Comprehensive Biology Review: Metabolism, Cell Membranes, and Cell Structure

Flashcard set covering metabolism, thermodynamics, enzymes, plasma membrane structure, transport, cell signaling, and eukaryotic cell organelles based on lecture notes.

What is metabolism and how does it arise in living organisms?

Metabolism is the totality of an organism's chemical reactions. It is an emergent property arising from orderly interactions between molecules.

How do the first and second laws of thermodynamics apply to biological processes?

The first law states that energy can be transferred and transformed, but cannot be created or destroyed (principle of conservation of energy). The second law states that every energy transfer or transformation increases the entropy (disorder) of the universe, with some energy lost to the surroundings as heat.

What is the key functional difference between catabolic and anabolic pathways?

A catabolic pathway releases energy by breaking down complex molecules into simpler compounds. An anabolic pathway builds complex molecules from simpler units and requires an input of energy.

How is free energy ($\Delta G$) defined in a chemical reaction?

Free energy is the portion of a system's energy that can do work when temperature and pressure are uniform throughout. The change in free energy is calculated as $ΔG = G_{\text{final state}} - G_{\text{initial state}}$.

What distinguishes an exergonic reaction from an endergonic reaction in terms of spontaneity and $\Delta G$?

An exergonic reaction proceeds with a net release of free energy, is spontaneous, and has a negative $\Delta G$. An endergonic reaction absorbs free energy from its surroundings, is non-spontaneous, and has a positive $\Delta G$.

What three main types of cellular work are powered by energy coupling?

Chemical work (pushing endergonic reactions), transport work (pumping substances across membranes against spontaneous movement), and mechanical work (such as beating cilia or contracting muscle cells).

What are the structural components of an ATP molecule?

ATP (adenosine triphosphate) consists of ribose (a sugar), adenine (a nitrogenous base), and a chain of three phosphate groups.

What products are generated when ATP undergoes hydrolysis?

Hydrolysis of ATP produces adenosine diphosphate (ADP), inorganic phosphate ($\text{P}_i$), and a release of energy resulting from the shift to a state of lower free energy.

How do enzymes affect the activation energy ($E_A$) and the free energy change ($\Delta G$) of a reaction?

Enzymes lower the activation energy barrier ($E_A$) required for reactants to reach the transition state, thereby speeding up the reaction rate, but leave $\Delta G$ completely unaffected.

What is the fluid mosaic model of the plasma membrane?

The fluid mosaic model describes the membrane as a mosaic of protein molecules bobbing flexibly within a fluid bilayer of amphipathic phospholipids.

How does cholesterol buffer plasma membrane fluidity at warm and cool temperatures?

At warm temperatures (such as $37\,^∘\text{C}$), cholesterol restrains movement of phospholipids to keep the membrane ordered; at cool temperatures, it prevents tight packing to keep the membrane fluid.

What six major functional roles do membrane proteins perform?

Transport, enzymatic activity, signal reception, cell-cell recognition, intercellular junction formation, and structural attachment/anchoring.

Which three chemical characteristics dictate how a molecule crosses the cell membrane?

Size, polarity, and charge.

How do animal and plant cells respond when placed in hypertonic versus hypotonic solutions?

In a hypertonic solution, water leaves both cells, causing animal cells to shrivel and plant cells to plasmolyze. In a hypotonic solution, water enters both cells, causing animal cells to swell/lyse and plant cells to become turgid.

What is the stoichiometric ion transport mechanism of the sodium-potassium pump?

Using energy from $1$ ATP, the sodium-potassium pump exports $3\,\text{Na}^+$ ions out of the cytoplasm and imports $2\,\text{K}^+$ ions into the cell against their respective concentration gradients.

What two forces combine to establish an electrochemical gradient across a membrane?

A chemical force (the ion concentration gradient) and an electrical force (the effect of membrane voltage on ion movement).

What are the three stages of cell signaling proposed by Earl W. Sutherland?

Reception (detection of a signal molecule), Transduction (conversion and relaying/amplification of the signal), and Response (cellular modification or action).

What are the four main ranges of cell signaling?

Contact (adjacent cells), Paracrine (nearby cells), Synaptic (precise local signaling across synapses), and Endocrine (long-distance signaling via hormones transported in the bloodstream).

How does an organic coenzyme differ from an inorganic cofactor?

An inorganic cofactor is typically a metal ion in ionic form that aids enzyme function, whereas an organic cofactor is specifically termed a coenzyme (often derived from vitamins).

How do competitive and noncompetitive inhibitors differ in their binding mechanisms?

A competitive inhibitor directly competes with the substrate by binding to the active site. A noncompetitive inhibitor binds to an alternate (allosteric) site, causing a conformational shape change in the active site.

What occurs during allosteric regulation of an enzyme?

A regulatory molecule binds to a separate site away from the active site, inducing a conformational change that stabilizes either the active shape or the inactive shape of the enzyme complex.

What is cooperativity in enzyme kinetics?

Cooperativity is a form of allosteric activation where substrate binding to one active site on a multi-subunit enzyme induces a shape change that locks all remaining subunits into their active state.

How does feedback inhibition regulate metabolic pathways?

The end product of a metabolic pathway binds allosterically to and inhibits an enzyme operating early in the pathway, shutting down further production when adequate product is accumulated.

What three core parameters define the quality of an image in light microscopy?

Magnification (ratio of image size to real size), Resolution (clarity or minimum distance between two distinguishable points), and Contrast (difference in brightness between light and dark regions).

What is the structural focus of Scanning Electron Microscopy (SEM) compared to Transmission Electron Microscopy (TEM)?

SEM focuses an electron beam onto the specimen's surface to produce a 3D-like topographical image. TEM transmits an electron beam through a specimen section to study internal cellular ultrastructure.

What four cellular structures constitute the shared cellular toolkit found in all prokaryotes and eukaryotes?

Plasma membrane, cytoplasm (cytosol), DNA, and ribosomes.

What metabolic functions distinguish Smooth ER from Rough ER?

Smooth ER synthesizes lipids, metabolizes carbohydrates, detoxifies drugs/poisons, and stores calcium ions ($\text{Ca}^{2+}$). Rough ER contains bound ribosomes that synthesize proteins and membranes for transport.

What is the main role of lysosomes in cellular waste management?

Lysosomes digest engulfed materials (phagocytosis) and recycle damaged organelles (autophagy) using hydrolytic enzymes that function optimally in an acidic environment.

What does the endosymbiont theory explain regarding mitochondria and chloroplasts?

It proposes that mitochondria and chloroplasts evolved from prokaryotic cells (an oxygen-using nonphotosynthetic prokaryote and a photosynthetic prokaryote) that were engulfed by ancestral eukaryotic host cells.

How do mitochondrial cristae contribute to cellular respiration efficiency?

Cristae are folds of the inner mitochondrial membrane that maximize surface area, allowing more space for electron transport chain proteins and ATP synthase complexes.

What are the structural compositions and diameters of the three main cytoskeletal fibers?

Microtubules are hollow tubulin polymers ($25\,\text{nm}$ diameter); Microfilaments are two intertwined strands of actin ($7\,\text{nm}$ diameter); Intermediate filaments are fibrous proteins like keratins coiled into cables ($8\text{--}12\,\text{nm}$ diameter).

What key molecular components form the Extracellular Matrix (ECM) of animal cells?

Glycoproteins such as collagen, proteoglycans, and fibronectin, which bind to transmembrane receptor proteins called integrins.

What three types of cell junctions facilitate adhesion and communication between animal epithelial cells?

Tight junctions, desmosomes, and gap junctions.