Cell Structure and Function Quiz

Cell Structure and Function

• Cells are the basic units of the body
• Cells are composed of various components

Organization of the Cell

• Cell membrane
• Cytoplasm: Contains the nucleoplasm and nucleus
• Nucleolus
• Nucleus
• Nuclear membrane

Cell Composition

• Water: 70-85%
• Ions
• Proteins: 10-20%
• Lipids: 2-95%
• Carbohydrates: 1-6%

Water

• The primary fluid medium in most cells (except fat cells)

Proteins

• Divided into two types:
  • Structural proteins: Form filaments like microtubules providing the cytoskeleton of cellular organelles
  • Functional proteins: Primarily enzymes within the cell

Lipids

• Important lipids include phospholipids and cholesterol
• Phospholipids and cholesterol primarily make up cell membranes and intracellular barriers
• Neutral fats (triglycerides) are the body's main energy storehouse in fat cells

Carbohydrates

• Little structural function in cells
• Nutritionally important, but most human cells only have 1% of their total carbohydrates, with higher percentages in muscle cells and liver cells.

Membranous Structure of the Cell

• Cell membrane
• Nuclear membrane
• Membrane of endoplasmic reticulum
• Membrane of mitochondria, lysosomes, and Golgi apparatus

Cell Membrane

• Thin, pliable, elastic structure
• 7.5-10 nanometers thick
• Composed of proteins and lipids
  • Protein: 55%
  • Phospholipids: 25%

Cell Membrane Components: Lipids

• Barrier to water and water-soluble substances
• Organized in a phospholipid bilayer
• Hydrophilic heads, hydrophobic tails

Cell Membrane Components: Proteins

• Give specificity to the membrane
• Defined by association with the lipid bilayer
  • Integral proteins: Channels, pores, carriers, enzymes, receptors
  • Peripheral proteins: Enzymes, intracellular signal mediators, controllers of substance transport

Cell Membrane Components: Carbohydrates

• Glycolipids (approximately 10%)
• Glycoproteins (majority of integral proteins)
• Proteoglycans (carbohydrates bound to protein cores)
• Glycocalyx: Loose carbohydrate coat on the outside cell surface and is involved in cell-cell attachments/interactions, immune reactions, acts as a receptor for hormones like insulin and has a negative charge

Cytoplasm and its Organelles

• Cytosol: The clear fluid portion of cytoplasm that disperses particles within it
• Particles dispersed in cytoplasm include:
  • Neutral fat globules
  • Glycogen granules
  • Ribosomes
  • Secretory vesicles
  • Other organelles

Cell Organelles (Diagram)

• Centrioles
• Secretory granules
• Microtubules
• Nuclear membrane
• Mitochondrion
• Golgi apparatus
• Smooth endoplasmic reticulum
• Granular endoplasmic reticulum
• Microfilaments
• Nucleus
• Nucleolus
• Glycogen
• Ribosomes
• Lysosome

Endoplasmic Reticulum (ER)

• Network of tubules and vesicles similar to plasma membrane
• Space inside the tubules is the endoplasmic matrix
  • Granular ER: Ribosomes on outer membrane, proteins extruded into the ER matrix for processing, e.g. folding, cross-linking, glycosylation, and cleavage
  • Smooth ER: Has no ribosomes, site of lipid synthesis (phospholipids and cholesterol), and generates transport vesicles for Golgi apparatus

Golgi Apparatus

• Composed of 4+ stacked layers of flat vesicular structures
• Structurally similar to smooth ER
• Prominent in secretory cells. Secretory substances released from the side of the cell facing secretory vesicles

Golgi Apparatus Function

• Receives transport vesicles from smooth ER
• Processes substances (phosphorylation and glycosylation)
• Concentrates, sorts, and packages substances for secretion into lysosomes, secretory vesicles, or cytoplasmic component
• Substances from the ER are processed before being transported/secreted

Lysosomes

• Vesicular organelle arising from the Golgi apparatus
• Intracellular digestive system
  • Digests damaged cellular structures
  • Digests ingested food particles
  • Digests unwanted material (e.g., bacteria)
• Contains hydrolytic enzymes (acid hydrolases)

Peroxisomes

• Similar in structure to lysosomes
• Formed by self-replication
• Contain oxidases (hydrogen peroxide and catalase) for oxidizing substances like alcohol

Secretory Granules

• Vesicles in acinar cells of the pancreas

Secretion

• Secretory vesicles contain proteins synthesized in the RER
• Processes substances (e.g., phosphorylation and glycosylation)
• Types of secretion:
  • Constitutive secretion: Happens randomly
  • Stimulated secretion: Requires a trigger

Exocytosis

• Secretory vesicles diffuse through the cytosol and fuse with the plasma membrane releasing their contents.
• Lysosomes can fuse with endocytotic vesicles and facilitate digestion of internalized cell material

Mitochondria

• Powerhouse of the cell
• Function: Extract energy from nutrients
• Self-replicating
• Matrix contains large amounts of dissolved enzymes

Cytoskeleton

• Fibrillar protein
• Synthesized by ribosomes
• Polymerizes to form filaments
• Microtubules provide rigid physical structure for the cytoskeleton

Nucleus

• Control center of the cell
• Contains large amounts of DNA (genes)
• Nuclear membrane: Two separated bilayer membranes
• Nuclear membrane is penetrated by thousands of pores

Chromatin

• Condensed DNA in the nucleoplasm
• Found in nucleolus, not membrane delimited
• Contains RNA and proteins
• Functions to form subunits of ribosomes

Ingestion by the cell: Receptor-mediated endocytosis

• Endocytosis processes are receptor-mediated and driven by ATP, and involve recruitment of actin and myosin

Digestion of Substances in Pinocytotic or Phagocytic Vehicles

• Pinocytosis and phagocytosis are types of endocytosis
• Substances to be digested are enveloped and are eventually carried to lysosomes for digestion

Digestion of Substances in Phagocytosis

• Phagocytosis: Same as pinocytosis, but involves large particles (e.g., bacteria, worn-out cells)

Regression of the Tissue & Autolysis of Cells

• Tissue regresses in size, driven in part by lysosomes to remove damaged cells
• Lysosomes contain bactericidal agents that kill phagocytized bacteria
• Lysozyme and lysoferrin are involved in this process, acting at a pH of ~5

Synthesis of Cellular Structures

• Proteins formed within the granular endoplasmic reticulum using ribosomes
• Lipids formed by the smooth endoplasmic reticulum, particularly phospholipids and cholesterol.

ATP Production

• Carbohydrates, proteins, and fats are broken down into glucose, amino acids, and fatty acids
• These products are processed into Acetyl-CoA
• Acetyl-CoA reacts with O2 to produce ATP

Locomotion of Cells

• Ameboid movement
• Cilia movements
• Flagellum movement

Ameboid Movement

• Cell movement in relation to surroundings
• Pseudopodium protrusion
• Cytoplasm flow
• Actin and myosin interaction for movement
• Continual endocytosis and exocytosis

Ameboid Locomotion

• Continual membrane formation and absorption
• Endocytosis at one end and Exocytosis at the other

Ameboid Locomotion Types of Cells

• White blood cells (WBCs)
• Fibroblasts
• Embryonic cells

Cell Movement and Chemotaxis

• Movement influenced by chemical substances
• Chemotaxis is the most important initiator of ameboid movement

cilia and ciliary movements

• Cilia are hair-like structures found in the respiratory system
• Movement for clearing mucus
• ATP dependent; requires Calcium & Magnesium

Flagellum

• Much longer than cilia and moves in quasi-sinusoidal waves

Transport Across Cell Membranes

• Simple diffusion
• Carrier-mediated transport
• Facilitated diffusion
• Primary active transport
• Co-transport
• Counter-transport

Permeability

• Ease with which a solute diffuses through the membrane
• Depends on solute and membrane characteristics

Carrier Mediated Transport

• Stereospecificity for example glucose
• Saturation
• Competition

Facilitated Diffusion

• Occurs down an electrochemical gradient
• Passive
• Carrier-mediated

Primary Active Transport

• Against electrochemical gradient
• Requires energy (ATP)
• Carrier mediated

Secondary Active Transport

• Coupling of two or more solutes
• One solute moves downhill and the other one uphill

Example of Na+-glucose co-transport

• Carrier for co-transport located in luminal membrane
• Glucose transported uphill, Na+ downhill
• Energy from Na+ movement inward (gradient)
• Na+-K+ pump maintains Na+ gradient

Osmolarity

• Concentration of osmotically active particles in a solution
• Calculated using the equation Osmolarity = g X c

Osmosis

• Flow of water across a semipermeable membrane
• From low solute concentration to high solute concentration due to osmotic pressure

Test your knowledge on the fundamental concepts of cell structure and composition. This quiz covers the various components of cells, their functions, and the importance of water, proteins, lipids, and carbohydrates in cellular activities. Perfect for biology students seeking to reinforce their understanding of cellular biology.