cytology Q&A

Comprehensive practice flashcard set containing 300 rigorous question-and-answer cards covering the entire cytology and cell biology curriculum based on the textbook 'An Introduction to Cell Biology (Cytology)' by Pr Ziad Abdel-Razzak.

How does the course textbook define "cell biology"?

Cell biology is the study of living things at the level of their cells, structurally and functionally, investigating the functions of cell organelles in addition to their structures.

What specific subfield of science deals strictly with the structural description of cells and their components?

Cytology.

What are the fundamental units of both structure and function in all living things according to the cell doctrine?

Cells.

According to the cell doctrine, from what do all cells arise?

Cells arise from preexisting cells through cell division.

What makes up an organism according to the cell doctrine?

Cells and their products (since cells secrete many substances).

Which biological processes place the cell at the basis of the continuity of life?

Mitosis, meiosis, and fertilization.

What is meant by the statement that each cell has a "double-life" or "double function"?

Each cell has a life of its own in addition to its integrated role in a multicellular organism.

What landmark contribution did Ibn Alhaytham (Alhazen) make in 1021 that aided the invention of microscopy?

He established the basic physical principles of optics and light behavior in his reference of optics entitled "Kitāb al-Manāzir" (lid), which helped the development and improvement of lenses.

What was the earliest recorded use of a magnifying instrument in a biological study, and who performed it in 1558?

Conrad Gesner performed a detailed structural study of a group of protists called foraminifer.

Who invented the first compound microscope in 1590, and what was its magnification range?

Janessen, an eyeglasses manufacturer; its magnification ranged between $10\times$ and $30\times$.

What optical milestone was achieved by Galilee in 1610?

He constructed his own microscope and performed several important biological investigations.

What two historical scientific instruments are illustrated in this figure?

On the left is the "Camera" (camera obscura principles) of Ibn Alhaytham, and on the right is the first compound microscope used by Robert Hooke.

What structural unit name did Malpighi give to the components he observed in plant tissues?

Malpighi suggested plant tissues were composed of structural units named "utricles" (which were later known as cells).

Which earlier scientists' work on blood circulation did Malpighi complete by describing capillaries?

The Arab physician Ibn Nafis ($13^{\text{th}}$ century) and the physiologist Harvey ($17^{\text{th}}$ century).

What biological specimens did Antonie van Leeuwenhoek describe using microscopes approaching $300\times$ magnification?

Microorganisms of the soil (such as bacteria and protozoa), as well as sperm and blood cells of many species.

Who introduced the term "cell" to biology after observing thin slices of dried cork, and in what year was it published?

Robert Hooke in 1665, who described cork as being perforated and porous like a honeycomb.

What statement did Henri Dutrochet publish in 1824 regarding animal and plant tissue composition?

He wrote that animal and plant tissues were "aggregates of globular cells".

What constant cellular structure did Robert Brown discover in plant cells in 1831, and what physical movement did he describe?

He discovered and named the "nucleus" (plural "nuclei") and described the streaming of chloroplasts, now known as Brownian movement.

Who introduced the term "protoplasm" to describe the contents of the cell?

Jan Evangelista Purkinje (1787–1869).

What did Matthias Schleiden call the cell nucleus, and what sub-nuclear structure was he first to describe?

He called the nucleus the "cytoblast" and was the first to describe nucleoli inside the nucleus.

What two critical conceptual contributions did Theodor Schwann make to the evolving cell doctrine?

He recognized that living things are composed of cells and "the product of cells" (such as extracellular matrix collagen) and introduced the term "metabolism".

What Latin phrase was coined by Rudolf Virchow to summarize the cellular basis of life's continuity?

"Omnis cellula e cellula" (all cells arise from preexisting cells).

Who described and named chromosomes in 1888?

Heinrich Wilhelm Gottfried von Waldeyer.

How many chemical elements among the more than 100 on Earth occur in living organisms?

$27$ chemical elements.

Which four chemical elements represent approximately $96\%$ of atoms in living cells?

Carbon ($\text{C}$), Hydrogen ($\text{H}$), Oxygen ($\text{O}$), and Nitrogen ($\text{N}$).

Which seven mineral elements represent about $4\%$ of the atoms in living cells?

Phosphorus ($\text{P}$), Calcium ($\text{Ca}$), Sulfur ($\text{S}$), Chlorine ($\text{Cl}$), Sodium ($\text{Na}$), Potassium ($\text{K}$), and Magnesium ($\text{Mg}$).

What are biological trace elements, and which elements belong to this category?

Elements that exist at very low concentrations in organisms, including $\text{B, F, Mn, Fe, Co, Cu, Zn, Se, I,}$ and $\text{Mo}$.

What four main classes of organic biomolecules occur in all cells?

Proteins, carbohydrates, lipids, and nucleic acids.

What is the average abundance of water in animal cells versus plant cells?

Water accounts for an average of $65\%$ of animal cell weight and $80\%$ of plant cell weight (representing at least $70\%$ in bacteria).

Why is the water ($\text{H}_2\text{O}$) molecule polar despite being electrically neutral?

The oxygen atom is partially negatively charged because it attracts electrons from the hydrogen atoms, which carry partial positive charges.

How strong is a hydrogen bond compared to a standard covalent bond?

A hydrogen bond is approximately $20$ times weaker than a covalent bond.

What structural role does oxygen play in forming hydrogen bonds in water?

Oxygen acts as a donor through its covalently bound hydrogen atoms and as an acceptor through its free electron doublets.

What is the physical state of mineral salts when dissolved in cellular water?

They are ionized into hydrated oppositely charged particles surrounded by water molecules due to water's polarity and ionic interactions.

Give two examples of insoluble mineral salts found in rigid animal structures.

Calcium carbonate ($\text{CaCO}_3$), calcium phosphate ($\text{Ca}_3(\text{PO}_4)_2$), and salts of silicon.

What term defines the complete set of small organic molecules (metabolites) in a cell?

Metabolome.

What percentage of a cell's dry weight is represented by proteins?

Between $55\%$ and $85\%$ of the cell dry weight.

What stereoisomeric form of amino acids is exclusively found in proteins?

$\text{L}$-stereoisomers.

Which amino acid lacks a chiral alpha-carbon ($\text{C}_\alpha$)?

Glycine.

How does the chemical structure of proline differ from the other 19 standard amino acids?

Its side chain is covalently linked to its amino nitrogen atom, forming a cyclic secondary amino group.

List the nine essential amino acids that must be supplied by the human diet.

Threonine, methionine, lysine, valine, leucine, isoleucine, histidine, phenylalanine, and tryptophan.

Which amino acids possess polar acidic, negatively charged side chains at physiological $\text{pH}$?

Aspartic acid and glutamic acid.

Which amino acids possess polar basic, positively charged side chains at physiological $\text{pH}$?

Lysine, arginine, and histidine.

What is a zwitterion in amino acid chemistry?

An amino acid having an uncharged side chain in which both the amino ($-\text{NH}_3^+$) and carboxyl ($-\text{COO}^-$) groups are ionized at $\text{pH} \approx 7$, giving a net electrical charge of zero.

What type of chemical reaction forms a peptide bond, and what molecule is eliminated?

A condensation reaction between the $\alpha$-amino group of one amino acid and the $\alpha$-carboxyl group of another, eliminating one $\text{H}_2\text{O}$ molecule to form an amide bond ($-\text{CO-NH-}$).

What three repeating atoms constitute the backbone of any polypeptide chain?

$\text{N-C}_\alpha\text{-C}$.

Which two distinct terminal chemical poles characterize every polypeptide chain?

The $\text{N}$-terminus (amino terminus) and the $\text{C}$-terminus (carboxy terminus).

What structural feature provides flexibility to the polypeptide backbone to permit folding?

Rotation of chemical groups around the covalent bonds ($\text{C}_\alpha\text{-CO}$, $\text{NH-C}_\alpha$, and $\text{NH-CO}$), forming three dihedral (torsion) angles.

What defines the primary structure of a protein, and what bonds stabilize it?

The linear sequence of amino acids encoded by the corresponding gene, stabilized by covalent peptide bonds.

What chemical interaction stabilizes regular secondary structures such as $\alpha$-helices and $\beta$-pleated sheets?

Hydrogen bonds formed between the carbonyl oxygen ($\text{C=O}$) and amide nitrogen ($\text{N-H}$) of the polypeptide backbone.

What is the specific hydrogen-bonding pattern that stabilizes an $\alpha$-helix?

A hydrogen bond forms between the $\text{C=O}$ of an amino acid at position $n$ and the $\text{N-H}$ of another amino acid at position $n+3$ (or $n+4$).

Describe the higher-order structural organization of collagen fibers in connective tissue.

Collagen consists of $50\text{ nm}$ fibers that result from the assembly of $300$ triple-helical molecules ($1.5\text{ nm}$ in diameter each) covalently cross-linked via lysine residues.

What special structural property does elastin confer to blood vessels and lungs?

It forms an irregularly, covalently interconnected network of polypeptide chains that provides elasticity, allowing stretching and recoil.

What defines the tertiary structure of a protein?

The three-dimensional conformation achieved by the folding back of helical and nonhelical secondary structures into a compact globular, fibrous, or ovoid shape.

Name the four types of interactions that stabilize the tertiary structure of proteins.

Hydrophobic interactions, hydrogen bonds, ionic bonds (salt bridges), and covalent disulfide bridges.

Between which amino acid residues are covalent disulfide linkages formed?

Between two distant cysteine residues via their sulfhydryl ($-\text{SH}$) side chains.

What is protein denaturation, and what physical or chemical factors cause it?

The unfolding and loss of secondary and tertiary structural organization caused by extremes of $\text{pH}$, high temperature, detergents, or urea.

What constitutes the quaternary structure of a protein?

The specific spatial assembly and orientation of two or more individual polypeptide chains (subunits), stabilized predominantly by weak noncovalent bonds.

Describe the subunit composition of adult functional hemoglobin.

It is a tetrameric protein composed of two $\alpha$ globin subunits and two $\beta$ globin subunits ($2\alpha 2\beta$), each containing a heme group.

What is an allosteric site on a protein?

A regulatory binding site distinct from the active/catalytic site that specifically binds a ligand, inducing a reversible conformational change that activates or inactivates the protein.

Distinguish between a holoprotein (apoprotein) and a heteroprotein.

A holoprotein consists exclusively of amino acids, whereas a heteroprotein contains polypeptide chains linked to a non-amino acid prosthetic group (e.g., lipid, carbohydrate, nucleic acid, or heme).

Which metal ion occupies the center of the heme ring in hemoglobin?

Iron ($\text{Fe}$).

What is the general empirical chemical formula for simple monosaccharides?

$\text{C}_n\text{H}_{2n}\text{O}_n$, where $n$ typically ranges between $3$ and $6$.

What is the fundamental functional group distinction between aldoses and ketoses?

Aldoses contain a reducing aldehyde group ($-\text{CHO}$), whereas ketoses contain a reducing ketone group ($\text{C=O}$).

Name the two simplest triose sugars produced during glycolysis and the Calvin cycle.

Glyceraldehyde (an aldose) and dihydroxyacetone (a ketose).

What is the structural difference between pyranose and furanose ring forms of carbohydrates?

Pyranoses are six-membered rings (e.g., glucose), while furanoses are five-membered rings (e.g., ribose and fructose).

How do $\alpha$ and $\beta$ cyclic sugar anomers differ structurally?

The newly formed hydroxyl group on the anomeric carbon is directed downward relative to the ring plane in the $\alpha$ anomer and upward in the $\beta$ anomer.

What modification converts glucose into glucosamine and $\text{N}$-acetylglucosamine?

Replacing the hydroxyl group at carbon $2$ with an amino group yields glucosamine; subsequent addition of an acetyl group to the amino nitrogen yields $\text{N}$-acetylglucosamine.

How is a uronic acid formed from an aldose sugar?

By the oxidation of the terminal alcohol group ($-\text{CH}_2\text{OH}$) into a carboxylic acid group ($-\text{COOH}$), such as converting glucose to glucuronic acid.

What is sialic acid ($\text{N}$-acetylneuraminic acid or NANA), and where does it attach during protein maturation?

A negatively charged modified sugar derived from $\text{N}$-acetylmannosamine, added to lipids and proteins in the Golgi apparatus during glycosylation.

What type of covalent linkage joins two monosaccharide units in a disaccharide?

A glycosidic bond.

Name the specific monosaccharide components of sucrose (saccharose), lactose, and maltose.

Sucrose consists of glucose and fructose; lactose consists of glucose and galactose; maltose consists of two glucose molecules.

Compare the monomer composition and linkage of glycogen and cellulose.

Glycogen is a branched polymer of $\alpha\text{-D-}$glucose containing $\alpha(1\rightarrow 4)$ and $\alpha(1\rightarrow 6)$ bonds; cellulose is an unbranched polymer of $\beta\text{-D-}$glucose joined by $\beta(1\rightarrow 4)$ glycosidic bonds.

What homopolysaccharide makes up the exoskeleton of insects and crustaceans?

Chitin (an unbranched polymer of $\text{N}$-acetylglucosamine).

What repeating disaccharide units compose hyaluronan (hyaluronic acid)?

$\text{D}$-glucuronic acid and $\text{N}$-acetylglucosamine.

What repeating disaccharide units compose chondroitin sulfate?

$\text{D}$-glucuronic acid and $\text{N}$-acetylgalactosamine.

What repeating units compose keratan sulfate, and where does it occur?

$\text{D}$-galactose and $\text{N}$-acetylglucosamine; it occurs in cartilage and the cornea.

What percentage of the cell dry weight is typically represented by lipids?

$10\%$ to $15\%$ (except in adipose tissue).

What defines a saponifiable lipid versus a nonsaponifiable lipid?

Saponifiable lipids contain fatty acids capable of forming soap salts upon alkaline hydrolysis; nonsaponifiable lipids (such as steroids and terpenes) do not contain fatty acids.

What is the general chemical formula of naturally occurring fatty acids?

$\text{CH}_3\text{-(CH}_2\text{)}_n\text{-COOH}$, where $n$ is an even number ranging from $2$ to $20$.

What physical property distinguishes saturated from polyunsaturated fatty acids at room temperature?

Fats rich in saturated fatty acids are solid (e.g., butter, animal fat), whereas unsaturated fatty acids with double bonds are liquid oils.

Identify the number of carbon atoms and double bonds in palmitic acid and stearic acid.

Palmitic acid has $16$ carbons ($16:0$); stearic acid has $18$ carbons ($18:0$).

How many double bonds and carbon atoms are present in arachidonic acid?

$20$ carbon atoms and $4$ double bonds ($20:4$).

What is the chemical composition of a triglyceride (neutral fat)?

One molecule of glycerol esterified with three fatty acid molecules.

What chemical feature confers amphipathic properties to glycerophosphatides?

Two hydrophobic fatty acids esterified to carbons $1$ and $2$ of glycerol, and a polar hydrophilic phosphate group (often linked to a polar head group) at carbon $3$.

Name the four common polar molecules esterified to phosphatidic acid in membrane phospholipids.

Choline, serine, ethanolamine, and inositol.

What amino-alcohol forms the backbone of sphingolipids instead of glycerol?

Sphingosine.

What is a ceramide?

A sphingosine molecule with a fatty acid linked to its amino ($-\text{NH}_2$) group.

What is the major sphingophospholipid abundant in the myelin sheath of nerve cells?

Sphingomyelin (ceramide esterified with phosphorylcholine).

Distinguish between cerebrosides and gangliosides.

Cerebrosides are neutral glycolipids containing a single monosaccharide (glucose or galactose); gangliosides contain complex branched oligosaccharides with one or more sialic acid (NANA) residues.

What is a ceride, and where does it naturally occur?

An ester of a fatty acid with a high molecular weight fatty alcohol (e.g., cetylic alcohol with palmitic acid); abundant in cork, plant cuticles, and bee wax.

From which $20$-carbon fatty acid do eicosanoids (prostaglandins and leukotrienes) derive?

Arachidonic acid.

What five-carbon building unit polymerizes to form terpenes?

Isoprene ($\text{CH}_2\text{=C(CH}_3\text{)-CH=CH}_2$).

Name three fat-soluble vitamins and two plant pigments that belong to the terpene family.

Vitamins $\text{A, E,}$ and $\text{K}$; pigments include lycopene and $\beta$-carotene.

What four-ring hydrocarbon nucleus forms the core structure of all steroids?

Perhydrocyclopentanophenanthrene (three fused cyclohexanes and one cyclopentane).

How does cholesterol act as a bidirectional regulator of membrane fluidity?

At high temperatures, it stabilizes membranes and restrains phospholipid movement; at low temperatures, it intercalates between phospholipids to prevent them from clustering and freezing.

What structures do amphipathic phospholipids form when dispersed in water?

Micelles, lipid monolayers, planar bilayers, and closed spherical liposomes.

What is the primary thermodynamic driving force that stabilizes lipid bilayers in water?

Hydrophobic interactions (the exclusion of nonpolar hydrocarbon tails from contact with water).

What three chemical components make up a single nucleotide?

A nitrogenous base (purine or pyrimidine), a pentose sugar (ribose or deoxyribose), and one to three phosphate groups.

Which nitrogenous bases are two-ring purines, and which are single-ring pyrimidines?

Adenine ($\text{A}$) and guanine ($\text{G}$) are purines; cytosine ($\text{C}$), thymine ($\text{T}$), and uracil ($\text{U}$) are pyrimidines.

What is the structural difference between ribose and $2'\text{-deoxyribose}$?

$2'\text{-deoxyribose}$ lacks a hydroxyl group ($-\text{OH}$) on carbon atom number $2'$, possessing only hydrogen.