Unit #1 – Physiology Basics, Cell Biology & Chemistry Review

80 Q&A flashcards covering structure-function relationships, homeostasis, cell/tissue organization, organelles, membranes, body fluids, feedback control, chemical messengers, biological rhythms, chemical bonding, water properties, macromolecules, protein structure & binding, enzymes, cytoskeleton, and key physiology principles for Unit #1 exam review.

What are the two overarching ‘Key Ideas of Physiology’ introduced in Chapter 1?

(1) Structure dictates function; (2) Homeostasis is maintained at all costs.

Name the four primary classes of cells in the human body.

Epithelial cells, connective-tissue cells, neurons, and muscle cells.

Which levels of organization lie between ‘cells’ and ‘organ systems’?

Cells → Tissues → Organs → Organ systems.

What are the three types of muscle cells and which are involuntary?

Skeletal (voluntary); Cardiac and Smooth (both involuntary).

Define a neuron and distinguish it from a nerve.

A neuron is a single excitable cell that conducts electrical signals; a nerve is a bundle of many neuronal axons plus supporting tissue and blood vessels.

Which epithelial surface faces the lumen: apical or basolateral?

The apical surface faces the lumen.

What type of cell-to-cell junction forms a virtually impermeable seal between adjacent epithelial cells?

Tight junctions.

List three examples of connective tissue types.

Loose connective tissue, dense connective tissue, blood, bone, cartilage, or adipose (any three).

Give two major functions of the extracellular matrix (ECM).

Provides a scaffold for cellular attachments and transmits chemical signals to regulate cell activity.

What percentage of body fluid is intracellular?

Approximately 67 % (two-thirds).

Define ‘plasma’ in the context of body-fluid compartments.

The fluid portion of the blood, representing about 20 – 25 % of extracellular fluid.

What term describes the maintenance of physiological variables within a dynamic, fluctuating range?

Homeostasis (dynamic constancy).

When homeostasis fails, the study of resulting disorders is called _.

Pathophysiology.

In feedback terminology, which type opposes the original stimulus?

Negative feedback.

Give one physiological example of a positive-feedback loop.

Blood clotting or uterine contractions during childbirth.

List the basic components of a reflex arc in order.

Stimulus → Receptor → Afferent pathway → Integrating center → Efferent pathway → Effector → Response.

What is a hormone?

A chemical messenger secreted into the blood by endocrine cells that acts on distant target cells.

Differentiate between paracrine and autocrine signaling.

Paracrine messengers act on neighboring cells; autocrine messengers act on the same cell that released them.

What are gap junctions?

Protein channels that directly link the cytosol of adjacent cells, allowing ions and small molecules to pass.

Contrast ‘adaptation’ with ‘acclimatization’.

Adaptation is an inherited characteristic enhancing survival; acclimatization is an improved function of an existing system after chronic exposure to a change.

What is the most common biological rhythm and its approximate period?

The circadian rhythm; ~24 hours.

Define ‘negative balance’ for a chemical substance in the body.

A state in which loss of the substance exceeds gain (loss > gain).

Which four elements constitute ~99 % of the atoms in the body?

Hydrogen, oxygen, carbon, and nitrogen.

What is the atomic number of an element?

The number of protons in its nucleus.

A positively charged ion is called a(n) .

Cation.

Rank the following bonds from strongest to weakest: ionic, non-polar covalent, hydrogen, polar covalent.

Non-polar covalent (strongest) > Polar covalent > Ionic > Hydrogen (weakest).

Why are molecules with many non-polar C–H bonds poorly soluble in water?

Because water is polar and ‘like dissolves like’; non-polar molecules are hydrophobic.

Define an amphipathic molecule and give an example.

A molecule with both polar (hydrophilic) and non-polar (hydrophobic) regions; e.g., a phospholipid.

State the physiological pH range of extracellular fluid.

Approximately 7.35 – 7.45.

What storage polysaccharide is formed from glucose in humans?

Glycogen.

Distinguish saturated from unsaturated fatty acids.

Saturated fatty acids have no C=C double bonds; unsaturated fatty acids contain one or more double bonds.

Why are phospholipids crucial to cell membranes?

Their amphipathic nature allows them to form lipid bilayers, creating selective barriers.

What four-ringed lipid molecules serve as precursors for steroid hormones?

Cholesterol (steroid nucleus).

How many different amino acids are used to build human proteins?

Twenty.

Define primary structure of a protein.

The specific sequence and number of amino acids in a polypeptide chain.

Name the two regular secondary protein structures.

Alpha helices and beta-pleated sheets.

What type of bond stabilizes many tertiary protein structures via cysteine residues?

Covalent disulfide bonds.

Hemoglobin, composed of four polypeptide chains, exhibits which level of protein structure?

Quaternary structure.

What term describes any molecule that binds reversibly to a protein’s binding site?

Ligand.

Explain the difference between chemical specificity and affinity.

Specificity: whether a ligand fits the binding site; Affinity: strength of the ligand-protein interaction.

What does 100 % saturation mean for a protein’s binding sites?

All available binding sites are occupied by ligand.

Describe allosteric modulation.

A modulator binds to a regulatory site on a protein, non-covalently altering the shape/activity of the functional site.

What enzyme class adds phosphate groups to proteins?

Protein kinases.

Define an enzyme.

A protein catalyst that lowers activation energy and speeds up a specific chemical reaction without being consumed.

What are cofactors and coenzymes?

Non-protein helpers; cofactors are often metal ions, coenzymes are organic molecules (usually vitamin-derived).

List four factors that increase the rate of a chemical reaction.

Higher reactant concentration, higher temperature, lower activation energy, presence of a catalyst (enzyme).

Which law states that reaction direction is influenced by relative concentrations of reactants and products?

Law of Mass Action.

What are the two broad categories of metabolism?

Catabolism (breakdown) and anabolism (synthesis).

Identify the three major kinds of cytoskeletal filaments from thinnest to thickest.

Actin filaments (microfilaments) → Intermediate filaments → Microtubules.

Which cytoskeletal element is most important for muscle contraction and cell movement?

Actin filaments.

What organelle is the primary site of ATP production via oxidative phosphorylation?

Mitochondrion.

State one key function each for rough ER and smooth ER.

Rough ER: synthesizes & processes membrane/secretory proteins; Smooth ER: lipid synthesis, detoxification, Ca²⁺ storage.

What cellular structure packages and sorts proteins into vesicles?

Golgi apparatus.

Which acidic, enzyme-rich organelle digests damaged organelles and ingested particles?

Lysosome.

Function of peroxisomes?

Detoxify certain molecules and break down fatty acids producing (and degrading) H₂O₂.

Define the nucleolus.

Dense region within the nucleus where rRNA and ribosomal subunits are synthesized.

What is the ‘fluid-mosaic model’ of membranes?

Membranes are a dynamic bilayer of phospholipids with embedded, mobile proteins creating a fluid, mosaic-like structure.

Differentiate integral and peripheral membrane proteins.

Integral proteins are amphipathic and embedded in the lipid bilayer; peripheral proteins attach to membrane surfaces and are not embedded.

Name the three main types of membrane junctions.

Desmosomes, tight junctions, and gap junctions.

Which junction anchors cells together in tissues subject to stretching, like skin?

Desmosomes.

What membrane lipid modulates fluidity and is abundant in plasma membranes but scarce in organelle membranes?

Cholesterol.

Explain ‘selectively permeable’ as applied to plasma membranes.

Membranes allow some substances to cross more easily than others, enabling regulation of intracellular composition.

Which organelle is directly continuous with the nuclear envelope?

Endoplasmic reticulum (especially rough ER).

What term describes water movement across membranes toward higher solute concentration?

Osmosis.

Give the equation for pH in terms of hydrogen ion concentration.

pH = –log₁₀[H⁺].

State one physiological example of feed-forward control.

Circadian rise in body temperature before waking, or salivation upon smelling food (anticipatory).

What messenger category includes norepinephrine acting at an adjacent neuron’s synapse?

Neurotransmitter.

Name the major cation and anion in extracellular fluid.

Cation: Na⁺ (sodium); Anion: Cl⁻ (chloride).

Which chemical bond within water molecules makes water highly polar?

Polar covalent bond between oxygen and hydrogen.

How do hydrogen bonds affect DNA structure?

They hold complementary nucleotide bases together between the two strands of the double helix.

What is the function of integrins?

Transmembrane proteins that link the extracellular matrix to the cytoskeleton, anchoring cells and transmitting signals.

Identify two roles of cholesterol in membranes.

Stabilizes fluidity by preventing fatty-acid packing; helps in vesicle formation.

Define ‘steady state’ versus ‘equilibrium’.

Steady state: constant condition maintained using energy; Equilibrium: balance without net energy expenditure.

Which fluid compartment is called the ‘interstitium’?

The space containing interstitial fluid surrounding tissue cells (part of ECF).

What is the typical intracellular vs extracellular Na⁺ concentration pattern?

Low Na⁺ inside (~5 mM), high Na⁺ outside (~140 mM).

Describe structural difference between cisternae of rough ER and Golgi.

Rough ER cisternae are flattened sheets with ribosomes; Golgi cisternae are stacked, curved, and lack ribosomes.

How does phosphorylation generally alter protein function?

By covalently adding a negative charge, it changes protein conformation, activating or inhibiting activity.

What vitamin-derived coenzyme carries electrons in cellular respiration (give one)?

NAD⁺ (from niacin) or FAD (from riboflavin).

Explain ‘feed-forward’ vs ‘feedback’.

Feed-forward anticipates change and acts before variable deviates; Feedback responds after a change is detected.

Which level of protein organization is most directly determined by DNA sequence?

Primary structure.

What chemical characteristic must a ligand possess to cross the phospholipid bilayer unaided?

Predominantly non-polar (lipophilic) character.

What is a micelle?

A spherical cluster formed by amphipathic molecules in water with hydrophobic tails inward and hydrophilic heads outward.

Why do enzymes display saturation kinetics?

Because they have a finite number of active sites that can all become occupied by substrate.

State one way enzyme activity is increased inside a cell (other than raising temperature).

Increase enzyme concentration, increase substrate concentration (below saturation), add an allosteric activator, or phosphorylate the enzyme if that activates it.

Define ‘proteasome’.

A large protein complex that unfolds and degrades ubiquitin-tagged proteins into peptides.

Which cytoskeletal component forms the mitotic spindle?

Microtubules.

What term describes plasma membrane proteins that span the bilayer several times forming ion channels?

Transmembrane proteins.