Cell Biology Quiz

Cell Organization

• Protoplasm: collective name for all substances within a cell
• Cell membrane encloses the cell
• Cytoplasm surrounds the nucleus
• Nucleoplasm is inside the nucleus
• Nucleus contains the nucleolus
• Nuclear membrane surrounds the nucleolus

Cell Composition

• Protoplasm (of cells)
• Water/Ions: 70-85% of cell mass

Cell Membrane: Bilayer of Phospholipids with Proteins

• Bilayer of phospholipids with proteins
• Extracellular fluid surrounds the cell
• Cytoplasm (the interior of the cell)
• Integral proteins traverse the bilayer
• Peripheral proteins are associated with the surface

Membrane Components: Lipids

• Barrier to water and water-soluble substances
• Organized in a phospholipid bilayer
• Molecules like CO₂, O₂, glucose, urea, and halothane pass through.
• Hydrophilic heads face outward, hydrophobic tails inward

Membrane Components: Proteins

• Provide specificity to the membrane
• Defined by association with the lipid bilayer
• Integral proteins: channels, pores, carriers, enzymes
• Peripheral proteins: inside the cell, help with signal mediation and enzymes

Membrane Components: Carbohydrates

• Glycolipids (approx. 10%)
• Glycoproteins (majority of integral proteins)
• Proteoglycans
• Glycocalyx: Negative charge repels other negative charges, involved in cell-cell interactions
• Acts as receptors for hormones like insulin, plays a role in immune responses

Cholesterol

• Present in membranes in varying amounts
• Generally decreases membrane fluidity and permeability (except in plasma membrane)
• Increases membrane flexibility and stability

Cell Organelles

• Centrioles,
• Secretory granules,
• Microtubules,
• Nuclear membrane,
• Chromosomes and DNA
• Golgi apparatus,
• Cell membrane,
• Nucleolus,
• Glycogen,
• Ribosomes,
• Lysosomes
• Mitochondrion,
• Granular endoplasmic reticulum
• Smooth endoplasmic reticulum
• Microfilaments

Membranous Structures of the Cell

• Cell membrane
• Nuclear membrane
• Endoplasmic reticulum membrane
• Mitochondria membrane
• Lysosomes
• Golgi apparatus

Cell Membrane

• Thin, pliable, elastic structure
• About 7.5-10 nanometers thick
• Composed mostly of proteins and lipids
• Approximate composition: 55% protein, 25% phospholipids, 13% cholesterol, 4% other lipids, and carbohydrates

Cytoplasm and its Organelles

• Cytosol: jelly-like fluid portion in the cytoplasm
• Contains dissolved proteins, electrolytes
• Various dispersed structures: neutral fat globules, glycogen granules, ribosomes, secretory vesicles
• Important organelles: endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, peroxisomes

The Endoplasmic Reticulum

• Network of tubular and flat vesicular structures
• Membrane similar to the plasma membrane
• Space inside tubules is the endoplasmic matrix

Rough or Granular ER

• Outer membrane surface covered with ribosomes
• Newly synthesized proteins extruded into the ER matrix
• Proteins are processed, crosslinked, folded, glycosylated (N-linked), cleaved inside the matrix

Smooth ER

• Site of lipid synthesis: phospholipids, cholesterol
• Growing ER membrane buds continually forming transport vesicles which migrate to the Golgi apparatus

The Golgi Apparatus

• Membrane composition similar to smooth ER and plasma membrane
• Composed of 4-or more stacked layers of flat vesicular structures
• Receives transport vesicles from smooth ER
• Substances formed in the ER are processed, phosphorylated, or glycosylated
• Substances concentrated, sorted, and packaged for secretion

Exocytosis

• Secretory vesicles diffuse through cytosol and fuse with the plasma membrane
• Lysosomes fuse with internal endocytotic vesicles

Secretion

• Secretory vesicles release synthesized proteins from Golgi apparatus to fuse with the plasma membrane
• Constitutive secretion occurs randomly
• Stimulated secretion requires a trigger

Lysosomal Storage Diseases

• Absence of one or more hydrolases: not synthesized, inactive, not properly sorted and packaged
• Result: Lysosomes engorged with undigested substrate
• Examples: Acid lipase A deficiency, I-cell disease, Tay-Sachs disease

Lysosomes

• Vesicular organelles formed from Golgi buds
• Contain hydrolytic enzymes (acid hydrolases): phosphatases, nucleases, proteases, lipid-degrading enzymes, lysozymes (bacteria digesting enzymes)
• Responsible for digestion.

Peroxisomes

• Similar physically to lysosomes
• Two major differences: formed by self-replication, contain oxidases
• Function: Oxidize substances (e.g., alcohol)

Secretory Granules

• These are secretory vesicles.
• Function in cells which release substances.

Mitochondria

• Primary function: extraction of energy from nutrients
• Has an outer membrane which encloses an inner membrane (crests) and an outer chamber.
• The matrix contains oxidative phosphorylation enzymes which produce energy.

The Cytoskeleton

• Intermediate filaments: comprised of cell-specific fibrillar proteins
• Microtubules: heterodimers (of alpha and beta tubulin), part of the spindle fibers/axoneme structure
• Thin filaments: F-actin, part of "stress fibers"
• Thick filaments: myosin

The Nuclear Membrane

• Permeated by thousands of nuclear pores
• 100nm in diameter, with functional diameter of 9nm
• Selectively permeable to molecules up to 44,000 MW

Nucleolus

• One or more per nucleus
• Contains RNA and proteins
• Not membrane delimited
• Functions to form granular subunits of ribosomes

Comparison of Animal Cells with Precellular Forms of Life

• Comparison of sizes

Receptor-mediated Endocytosis

• Molecules attach to cell surface receptors; receptors concentrated in clathrin-coated pits
• Receptor binding causes invagination
• ATP-dependent recruitment of actin and myosin

Digestion of Substances in Pinocytotic or Phagocytic Vesicles

• Process by which lysosomes digest substances in vesicles
• The substances are broken down by enzymes after fusing with a lysosome.

Pinocytosis

• Vesicle that engulfs extracellular fluid

Endocytosis

• Active movement of substances into a cell inside membrane-bound vesicles

Phagocytosis

• Specific form of endocytosis in specialized cells (phagocytes)
• Occurs in response to microbes, dead cells, and cellular debris
• Receptors on phagocyte surface bind to particles
• Plasma membrane extensions (pseudopods) surround the particles
• Vesicle forms (phagosome)
• The phagosome fuses with a lysosome to digest enzymes

ATP Production

• Carbohydrates, Glucose, proteins and fats are converted to produce ATP (energy).
• Acetyl CoA is used in step 3 to generate ATP.

The Use of ATP for Cellular Function

• ATP is crucial for cell processes
• It fuels membrane transport, chemical compound synthesis, and mechanical work

Ameboid Locomotion

• Continual endocytosis at the "tail" and exocytosis at the leading edge of the pseudopodium
• Movement facilitated by receptor proteins and actin/myosin interactions (ATP-dependent)

Chemotaxis

• Cell movement influenced by chemical substances
• Movement toward high concentrations
• Movement away from low concentrations

Cilia and Ciliary Movements

• Occurs in airway and fallopian tubes
• Each cilium is made of microtubules: 9 double tubules, 2 single tubules; an outgrowth of basal bodies and covered by membrane; movement is ATP dependent

Mechanism of Ciliary Movement

• Four stages involved in producing ciliary movement.
• Fifth, there are multiple protein arms which are activated by adenosine triphosphate (ATP).
• The double tubule moves in a specific direction to generate movement.

Non-motile Primary Cilia

• Found on nearly every cell type (except red blood cells)
• Non-motile cilia act as antenna
• Involved in chemical and mechanical sensations to coordinate cellular signaling, cell growth, and signal transduction