Cell Structure and Functions

Cell Structure and Functions

General Overview

• Classification of Cells:

  • Prokaryotic Cells:

  • Lack a nucleus.

  • Example: Bacteria.

  • Simple structure.

  • Eukaryotic Cells:

  • Have a nucleus.

  • Examples: Plants, animals, fungi.

  • More complex structure.

Key Organelles and Their Functions

• Nucleus:

  • Control center of the cell.

  • Houses genetic material (DNA).

• Cytoplasm:

  • Gel-like substance within the cell membrane.

  • Contains organelles and facilitates metabolic processes.

• Mitochondria:

  • Powerhouse of the cell.

  • Responsible for energy production through cellular respiration.

• Ribosomes:

  • Sites of protein synthesis.

  • Can be found free in the cytoplasm or attached to the Rough Endoplasmic Reticulum (Rough ER).

• Endoplasmic Reticulum (ER):

  • Rough ER:

  • Studded with ribosomes.

  • Involved in protein synthesis and modification.

  • Smooth ER:

  • Lacks ribosomes.

  • Involved in lipid synthesis and detoxification processes.

• Golgi Body (Golgi Apparatus):

  • Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosomes:

  • Contain digestive enzymes.

  • Responsible for breaking down waste materials and cellular debris.

• Vacuole:

  • Storage organelle.

  • Stores substances such as water, nutrients, and waste products.

• Chloroplast:

  • Found only in plant cells.

  • Site of photosynthesis.

  • Contains chlorophyll, the pigment that captures light energy.

Cell Membrane

• Function:

  • Semi-permeable barrier.

  • Controls entry and exit of substances.

Types of Transport Across Cell Membrane

• Passive Transport:

  • No energy required.

  • Movement from areas of high concentration to low concentration.

  • Example: Diffusion, Osmosis.

• Active Transport:

  • Requires energy (ATP).

  • Movement against the concentration gradient (from low to high concentration).

Specific Processes

• Diffusion:

  • Movement of molecules from an area of higher concentration to an area of lower concentration.

• Osmosis:

  • Special case of diffusion.

  • Movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration.

Concentration Gradient:

• The difference in concentration of a substance across a space.

• Movement occurs along the gradient (high to low) in passive transport and against the gradient (low to high) in active transport.

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General Overview - Classification of Cells: - Prokaryotic Cells: - Lack a nucleus and membrane-bound organelles. - Example: Bacteria and Archaea. - Simple structure; usually much smaller ($0.1-5.0 \mu m$). - Genetic material is found in a region called the nucleoid. - Eukaryotic Cells: - Have a nucleus and membrane-bound organelles. - Examples: Plants, animals, fungi, and protists. - More complex structure; larger size ($10-100 \mu m$). ### Key Organelles and Their Functions - Nucleus: - Control center of the cell. - Houses genetic material ($DNA$) in the form of chromatin. - Contains the nucleolus, where ribosome subunits are assembled. - Surrounded by a double-layered nuclear envelope with pores. - Cytoplasm: - Gel-like substance (cytosol) within the cell membrane. - Contains organelles and facilitates metabolic processes and signal transduction. - Mitochondria: - Powerhouse of the cell. - Responsible for energy production via cellular respiration, generating $ATP$. - Features a double membrane; the inner membrane has folds called cristae to increase surface area for chemical reactions. - Ribosomes: - Sites of protein synthesis. - Composed of ribosomal $RNA$ and proteins. - Can be found free in the cytoplasm or attached to the Rough Endoplasmic Reticulum (Rough ER). - Endoplasmic Reticulum (ER): - Rough ER: - Studded with ribosomes. - Involved in protein synthesis, folding, and quality control. - Smooth ER: - Lacks ribosomes. - Involved in lipid synthesis, metabolism of carbohydrates, and detoxification of drugs and poisons. - Golgi Body (Golgi Apparatus): - Stack of flattened membranous sacs (cisternae). - Modifies, sorts, and packages proteins and lipids into vesicles for secretion or delivery to other organelles. - Lysosomes: - Contain hydrolytic enzymes. - Responsible for breaking down waste materials, cellular debris, and managing programmed cell death (apoptosis). - Vacuole: - Storage organelle for water, nutrients, and waste. - Plant cells contain a large Central Vacuole that provides structural support via turgor pressure. - Chloroplast: - Found in plant cells and algae. - Site of photosynthesis: $6CO<em>2 + 6H</em>2O + light \rightarrow C<em>6H</em>{12}O<em>6 + 6O</em>2$. - Contains chlorophyll and thylakoids organized into stacks called grana. ### Cell Membrane and Transport - Structure: - Described by the Fluid Mosaic Model. - Composed of a phospholipid bilayer with embedded proteins, cholesterol (for stability), and carbohydrates (for recognition). - Function: - Semi-permeable (selective) barrier. - Controls the entry and exit of substances to maintain cellular homeostasis. #### Types of Transport Across Cell Membrane - Passive Transport: - No energy expenditure required. - Movement down the concentration gradient (high to low). - Simple Diffusion: Movement of small or non-polar molecules like $O<em>2$ and $CO</em>2$ directly through the bilayer. - Facilitated Diffusion: Movement of polar or larger molecules through specific protein channels or carriers. - Osmosis: The diffusion of water across a semi-permeable membrane. - Active Transport: - Requires energy in the form of $ATP$. - Movement against the concentration gradient (low to high). - Protein Pumps: Specialized proteins that move ions (e.g., Sodium-Potassium pump). - Bulk Transport: - Endocytosis: The cell takes in macromolecules by forming new vesicles from the plasma membrane. - Exocytosis: The cell secretes molecules by the fusion of vesicles with the plasma membrane. #### Concentration Gradient: - The difference in concentration of a substance across a space. - Movement occurs along the gradient in passive transport and against the gradient