Cell Structure and Function

Cell Structure and Function

Unit 2.1 Overview

  • Focus on the contribution of cell components to overall cell function.

Learning Objective 2.1.A

  • Explain how the structure and function of subcellular components and organelles contribute to the function of cells.

BIG IDEA 4: Systems Interactions

  • Biological systems interact, and these systems and their interactions exhibit complex properties.

Detailed Learning Objectives and Essential Knowledge

Essential Knowledge 2.1.A.1

  • Ribosomes:

    • Composed of ribosomal RNA (rRNA) and proteins.

    • Non-membrane structures found in all life forms, indicating common ancestry.

    • Function: Synthesize proteins based on messenger RNA (mRNA) sequences.

Essential Knowledge 2.1.A.2

  • Endomembrane System:

    • Comprises membrane-bound organelles (endoplasmic reticulum (ER), Golgi complex, lysosomes, vacuoles, and transport vesicles).

    • Functions to modify, package, and transport polysaccharides, lipids, and proteins intercellularly.

Essential Knowledge 2.1.A.3

  • Endoplasmic Reticulum (ER):

    • Rough ER:

    • Studded with ribosomes.

    • Important for protein synthesis and modification.

    • Smooth ER:

    • Involved in lipid synthesis and detoxification.

    • Exclusion Statement: Detailed functions of specialized cells in smooth ER are beyond the AP Exam scope.

Essential Knowledge 2.1.A.4

  • Golgi Complex:

    • A series of flattened membrane sacs.

    • Functions include:

    • Folding and modifying proteins.

    • Packaging proteins for trafficking.

    • Exclusion Statement: Specific phospholipid synthesis and enzyme packaging details are beyond the AP Exam scope.

Essential Knowledge 2.1.A.5

  • Mitochondria:

    • Contains a double membrane.

    • Enables compartmentalization for metabolic reactions in aerobic respiration.

    • Inner membrane is convoluted with folds to increase ATP synthesis efficiency.

Essential Knowledge 2.1.A.6

  • Lysosomes:

    • Membrane-enclosed sacs that contain hydrolytic enzymes.

    • Function: Digestion of materials and involvement in apoptosis (programmed cell death).

Essential Knowledge 2.1.A.7

  • Vacuoles:

    • Membrane-bound sacs with various functions:

    • In plant cells: Large vacuole for turgor pressure and storage.

    • In animal cells: Smaller vacuoles for storage of materials.

Essential Knowledge 2.1.A.8

  • Chloroplasts:

    • Double-membrane organelles found in plants and photosynthetic algae.

    • Location of photosynthesis.

Organelles Summary

  • Organelles: Various structures within cells, categorized as either non-membrane-bound or membrane-bound.

Non-membrane Bound Organelles:

  • Ribosomes, Cell Membrane, Cytoplasm, Cell Wall, Cytoskeleton.

Membrane-bound Organelles:

  • Nucleus, Vacuole, Mitochondria, Chloroplast, Golgi Apparatus, Endoplasmic Reticulum, Lysosomes, Peroxisomes.

Cell Membrane and Cell Wall

  • Cell Membrane:

    • Structure: Phospholipid bilayer regulating entry/exit and offering protection.

    • Functions as a permeability barrier for certain substances.

  • Cell Wall:

    • Rigid structure made of carbohydrates found in plants, fungi, and bacteria.

    • Provides structural support and protection against osmotic lysis.

Ribosome Structure

  • Composed of rRNA and proteins, functioning in protein synthesis by reading mRNA sequences.

    • Can be found free-floating in the cytoplasm or attached to rough ER.

Cytoplasm and Cytoskeleton

  • Cytoplasm:

    • Composed mainly of water, salt, and nutrients; site for many metabolic reactions.

  • Cytoskeleton:

    • Maintains cell shape and aids in transport with components like actin and microtubules.

Centriole and Spindle Fibers

  • Centriole Functions:

    • Involved in mitosis/meiosis by forming spindle fibers that assist in chromosome separation.

Flagella and Cilia

  • Aid in cellular movement:

    • Flagella: Long, propeller-like structures.

    • Cilia: Shorter, bead-like structures.

Membrane-bound Organelles

  • Nucleus: Houses DNA, site of transcription and rRNA synthesis.

  • Nucleolus: Responsible for ribosome synthesis.

  • Smooth vs. Rough ER:

    • Smooth ER: Lipid synthesis and detoxification;

    • Rough ER: Protein synthesis and folding.

  • Golgi Apparatus: Functions in folding, modifying, and packaging proteins/lipids into vesicles for transport.

Pathways of Protein Secretion:

  • Memory aid:REGVC (Ribosomes, ER, Golgi, Vesicles, Cell Membrane).

Lysosomes and Peroxisomes

  • Peroxisomes:

    • Involved in lipid hydrolysis and breaking down hydrogen peroxide.

  • Lysosomes:

    • Contain hydrolytic enzymes involved in digestion; contribute to apoptosis.

Vacuoles

  • Store fluids/biomolecules and cellular waste.

    • In plants: Large vacuoles maintain turgor pressure.

    • In animals: Smaller vacuoles for various storage functions.

Mitochondria

  • Key role in ATP production via aerobic respiration.

    • Structure: Double-membrane structure, with inner membrane being highly convoluted for increased surface area.

Chloroplasts

  • Key site for photosynthesis in plant cells.

    • Contains thylakoid membranes organized in stacks (grana) to maximize surface area for light reactions.

Study Questions and Practice

  • Engage with questions about cell structure and functions to reinforce comprehension, such as the impact of organelles on homeostasis and membrane permeability assessment in experimental scenarios.

Cell Transport Summary

Membrane Transport Mechanisms:

  • Passive Transport: High to low concentration without energy input.

  • Active Transport: Low to high concentration requiring energy (ATP).

  • Endocytosis/Exocytosis: Bulk transport mechanisms requiring energy to move large substances.

Diffusion Principles:

  • Concentration Gradient: Movement from high to low concentration areas.

  • Molecular Energy: Natural vibration and movement of molecules.

  • Dynamic Equilibrium: Achieved when net movement of molecules is zero.

Osmosis and Tonicity:

  • Osmosis: Movement of water across membranes influenced by solute concentrations.

  • Tonicity: Refers to the relative concentration of solutes in solutions affecting cell water movement.

  • Types of tonicity:

    • Hypotonic: Low solute concentration, water enters cells.

    • Hypertonic: High solute concentration, water exits cells.

    • Isotonic: Equal solute concentration, no net water movement.

Water Potential Equation:

  • Ψ = Ψp + Ψs

    • Ψ: Water potential

    • Ψ_p: Pressure potential

    • Ψs: Solute potential ✍️ (Solute potential calculated as Ψs = -iCRT, where i is the ionization constant, C is molar concentration, R is pressure constant, T is temperature in Kelvin).

Cellular Compartmentalization and Its Importance

Learning Objectives 2.9.A and 2.10.A

  • Describe membrane-bound structures and explain compartmentalization in eukaryotic/prokaryotic cells.

Compartmentalization Benefits:

  • Enhances cellular efficiency by separating incompatible chemical reactions and providing specialized environments for various functions.

Evolution

Endosymbiotic Theory

  • Eukaryotic cells originated through a symbiotic relationship between ancestral prokaryotes and proto-prokaryotic cells, leading to the evolution of mitochondria and chloroplasts.

    • Evidence: Double membranes, similarity to prokaryotic DNA, susceptibility to antibiotics, and reproductive similarities.

Practice Questions:

  • Engage with questions about cellular structures, the endosymbiotic theory, and membrane functions to solidify understanding of cell biology concepts.