DTU Life Science Questions Slide 1- Cells: Structure and Function

Vocabulary practice flashcards covering cell structure, protein organization, organelles, and core biological concepts from DTU Life Science Lecture 1.

Protein (protein)

A biological macromolecule composed of one or more folded polypeptide chains of amino acids (aminosyrer) linked by peptide bonds (peptidbindinger), performing catalytic, structural, transport, and signaling functions.

Amino acid (aminosyre)

An organic molecule containing a central $\alpha$-carbon ($\alpha$-carbon) bonded to a hydrogen atom, an amino group ($\text{-NH}_3^+$), a carboxyl group ($\text{-COO}^-$), and a variable side chain (sidekæde) or R-group (R-gruppe).

Peptide bond (peptidbinding)

A covalent amide linkage formed between the carboxyl group ($\text{-COO}^-$) of one amino acid and the amino group ($\text{-NH}_3^+$) of another through a condensation reaction.

N-terminus (N-terminus)

The starting end of a polypeptide chain (polypeptidkæde) featuring a free amino group ($\text{-NH}_3^+$) on the first amino acid residue.

C-terminus (C-terminus)

The final end of a polypeptide chain (polypeptidkæde) featuring a free carboxyl group ($\text{-COO}^-$) on the last amino acid residue.

Side chain / R-group (sidekæde / R-gruppe)

The distinct chemical structure attached to the $\alpha$-carbon ($\alpha$-carbon) of an amino acid that determines its unique chemical properties, charge, and reactivity.

Hydrophilic (hydrofil)

A chemical property of polar or charged molecules or side chains (sidekæder) that allows them to readily interact with and dissolve in water through hydrogen bonding or ionic interactions.

Hydrophobic (hydrofob)

A chemical property of non-polar molecules or side chains (sidekæder) that causes them to avoid contact with water and aggregate together in aqueous environments.

Disulfide bridge (disulfidbro)

A covalent bond ($\text{-S-S-}$) formed by the oxidation of two thiol groups ($\text{-SH}$) in cysteine (cystein) residues, stabilizing protein tertiary and quaternary structures.

Ionic bond / Salt bridge (ionbinding / saltbro)

An electrostatic attraction formed between oppositely charged amino acid side chains (sidekæder), such as a negatively charged carboxylate group and a positively charged amino group.

Hydrogen bond (brintbinding)

A weak non-covalent dipole-dipole attraction between an electronegative atom (such as oxygen or nitrogen) and a hydrogen atom covalently bonded to another electronegative atom.

Primary structure (primær struktur)

The linear, specific sequence of amino acids (aminosyresekvens) in a polypeptide chain linked exclusively by covalent peptide bonds (peptidbindinger).

Secondary structure (sekundær struktur)

Local structural arrangements along a polypeptide backbone, primarily $\alpha$-helices ($\alpha$-helixer) and $\beta$-pleated sheets ($\beta$-pladestrukturer), stabilized by backbone hydrogen bonds.

Tertiary structure (tertiær struktur)

The overall three-dimensional spatial conformation of a single polypeptide chain, stabilized by interactions among side chains (sidekæder).

Quaternary structure (kvarternær struktur)

The functional spatial assembly and association of two or more independent polypeptide chains or subunits (underenheder).

Denaturation (denaturering)

The process by which environmental factors (such as heat or extreme pH) disrupt non-covalent interactions and disulfide bridges, unfolding secondary, tertiary, and quaternary structures without breaking primary peptide bonds.

Prokaryote (prokaryot)

A single-celled organism (such as bacteria or archaea) lacking a membrane-enclosed nucleus (cellekærne) and membrane-bound organelles (organeller).

Eukaryote (eukaryot)

An organism whose cells contain a true membrane-enclosed nucleus (cellekærne) and distinct membrane-bound organelles (organeller).

Organelle (organel)

A specialized membrane-enclosed intracellular compartment that performs specific metabolic, structural, or transport functions within eukaryotic cells (eukaryoter).

Cell theory (celleteorien)

A fundamental biological principle stating that cells are the basic structural units of life, all living organisms consist of cells, and all modern cells arise from pre-existing cells.

How do the chemical properties of amino acid side chains (sidekæder) dictate the 3D folding pattern of a globular protein in an aqueous cytosol?

Hydrophobic (hydrofobe) non-polar side chains aggregate inside the protein core to minimize water exposure, while hydrophilic (hydrofile) polar or charged side chains position themselves on the outer surface to interact with surrounding water molecules.

Which specific interaction stabilizes secondary structure (sekundær struktur) motifs like the $\alpha$-helix ($\alpha$-helix) and $\beta$-pleated sheet ($\beta$-pladestruktur)?

Hydrogen bonds (brintbindinger) formed specifically along the polypeptide backbone between carbonyl oxygen atoms ($\text{C=O}$) and amino hydrogen atoms ($\text{N-H}$), independently of side chain (sidekæde) identity.

How do tertiary structure (tertiær struktur) interactions differ fundamentally from secondary structure (sekundær struktur) interactions?

Secondary structure relies exclusively on hydrogen bonding along the peptide backbone, whereas tertiary structure is driven by interactions among side chains (sidekæder), including hydrophobic interactions, ionic salt bridges, hydrogen bonds, and covalent disulfide bridges.

When a protein undergoes thermal denaturation (denaturering), which structural levels are disrupted and which level remains completely intact?

Secondary, tertiary, and quaternary structures are disrupted due to the breakdown of weak non-covalent interactions and disulfide bridges, while the primary structure (primær struktur) remains intact because covalent peptide bonds are not cleaved.

How does the side chain modification in Insulin Aspart (Pro B28 Asp) alter its quaternary structure (kvarternær struktur) to achieve rapid absorption?

Replacing Proline with negatively charged Aspartate at position B28 causes charge repulsion ($\text{-Asp}^-$ vs $\text{-Asp}^-$) at the dimer interface, promoting rapid dissociation of inactive hexamers into active monomers.

Why does an increase in cell size force a growing cell to undergo cell division (celledeling)?

As cell size increases, volume ($V \propto r^3$) grows much faster than surface area ($SA \propto r^2$), decreasing the surface area-to-volume ratio and limiting nutrient uptake and waste exchange across the plasma membrane (cellemembran).

What is the primary function of the Nucleus (cellekærne) in eukaryotic cells (eukaryoter)?

It houses the cellular genomic DNA, serves as the site for DNA replication and RNA transcription, and regulates gene expression (genekspression).

What structural feature characterizes the Rough Endoplasmic Reticulum (ru ER / RER), and what is its primary role?

It is studded with bound ribosomes (ribosomer) on its outer surface, where it synthesizes, folds, and chemically modifies nascent proteins before dispatching them in transport vesicles.

Which metabolic processes specifically take place within the Smooth Endoplasmic Reticulum (glat ER / SER)?

Synthesis of lipids and steroids (lipider og steroider), detoxification of small toxic molecules, breakdown of glycogen (glykogen) in animal cells, and storage of calcium ions ($\text{Ca}^{2+}$).

What is the key functional role of the Golgi apparatus (Golgiapparatet) within the endomembrane system (endomembransystemet)?

It receives transport vesicles from the RER, chemically modifies carbohydrate chains, packages, concentrates, and routes proteins to destinations like lysosomes, the plasma membrane, or extracellular secretion.

How do Lysosomes (lysosomer) digest cellular debris safely without degrading the surrounding cytoplasm (cytoplasma)?

They maintain an acidic internal lumen containing hydrolytic enzymes (fordøjelsesenzymer) sequestered within a membrane, allowing controlled autophagy (autofagi) and phagocytosis (fagocytose).

What structural feature of the Mitochondrion (mitokondrium) maximizes its capacity to generate ATP during cellular respiration (celleånding)?

The inner membrane folds into extensive cristae (cristae), which greatly increases the surface area for electron transport chain proteins and ATP synthase enzymes.

Where within Chloroplasts (kloroplaster) do the light harvesting reactions and carbohydrate synthesis reactions take place?

Chlorophyll pigments in thylakoid membranes (thylakoidmembraner) harvest light energy, while carbohydrate synthesis occurs using chemical energy in the surrounding fluid stroma (stroma).

What is the primary enzymatic function of Peroxisomes (peroxisomer) in cellular metabolism?

They isolate and safely neutralize toxic metabolic byproducts, specifically decomposing harmful hydrogen peroxide ($\text{H}_2\text{O}_2$) into water and oxygen using specialized enzymes like catalase.

According to the Endosymbiotic Theory (endosymbiontteorien), what were the evolutionary origins of Mitochondria and Chloroplasts?

They originated as free-living prokaryotes (fritlevende prokaryoter)—aerobic bacteria and photosynthetic cyanobacteria, respectively—that were engulfed by ancestral eukaryotic host cells and formed a permanent symbiotic relationship.

What key structural features support the Endosymbiotic Theory (endosymbiontteorien) for Mitochondria and Chloroplasts?

Both organelles possess double membranes, their own circular DNA genomes, prokaryote-like ribosomes, and the ability to divide independently within the host eukaryotic cell.

What is the sequential pathway taken by a protein destined for extracellular secretion?

Synthesis on bound ribosomes into the Rough ER (ru ER) $\rightarrow$ transport vesicle $\rightarrow$ Golgi apparatus (Golgiapparatet) $\rightarrow$ secretory vesicle $\rightarrow$ plasma membrane (cellemembran) fusion and exocytosis.

What are the distinct functional roles of bacterial flagella (flageller), pili (pili), and fimbriae (fimbrier)?

Flagella drive cellular motility/swimming; pili facilitate cell-to-cell attachment and conjugation; fimbriae are shorter projections that enable adherence to environmental surfaces and host cells.

Why does a protein isolated from human blood perform the exact same biological function as an identical protein isolated from chimpanzee blood?

Identical primary structures (aminosyresekvenser) dictate identical 3D secondary and tertiary folding patterns, producing identical active sites and chemical properties regardless of species.

How do basic side chains like Arginine (Arg / R) interact with acidic side chains like Aspartate (Asp / D) at physiological pH?

Positively charged basic amino groups ($\text{-NH}_3^+$) form ionic bonds or salt bridges (saltbroer) with negatively charged acidic carboxylate groups ($\text{-COO}^-$).

Why are non-polar amino acid side chains like Alanine (Ala / A) classified as hydrophobic (hydrofobe)?

Their hydrocarbon side chains ($\text{-CH}_3$) lack polar bonds or charged atoms, rendering them incapable of forming favorable hydrogen bonds with water molecules.

What structural component of prokaryotic cell walls distinguishes them from eukaryotic cell boundaries?

Prokaryotes possess a rigid extracellular cell wall containing peptidoglycans (peptidoglycaner) outside their plasma membrane, providing structural support against osmotic pressure.

How does the Endomembrane System (endomembransystemet) facilitate coordinate transport within eukaryotic cells?

It utilizes membrane-bound transport vesicles that continuously bud off from one organelle compartment (e.g., RER) and fuse with another (e.g., Golgi), ensuring compartmentalized processing.

What structural role do cysteine (cystein) residues play in stabilizing extracellular secreted proteins?

They undergo oxidation between their thiol side chains ($\text{-SH}$) to form covalent disulfide bridges (disulfidbroer), providing mechanical and thermal stability against denaturation.

How does the nucleolus (kernenode) within the eukaryotic nucleus contribute to protein synthesis (proteinsyntese)?

It is the specialized nuclear region responsible for transcribing ribosomal RNA (rRNA) and assembling the ribosomal subunits required for polypeptide translation.