Dal Biol 2020 Cell bio - Final exam

Q: What are the four main types of macromolecules?

A: Proteins, Polysaccharides (Carbohydrates), Lipids, and Nucleic Acids.

Q: What is the primary function of proteins?

A: Proteins perform a wide range of cellular functions and are encoded by DNA.

Q: What is the key structural feature of lipids?

A: Lipids are hydrophobic and soluble in nonpolar solvents.

Q: What are the building blocks of proteins?

A: Amino acids.

Q: How are amino acids linked in proteins?

A: By peptide bonds to form polypeptides.

Q: Name the four levels of protein structure.

A: Primary, Secondary, Tertiary, and Quaternary.

Q: What is the function of phospholipids in cells?

A: They form the cell membrane with their hydrophilic heads and hydrophobic tails.

Q: Define amphipathic.

A: Having both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts.

Q: What is the main storage carbohydrate in plants?

A: Starch.

Q: What is cellulose, and where is it found?

A: A structural polysaccharide found in the cell walls of green plants.

Q: What are nucleotides, and what are their components?

A: Nucleotides are the building blocks of nucleic acids, consisting of a nitrogenous base, a five-carbon sugar, and a phosphate group.

Q: What distinguishes DNA from RNA?

A: DNA is double-stranded and contains thymine; RNA is single-stranded and contains uracil instead.

Q: What are the two processes involved in the Central Dogma?

A: Transcription (DNA to RNA) and Translation (RNA to Protein).

Q: What causes sickle-cell disease?

A: A single amino acid substitution (valine for glutamic acid) in hemoglobin, altering protein structure and function.

Q: What is the difference between saturated and unsaturated fatty acids?

A: Saturated fatty acids have no double bonds; unsaturated fatty acids have one or more double bonds in their hydrocarbon chain.

Q: What bonds connect nucleotides in a DNA strand?

A: Phosphodiester bonds.

Q: What is the function of carbohydrates?

A: They serve as energy storage molecules and provide structural support.

Q: What is chitin, and what is its role?

A: Chitin is a long-chain polymer of N-acetylglucosamine and forms the main component of insect exoskeletons.

Q: What are the two types of nitrogenous bases in nucleotides?

A: Purines (Adenine, Guanine) and Pyrimidines (Cytosine, Thymine/Uracil).

Q: How is the DNA double helix structured?

A: Two antiparallel strands of nucleotides coil around each other, with complementary base pairing (A-T and G-C).

Q: What are the two main processes in protein synthesis?

A: Transcription (DNA → RNA) and Translation (RNA → Protein).

Q: Where does transcription occur, and what enzyme catalyzes it?

A: Transcription occurs in the nucleus and is catalyzed by RNA polymerase.

Q: What is the central dogma of molecular biology?

A: DNA → RNA → Protein.

Q: What is the role of the TATA box in transcription?

A: It is a DNA sequence that signals RNA polymerase to start transcription, recognized by TATA-binding proteins.

Q: What is the difference between introns and exons?

A: Introns are non-coding regions removed during RNA splicing; exons are coding regions that remain in the final mRNA.

Q: What is the function of spliceosomes?

A: They remove introns and connect exons to form mature mRNA.

Q: How does mRNA leave the nucleus?

A: Through the Nuclear Pore Complex (NPC).

Q: What are the two subunits of a ribosome, and what do they do?

A: Small Subunit: Matches mRNA codons with tRNA anticodons. Large Subunit: Contains the active site for peptide bond formation.

Q: What is the role of tRNA in translation?

A: tRNA acts as an adaptor, pairing its anticodons with mRNA codons and delivering the corresponding amino acids.

Q: What is a codon, and how many nucleotides does it contain?

A: A codon is a three-nucleotide sequence on mRNA that codes for one amino acid.

Q: What is the start codon, and what amino acid does it code for?

A: The start codon is AUG, and it codes for methionine.

Q: What signals the end of translation?

A: A stop codon (UAA, UAG, UGA) and a translation termination factor.

Q: Why is a nucleus important in eukaryotic cells?

A: It prevents unprocessed mRNA from being prematurely translated.

Q: What happens during RNA splicing?

A: Introns are removed, and exons are joined to create mature mRNA.

Q: What is the function of rRNA in ribosomes?

A: It forms the ribosome's structural core and catalyzes peptide bond formation.

Q: What is the role of the nuclear pore complex (NPC)?

A: It regulates the movement of mRNA, proteins, and ribosomes between the nucleus and cytoplasm.

Q: How is translation faster in bacteria compared to eukaryotes?

A: Bacteria lack a nucleus, so transcription and translation occur simultaneously.

Q: What allows one gene to code for multiple proteins?

A: RNA splicing, which can produce different mRNA variants from the same gene.

Q: What are the two main functions of lipids?

A: Membrane formation and energy storage.

Q: What does it mean for lipids to be amphipathic?

A: They have both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions.

Q: What are triacylglycerols (TAGs), and where are they synthesized?

A: TAGs are energy-storing lipids synthesized in the smooth ER.

Q: What enzymes are involved in TAG synthesis?

A: Acyltransferases, which move fatty acids, and acyl-CoA, the fatty acid donor.

Q: What are lipid droplets (LDs), and where do they originate?

A: LDs are storage organelles for TAGs and sterols that originate from the smooth ER.

Q: What is the structural composition of lipid droplets?

A: A hydrophobic core of neutral lipids and a single-layer phospholipid monolayer.

Q: What protein assists in lipid droplet formation?

A: Seipin, which facilitates budding from the ER.

Q: What are perilipins, and what is their role?

A: Perilipins are proteins that coat lipid droplets and regulate their function.

Q: What is the starting point for phospholipid synthesis?

A: Phosphatidic acid, the smallest phospholipid.

Q: How is phosphatidic acid used to make TAGs or phospholipids?

A: Remove the phosphate group to make TAGs. Retain the phosphate group to form phospholipids.

Q: What organelle contains enzymes for phospholipid synthesis?

A: The endoplasmic reticulum (ER).

Q: What is PIP2, and where is it found?

A: PIP2 (phosphatidylinositol 4,5-bisphosphate) is a signaling phospholipid found in the cell membrane.

Q: How do lipid droplets grow?

A: By synthesizing more TAG locally or fusing with other lipid droplets.

Q: What distinguishes TAGs from phospholipids?

A: TAGs store energy in lipid droplets, while phospholipids form structural components of membranes.

Q: Why are lipid droplets important for cells?

A: They store neutral lipids like TAGs and sterols and interact with organelles via membrane proteins.

Q: What are the three classifications of cells?

A: Bacteria, Archaea, and Eukaryotes.

Q: What distinguishes eukaryotic cells from prokaryotic cells?

A: Eukaryotic cells have membrane-bound organelles, including a nucleus; prokaryotic cells do not.

Q: What is the main function of the nucleus?

A: Stores DNA as chromatin and is the site of transcription (DNA → mRNA).

Q: What is the function of the Nuclear Pore Complex (NPC)?

A: Allows transport of mRNA and proteins between the nucleus and cytoplasm.

Q: What processes occur in mitochondria?

A: TCA cycle (Krebs cycle) and electron transport chain (ETC) to generate ATP.

Q: What is unique about mitochondria and chloroplasts compared to other organelles?

A: They contain their own DNA (mtDNA for mitochondria, cpDNA for chloroplasts) and replicate independently.

Q: What is the function of chloroplasts?

A: Perform photosynthesis (CO₂ + light → sugars) and fix carbon in the stroma.

Q: What are the two types of ER, and what are their functions?

A: Rough ER: Synthesizes proteins. Smooth ER: Synthesizes lipids and steroids and detoxifies substances.

Q: What does the Golgi apparatus do?

A: Modifies, tags, and sorts proteins into vesicles for secretion or transport.

Q: What is the function of lysosomes?

A: Contain pH-sensitive enzymes to degrade and recycle cellular molecules.

Q: What enzyme is found in peroxisomes, and what is its function?

A: Catalase, which breaks down hydrogen peroxide (H₂O₂) into water and oxygen.

Q: What are lipid droplets, and where do they originate?

A: Lipid droplets are storage organelles for neutral lipids and originate from the smooth ER.

Q: What proteins are involved in lipid droplet formation and regulation?

A: Seipin helps budding from the ER, and perilipins coat lipid droplets to regulate them.

Q: What is the role of ribosomes in the cell?

A: Translate mRNA into proteins using tRNA.

Q: What are the main components of the extracellular matrix (ECM)?

A: Collagen, proteoglycans, fibronectin, and laminins.

Q: What is the function of the extracellular matrix (ECM)?

A: Provides structural support, connects cells, and acts as a "glue" for tissues.

Q: How do organelles communicate within the cell?

A: Through extensive interactions and membrane contacts, forming an interconnected network.

Q: What is the main function of chloroplast thylakoids?

A: They house chlorophyll and perform the light-dependent reactions of photosynthesis.

Q: What distinguishes rough ER from smooth ER structurally?

A: Rough ER has ribosomes on its surface; smooth ER does not.

Q: What is the importance of cristae in mitochondria?

A: They increase surface area for energy production processes like the ETC.

Q: What is the fluid mosaic model?

A: It describes the membrane as a fluid bilayer of lipids with a mosaic of embedded proteins.

Q: What maintains lipid asymmetry in membranes?

A: Translocases, which move lipids between layers.

Q: What method is used to study molecule mobility in membranes?

A: FRAP (Fluorescence Recovery After Photobleaching).

Q: Name the three types of membrane proteins.

A: Integral, Peripheral, and Lipid-Anchored proteins.

Q: What distinguishes integral membrane proteins?

A: They span the bilayer (transmembrane) or embed into one side of the membrane (monotopic).

Q: What are examples of integral membrane proteins?

A: GLUT transporters, calcium pumps, and acetylcholine receptors.

Q: How do peripheral membrane proteins associate with the membrane?

A: They form reversible, weak bonds with integral proteins or the membrane surface.

Q: How are lipid-anchored proteins attached to the membrane?

A: They are covalently linked to fatty acids or isoprenyl groups that insert into the bilayer.

Q: What is glycosylation, and where does it occur?

A: The attachment of carbohydrates to proteins or lipids, occurring on the extracellular side of the membrane.

Q: Name two types of glycosylation and the amino acids involved.

A: O-linked: Serine (Ser) or Threonine (Thr). N-linked: Asparagine (Asn).

Q: What role do membrane proteins play in signaling?

A: They detect external signals (e.g., insulin) and transmit them inside the cell.

Q: What proteins mediate cell adhesion?

A: Cadherins, which connect cells to each other.

Q: What are the main functions of transmembrane proteins?

A: Transport ions, detect signals, and facilitate molecule movement across membranes.

Q: What is the role of glycosylation in membranes?

A: It helps in cell-cell recognition and protects the cell surface.

Q: What types of post-translational modifications help anchor proteins to membranes?

A: Lipophilic modifications like GPI anchors and isoprenyl groups.

Q: How do membrane proteins contribute to ion transport?

A: They undergo conformational changes to pump ions across the membrane (e.g., calcium pump).

Q: What is the difference between peripheral and integral proteins?

A: Peripheral proteins associate temporarily, while integral proteins are embedded within the membrane.

Q: What distinguishes monotopic integral proteins?

A: They embed in only one side of the membrane and often catalyze hydrophobic reactions.

Q: Why is the membrane called "asymmetric"?

A: Lipid and protein compositions differ between the inner and outer layers.

Q: What is an example of a lipid-anchored protein?

A: Trehalase, which is bound to glycosylphosphatidylinositol (GPI).

Q: What types of molecules can diffuse freely across membranes?

A: Small, uncharged molecules like oxygen and carbon dioxide.

Q: Which types of molecules cannot diffuse freely across membranes?

A: Large polar molecules and charged ions.

Q: What is facilitated diffusion?

A: Protein-mediated movement of molecules down a concentration gradient, requiring no energy (ATP).

Q: Name the two main types of proteins involved in facilitated diffusion.

A: Channels and carriers.

Q: How do carrier proteins transport molecules?

A: By undergoing conformational changes to move solutes across the membrane.

Q: What are the three types of carrier proteins?

A: Uniporters: Transport one molecule. Symporters: Transport two molecules in the same direction. Antiporters: Transport two molecules in opposite directions.

Q: What is an example of a symporter?

A: LacY, which transports lactose and H⁺ into the cell.